Abstract
Hydrogen is a zero-carbon footprint energy source with high energy density that could be the basis of future energy systems. Membrane-based water electrolysis is one means by which to produce high-purity and sustainable hydrogen. It is important that the scientific community focus on developing electrolytic hydrogen systems which match available energy sources. In this review, various types of water splitting technologies, and membrane selection for electrolyzers, are discussed. We highlight the basic principles, recent studies, and achievements in membrane-based electrolysis for hydrogen production. Previously, the Nafion™ membrane was the gold standard for PEM electrolyzers, but today, cheaper and more effective membranes are favored. In this paper, CuCl–HCl electrolysis and its operating parameters are summarized. Additionally, a summary is presented of hydrogen production by water splitting, including a discussion of the advantages, disadvantages, and efficiencies of the relevant technologies. Nonetheless, the development of cost-effective and efficient hydrogen production technologies requires a significant amount of study, especially in terms of optimizing the operation parameters affecting the hydrogen output. Therefore, herein we address the challenges, prospects, and future trends in this field of research, and make critical suggestions regarding the implementation of comprehensive membrane-based electrolytic systems.
Keywords: membrane, electrolysis, hydrogen production, electrolysis technologies, zero-carbon footprint, water splitting technologies, membrane-based electrolysis, electrolyzer, efficient
1. Introduction
The world’s population as of August 2021 is almost 7.9 billion, as reported by the United Nations, surpassing the earlier prediction of 7.5 billion by 2025 [1]. The world needs enough food for the entire population. To fulfill this need, energy resources are required to move people around, powering agriculture and agro-based industries, as well as other activities [2,3,4]. It is anticipated that the world’s energy demand will be in the range of 600 to 1000 EJ by 2050 [5,6,7]. A smart approach is essential to balance power demands and effective management of produced energy [8,9]. Due to the intense usage of conventional fuels in the production of electricity, the depletion of ozone layer is now at an alarming level because of the effect of the greenhouse gas (GHG) emissions like carbon dioxide and methane [10,11,12]. As the world is united and committed to reducing GHG emissions, the Montreal Protocol (1987), Kyoto Protocol (1997) and Paris Agreement (2015) have been signed in the hope of preventing further damage to the ozone layer and reducing the impact of climate change by 2050 [13,14,15,16]. Unlike the Montreal and Kyoto protocols (that targeted only developed nations), the Paris Agreement (2015) is more universal in its ambition to reduce GHG emissions, setting a target of a maximum of a 2 °C temperature increase through the collective commitment of all nations to cut their pollution levels [17,18].
One of the most promising clean and green energy sources, i.e., without any GHG emission and with a zero carbon footprint, is green hydrogen [19,20]. Hydrogen does not occur naturally in a gas form; rather, it always occurs as a compound in compounds such as water (H2O), methane (CH4), butane (CH4H10), or other liquids and hydrocarbon gases [21,22]. There are many techniques to produce hydrogen. For example, it can be produced from renewable sources as in the biomass [23] and water splitting processes (thermolysis, photolysis, electrolysis) [18,24]. Electrolysis can be further divided into alkaline, solid oxide, PEM, AEM, acidic–alkaline amphoteric, microbial and photoelectrochemical, as depicted in Figure 1.
At present, nonrenewable, fossil fuel-based processes, specifically, steam reforming of methane, coal gasification and other chemical processes, account for 96% of worldwide hydrogen generation, with electrolysis contributing just 4% [25,26,27,28]. Nonetheless, hydrogen originating from fossil fuels is low in purity and leads to the release of greenhouse gases including carbon monoxide, sulfur oxides, nitrogen oxides and carbon dioxide [19,29,30]. Hydrogen has several appealing features as an energy vector, including a high heating value (140 MJ/kg) that is almost three times that of conventional petroleum fuels (50 MJ/kg) [9,19]. Currently, global hydrogen production is estimated to be approximately 500 billion cubic meters per year. Hydrogen is widely utilized in a variety of sectors, including in the production of fertilizers, petrochemical processes, energy generation from fuel cells, and in various chemical industries [20,23,31].
There is also a need for innovative energy techniques with zero carbon footprint because of ever-increasing global energy demands and the limited supply of fossil fuels [7,23,32]. Environmentally friendly energy solutions are gaining traction today as viable alternatives to fossil fuel-based systems. It is estimated that less than 1% of the world’s hydrogen consumption is met by green hydrogen, i.e., which used renewable sources in its production [9,33]. One ecological method is polymer electrolyte water electrolysis; this approach yields hydrogen with a purity of hydrogen up to 99.999% [33,34,35].
Green hydrogen is produced from 100% renewable sources in an electrolysis process that uses fully renewable power and generates pure oxygen and hydrogen [25,35]. Gray hydrogen refers to the hydrogen synthesized via the steam methane reforming (SMR) method, as well as the residual hydrogen from chemical processes in chlor-alkali plants. Blue hydrogen refers to a gray hydrogen that has undergone a postproduction step called carbon capture and utilization (CCU) process [25,35,36].
The term “hydrogen economy” was introduced by John Bockris at the General Motors Technical Centre in 1970, in reference to a potential future method of generating energy [37]. Today, in Malaysia, the same term refers to the distribution of energy derived from hydrogen rather than fossil-fuel-based systems [38]. Over the course of the half century since the term was coined, the hydrogen technology landscape has evolved tremendously. Hydrogen is seen by some as the ultimate solution to climate change [14,25]. This is because, by introducing green hydrogen production, there will be a zero carbon footprint [24,39].
Although there are other methods of producing hydrogen, the advantages of membrane-based electrolysis include no net carbon release into the atmosphere (only hydrogen, oxygen and water are generated during the operation), ease of replication and the ability to combine multiple single unit membrane electrodes into a stack. Most of all, membrane-based electrolysis can be customized according to specific needs, location, and resource availability [40,41]. Therefore, this paper will review current membrane-based electrolysis for hydrogen production technologies.
2. Types of Membranes for Hydrogen Production
Membranes come in a solid polymer exchange strip that separates the two electrodes, acts as an ion conductor and prevents any fuel diffusivity [42,43,44,45]. In a membrane-based electrolysis process, a good quality membrane is vital to ensure durable operation and sufficient purity of the output product. Perfluorinated sulfonic acid (PFSA) type membranes are now the most frequently utilized solid electrolytes for proton exchange membrane fuel cell (PEMFCs) and proton exchange membrane electrolyzers (PEMEs) [46,47,48,49]. The phase inversion method is the most frequently used method for the production of polymeric membranes [50,51]. Below are some of the characteristics of a high-performance membrane for hydrogen production [21,52,53]:
High thermal and mechanical stability
Cost-effective and economic fabrication process
Excellent ionic conductivity
Excellent electrical insulation
High oxidative and hydrolytic stability
Excellent ability to block ion crossover via membrane/low diffusivity
Low swelling
Easy fabrication of the membrane electrode assemblies (MEA)
High chemical/electrochemical stability
2.1. Nafion™
Nafion™ is a well-known perfluorosulfonic acid (PFSA) membrane that is frequently utilized in PEM fuel cells and PEM electrolyzers [21,52,54]. Nafion™ functions well and is currently very popular because of its good ionic conductivity and excellent physicochemical properties. In 1966, General Electric Co. (Boston, MA, USA) was the first to create a proton exchange membrane (PEM) electrolyzer from a solid polymer electrolyte; it consisted of a membrane, an anode, and a cathode. DuPont’s Nafion™ membrane is the most well-known membrane; it is composed of a perluorinated polymer with sulfonic acid functionalization, as shown in Figure 2.
The significance of Nafion™ in the field of fuel cells and electrolyzers is apparent. It has excellent mechanical strength, proton conductivity, and chemical and thermal stability [56,57,58]. However, its apparent flaw, which has yet to be resolved, is the high fuel permeability, which causes PEM fuel cell and direct methanol fuel cell systems to lose a lot of fuel, reducing performance [42,52,59]. There are also ion crossovers in PEM electrolyzers which decrease the hydrogen yield. Furthermore, Nafion™ is very expensive due to the high production cost of the membrane [60,61].
Recently, many attempts have been made to address these shortcomings, including the introduction of inorganic fillers, acid doping and the introduction different polymer backbones into the Nafion™ membrane [27,62]. Moreover, operating an electrolyzer cell at higher temperatures induces more efficient hydrogen production due to the increase in ionic conductivity and a reduction in the anode and cathode activation overpotential [63]. In PEM fuel cells, operating at higher temperatures improves performance by decreasing carbon monoxide (CO) emissions; however, it also accelerates the degradation of the fuel cell components [64]. In the electrolyzer, a higher operating temperature results in an increased hydrogen yield [65].
2.2. Polybenzimidazole (PBI)
Polybenzimidazole (PBI) is a term denoting the presence of several benzimidazole units in the structure of aromatic heterocyclic polymers. Compared to Nafion™ membranes, PBI offers a few benefits, including high tensile strength, good chemical stability, and exclusive affinity for polyaryletherketone and some other polymers. The production of PBI is depicted in Figure 3.
The rigid aromatic structure in polybenzimidazole (PBI) contributes to its good chemical stability, high mechanical strength, and remarkable thermal stability. Owing to these characteristics, polybenzimidazole-based (PBI-based) membranes have been intensively explored for use in fuel cells, water electrolysis, and flow batteries [67,68,69].
Even though Nafion™ membranes are excellent at operating temperatures ranging from 20 to 80 °C, they are not suitable for high-temperature applications (>100 °C) due to their mechanical instability and the considerable drop in proton conductivity that occurs with elevated temperature [21,44,48]. Wainright first used polybenzimidazole (PBI) for high-temperature polymer electrolyte membranes in 1995 [27,64]. However, compared to Nafion™, pure PBI has relatively low conductivity, making it unsuitable as a substitute.
The proton conductivity of pure PBI can be improved by treating it with a variety of inorganic acids via hybrid membrane synthesis methods. For example, ion cross-linked structures can be prepared by blending PBI with sulfonated polyether ether ketone (SPEEK), sulfonated polysulfone, or sulfonated partially fluorinated arylene polyether [30,70]. The proton conductivity of phosphoric acid (PA) -doped PBI membranes is significantly dependent on the acid doping level, which is defined as the number of PA molecules per polymer repeating unit. The proton conductivities of acid-doped PBI membranes are also influenced by the doping acids in the following order: H2SO4 > H3PO4 > HClO4 > HNO3 > HCl. Due to the presence of more effective acid sites, sulfonated PBI membranes have greater proton conductivity than pure PBI membranes [71].
2.3. Sulfonated Polyether Ether Ketone (SPEEK)
Victrex is now the world’s top producer of PEEK polymers. In the sulfonation procedure for SPEEK membranes (Figure 4), sulfonic acid groups (SO3H) are attached, via alteration or polymerization of sulfonated monomers, to the backbone structure of the PEEK polymer [72]. The excess acid in the form of sulfonic acid groups in the PEEK polymer is the basis for the hydrophilic properties of the membrane. The sulfonic acid groups serve as hydrogen bonding sites between the polymer and the water [52,70]. Proton charge carriers are formed in PEEK hydrated membranes as a result of sulfonic acid group segregation and proton conductivity due to water activity [73,74].
Previous research has demonstrated that PEEK polymers with altered characteristics can be used to replace Nafion™ membranes in PEMFC, DEMFC, and PEME systems [27,50]. PEEK electrophilic sulfonation (S-PEEK), SPEEK and nonfunctional polymer mixing, and SPEEK heteropolycompounds with poly-etherimide doping with organic acids are all required in order to PEM from PEEK polymer [50,73]. Therefore, controlling the degree of sulfonation (DS) is critical, since this affects the thermochemical stability of PEEK-based membranes [76,77].
2.4. Others
Apart from Nafion™, PBI, and SPEEK, other base membranes could be used in hydrogen production processes. For example, other polymers with aromatic rings, such as polyoxadiazole, polysulfone (PSf), and polyimides, could reduce production costs while providing adequate physicochemical properties; however, these compounds need further improvements and investigation. Additionally, the physicochemical properties of these membranes could further be improved by hybrid membrane preparation (solution mixing, acid doping etc). Currently, these polymers and their derivatives (e.g., polyimides/SPAES, polysulfone/PEEK) are mainly used in fuel cell applications and, occasionally, in water electrolysis [31,78].
