Skip to main content
NCBI home page
ACS Omega logoLink to ACS Omega
. 2021 Nov 22;6(48):33024–33032. doi: 10.1021/acsomega.1c05183

Microwave-Assisted Auto-Combustion Synthesis of Binary/Ternary CoxNi1−xFerrite for Electrochemical Hydrogen and Oxygen Evolution

Sanaz Chamani †, Maasoumeh Khatamian †,*, Naeimeh Sadat Peighambardoust ‡, Umut Aydemir ‡,§,*
PMCID: PMC8655901  PMID: 34901654

Abstract

graphic file with name ao1c05183_0011.jpg

Enormous efforts have been dedicated to engineering low-cost and efficient electrocatalysts for both hydrogen evolution and oxygen evolution reactions (HER and OER, respectively). For this, the current contribution reports the successful synthesis of binary/ternary metal ferrites (CoxNi1–xFerrite; x = 0.0, 0.1, 0.3, 0.5, 0.7, and 1.0) by a simple one-step microwave technique and subsequently discusses its chemical and electrochemical properties. The X-ray diffraction analysis substantiated the phase purity of the as-obtained catalysts with various compositions. Additionally, the morphology of the nanoparticles was identified via transmission electron microscopy. Further, the vibrating sample magnetometer justified the ferromagnetic character of the as-prepared products. The electrochemical measurements revealed that the as-prepared materials required the overpotentials of 422–600 and 419–467 mV for HER and OER, respectively, to afford current densities of 10 mA cm–2. In the general sense, Ni cation substitution with Co influenced favorably toward both HER and OER. Among all synthesized electrocatalysts, Co0.9Ni0.1Ferrite displayed the highest performance in terms of OER in 1 M KOH solution, which is related to the synergistic effect of multiple parameters including the optimal substitution amount of Co, the highest Brunauer–Emmett–Teller surface area, the smallest particle size among all samples (26.71 nm), and the lowest charge transfer resistance. The successful synthesis of ternary ferrites carried out for the first time via a microwave-assisted auto-combustion route opens up a new path for their applications in renewable energy technologies.

1. Introduction

The huge consumption of unsustainable carbon-emitting fossil fuels is the primary culprit for the current energy crunch and environmental concerns.1,2 Hydrogen, a carbon-free energy source is a favorable response to confront the energy crisis and environmental issues such as global warming.3,4 Discovering a completely new, environmentally benign, cheap, and efficacious strategy to generate hydrogen is a persistent challenge. Electrochemical water splitting stands out among other systems regarding its benefits including hydrogen production with high purity and leaving no carbon footprints.5−7 This process consists of two half-reactions, namely, hydrogen evolution reaction (HER) on the cathode and oxygen evolution reaction (OER) on the anode.6,8 So far, precious-metal-based electrocatalysts such as Pt/C and RuO2 have been identified as state-of-the-art materials to drive the reaction and lower the overpotential higher than the theoretical one, 1.23 V.9,10

Over the past decades, plenty of attempts have been made to design and develop catalysts that alloys,11−13 carbides,14,15 nitrides,16,17 oxides,18−20 phosphides,21−23 borides,24,25 and chalcogenides26,27 are some of the materials that have been widely explored. Amidst a wide spectrum of electrocatalytic chemicals, the well-known metal compounds of Fe, Co, and Ni—located in the same group with Ru, Ir, and Pt, individually and hence expected to show relatively identical catalytic traits5—and different compositions of their mixed oxides are believed to have outstanding catalytic activity for electrolysis of water.28,29 It is generally presumed that multinary mixed oxides should outperform their unary counterparts by the virtue of their intrinsic merits such as desirable electrical and catalytic abilities.30−34 Keeping this in mind, to accurately evaluate the performance of these oxides, their compositions and particularly content of metal ions should be taken into consideration.34

To narrow down the list of mixed metal oxides, some can hold a high potential for energy conversion and storage.31−33,35 For instance, NiCo2O436,37 Ni–Fe mixed oxide,38 and (Fe, Co, Ni, and Mn) oxides39,40 are favorable electrocatalysts for HER and/or OER. To this end, magnetic ferrites with a general formula of MFe2O4 (M = Ni, Co, Cu, Mn, and so on) are a critical family of mixed metal oxides with innate benefits such as tunable redox properties, high abundance, and inexpensiveness35 have attracted a great deal of research interest. The so-called nano-structured spinel ferrite represents a cubic, close packing configuration of oxygen atoms, in which M2+ (M = Co, Ni) and Fe3+ ions can fill tetrahedral or octahedral interstitial sites.41,42 Spinel ferrites have diverse applications in multidisciplinary areas but are not limited to high-density magnetic recording, magnetic fluids, sensors, and catalysis to name but a few.43,44

Thus far, multiple approaches have been adopted for the synthesis of nano-structured ferrites including but not limited to sol–gel, hydrothermal, solvothermal, high-energy ball milling, chemical co-precipitation, and citric acid combustion.45−48 Nonetheless, costly and complicated processes along with low production rates are the typical flaws from which these methods suffer.45 Amidst the documented techniques, microwave combustion synthesis has gained extensive research interest. High rates of reaction, shorter reaction time, less energy usage, high yield, and quality of resulting products are some of the merits of the microwave combustion method as opposed to other synthetic routes.45−48

We present herein the synthesis of binary/ternary metal ferrites [CoxNi1–xFerrite (x = 0.0, 0.1, 0.3, 0.5, 0.7, and 1.0)] by the aid of auto-combustion approach using microwave for the first time. The as-prepared materials were explored for their magnetic, chemical, and electrochemical properties. The results disclosed that increasing Co concentration, in general, has a positive impact on both HER and OER performance.