3. Types of Water Electrolysis Technologies
Electrolysis technologies have existed for more than 100 years. At present, fuel cells (which use the opposite process to electrolyzers) are more popular than traditional hydrogen conversion tools for applications in the automobile industry. In the hydrogen production process, the electrolyzer is the most important component, as it determines the production efficiency [79].
3.1. Nonmembrane-Based Electrolysis
Alkaline Electrolysis
Hydrogen production by electrolysis of alkaline water is now a mature technology that is economical, durable, and has been widely used in chlor-alkali chemical industries for more than 100 years [79,80]. The drawbacks of having an alkaline electrolysis system are low hydrogen purity, limited current density (below 400 mA/cm2), low range of operating pressure with low energy efficiency [81,82,83]. The schematic for alkaline electrolysis is shown in Figure 5.
The half-cell reaction at the anode in an alkaline electrolysis is shown in Equation (1):
Anode: 2OH− → H2O + ½ O2 + 2e− | (1) |
As for the cathode, the half-cell reaction in alkaline electrolysis is depicted in Equation (2).
Cathode: 2H2O + 2e− → H2O + 2OH− | (2) |
The overall reaction for alkaline electrolysis is represented by Equation (3):
Overall: H2O → H2 + ½ O2 | (3) |
The hydrogen evolution reaction (HER) starts when the water molecule is reduced at the cathode, producing one hydrogen (H2) molecule and two hydroxyl ions (OH-) [34,84]. The hydroxyl ions then move to the anode via the porous diaphragm due to the electrical potential which is applied at both electrodes, releasing half a molecule of oxygen (O2) and one molecule of water (H2O) [82]. Typically, alkaline electrolyzers use 30 wt% KOH solution or 25 wt% NaOH solution and operate at 30–80 °C. These devices are able to produce hydrogen which is up to 99% pure with an efficiency of around 60–80% [79,83].
3.2. Membrane-Based Electrolysis
3.2.1. Proton Exchange Membrane Electrolysis
Proton exchange membranes (PEMs) are widely used in fuel cells to produce electricity and in electrolyzers to produce hydrogen. PEMs also act as a means of separating the anode from the cathode. Nafion™ and Nafion™-based membranes are the most popular PEMs due to their high ionic conductivity, thermostability, good mechanical strength, excellent chemical stability, and durability at low temperature under high levels of relative humidity [56,84,85,86]. However, Nafion™ has two major problems, i.e., a time-consuming synthesis procedure and poor proton conductivity at high-temperatures in low humidity environments [62,87]. Moreover, the main obstacles for the use of Nafion™ membranes are their exorbitant price, the unsafe membrane synthesis process, and the fact that ionic conductivity drops when the operating temperature exceeds 90 °C under low relative humidity [49,88,89].
The advantages of PEM electrolyzers are their abilities to operate at high current densities with high voltage and to produce a very pure hydrogen gas, i.e., up to 99.995% [90]. The downsides of using a PEM electrolysis system are the high cost of the catalyst and the need for an expensive membrane which has only average durability. Furthermore, PEM electrolyzer stack materials are more costly than those of alkaline electrolyzers [21,30]. A schematic of the PEM electrolysis process is shown in Figure 6.
The oxygen evolution reaction (OER) starts when hydrogen ions move to the cathode via the PEM due to an electrical potential applied at both electrodes releasing half a molecule of oxygen (O2) and electrons via the water splitting process. The hydrogen evolution reaction (HER) starts when hydrogen ions are reduced at the cathode, liberating one hydrogen (H2) molecule.
The half-cell reaction at the anode in PEM water electrolysis is shown in Equation (4):
Anode: H2O → 2H+ + ½ O2 + 2e− | (4) |
The half-cell reaction at the cathode in PEM water electrolysis is shown in Equation (5).
Cathode: 2H+ + 2e− →H2 | (5) |
The overall reaction for PEM electrolysis is represented by Equation (3):
Overall: 2H2O → H2 + ½ O2 | (6) |
Apart from traditional PEM water electrolysis, another type exists which utilizes copper chloride-hydrochloric acid (CuCl-HCl) as the electrolytes. In the past decade, studies carried out on CuCl-HCl electrolysis at low operating temperature (<80 °C) using a Nafion™ and Nafion™-based membranes revealed promising hydrogen production results [91,92,93,94,95,96,97]. A schematic of the CuCl-HCl electrolysis process is shown in Figure 7. The reaction for CuCl electrolysis produces two CuCl2 molecules and one H.2 molecule.
One study revealed that Nafion™ functions as an exceptional intermediate for ionic transfer without material compatibility issues in CuCl-HCl electrolytic systems when 0.2–1 M CuCl is added to the 2–10 M HCl electrolytes [92]. In some studies, milder electrolytes were utilized, with CuCl concentrations ranging from 0.01 to 0.2 M and HCl concentrations of 0.5–1 M [21,48]. However, some issues have been reported with Nafion™ membranes, namely, high copper diffusion, swelling, and the need for expensive membranes [97,98]. In contrast, a polybenzimidazole (PBI) membrane doped with phosphoric acid offers superior thermochemical and mechanical stabilities for working temperatures over 80 °C [21,98].
The half-cell reaction at the anode in CuCl-HCl electrolysis is shown in Equation (7):
Anode: 2CuCl + 2Cl− → 2CuCl2 + 2e− | (7) |
The half-cell reaction at the cathode in CuCl-HCl electrolysis is depicted in Equation (8).
Cathode: 2H+ + 2e− → H2 | (8) |
The overall reaction for an alkaline electrolysis is represented by Equation (9):
Overall: 2CuCl + 2Cl− + 2H+ → 2CuCl2 + H2 | (9) |
Recent findings suggested that high-temperature CuCl-HCl electrolysis using hybrid PBI/zirconium phosphate (PBI/ZrP) can increase the hydrogen production; therefore, this approach has the potential to make Nafion™ membranes redundant [21,48,98]. Kamaroddin et al. (2020) reported high-temperature CuCl-HCl electrolysis for hydrogen production at a temperature range of 100–130 °C with lower HCl concentration and electrolyte flowrate using a hybrid PBI/ZrP membrane [21]. Theirs was the first study that used a non-Nafion™ membrane in high-temperature CuCl-HCl electrolysis for hydrogen production. In another study, manipulations of the electrolyte concentrations and current densities were shown to increase hydrogen production, although this requires further investigation [48]. A summary of a CuCl-HCl electrolysis system for hydrogen production via Nafion™ and hybrid PBI/ZrP membrane is depicted in Table 1.
Table 1.
Authors | Electrolyte(s) Concentration (M) |
Temperature (°C) |
Membrane | Electrolyte Flowrate (cm3 min−1) |
---|---|---|---|---|
Kamaroddin M.F.A et al., 2020 [21] | 0.01–0.2 M CuCl | 100–130 | PBI/ZrP | CuCl: 3–30 HCl: 3–30 |
1 M HCl | ||||
Abdo & Easton 2016 [95] | 0.2 M CuCl, 2 M HCl | 25 | Nafion™/Polyaniline (PANI) | CuCl/HCl: 60 DI water: 60 |
DI water | ||||
Naterer et al., 2015 [94] | 0.5–1.0 M CuCl | 45–60 | Nafion™ 117 | CuCl: 600 |
6–10 M HCl | HYDRion | HCl: 600 | ||
Aghahosseini et al., 2013 [99] | 0.5–1.0 M CuCl | 25–60 | Nafion™ 117 | CuCl: 100–500 |
6–10 M HCl | HCl: 100–500 | |||
Edge 2013 [91] | 0.002–0.2 M CuCl | 25–80 | Nafion™ | CuCl: 40–200 |
2 M HCl | HCl: 40–200 | |||
Schatz et al., 2013 [100] | 1–2 M CuCl | 80 | Nafion™ | CuCl: 59 |
6 M HCl | HCl: 130 | |||
Balashov 2011 [92] | 0.2–1.0 M CuCl | 22–30 | Nafion™ 115 | CuCl: 30 & 68 |
2 M HCl | HCl: 28.5 | |||
Gong et al., 2010 [100] | 0.2–1.0 M CuCl | 24–65 | Nafion™ | CuCl: 3.4–22 |
2–6 M HCl | HCl: 4.4–27 |
Choosing the right process using CuCl2 with spent residues can increase the yield of the electrolysis process [21,101]. CuCl2 can be further recycled to generate CuCl for the next round of electrolysis. Despite the challenges, hydrogen production via high-temperature electrolysis of CuCl-HCl can be seen as a suitable option because hydrogen is a clean, energy dense substance and a nontoxic energy source [48,102]. Therefore, high-temperature electrolysis of CuCl-HCl is a potential alternative to fossil fuels which may reduce the production costs of hydrogen by utilizing a cheaper membrane.
3.2.2. Anion Exchange Membrane (AEM) Electrolysis
AEM water electrolysis is a hybrid method that combines the advantages of having PEM and alkaline electrolysis in a cell made up of a hydrocarbon-based anion exchange membrane and two transition metal (e.g., iridium (Ir), platinum (Pt), etc.) catalyst-based electrodes [71,81,103]. The advantages of this process compared to alkaline electrolysis are the use milder alkaline electrolytes or distilled water instead of a concentrated KOH solution and the possibilities of using a cheaper catalyst and an inexpensive nickel-based stack components [81,104]. However, current AEM electrolyzers shows low ionic conductivity, low power efficiency, medium range membrane stability with large Ohmic resistance loss and significant catalyst loading [81,105]. There is growing interest among the scientific community in developing a solid polymer anion exchange membrane, but more efforts are required regarding the catalyst design and synthesis [103,106]. A schematic and the overall cell reaction for AEM electrolysis are shown in Figure 8.
The half-cell reaction at the anode in an AEM electrolysis is shown in Equation (10):
Anode: 4OH− → 2H2O + O2 + 4e− | (10) |
The half-cell reaction at the cathode is depicted in Equation (11).
Cathode: 4H2O + 4e− → 4OH− + 2H2 | (11) |
The overall reaction for an AEM electrolysis is represented by Equation (12):
Overall: 4H2O → 2H2O + O2 + 2H2 | (12) |
A summary of the AEM electrolysis system is shown in Table 2.
Table 2.
Authors | Membrane Electrode Assembly GDL * (anode/cathode) |
Temperature (°C) |
Membrane | Electrolyte | Voltage (V) |
---|---|---|---|---|---|
Leng et al., 2012 [108] | Ti foam/Ti foam | 50 | A-201, Takuyama | Deionized water | 1.8 |
Pavel et al., 2014 [109] | Ni foam/carbon cloth | 50 | A-201 Takuyama | 1% K2CO3/KHCO3 | 1.9 |
Xiao et al., 2012 [110] | Ni form/stainless steel fiber felt | 70 | xQAPS | Ultrapure water | 1.85 |
Wu et al., 2011 [111] | Stainless steel mesh/stainless steel mesh | 25 | Quaternary ammonium | 1 M KOH | 1.8 |
Seetharaman et al., 2013 [112] | NiO/NiO | 80 | Selemion AMV | 0–5.36 M KOH | 1.9 |
Joe et al., 2014 [113] | Ni oxide/Ni | 30 | Selemion AMV | Deionized water | 2.0 |
* GDL—gas diffusion layer.
The above summary provides an overview of the type of membrane electrode assemblies, temperatures, membrane, types of electrolyte and voltages of the system. Common membranes used for AEM electrolysis are A-201, Takuyama, and Selemion AMV; a voltage range of 1.8–2.0 V is sufficient to produce hydrogen in the AEM electrolysis process. Currently, research on AEM is still at the laboratory scale, but recent studies have yielded significant information regarding the AEM electrolysis mechanism, as well as improvements of the electrocatalysts, membranes, electrodes, and membrane electrode assemblies (MEA) [27,81].
3.2.3. Solid Oxide Electrolysis
Solid oxide electrolysis (SOE) has received a lot of attention, as it is regarded as a high-efficiency process that converts electrical energy into chemical energy and produces high purity hydrogen [114]. Donitz and Erdle invented the technique in 1980, although it is still undergoing refinement [114]. SOE works at a high temperatures, i.e., 500–1000 °C, or the same as the output temperature of a nuclear reactor. SOE uses a solid ceramic membrane, which makes it compact and gives it a fast response time, i.e., comparable to that of a PEM electrolyzer cell. The advantages of having a solid-oxide electrolyzer include the fact that it can be a dual-function fuel cell/electrolyzer, and its superior ionic conductivity [29]. However, solid oxide electrolysis comes with a few disadvantages, e.g., the relative immaturity of the technology, the energy intensive nature of the process, high cost, low durability, and the need for ultrahigh operating temperatures [44,100]. Solid oxide electrolyzers (Figure 9) are unique on account of their need for high temperature operation, as extra heat input is required in addition to electrical input [29,114,115].
Half-cell reaction at the anode in solid oxide electrolysis is shown in Equation (13):
Anode: O2− → ½ O2 + 2e− | (13) |
Half-cell reaction at the cathode is depicted in Equation (14).
Cathode: H2O + 2e− → H2 + O2- | (14) |
The overall reaction for a solid oxide electrolysis is represented by Equation (15):
Overall: H2O → H2 + ½ O2 | (15) |
A summary of a SOE system for membrane-based electrolysis is shown in Table 3. SOE operating temperatures and voltages range from 700 to 800 °C and 0.95 to 1.40 V, respectively. The majority of the SOE systems use water as the electrolysis reactant.
Table 3.
References | Membrane | Temperature (°C) | Durability Test Time (h) | Electrolysis Reactant | Voltage (V) |
---|---|---|---|---|---|
[116] | YSZ */CGO | 750 | 120 | H2O | 1.15 |
[117] | SSZ | 700 | 330 | H2O | 1.30 |
[118] | SSZ | 700 | 1000 | H2O | 1.30 |
[119] | LDC/LSGM/LDC | 800 | - | H2O | 0.95 |
[120] | YSZ * | 800 | 300 | H2O/CO2 | 1.40 |
* YSZ—Yittria-zirconized zirconia, CGO—Gadolinium doped ceria, SSZ—Scadinia stabilized. zirconia, LDC—lanthanum doped cerium, LSGM—La0.9Sr0.1Ga0.8Mg0.2O3−δ.
SOE holds great promise if we are able to utilize the waste heat from power plants or other chemical processes as heat sources.
3.2.4. Microbial Electrolysis
Microbial electrolysis cell (MEC) technology is capable of producing hydrogen from organic matter, including wastewaters and industrial biomass waste. In MECs, electrical energy is transformed into chemical energy. MEC technology is very similar to that of microbial fuel cells (MFCs), except that the operating concept is the opposite [121]. In 2005, two university groups from Penn State University, USA, and Wageningen University in the Netherlands, presented the first microbial electrolysis cell (MEC) method [20,122]. A schematic for microbial electrolysis is shown in Figure 10.
The half-cell reaction at the anode in a microbial electrolysis is shown in Equation (16):
Anode: CH3COO− + 4H2O → 2HCO3− + 9H+ + 8e− | (16) |
The half-cell reaction at the cathode is depicted in Equation (17).
Cathode: 8H+ + 8e− →4H2 | (17) |
The overall reaction for a microbial electrolysis is represented by Equation (18):
Overall: CH3COO− + 4H2O → 2HCO3− + H+ + 4H2 | (18) |
The evolution of microbial electrolysis cell technology from 2005 to 2021 is summarized in Table 4. In previous studies, several membranes, e.g., SPEEK, SPEEK/PES, SPAES/polyimide, SPEEK/PES, Nafion™, AMI-7001, bipolar membranes, charge-mosaic membranes, and microporous membranes, were tested and showed promising results in microbial electrolysis cells [123,124,125,126]. The advantages of MEC include the fact that it can generate hydrogen from organic molecules under the influence of a low external voltage [126,127]. However, there are disadvantages that need to be taken into account, e.g., it has high internal resistance, a complicated design, high fabrication and operation costs, and is a technology that is still under development [128].
Table 4.
Year | Description | References |
---|---|---|
2005 | Hydrogen gas generated from acetate using a full anaerobic microbial fuel cell | [129] |
2008 | Biocathode was used in MEC | [130] |
2009 | Effort to increase the hydrogen production by using an economical cathode SS A286 and nickel | [131] |
2010 | Establishment of a life cycle assessment for microbial electrolysis cells | [132] |
2012 | Conversion of CO2 to methane using MEC technology | [133] |
2015 | Dark fermentation and MEC were integrated and evaluated by producing hydrogen from sugar beet juice | [134] |
2016 | Removal of cadmium by using MEC | [135] |
2018 | Prefermentation of MEC as the medium with which to check the role of free nitrous acid | [136] |
2019 | A method to quantify the internal resistance of MECs was developed | [137] |
2020 | The effectiveness of chloroform as a homoacetogen inhibitor was demonstrated | [138] |
2021 | The effect of high applied voltages on bioanodes in the presence of chlorides was studied | [81] |
3.2.5. Acid-Alkaline Amphoteric Electrolysis
Large-scale, acid-alkaline amphoteric (AAA) water electrolysis is deemed a promising method for effective hydrogen generation; however, a functionalized polymer for constructing membranes is still either unable to yield good electrolysis performance or is not durable enough [34,83]. Current studies on a variety of H2SO4-doped PBI-based membranes for use in AAA water electrolysis systems (Figure 11), including poly (2,2’(m-phenylene)-5,5’-bibenzimidazole) (m-PBI), poly (4,4’diphenylether-5,5’-bibenzimidazole) (OPBI), Nafion™ 117 (N117) and Nafion™ 115 (N115), are considered to be good potential membranes for amphoteric electrolysis [83,139].
The half-cell reaction at the anode in acid-alkaline amphoteric electrolysis is shown in Equation (19):
Anode: 4OH− → 2H2O + O2 + 4e− | (19) |
The half-cell reaction at the cathode is depicted in Equation (20).
Cathode: 2H+ + 2e− → H2 | (20) |
The overall reaction for an acid-alkaline amphoteric electrolysis is represented by Equation (21):
Overall: 4OH− + 4H+ → 2H2O + O2 + 2H2 | (21) |
The summary of acid-alkaline amphoteric electrolysis for hydrogen production is depicted in Table 5. The electrolytes used are sulfuric acid (H2SO4) and potassium hydroxide (KOH) with operating conditions range from 20 to 60 °C (temperature), 1.98 to 2.2 V (voltage) and 200 to 800 A cm−2 (current density). It was reported that the AAA electrolysis efficiency can consistently achieved up to 100% with few more advantages which includes a reduction in overpotential and energy consumption (30% of pure alkaline electrolysis requirement) and up to 4 times more hydrogen production compared to alkaline electrolysis [34]. However, due to characteristic of the AAA, the setup has higher membrane resistance compare to alkaline electrolysis, the need to use bipolar ion-exchange membrane and it requires simultaneous usage of acidic and alkaline electrolytes in the system [83].
Table 5.
3.2.6. Photoelectrochemical Electrolysis
The first report of photoelectrochemical (PEC) water splitting was published in 1970s, when a conductive electrode composed of TiO2 was illuminated in aqueous solution [140,141]. Photoelectrochemical (PEC) electrolysis system (Figure 12), which converts solar energy directly to hydrogen by using a direct and simple setup has sparked considerable attention in recent years. Water decomposes into hydrogen and oxygen by absorbing solar photons in a semiconductor material attached with electrocatalysts [142,143,144].
In the PEC approach, photocatalysts are first produced as electrodes on conductive substrates, and a modest bias is then applied for water splitting. The half-cell reaction at the anode in PEC electrolysis is shown in Equation (22):
Anode: 2H2O → 4H+ + O2 + 4e− | (22) |
The half-cell reaction at the cathode is depicted in Equation (23).
Cathode: 4H+ + 4e− →2H2 | (23) |
The overall reaction for a PEC electrolysis is represented by Equation (24):
Overall: 2H2O + 4H+ → 4H+ + O2 + 2H2 | (24) |
Table 6 shows a summary of photoelectrochemical electrolysis for hydrogen production in which the membrane is integrated with a semiconductor material in order to activate the photoelectrochemical reaction when immersed in an appropriate agent (e.g., methanol, water or ethanol). PEC electrolysis, that can directly use the free energy obtained from solar panels to produce hydrogen, holds tremendous potential due to its simple setup, although efficiency remains quite low < 10% due to the fact that the technology is still in its infancy [142,144]. Therefore, there should be collaborative efforts in the scientific community to increase the efficiency of PEC electrolysis, with the goal of matching that of photovoltaic assisted water splitting processes.
Table 6.
References | Membrane | Agent | Reactor |
---|---|---|---|
[145] | TiO2-Nafion-Pt | Methanol | - |
[146] | Pt/SrTiO3Rh-Nafion | Water | H-type integrated |
[147] | BiVO4-Nafion | Water | Dual |
[148] | Porous Nafion-Pt-TiO2 | Ethanol | |
[149] | WO3-TiO2-Pt-Nafion | Water | H-type |
[150] | Carbon coated Degussa TiO2-P25 | Water | - |
[151] | Nafion, FKE Fumatech, sulfonated polyethersulfone (sPES), sPES/mesoporous-Si-MCM41-nanoparticles | Water | - |
3.3. Summary
Various methods of hydrogen production have been discussed above, each of which has its advantages and disadvantages. At the end of the day, we need to consider the greenest possible way to generate hydrogen without releasing greenhouse gases into the atmosphere in an effort to curb climate change. The efficiency of the electrolyzer for hydrogen production can be determined using the formulae in Equations (25)–(27):
Efficiency (%) = VH2 real/VH2 ideal × 100 | (25) |
with VH2 real = VH2 measured × Tstandard/Tmeasured and; | (26) |
VH2 ideal = I × Vm × t/(2 × F) | (27) |
where I is current (A), Vm is a molar volume of an ideal gas, t is time (s) and F is Faraday’s constant, i.e., 96485 A.s/mol.
A summary of hydrogen production by water splitting technologies, along with their advantages, disadvantages and efficiencies, is depicted in Table 7.
Table 7.
Water Splitting Technologies | Advantages | Disadvantages | Efficiency |
---|---|---|---|
Alkaline Type of diaphragm: porous inorganic (asbestos, ceramic, cement) |
Well established technology Economical Very durable Operates at low temperature (30–80 °C) Inexpensive electrocatalyst |
High concentration corrosive electrolytes Limited current density (below 400 mA/cm2) Low operating pressure Low energy efficiency Low gas purity |
60–80% |
Solid oxide Types of membranes: oxygen ion ceramic electrolyte membrane, YSZ |
Dual-function fuel cell and electrolyzer Superior ionic conductivity Ultrapure hydrogen Excellent efficiency |
Very high operating temperature (500–850 °C) Energy intensive process and not economical Low durability (stability and degradation)Still immature technology—lab scale |
90–~100% |
PEM Type of membranes: Nafion™, PBI, SPEEK, polyethylene |
High hydrogen purity (up to 99.995%), High current density High voltage efficiency Dynamic operation |
High-cost catalysts Mildly durable Costly membrane More expensive stack materials compared to alkaline Partially established technology |
70–90% |
AEM Types of membranes: A201 membrane, Selenion AMV, A901 membrane |
Lower cost of catalysts Inexpensive stack components -(Nickel-based) |
Low ionic conductivity Early stage of development Low power efficiency Low membrane stability Large Ohmic resistance loss Large catalyst loading |
50–70% |
Acid-alkaline amphoteric Types of membranes: bipolar membrane, acid-doped PBI-based membranes, Nafion™ |
Reduced energy consumption Reduced overpotential Hydrogen production four times that of alkaline electrolysis |
Increased membrane resistance Need to use bipolar ion-exchange membrane Need to use both acidic and alkaline electrolytes |
~100% |
Microbial Types of membranes: SPAES */polyimide, SPEEK, SPEEK/PES, Nafion™, AMI-7001, bipolar membranes, charge-mosaic membranes, microporous membranes |
Requires only a low external voltage Uses organic materials |
Still under development High internal resistance Complicated design Low rates of hydrogen production Fabrication and operational costs are high |
60–70% |
Photoelectrochemical Types of membranes: polyamide, Nafion™ based membrane |
Direct solar to hydrogen conversion Simpler setup |
Low conversion factor Low hydrogen production Still at infancy stage |
<10% |
* SPAES—sulfonated poly (arylene ether sulfone).
Since water splitting technologies mainly involve either oxygen evolution (OER) or hydrogen evolution (HER) reactions at their respective electrodes, the electrode potentials can be summarized for acidic and alkaline media. A summary of electrode half potentials for various membrane-based electrolysis for hydrogen production is given in Figure 13.
This is a comprehensive way of visualizing the electrode half potentials for various membrane-based electrolysis systems, as there are duplications for the anode and cathode half-cell reactions. Despite using a different type of membrane, the process is nonetheless based on the water splitting technologies, and the standard electrode potential is the same for both acid and alkaline electrolysis (1.23 V), except with amphoteric electrolysis, which has only 0.401 V.
It can be concluded that each water splitting technology has its advantages and disadvantages. However, membrane-based electrolysis appears to offer a lot of potential for hydrogen production. Therefore, the research, development and commercialization of more economical membranes should be a major focus if we are to exploit the full potential of these technologies.
4. Parameters Affecting the Membrane-Based Electrolysis
Many factors determine the electrolyzer performance in an electrolysis system [14]. Apart from the selection of an appropriate material for the construction of the electrolyzer, the operating parameters affecting hydrogen yield are very important [14,152,153]. In this study, four operating parameters influencing hydrogen production in membrane-based electrolysis are outlined, i.e., temperature, electrolysis concentration, electrolysis flowrate and miscellaneous.
4.1. Temperature
Alkaline electrolysis is the most established hydrogen production technology; it is generally applied for industrial-scale electrolytic hydrogen production with a typical operating temperature of 40–90 °C [114], or 30–100 °C if highly concentrated KOH is used, with an estimated overall efficiency of 70–80% [154]. On the other hand, a typical PEM electrolysis process operates at between 30–90 °C, with a standard Nafion™-based membrane being the core component of the membrane electrode [88,155,156]. Although some studies have reported the use of PEM electrolyzers at high temperature, efforts in this endeavor were hindered by the inability of the Nafion™ membrane to withstand operating temperatures above 90 °C, as this leads to mechanical degradation and a loss of ionic conductivity [44,157,158]. Toghyani et. al. (2018) reported that the hydrogen and oxygen reaction rate increased dramatically at higher operating temperatures as a result of the faster kinetics of the electrochemical reactions [63]. Recently, Kamaroddin et al. (2020) revealed a PBI/ZrP hybrid membrane that can operate at 100–130 °C by synthesizing a PBI-based hybrid membrane using a solution mixing method with the addition of a ZrO2 inorganic filler, followed by phosphoric acid doping. Therefore, by better integrating the polymer backbone through the use of ZrO2, more acid sites attach to the PBI, resulting in enhanced proton movement via the Grotthus mechanism, as well as improved ionic conductivity, tensile strength and ion exchange capacity [21].
The operating temperature required for water splitting technologies for hydrogen production is often noted as one of the biggest factors influencing operation costs. SOE requires the highest operating temperature, i.e., 500–1000 °C, but has an efficiency close to 100% [25,159]. Due to its advantageous thermodynamics and kinetics, high temperature steam water electrolysis can deliver high efficiency at a lower overall cost than conventional low temperature electrolysis [114,156]. Furthermore, because of the operating temperatures of SOEs, it is possible to simultaneously electrolyze CO2 and H2O. However, in order for a system to be feasible, the heat must be from a renewable source, or from exothermic waste heat [31,64,160].
4.2. Electrolytes Concentration
In some water splitting processes, electrolyte concentration plays a vital role in determining the rate of the reaction and the amount of the hydrogen produced [44,159]. Chakik et al. (2017) reported that the amount of hydrogen produced is strongly correlated with the electrolyte concentration, i.e., a higher concentration in the electrolyte increases the ionic conductivity of the solution which, in turn, promotes hydrogen evolution reactions and improves yield [161]. According to Lei et al. (2019), a quadruple increase was observed in the hydrogen production rate in an amphoteric electrolysis that used 4 M KOH and 2 M H2SO4 within a temperature range of 30 to 50 °C.
However, excessive electrolyte concentration can deteriorate the MEA components including the membrane, electrodes, gasket, current collector, bipolar plates, etc., which, in turn, affects the hydrogen yield [47,162,163]. The corrosive nature of concentrated electrolytes, be it acidic or alkaline, can also cause damage to the peristaltic pump and its components, the electrolyte tubing, thermocouples, heating elements, etc. [27,164]. Therefore, considerable research must be carried out regarding a suitable electrolyte concentration to achieve the optimum concentration to maximize yield.
4.3. Electrolytes Flowrate
As the membrane serves as the core component in the electrolyzer, the flowrate of the electrolytes is a crucial factor that determines the kinetics of the electrolysis reaction [21]. Although many elements of the electrolyzer have improved over the previous decade, the impacts of the various operating parameters are still being investigated. Notably, the main limiting variables have yet to be identified using kinetic and thermodynamic relationships [165,166]. However, a faster electrolyte flowrate will not necessarily increase the rate of hydrogen production, and instead may be a limiting factor, negatively influencing the rate of ionization in an HER or OER. Therefore, a good balance between an optimal electrolyte flowrate and other parameters must be found in order to achieve an optimal hydrogen yield, depending on the type of available energy.
4.4. Others
Apart from all the above parameters, the electrode material plays an important role in the electrolyzer setup in terms of ensuring a durable and highly efficient process. The electrode materials should be nonreactive with excellent corrosion resistance, good proton conductivity, and the ability to support active catalytic activity for HER and OER [154,167].
The volume of hydrogen generated during the electrolysis process grows steadily as the applied current increases [161,168]. Moreover, both the catalyst composition and its morphology function as synergistic factors that enhance HER and OER [20]. As a rule of thumb, the MEA manufacturing procedure is critical in defining performance, production costs, and durability [169,170].
5. Challenges and Future Trends
The present overview of membrane-based electrolysis approaches for hydrogen production is largely based upon the results and discussions presented in the literature. A literature search in the Web of Science Core Collection portal (accessed 1 September, 2021) for alkaline, solid oxide, PEM, AEM, acidic-alkaline amphoteric, microbial, and PEC membrane-based electrolysis yielded a total of 1193 results from over a 10-year time span (2010–2021) using as keywords “membrane electrolysis” and “hydrogen production”. For a comparison, a quick search on the MDPI portal yielded only 20 results for this period using the same keywords.
The past decade has witnessed growing research interest in membrane-based electrolysis for hydrogen production. This is due to the increasing demand for green energy and the implementation of zero carbon footprint initiatives. Nevertheless, there are still major obstacles which need to be overcome before membrane-based electrolysis can be considered an economically viable, large-scale hydrogen generation solution, including the cost, availability, and the durability of the membrane, type of catalyst, the cost of using platinum group metal-based catalysts, and corrosion problems associated with the electrodes and separator plates.
6. Conclusions
Despite significant advancements in the development of all required components for membrane-based electrolytic hydrogen production systems, giving rise to significant improvements in durability, performance and efficiency, some electrolysis technologies are still in the early stages of development, e.g., solid-oxide, anion exchange membrane, microbial and photoelectrochemical electrolysis. In this review, we have provided a short introduction to various water splitting technologies for hydrogen production, including discussion of the type of membrane that are currently being used and the associated progress in their development. In addition, we have highlighted and emphasized recent development in membrane-based electrolysis. The present review not only discusses in detail the availability of the hydrogen production technology, but also summarizes trends of PEM water splitting technologies over the past decade, presenting a review of hydrogen production including the advantages, disadvantages and efficiencies of the various technologies. Parameters affecting the performance of membrane-based electrolysis are also discussed. Finally, we have summarized the challenges to the development of membrane-based electrolysis technologies, and have outlined our ideas for future research directions with the aim of fully tapping into this potential energy source which has a zero-carbon footprint. Future development of membranes for water splitting technologies, especially for the membrane-based electrolysis, should be focused on more economical models, like PBI, SPEEK, polysulfone, polyimides, polyethylene etc., in order to fully benefit from the emerging hydrogen economy ecosystem via the creation of efficient hydrogen generators for fuel cell cars and fuel cell power supply, as well as mobile electrolyzers to power critical equipment in remote areas such as telecommunication towers or safety and security surveillance. The application of membrane-based electrolysis and other auxiliary equipment allowing the use of hydrogen in transportation and industrial activities will be of at great interest over the next 5 to 10 years.
Abbreviation
AEM | Anion exchange membrane |
AAA | Acidic-alkaline amphoteric |
PA | Phosphoric acid |
PBI | Polybenzimidazole |
PEEK | Poly ether ether ketone |
PEM | Proton Exchange Membrane |
SPEEK | Sulfonated poly ether ether ketone |
MEC | Microbial electrolysis cell |
PEC | Photoelectrochemical |
SOE | Solid oxide electrolysis |
CuCl-HCl | Copper chloride-hydrochloric acid |
OER | Oxygen evolution reaction |
HER | Hydrogen evolution reaction |
MFC | Microbial fuel cell |
GHG | Greenhouse gases |
PBI/ZrP | Polybenzimidazole/Zirconium phosphate |
PEME | Proton exchange membrane electrolyzer |
PFSA | Perfluorinated sulfonic acid |
PEMFC | Proton exchange membrane fuel cell |
MEA | Membrane electrode assemblies |
SPES | Sulfonated polyether sulfone |
YSZ | Yittria stabilized zirconia |
CGO | Gadolinium doped ceria |
SSZ | Scadinia stabilized zirconia |
LDC | Lanthanum doped cerium |
LSGM | Lanthanum gallate-based electrolyte |
SPAES | Sulfonated Polyaryl Ether Sulfone |
Acknowledgments
The authors sincerely appreciate the critical and insightful comments that will be raised by the reviewers to improve the quality of this review article.
Author Contributions
M.F.A.K.: drafting, writing and analysis; L.C.A.: supervision; S.I.S.: supervision; A.A.J.: writing; A.A.: project management; N.S.: writing, supervision, and project management; T.A.T.A.: writing, supervision, and project management. All authors have read and agreed to the drafted version of the manuscript.
Funding
This research was funded by MINISTRY OF HIGHER EDUCATION OF MALAYSIA (MOHE) through the Putra Grant GP-IPS/2018/9634400 University Putra Malaysia and research excellence consortium grant number 4L947 University Teknologi Malaysia.
Institutional Review Board Statement
Not applicable.
Informed Consent Statement
Not applicable.
Data Availability Statement
Not applicable.
Conflicts of Interest
The authors declare no conflict of interest.
Footnotes
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.
References
- 1.Da Silva Veras T., Mozer T.S., da Costa Rubim Messeder dos Santos D., da Silva César A. Hydrogen: Trends, production and characterization of the main process worldwide. Int. J. Hydrogen Energy. 2017;42:2018–2033. doi: 10.1016/j.ijhydene.2016.08.219. [DOI] [Google Scholar]
- 2.Abe J.O., Popoola A.P.I., Ajenifuja E., Popoola O.M. Hydrogen energy, economy and storage: Review and recommendation. Int. J. Hydrogen Energy. 2019;44:15072–15086. doi: 10.1016/j.ijhydene.2019.04.068. [DOI] [Google Scholar]
- 3.Midilli A., Kucuk H., Topal M.E., Akbulut U., Dincer I. A comprehensive review on hydrogen production from coal gasification: Challenges and Opportunities. Int. J. Hydrogen Energy. 2021;46:25385–25412. doi: 10.1016/j.ijhydene.2021.05.088. [DOI] [Google Scholar]
- 4.Roeb M., Monnerie N., Houaijia A., Thomey D., Sattler C. Renewable Hydrogen Technologies. Elsevier; Amsterdam, The Netherlands: 2013. Solar Thermal Water Splitting; pp. 63–86. [Google Scholar]
- 5.Hosseini S.E., Wahid M.A. Hydrogen production from renewable and sustainable energy resources: Promising green energy carrier for clean development. Renew. Sustain. Energy Rev. 2016;57:850–866. doi: 10.1016/j.rser.2015.12.112. [DOI] [Google Scholar]
- 6.Carey J., Kennedy S., Mastny L. Global Renewables Outlook: Energy Transformation 2050. IRENA; Abu Dhabi, United Arab Emirates: 2020. [Google Scholar]
- 7.Kumar R., Kumar A., Pal A. An overview of conventional and non-conventional hydrogen production methods. Mater. Today Proc. 2020 doi: 10.1016/j.matpr.2020.08.793. [DOI] [Google Scholar]
- 8.Awadallah A.E., Mostafa M.S., Aboul-Enein A.A., Hanafi S.A. Hydrogen production via methane decomposition over Al2O3–TiO2 binary oxides supported Ni catalysts: Effect of Ti content on the catalytic efficiency. Fuel. 2014;129:68–77. doi: 10.1016/j.fuel.2014.03.047. [DOI] [Google Scholar]
- 9.Ahmad M.S., Ali M.S., Rahim N.A. Hydrogen energy vision 2060: Hydrogen as energy Carrier in Malaysian primary energy mix—Developing P2G case. Energy Strateg. Rev. 2021;35:100632. doi: 10.1016/j.esr.2021.100632. [DOI] [Google Scholar]
- 10.Owgi A.H.K., Jalil A.A., Hussain I., Hassan N.S., Hambali H.U., Siang T.J., Vo D.V.N. Catalytic systems for enhanced carbon dioxide reforming of methane: A review. Environ. Chem. Lett. 2021;19:2157–2183. doi: 10.1007/s10311-020-01164-w. [DOI] [Google Scholar]
- 11.Oladokun O., Ahmad A., Abdullah T.A.T., Nyakuma B.B., Kamaroddin M.F.A., Ahmed M., Alkali H. Sensitivity analysis of biohydrogen production from Imperata cylindrica using stoichiometric equilibrium model. J. Teknol. 2016;78:137–142. doi: 10.11113/jt.v78.9577. [DOI] [Google Scholar]
- 12.Omoniyi O., Bacquart T., Moore N., Bartlett S., Williams K., Goddard S., Lipscombe B., Murugan A., Jones D. Hydrogen gas quality for gas network injection: State of the art of three hydrogen production methods. Processes. 2021;9:1056. doi: 10.3390/pr9061056. [DOI] [Google Scholar]
- 13.Abdullah W.S.W., Osman M., Kadir M.Z.A.A., Verayiah R. The potential and status of renewable energy development in Malaysia. Energies. 2019;12:2437. doi: 10.3390/en12122437. [DOI] [Google Scholar]
- 14.Stokes I. Technology Roadmap. Train. Proj. Manag. 2020:241–246. doi: 10.4324/9781315264783-86. [DOI] [Google Scholar]
- 15.Kimura S., Li Y. Demand and Supply Potential of Hydrogen Energy in East Asia. Volume 01 Economic Research Institute for ASEAN and East Asia; Jakarta, Indonesia: 2019. [Google Scholar]
- 16.Sanguesa J.A., Torres-Sanz V., Garrido P., Martinez F.J., Marquez-Barja J.M. A Review on Electric Vehicles: Technologies and Challenges. Smart Cities. 2021;4:372–404. doi: 10.3390/smartcities4010022. [DOI] [Google Scholar]
- 17.Gielen D., Saygin D., Rigter J. Renewable Energy Prospects: Indonesia. IRENA; Abu Dhabi, United Arab Emirates: 2017. [Google Scholar]
- 18.Baykara S.Z. Hydrogen: A brief overview on its sources, production and environmental impact. Int. J. Hydrogen Energy. 2018;43:10605–10614. doi: 10.1016/j.ijhydene.2018.02.022. [DOI] [Google Scholar]
- 19.Shiva Kumar S., Himabindu V. Hydrogen production by PEM water electrolysis—A review. Mater. Sci. Energy Technol. 2019;2:442–454. doi: 10.1016/j.mset.2019.03.002. [DOI] [Google Scholar]
- 20.Dawood F., Anda M., Shafiullah G.M. Hydrogen production for energy: An overview. Int. J. Hydrogen Energy. 2020;45:3847–3869. doi: 10.1016/j.ijhydene.2019.12.059. [DOI] [Google Scholar]
- 21.Kamaroddin M.F.A., Sabli N., Nia P.M., Abdullah T.A.T., Abdullah L.C., Izhar S., Ripin A., Ahmad A. Phosphoric acid doped composite proton exchange membrane for hydrogen production in medium-temperature copper chloride electrolysis. Int. J. Hydrogen Energy. 2020;45:22209–22222. doi: 10.1016/j.ijhydene.2019.10.030. [DOI] [Google Scholar]
- 22.Nicoletti G., Arcuri N., Nicoletti G., Bruno R. A technical and environmental comparison between hydrogen and some fossil fuels. Energy Convers. Manag. 2015;89:205–213. doi: 10.1016/j.enconman.2014.09.057. [DOI] [Google Scholar]
- 23.Ren X., Dong L., Xu D., Hu B. Challenges towards hydrogen economy in China. Int. J. Hydrogen Energy. 2020;45:34326–34345. doi: 10.1016/j.ijhydene.2020.01.163. [DOI] [Google Scholar]
- 24.Nikolaidis P., Poullikkas A. A comparative overview of hydrogen production processes. Renew. Sustain. Energy Rev. 2017;67:597–611. doi: 10.1016/j.rser.2016.09.044. [DOI] [Google Scholar]
- 25.ESMAP . Green Hydrogen in Amsterdam. ESMAP; Washington DC, USA: 2020. [Google Scholar]
- 26.Soltani R., Dincer I., Rosen M.A. Kinetic and electrochemical analyses of a CuCI/HCl electrolyzer. Int. J. Energy Res. 2019:er.4703. doi: 10.1002/er.4703. [DOI] [Google Scholar]
- 27.Bessarabov D., Wang H., Li H., Zhao N. In: PEM Electrolysis for Hydrogen Production: Principles and Applications. Bessarabov D., Wang H., Li H., Zhao N., editors. Taylor & Francis; Boca Raton, FL, USA: 2016. [Google Scholar]
- 28.Olabi A.G., Bahri A.s., Abdelghafar A.A., Baroutaji A., Sayed E.T., Alami A.H., Rezk H., Abdelkareem M.A. Large-vscale hydrogen production and storage technologies: Current status and future directions. Int. J. Hydrogen Energy. 2021;46:23498–23528. doi: 10.1016/j.ijhydene.2020.10.110. [DOI] [Google Scholar]
- 29.Pinsky R., Sabharwall P., Hartvigsen J., O’Brien J. Comparative review of hydrogen production technologies for nuclear hybrid energy systems. Prog. Nucl. Energy. 2020;123:103317. doi: 10.1016/j.pnucene.2020.103317. [DOI] [Google Scholar]
- 30.Carmo M., Fritz D.L., Mergel J., Stolten D. A comprehensive review on PEM water electrolysis. Int. J. Hydrogen Energy. 2013;38:4901–4934. doi: 10.1016/j.ijhydene.2013.01.151. [DOI] [Google Scholar]
- 31.Volkov V.V., Federation R., Deville S. Encyclopedia of Membranes. Springer; New York, NY, USA: 2016. [Google Scholar]
- 32.Hui T., Selvaraj J., Chein S., Chyi S. Energy policy and alternative energy in Malaysia: Issues and challenges for sustainable growth—An update. Renew. Sustain. Energy Rev. 2018;81:3021–3031. [Google Scholar]
- 33.Edwards R.L., Font-Palma C., Howe J. The status of hydrogen technologies in the UK: A multi-disciplinary review. Sustain. Energy Technol. Assess. 2021;43:100901. doi: 10.1016/j.seta.2020.100901. [DOI] [Google Scholar]
- 34.Lei Q., Wang B., Wang P., Liu S. Hydrogen generation with acid/alkaline amphoteric water electrolysis. J. Energy Chem. 2019;38:162–169. doi: 10.1016/j.jechem.2018.12.022. [DOI] [Google Scholar]
- 35.Luo M., Yi Y., Wang S., Wang Z., Du M., Pan J., Wang Q. Review of hydrogen production using chemical-looping technology. Renew. Sustain. Energy Rev. 2018;81:3186–3214. doi: 10.1016/j.rser.2017.07.007. [DOI] [Google Scholar]
- 36.Natural Resources Canada (NRCan) Seizing the Opportunities for Hydrogen. Natural Resources Canada (NRCan); Hamilton, ON, Canada: 2020. [Google Scholar]
- 37.Bockris J.O.M. The hydrogen economy: Its history. Int. J. Hydrogen Energy. 2013;38:2579–2588. doi: 10.1016/j.ijhydene.2012.12.026. [DOI] [Google Scholar]
- 38.Daud W.R.W., Ahmad A., Mohamed A.B., Kamarudin S.K., Koh J.I.S., Rasid N., Daud Z.B., Hasran U.A., Samuel N., Abdullah M.I. The Blueprint for Fuel Cell Industries in Malaysia. Academy of Sciences Malaysia; Kuala Lumpur, Malaysia: 2017. [Google Scholar]
- 39.Ambrose A.F., Al-Amin A.Q., Rasiah R., Saidur R., Amin N. Prospects for introducing hydrogen fuel cell vehicles in Malaysia. Int. J. Hydrogen Energy. 2017;42:9125–9134. doi: 10.1016/j.ijhydene.2016.05.122. [DOI] [Google Scholar]
- 40.IRENA . Future of Solar Photovoltaic: Deployment, Investment, Technology, Grid Integration and Socio-Economic Aspects (A Global Energy Transformation: Paper) IRENA; Abu Dhabi, United Arab Emirates: 2019. [Google Scholar]
- 41.Millet P., Grigoriev S. Renewable Hydrogen Technologies: Production, Purification, Storage, Applications and Safety. Elsevier; Amsterdam, The Netherlands: 2013. Water Electrolysis Technologies; pp. 19–41. [Google Scholar]
- 42.Wu Q.X., Pan Z.F., An L. Recent advances in alkali-doped polybenzimidazole membranes for fuel cell applications. Renew. Sustain. Energy Rev. 2018;89:168–183. doi: 10.1016/j.rser.2018.03.024. [DOI] [Google Scholar]
- 43.Fahid Amin H.M. Master’s Thesis. Politecnico di Milano; Milan, Italy: 2010. Heat Transfer Analysis of PEMFC System Using FEM. [Google Scholar]
- 44.Kamaroddin M.F.A., Sabli N., Abdullah T.A.T. Advances In Hydrogen Generation Technologies. InTech; London, UK: 2018. Hydrogen Production by Membrane Water Splitting Technologies; pp. 19–37. [Google Scholar]
- 45.María Barragán V. Short-circuit current in polymeric membrane-based thermocells: An experimental study. Membranes. 2021;11:480. doi: 10.3390/membranes11070480. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 46.Özdemir Y., Özkan N., Devrim Y. Fabrication and Characterization of Cross-linked Polybenzimidazole Based Membranes for High Temperature PEM Fuel Cells. Electrochim. Acta. 2017;245:1–13. doi: 10.1016/j.electacta.2017.05.111. [DOI] [Google Scholar]
- 47.Abbasi R., Setzler B.P., Lin S., Wang J., Zhao Y., Xu H., Pivovar B., Tian B., Chen X., Wu G., et al. A Roadmap to Low-Cost Hydrogen with Hydroxide Exchange Membrane Electrolyzers. Adv. Mater. 2019;1805876:1–14. doi: 10.1002/adma.201805876. [DOI] [PubMed] [Google Scholar]
- 48.Kamaroddin M.F.A., Sabli N., Abdullah T.A.T., Abdullah L.C., Izhar S., Ripin A., Ahmad A. Effect of temperature and current density on polybenzimidazole zirconium phosphate hybrid membrane in copper chloride electrolysis for hydrogen production. Int. J. Integr. Eng. 2019;11:182–189. doi: 10.30880/ijie.2019.11.07.024. [DOI] [Google Scholar]
- 49.Escorihuela J., Sahuquillo Ó., García-Bernabé A., Giménez E., Compañ V. Phosphoric acid doped polybenzimidazole (PBI)/Zeolitic imidazolate framework composite membranes with significantly enhanced proton conductivity under low humidity conditions. Nanomaterials. 2018;8:775. doi: 10.3390/nano8100775. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 50.Da Burgal J.P.S. Ph.D. Thesis. Imperial College London; London, UK: 2016. Development of Poly (ether ether ketone) Nanofiltration Membranes for Organic Solvent Nanofiltration in Continuous Flow Systems. [Google Scholar]
- 51.Valtcheva I. Ph.D. Thesis. Imperial College London; London, UK: 2016. Polybenzimidazole Membranes for Organic Solvent Nanofiltration: Formation Parameters and Applications. [Google Scholar]
- 52.Shaari N., Kamarudin S.K. Recent advances in additive-enhanced polymer electrolyte membrane properties in fuel cell applications: An overview. Int. J. Energy Res. 2019;43:2756–2794. doi: 10.1002/er.4348. [DOI] [Google Scholar]
- 53.Di Noto V., Zawodzinski T.A., Herring A.M., Giffin G.A., Negro E., Lavina S. Polymer electrolytes for a hydrogen economy. Int. J. Hydrogen Energy. 2012;37:6120–6131. doi: 10.1016/j.ijhydene.2012.01.080. [DOI] [Google Scholar]
- 54.Grigoriev S.A., Fateev V.N. Hydrogen Production by Water Electrolysis, Hydrogen Production Technologies. Scrivener Publishing LLC; Beverly, MA, USA: 2019. pp. 231–276. [Google Scholar]
- 55.Sahu A.K., Pitchumani S., Sridhar P., Shukla A.K. Nafion and modified-Nafion membranes for polymer electrolyte fuel cells: An overview. Bull. Mater. Sci. 2009;32:285–294. doi: 10.1007/s12034-009-0042-8. [DOI] [Google Scholar]
- 56.Rahim A.H.A., Salami A., Kamarudin S.K., Hanapi S. An overview of polymer electrolyte membrane electrolyzer for hydrogen production: Modeling and mass transport. J. Power Sources. 2016;309:56–65. doi: 10.1016/j.jpowsour.2016.01.012. [DOI] [Google Scholar]
- 57.Lade H., Kumar V., Arthanareeswaran G., Ismail A.F. Sulfonated poly(arylene ether sulfone) nanocomposite electrolyte membrane for fuel cell applications: A review. Int. J. Hydrogen Energy. 2017;42:1063–1074. doi: 10.1016/j.ijhydene.2016.10.038. [DOI] [Google Scholar]
- 58.Hooshyari K., Javanbakht M., Shabanikia A., Enhessari M. Fabrication BaZrO3/PBI-based nanocomposite as a new proton conducting membrane for high temperature proton exchange membrane fuel cells. J. Power Sources. 2015;276:62–72. doi: 10.1016/j.jpowsour.2014.11.083. [DOI] [Google Scholar]
- 59.Romano S.M. Ph.D. Thesis. Universitat Politècnica de València; Valencia, Spain: 2015. Application of Nanofibres in Polymer Composite Membranes for Direct Methanol Fuel Cells. [Google Scholar]
- 60.Mu D., Yu L., Liu L., Xi J. Rice Paper Reinforced Sulfonated Poly(ether ether ketone) as Low-Cost Membrane for Vanadium Flow Batteries. ACS Sustain. Chem. Eng. 2017;5:2437–2444. doi: 10.1021/acssuschemeng.6b02784. [DOI] [Google Scholar]
- 61.Paidar M., Fateev V., Bouzek K. Membrane electrolysis—History, current status and perspective. Electrochim. Acta. 2016;209:737–756. doi: 10.1016/j.electacta.2016.05.209. [DOI] [Google Scholar]
- 62.Ying Y.P., Kamarudin S.K., Masdar M.S. Silica-related membranes in fuel cell applications: An overview. Int. J. Hydrogen Energy. 2018:1–17. doi: 10.1016/j.ijhydene.2018.06.171. [DOI] [Google Scholar]
- 63.Toghyani S., Afshari E., Baniasadi E., Atyabi S.A., Naterer G.F. Thermal and electrochemical performance assessment of a high temperature PEM electrolyzer. Energy. 2018;152:237–246. doi: 10.1016/j.energy.2018.03.140. [DOI] [Google Scholar]
- 64.Araya S.S., Zhou F., Liso V., Sahlin S.L., Vang J.R., Thomas S., Gao X., Jeppesen C., Kær S.K. A comprehensive review of PBI-based high temperature PEM fuel cells. Int. J. Hydrogen Energy. 2016;41:21310–21344. doi: 10.1016/j.ijhydene.2016.09.024. [DOI] [Google Scholar]
- 65.Abdol Rahim A.H., Tijani A.S., Shukri F.H. Simulation analysis of the effect of temperature on overpotentials in PEM electrolyzer system. J. Mech. Eng. 2015;12:47–65. [Google Scholar]
- 66.Ainla A., Brandell D. Nafion®-polybenzimidazole (PBI) composite membranes for DMFC applications. Solid State Ionics. 2007;178:581–585. doi: 10.1016/j.ssi.2007.01.014. [DOI] [Google Scholar]
- 67.Wang Y., Wang Q., Wan L.Y., Han Y., Hong Y., Huang L., Yang X., Wang Y., Zaghib K., Zhou Z. KOH-doped polybenzimidazole membrane for direct hydrazine fuel cell. J. Colloid Interface Sci. 2020;563:27–32. doi: 10.1016/j.jcis.2019.12.046. [DOI] [PubMed] [Google Scholar]
- 68.Sana B., Jana T. Polymer electrolyte membrane from polybenzimidazoles: Influence of tetraamine monomer structure. Polymer (Guildf). 2018;137:312–323. doi: 10.1016/j.polymer.2018.01.029. [DOI] [Google Scholar]
- 69.Yang J., Aili D., Li Q., Xu Y., Liu P., Che Q., Jensen J.O., Bjerrum N.J., He R. Benzimidazole grafted polybenzimidazoles for proton exchange membrane fuel cells. Polym. Chem. 2013;4:4768–4775. doi: 10.1039/c3py00408b. [DOI] [Google Scholar]
- 70.Javad M., Rowshanzamir S., Gashoul F. Comprehensive investigation of physicochemical and electrochemical properties of sulfonated poly (ether ether ketone) membranes with different degrees of sulfonation for proton exchange membrane fuel cell applications. Energy. 2017;125:614–628. doi: 10.1016/j.energy.2017.02.143. [DOI] [Google Scholar]
- 71.Zhou Z., Zholobko O., Wu X.-F., Aulich T., Thakare J., Hurley J. Polybenzimidazole-Based Polymer Electrolyte Membranes for High-Temperature Fuel Cells: Current Status and Prospects. Energies. 2021;14:135. doi: 10.3390/en14010135. [DOI] [Google Scholar]
- 72.Wan Mohd Noral Azman W.N.E., Jaafar J., Salleh W.N.W., Ismail A.F., Othman M.H.D., Rahman M.A., Rasdi F.R.M. Highly selective SPEEK/ENR blended polymer electrolyte membranes for direct methanol fuel cell. Mater. Today Energy. 2020;17:100427. doi: 10.1016/j.mtener.2020.100427. [DOI] [Google Scholar]
- 73.Iulianelli A., Basile A. Sulfonated PEEK-based polymers in PEMFC and DMFC applications: A review. Int. J. Hydrogen Energy. 2012;37:15241–15255. doi: 10.1016/j.ijhydene.2012.07.063. [DOI] [Google Scholar]
- 74.Mossayebi Z., Saririchi T., Rowshanzamir S., Parnian M.J. Investigation and optimization of physicochemical properties of sulfated zirconia/sulfonated poly (ether ether ketone) nanocomposite membranes for medium temperature proton exchange membrane fuel cells. Int. J. Hydrogen Energy. 2016;41:12293–12306. doi: 10.1016/j.ijhydene.2016.05.017. [DOI] [Google Scholar]
- 75.Zhai S., Dai W., Lin J., He S., Zhang B., Chen L. Enhanced proton conductivity in sulfonated poly(ether ether ketone) membranes by incorporating sodium dodecyl benzene sulfonate. Polymers. 2019;11 doi: 10.3390/polym11020203. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 76.Tahrim A.A., Amin I.N.H.M. Advancement in Phosphoric Acid Doped Polybenzimidazole Membrane for High Temperature PEM Fuel Cells: A Review. J. Appl. Membr. Sci. Tech. 2019;23:37–62. doi: 10.11113/amst.v23n1.136. [DOI] [Google Scholar]
- 77.Salarizadeh P., Javanbakht M., Pourmahdian S., Beydaghi H. Influence of amine-functionalized iron titanate as filler for improving conductivity and electrochemical properties of SPEEK nanocomposite membranes. Chem. Eng. J. 2016;299:320–331. doi: 10.1016/j.cej.2016.04.086. [DOI] [Google Scholar]
- 78.Ahmad H., Kamarudin S.K., Hasran U.A., Daud W.R.W. Overview of hybrid membranes for direct-methanol fuel-cell applications. Int. J. Hydrogen Energy. 2010;35:2160–2175. doi: 10.1016/j.ijhydene.2009.12.054. [DOI] [Google Scholar]
- 79.Guo Y., Li G., Zhou J., Liu Y. Comparison between hydrogen production by alkaline water electrolysis and hydrogen production by PEM electrolysis. IOP Conf. Ser. Earth Environ. Sci. 2019;371 doi: 10.1088/1755-1315/371/4/042022. [DOI] [Google Scholar]
- 80.Li X., Zhao L., Yu J., Liu X., Zhang X., Liu H., Zhou W. Water Splitting: From Electrode to Green Energy System. Nano-Micro Lett. 2020;12:1–29. doi: 10.1007/s40820-020-00469-3. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 81.Li C., Baek J.B. The promise of hydrogen production from alkaline anion exchange membrane electrolyzers. Nano Energy. 2021;87:106162. doi: 10.1016/j.nanoen.2021.106162. [DOI] [Google Scholar]
- 82.Yue M., Lambert H., Pahon E., Roche R., Jemei S., Hissel D. Hydrogen energy systems: A critical review of technologies, applications, trends and challenges. Renew. Sustain. Energy Rev. 2021;146:111180. doi: 10.1016/j.rser.2021.111180. [DOI] [Google Scholar]
- 83.Wan L., Xu Z., Wang P., Lin Y., Wang B. H2SO4-doped polybenzimidazole membranes for hydrogen production with acid-alkaline amphoteric water electrolysis. J. Memb. Sci. 2021;618:118642. doi: 10.1016/j.memsci.2020.118642. [DOI] [Google Scholar]
- 84.Escorihuela J., García-Bernabé A., Compañ V. A deep insight into different acidic additives as doping agents for enhancing proton conductivity on polybenzimidazole membranes. Polymers. 2020;12:1374. doi: 10.3390/polym12061374. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 85.Escorihuela J., García-Bernabé A., Montero A., Andrio A., Sahuquillo Ó., Gimenez E., Compañañ V. Proton Conductivity through Polybenzimidazole Composite Membranes Containing Silica Nanofiber Mats. Polymers. 2019;11:1182. doi: 10.3390/polym11071182. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 86.Sun X., Xu K., Fleischer C., Liu X., Grandcolas M., Strandbakke R., Bjørheim T.S., Norby T., Chatzitakis A. Earth-abundant electrocatalysts in proton exchange membrane electrolyzers. Catalysts. 2018;8:657. doi: 10.3390/catal8120657. [DOI] [Google Scholar]
- 87.Kim D.J., Choi D.H., Park C.H., Nam S.Y. Characterization of the sulfonated PEEK/sulfonated nanoparticles composite membrane for the fuel cell application. Int. J. Hydrogen Energy. 2016;41:5793–5802. doi: 10.1016/j.ijhydene.2016.02.056. [DOI] [Google Scholar]
- 88.Sun X., Simonsen S.C., Norby T., Chatzitakis A. Composite Membranes for High Temperature PEM Fuel Cells and Electrolysers: A Critical Review. Membranes. 2019;9:83. doi: 10.3390/membranes9070083. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 89.Dong Y., Liu J., Sui M., Qu Y., Ambuchi J.J., Wang H., Feng Y. A combined microbial desalination cell and electrodialysis system for copper-containing wastewater treatment and high-salinity-water desalination. J. Hazard. Mater. 2017;321:307–315. doi: 10.1016/j.jhazmat.2016.08.034. [DOI] [PubMed] [Google Scholar]
- 90.Hitam C.N.C., Jalil A.A. A review on biohydrogen production through photo-fermentation of lignocellulosic biomass. Biomass Convers. Biorefinery. 2020 doi: 10.1007/s13399-020-01140-y. [DOI] [Google Scholar]
- 91.Edge P. Master’s Thesis. University of Ontario Institute of Technology; Oshawa, ON, Canada: 2013. The Production and Characterization of Ceramic Carbon Electrode Materials for CuCl—HCl Electrolysis. [Google Scholar]
- 92.Balashov V.N., Schatz R.S., Chalkova E., Akinfiev N.N., Fedkin M.V., Lvov S.N. CuCl Electrolysis for Hydrogen Production in the Cu–Cl Thermochemical Cycle. J. Electrochem. Soc. 2011;158:B266–B275. doi: 10.1149/1.3521253. [DOI] [Google Scholar]
- 93.Aghahosseini S. Ph.D. Thesis. University of Ontario Institute of Technology; Oshawa, ON, Canada: 2013. System Integration and Optimization of Copper-Chlorine Thermochemical Cycle with Various Options for Hydrogen Production. [Google Scholar]
- 94.Naterer G.F., Suppiah S., Stolberg L., Lewis M., Wang Z., Rosen M.A., Dincer I., Gabriel K., Odukoya A., Secnik E., et al. Progress in thermochemical hydrogen production with the copper-chlorine cycle. Int. J. Hydrogen Energy. 2015;40:6283–6295. doi: 10.1016/j.ijhydene.2015.02.124. [DOI] [Google Scholar]
- 95.Abdo N., Bradley Easton E. Nafion/Polyaniline composite membranes for hydrogen production in the Cu-Cl thermochemical cycle. Int. J. Hydrogen Energy. 2016;41:7892–7903. doi: 10.1016/j.ijhydene.2015.11.180. [DOI] [Google Scholar]
- 96.Naterer G.F., Suppiah S., Stolberg L., Lewis M., Ferrandon M., Wang Z., Dincer I., Gabriel K., Rosen M.A., Secnik E., et al. Clean hydrogen production with the Cu–Cl cycle—Progress of international consortium, II: Simulations, thermochemical data and materials. Int. J. Hydrogen Energy. 2011;36:15486–15501. doi: 10.1016/j.ijhydene.2011.08.013. [DOI] [Google Scholar]
- 97.Subianto S. Recent advances in polybenzimidazole/phosphoric acid membranes for high-temperature fuel cells. Polym. Int. 2014;63:1134–1144. doi: 10.1002/pi.4708. [DOI] [Google Scholar]
- 98.Kamaroddin M.F.A., Sabli N., Abdullah T.A.T., Abdullah L.C., Izhar S., Ripin A., Ahmad A. Proceedings of the IOP Conference Series: Earth and Environmental Science. Volume 268. Institute of Physics Publishing; England, UK: 2019. Phosphoric Acid Doped Polybenzimidazole and Sulfonated Polyether Ether Ketone Composite Membrane for Hydrogen Production in High-Temperature Copper Chloride Electrolysis; pp. 1–6. [Google Scholar]
- 99.Aghahosseini S., Dincer I., Naterer G.F. Linear sweep voltammetry measurements and factorial design model of hydrogen production by HCl/CuCl electrolysis. Int. J. Hydrogen Energy. 2013;38:12704–12717. doi: 10.1016/j.ijhydene.2013.07.105. [DOI] [Google Scholar]
- 100.Schatz R., Kim S., Khurana S., Fedkin M., Lvov S.N. High Efficiency CuCl Electrolyzer for Cu-Cl Thermochemical Cycle. ECS Trans. 2013;50:153–164. doi: 10.1149/05049.0153ecst. [DOI] [Google Scholar]
- 101.Marin G.D., Wang Z., Naterer G.F., Gabriel K. Byproducts and reaction pathways for integration of the Cu–Cl cycle of hydrogen production. Int. J. Hydrogen Energy. 2011;36:13414–13424. doi: 10.1016/j.ijhydene.2011.07.103. [DOI] [Google Scholar]
- 102.Krüger A.J., Kerres J., Kerres J., Krieg H.M., Bessarabov D. Electrochemical Hydrogen Production from SO2 and Water in a SDE Electrolyzer. Hydrog. Prod. Technol. 2017:277–303. doi: 10.1002/9781119283676.ch7. [DOI] [Google Scholar]
- 103.Giddey S., Badwal S.P.S., Ju H. Current Trends and Future Developments on (Bio-); Membranes. Elsevier Inc.; Amsterdam, The Netherlands: 2019. Polymer electrolyte membrane technologies integrated with renewable energy for hydrogen production; pp. 235–259. [Google Scholar]
- 104.Chi J., Yu H. Water electrolysis based on renewable energy for hydrogen production. Cuihua Xuebao/Chin. J. Catal. 2018;39:390–394. doi: 10.1016/S1872-2067(17)62949-8. [DOI] [Google Scholar]
- 105.Escorihuela J., García-Bernabé A., Montero Á., Sahuquillo Ó., Giménez E., Compañ V. Ionic liquid composite polybenzimidazol membranes for high temperature PEMFC applications. Polymers. 2019;11:732. doi: 10.3390/polym11040732. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 106.Babic U., Suermann M., Büchi F.N., Gubler L., Schmidt T.J. Critical Review—Identifying Critical Gaps for Polymer Electrolyte Water Electrolysis Development. J. Electrochem. Soc. 2017;164:F387–F399. doi: 10.1149/2.1441704jes. [DOI] [Google Scholar]
- 107.Park J.E., Kang S.Y., Oh S.H., Kim J.K., Lim M.S., Ahn C.Y., Cho Y.H., Sung Y.E. High-performance anion-exchange membrane water electrolysis. Electrochim. Acta. 2019;295:99–106. doi: 10.1016/j.electacta.2018.10.143. [DOI] [Google Scholar]
- 108.Leng Y., Chen G., Mendoza A.J., Tighe T.B., Hickner M.A. Solid-State Water Electrolysis with an Alkaline Membrane. J. Am. Chem. Soc. 2012;134:9054–9057. doi: 10.1021/ja302439z. [DOI] [PubMed] [Google Scholar]
- 109.Pavel C.C., Cecconi F., Emiliani C., Santiccioli S., Scaffidi A., Catanorchi S., Comotti M. Highly efficient platinum group metal free based membrane-electrode assembly for anion exchange membrane water electrolysis. Angew. Chemie—Int. Ed. 2014;53:1378–1381. doi: 10.1002/anie.201308099. [DOI] [PubMed] [Google Scholar]
- 110.Qian W., Shang Y., Fang M., Wang S., Xie X. Sulfonated polybenzimidazole/zirconium phosphate composite membranes for high temperature applications. Int. J. Hydrogen Energ. 2012;7:5–10. doi: 10.1016/j.ijhydene.2012.05.076. [DOI] [Google Scholar]
- 111.Wu X., Scott K. CuxCo3-xO4 (0 ≤ x <1) nanoparticles for oxygen evolution in high performance alkaline exchange membrane water electrolysers. J. Mater. Chem. 2011;21:12344–12351. doi: 10.1039/c1jm11312g. [DOI] [Google Scholar]
- 112.Seetharaman S., Balaji R., Ramya K., Dhathathreyan K.S., Velan M. Graphene oxide modified non-noble metal electrode for alkaline anion exchange membrane water electrolyzers. Int. J. Hydrogen Energy. 2013;38:14934–14942. doi: 10.1016/j.ijhydene.2013.09.033. [DOI] [Google Scholar]
- 113.Joe J.D., Kumar D.B.S., Sivakumar P. Production of Hydrogen By Anion Exchange Membrane Using AWE. Int. J. Sci. Technol. Res. 2014;3:38–42. [Google Scholar]
- 114.Anwar S., Khan F., Zhang Y., Djire A. Recent development in electrocatalysts for hydrogen production through water electrolysis. Int. J. Hydrogen Energy. 2021;46:32284–32317. doi: 10.1016/j.ijhydene.2021.06.191. [DOI] [Google Scholar]
- 115.Dingenen F., Verbruggen S.W. Tapping hydrogen fuel from the ocean: A review on photocatalytic, photoelectrochemical and electrolytic splitting of seawater. Renew. Sustain. Energy Rev. 2021;142:110866. doi: 10.1016/j.rser.2021.110866. [DOI] [Google Scholar]
- 116.Nechache A., Han F., Semerad R., Schiller G., Costa R. Evaluation of Performance and Degradation Profiles of a Metal Supported Solid Oxide Fuel Cell under Electrolysis Operation. ECS Trans. 2017;78:3039–3047. doi: 10.1149/07801.3039ecst. [DOI] [Google Scholar]
- 117.Chen T., Zhou Y., Liu M., Yuan C., Ye X., Zhan Z., Wang S. High performance solid oxide electrolysis cell with impregnated electrodes. Electrochem. Commun. 2015;54:23–27. doi: 10.1016/j.elecom.2015.02.015. [DOI] [Google Scholar]
- 118.Shen F., Wang R., Tucker M.C. Long term durability test and post mortem for metal-supported solid oxide electrolysis cells. J. Power Sources. 2020;474:228618. doi: 10.1016/j.jpowsour.2020.228618. [DOI] [Google Scholar]
- 119.Wu S.-H., Lin J.-K., Shiu W.-H., Liu C.-K., Lin T.-N., Lee R.-Y., Ting H.-C., Lin H.-H., Cheng Y.-N. Proceedings of the 42nd International Conference on Advanced Ceramics and Composites, Ceramic Engineering and Science. Volume 39. John Wiley & Sons; Hoboken, NJ, USA: 2019. Performance Test for Anode-Supported And Metal-Supported Solid Oxide Electrolysis Cell Under Different Current Densities; pp. 139–148. [DOI] [Google Scholar]
- 120.Hwang C.S., Tsai C.H., Hwang T.J., Chang C.L., Yang S.F., Lin J.K. Novel Metal Substrates for High Power Metal-supported Solid Oxide Fuel Cells. Fuel Cells. 2016;16:244–251. doi: 10.1002/fuce.201500216. [DOI] [Google Scholar]
- 121.Kumar G., Sivagurunathan P., Pugazhendhi A., Thi N.B.D., Zhen G., Chandrasekhar K., Kadier A. A comprehensive overview on light independent fermentative hydrogen production from wastewater feedstock and possible integrative options. Energy Convers. Manag. 2017;141:390–402. doi: 10.1016/j.enconman.2016.09.087. [DOI] [Google Scholar]
- 122.Haron R., Mat R., Tuan Abdullah T.A., Rahman R.A. Overview on utilization of biodiesel by-product for biohydrogen production. J. Clean. Prod. 2018;172:314–324. doi: 10.1016/j.jclepro.2017.10.160. [DOI] [Google Scholar]
- 123.Park S.G., Chae K.J., Lee M. A sulfonated poly(arylene ether sulfone)/polyimide nanofiber composite proton exchange membrane for microbial electrolysis cell application under the coexistence of diverse competitive cations and protons. J. Memb. Sci. 2017;540:165–173. doi: 10.1016/j.memsci.2017.06.048. [DOI] [Google Scholar]
- 124.Chae K.J., Kim K.Y., Choi M.J., Yang E., Kim I.S., Ren X., Lee M. Sulfonated polyether ether ketone (SPEEK)-based composite proton exchange membrane reinforced with nanofibers for microbial electrolysis cells. Chem. Eng. J. 2014;254:393–398. doi: 10.1016/j.cej.2014.05.145. [DOI] [Google Scholar]
- 125.Lim S.S., Daud W.R.W., Md Jahim J., Ghasemi M., Chong P.S., Ismail M. Sulfonated poly(ether ether ketone)/poly(ether sulfone) composite membranes as an alternative proton exchange membrane in microbial fuel cells. Int. J. Hydrogen Energy. 2012;37:11409–11424. doi: 10.1016/j.ijhydene.2012.04.155. [DOI] [Google Scholar]
- 126.Kadier A., Simayi Y., Abdeshahian P., Azman N.F., Chandrasekhar K., Kalil M.S. A comprehensive review of microbial electrolysis cells (MEC) reactor designs and configurations for sustainable hydrogen gas production. Alexandria Eng. J. 2016;55:427–443. doi: 10.1016/j.aej.2015.10.008. [DOI] [Google Scholar]
- 127.Martínez-Merino V., Gil M.J., Cornejo A. Biological Hydrogen Production. Renew. Hydrog. Technol. Prod. Purif. Storage Appl. Saf. 2013:171–199. doi: 10.1016/B978-0-444-56352-1.00008-8. [DOI] [Google Scholar]
- 128.Islam A.K.M.K., Dunlop P.S.M., Hewitt N.J., Lenihan R., Brandoni C. Bio-Hydrogen Production from Wastewater: A Comparative Study of Low Energy Intensive Production Processes. Clean Technol. 2021;3:156–182. doi: 10.3390/cleantechnol3010010. [DOI] [Google Scholar]
- 129.Liu H., Grot S., Logan B.E. Electrochemically assisted microbial production of hydrogen from acetate. Environ. Sci. Technol. 2005;39:4317–4320. doi: 10.1021/es050244p. [DOI] [PubMed] [Google Scholar]
- 130.Rozendal R.A., Jeremiasse A.W., Hamelers H.V.M., Buisman C.J.N. Hydrogen production with a microbial biocathode. Environ. Sci. Technol. 2008;42:629–634. doi: 10.1021/es071720+. [DOI] [PubMed] [Google Scholar]
- 131.Selembo P.A., Merrill M.D., Logan B.E. The use of stainless steel and nickel alloys as low-cost cathodes in microbial electrolysis cells. J. Power Sources. 2009;190:271–278. doi: 10.1016/j.jpowsour.2008.12.144. [DOI] [Google Scholar]
- 132.Foley J.M., Rozendal R.A., Hertle C.K., Lant P.A., Rabaey K. Life cycle assessment of high-rate anaerobic treatment, microbial fuel cells, and microbial electrolysis cells. Environ. Sci. Technol. 2010;44:3629–3637. doi: 10.1021/es100125h. [DOI] [PubMed] [Google Scholar]
- 133.Van Eerten-Jansen M.C.A., Eerten-Jansen V., Ter Heijne A., Buisman C.J.N., Hamelers H.V.M. Microbial electrolysis cells for production of methane from CO2: Long-term performance and perspectives. Int. J. Energy Res. 2012;36:809–819. doi: 10.1002/er.1954. [DOI] [Google Scholar]
- 134.Dhar B.R., Elbeshbishy E., Hafez H., Lee H.S. Hydrogen production from sugar beet juice using an integrated biohydrogen process of dark fermentation and microbial electrolysis cell. Bioresour. Technol. 2015;198:223–230. doi: 10.1016/j.biortech.2015.08.048. [DOI] [PubMed] [Google Scholar]
- 135.Colantonio N., Kim Y. Cadmium (II) removal mechanisms in microbial electrolysis cells. J. Hazard. Mater. 2016;311:134–141. doi: 10.1016/j.jhazmat.2016.02.062. [DOI] [PubMed] [Google Scholar]
- 136.Liu Z., Zhou A., Zhang J., Wang S., Luan Y., Liu W., Wang A., Yue X. Hydrogen Recovery from Waste Activated Sludge: Role of Free Nitrous Acid in a Prefermentation-Microbial Electrolysis Cells System. ACS Sustain. Chem. Eng. 2018;6:3870–3878. doi: 10.1021/acssuschemeng.7b04201. [DOI] [Google Scholar]
- 137.Miller A., Singh L., Wang L., Liu H. Linking internal resistance with design and operation decisions in microbial electrolysis cells. Environ. Int. 2019;126:611–618. doi: 10.1016/j.envint.2019.02.056. [DOI] [PubMed] [Google Scholar]
- 138.Wang L., Chen Y., Long F., Singh L., Trujillo S., Xiao X., Liu H. Breaking the loop: Tackling homoacetogenesis by chloroform to halt hydrogen production-consumption loop in single chamber microbial electrolysis cells. Chem. Eng. J. 2020;389:124436. doi: 10.1016/j.cej.2020.124436. [DOI] [Google Scholar]
- 139.Xu J., Amorim I., Li Y., Li J., Yu Z., Zhang B., Araujo A., Zhang N., Liu L. Stable overall water splitting in an asymmetric acid/alkaline electrolyzer comprising a bipolar membrane sandwiched by bifunctional cobalt-nickel phosphide nanowire electrodes. Carbon Energy. 2020;2:646–655. doi: 10.1002/cey2.56. [DOI] [Google Scholar]
- 140.Alfaifi B.Y., Ullah H., Alfaifi S., Tahir A.A., Mallick T.K. Photoelectrochemical solar water splitting: From basic principles to advanced devices. Veruscript Funct. Nanomater. 2018;2:BDJOC3. doi: 10.22261/FNAN.BDJOC3. [DOI] [Google Scholar]
- 141.Hashimoto K., Irie H., Fujishima A. Invited Review Paper TiO 2 Photocatalysis: A Historical Overview and Future Prospects. Jpn. J. Appl. Phys. 2005;44:8269–8285. doi: 10.1143/JJAP.44.8269. [DOI] [Google Scholar]
- 142.Grimm A., de Jong W.A., Kramer G.J. Renewable hydrogen production: A techno-economic comparison of photoelectrochemical cells and photovoltaic-electrolysis. Int. J. Hydrogen Energy. 2020;45:22545–22555. doi: 10.1016/j.ijhydene.2020.06.092. [DOI] [Google Scholar]
- 143.Joy J., Mathew J., George S.C. Nanomaterials for photoelectrochemical water splitting—Review. Int. J. Hydrogen Energy. 2018;43:4804–4817. doi: 10.1016/j.ijhydene.2018.01.099. [DOI] [Google Scholar]
- 144.Zhang B., Zhang S.-X., Yao R., Wu Y.-H., Qiu J.-S. Progress and prospects of hydrogen production: Opportunities and challenges. J. Electron. Sci. Technol. 2021:100080. doi: 10.1016/j.jnlest.2021.100080. [DOI] [Google Scholar]
- 145.Seger B., Pedersen T., Laursen A.B., Vesborg P.C.K., Hansen O., Chorkendorff I. Using TiO2 as a conductive protective layer for photocathodic H2 evolution. J. Am. Chem. Soc. 2013;135:1057–1064. doi: 10.1021/ja309523t. [DOI] [PubMed] [Google Scholar]
- 146.Lo C.C., Huang C.W., Liao C.H., Wu J.C.S. Novel twin reactor for separate evolution of hydrogen and oxygen in photocatalytic water splitting. Int. J. Hydrogen Energy. 2010;35:1523–1529. doi: 10.1016/j.ijhydene.2009.12.032. [DOI] [Google Scholar]
- 147.Yu S.C., Huang C.W., Liao C.H., Wu J.C.S., Chang S.T., Chen K.H. A novel membrane reactor for separating hydrogen and oxygen in photocatalytic water splitting. J. Memb. Sci. 2011;382:291–299. doi: 10.1016/j.memsci.2011.08.022. [DOI] [Google Scholar]
- 148.Tsydenov D.E., Parmon V.N., Vorontsov A.V. Toward the design of asymmetric photocatalytic membranes for hydrogen production: Preparation of TiO2-based membranes and their properties. Int. J. Hydrogen Energy. 2012;37:11046–11060. doi: 10.1016/j.ijhydene.2012.04.054. [DOI] [Google Scholar]
- 149.Liao C.H., Huang C.W., Wu J.C.S. Novel dual-layer photoelectrode prepared by RF magnetron sputtering for photocatalytic water splitting. Int. J. Hydrogen Energy. 2012;37:11632–11639. doi: 10.1016/j.ijhydene.2012.05.107. [DOI] [Google Scholar]
- 150.Marschall R., Klaysom C., Mukherji A., Wark M., Lu G.Q., Wang L. Composite proton-conducting polymer membranes for clean hydrogen production with solar light in a simple photoelectrochemical compartment cell. Int. J. Hydrogen Energy. 2012;37:4012–4017. doi: 10.1016/j.ijhydene.2011.11.097. [DOI] [Google Scholar]
- 151.Klaysom C., Marschall R., Wang L., Ladewig B.P., Lu G.Q.M. Synthesis of composite ion-exchange membranes and their electrochemical properties for desalination applications. J. Mater. Chem. 2010;20:4669–4674. doi: 10.1039/b925357b. [DOI] [Google Scholar]
- 152.Saba S.M., Müller M., Robinius M., Stolten D. The investment costs of electrolysis – A comparison of cost studies from the past 30 years. Int. J. Hydrogen Energy. 2018;43:1209–1223. doi: 10.1016/j.ijhydene.2017.11.115. [DOI] [Google Scholar]
- 153.Toghyani S., Fakhradini S., Afshari E., Baniasadi E., Abdollahzadeh Jamalabadi M.Y., Safdari Shadloo M. Optimization of operating parameters of a polymer exchange membrane electrolyzer. Int. J. Hydrogen Energy. 2019;44:6403–6414. doi: 10.1016/j.ijhydene.2019.01.186. [DOI] [Google Scholar]
- 154.Colli A.N., Girault H.H., Battistel A. Non-precious electrodes for practical alkaline water electrolysis. Materials. 2019;12:1336. doi: 10.3390/ma12081336. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 155.Naterer G.F., Suppiah S., Rosen M.A., Gabriel K., Dincer I., Jianu O.A., Wang Z., Easton E.B., Ikeda B.M., Rizvi G., et al. Advances in unit operations and materials for the Cu-Cl cycle of hydrogen production. Int. J. Hydrogen Energy. 2017;42:15708–15723. doi: 10.1016/j.ijhydene.2017.03.133. [DOI] [Google Scholar]
- 156.Sapountzi F.M., Gracia J.M., Weststrate C.J., Fredriksson H.O.A., Niemantsverdriet F.J.W. Electrocatalysts for the generation of hydrogen, oxygen and synthesis gas. Prog. Energy Combust. Sci. 2017;58:1–35. doi: 10.1016/j.pecs.2016.09.001. [DOI] [Google Scholar]
- 157.Mališ J., Mazúr P., Paidar M., Bystron T., Bouzek K. Nafion 117 stability under conditions of PEM water electrolysis at elevated temperature and pressure. Int. J. Hydrogen Energy. 2016;41:2177–2188. doi: 10.1016/j.ijhydene.2015.11.102. [DOI] [Google Scholar]
- 158.Avramov S.G., Lefterova E., Penchev H., Sinigersky V., Slavcheva E. Comparative study on the proton conductivity of perfluorosulfonic and polybenzimidazole based polymer electrolyte membranes. Bulg. Chem. Commun. 2016;48:43–50. [Google Scholar]
- 159.Nguyen T., Abdin Z., Holm T., Mérida W. Grid-connected hydrogen production via large-scale water electrolysis. Energy Convers. Manag. 2019;200:112108. doi: 10.1016/j.enconman.2019.112108. [DOI] [Google Scholar]
- 160.Dincer I., Acar C. Innovation in hydrogen production. Int. J. Hydrogen Energy. 2017;42:14843–14864. doi: 10.1016/j.ijhydene.2017.04.107. [DOI] [Google Scholar]
- 161.Chakik F.E., Kaddami M., Mikou M. Effect of operating parameters on hydrogen production by electrolysis of water. Int. J. Hydrogen Energy. 2017;42:25550–25557. doi: 10.1016/j.ijhydene.2017.07.015. [DOI] [Google Scholar]
- 162.Haque M.A., Sulong A.B., Loh K.S., Majlan E.H., Husaini T., Rosli R.E. Acid doped polybenzimidazoles based membrane electrode assembly for high temperature proton exchange membrane fuel cell: A review. Int. J. Hydrogen Energy. 2017;42:9156–9179. doi: 10.1016/j.ijhydene.2016.03.086. [DOI] [Google Scholar]
- 163.Rashid M., Al Mesfer M.K., Naseem H., Danish M. Hydrogen Production by Water Electrolysis: A Review of Alkaline Water Electrolysis, PEM Water Electrolysis and High Temperature Water Electrolysis. Int. J. of Eng. Adv. Technol. (IJEAT) 2015;4:80–93. [Google Scholar]
- 164.Ursua A., Sanchis P., Gandia L.M. Hydrogen Production from Water Electrolysis: Current Status and Future Trends. Proc. IEEE. 2012;100:410–426. doi: 10.1109/JPROC.2011.2156750. [DOI] [Google Scholar]
- 165.Hall D.M., Lvov S.N. Modeling a CuCl(aq)/HCl(aq) Electrolyzer using Thermodynamics and Electrochemical Kinetics. Electrochim. Acta. 2016;190:1167–1174. doi: 10.1016/j.electacta.2015.12.184. [DOI] [Google Scholar]
- 166.Han B., Mo J., Kang Z., Yang G., Barnhill W. Modeling of two-phase transport in proton exchange membrane electrolyzer cells for hydrogen energy. Int. J. Hydrogen Energy. 2017;42:4478–4489. doi: 10.1016/j.ijhydene.2016.12.103. [DOI] [Google Scholar]
- 167.Koponen J., Kosonen A., Ahola J. Review of Water Electrolysis Technologies and Design of Renewable Hydrogen Production Systems. Lappeenranta University of Technology; Lappeenranta, Finland: 2015. [Google Scholar]
- 168.Godula-Jopek A., editor. Hydrogen Production by Electrolysis. Wiley-VCH; Hoboken, NJ, USA: 2015. [Google Scholar]
- 169.Siracusano S., Van Dijk N., Backhouse R., Merlo L., Baglio V., Aricò A.S. Degradation issues of PEM electrolysis MEAs. Renew. Energy. 2018;123:52–57. doi: 10.1016/j.renene.2018.02.024. [DOI] [Google Scholar]
- 170.Kim S., Schatz R., Khurana S., Fedkin M., Wang C., Lvov S. Advanced CuCl Electrolyzer for Hydrogen Production via the Cu-Cl Thermochemical Cycle. ECS Trans. 2019;35:257–265. doi: 10.1149/1.3655709. [DOI] [Google Scholar]
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