2. Results and Discussion

2.1. Characterization

The X-ray diffractometer (XRD) was employed to verify the structural phase purity and determine the crystallite size of the prepared spinel nanoparticles. Figure 1a depicts the reflected characteristic peaks of the CoxNi1–xFerrites nanoparticles. The appeared XRD peaks at 2θ about 18.41, 30.29, 35.68, 37.33, 43.37, 53.82, 57.37, 63.1, and 74.57 can be indexed to the (111), (220), (311), (222), (400), (422), (511), (440), and (533) planes, separately, which confirmed the presence of a single-phase cubic spinel structure without secondary phases matched very well with the JCPDS card no. 74-2081 for NiFe2O4 and JCPDS card no. 77-0426 for CoFe2O4, respectively. To calculate the average particle size the Scherrer’s equation was exploited according to the following relation

2.1.

where D denotes the average particle size, k = 0.89 is the shape factor of a particle, λ = 1.5406 Å is the X-ray wavelength used, β is the full width at half-maximum of the XRD (311) peak, and θ is Bragg’s angle in degrees unit. The average particle size of the magnetic nanoparticles was estimated in the range of 26–43 nm (refer to Table S1). It should be pointed out that dashed line around 2θ of 63.1 from top to the bottom by increasing Co quantity, peak shifts to smaller 2θ which is an indication of Co substitution in the structure of NiFerrite, and therefore larger lattice parameters (see Figure 1b).

Figure 1.

Figure 1

Open in a new tab

(a,b) XRD patterns of the prepared CoxNi1-xFerrite samples.

The construction of CoxNi1–xFerrite nanoparticles was substantiated by Fourier transform infrared characterization (FT-IR). In accordance with Figure 2, no secondary absorption bands regarding organic groups were detected above 1000 cm–1. The two metal–oxygen (M–O) absorption bands observed in the range of 400–600 cm–1 can be attributed to the vibration of ions in the crystal lattices. The presence of maximum bands within the 500–600 cm–1 corresponds to cardinal stretching vibrations of the metal at the tetrahedral site, whereas the bands usually witnessed under 450 cm–1, are indexed to the octahedral metal stretching site.

Figure 2.

Figure 2

Open in a new tab

FT-IR spectrum of synthesized CoxNi1–xFerrite samples.

To inspect the surface morphology and chemical composition of the ferrite powders. Scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS) elemental analyses were conducted. Figure 3a–c exhibits the dense agglomeration of nanoparticles for both doped and undoped samples which can be attributed to the magnetic properties of the synthesized materials (SEM images of remaining materials are included in Figure S1). Even though the accurate shape of particles cannot be evidenced, the transmission electron microscopy (TEM) image shown in Figure 3d manifests the cubic shape of the particles. It should be noted that further data regarding the elemental studies of the samples can be observed in Supporting Information, Figure S2, and Table S2. The high-resolution TEM (HRTEM) images of Co0.9Ni0.1Ferrite (Figure 4) shows the lattice fringes with a lattice spacing of 0.496 nm, corresponding to the (111) of CoFerrite.

Figure 3.

Figure 3

Open in a new tab

SEM images of (a) NiFerrite, (b) CoFerrite, (c) Co0.9Ni0.1Ferrite, and (d) TEM of Co0.9Ni0.1Ferrite nanoparticles.

Figure 4.

Figure 4

Open in a new tab

(a,b) HRTEM images of Co0.9Ni0.1Ferrite.

The magnetic properties of CoxNi1-xFerrite nanoparticles were achieved through a vibrating sample magnetometer at room temperature. A very clear hysteresis loop was exhibited (Figure 5) from the M–H measurements, which proves the ferromagnetic nature of magnetic ferrite nanoparticles. Multiple magnetic features can be achieved via the hysteresis loops including saturation magnetization (Ms), coercivity (Hc), and remanence magnetization (Mr), and the observed values are summarized in Table 1. It was observed that the highest Ms value and coercivities (Hc) for CoFerrite is 66.4 emu/g and 1174.5 Oe. The result manifests that Ms and Hc of the samples are in direct correlation with Co content. The magnetic moments of Ni2+and Co2+ are 2.82 μB and 3.87 μB (Bohr magneton), respectively. Therefore, proliferation in the number of Ni2+sites replaced by Co2+brings about larger Ms and Mr (remanence) values. On the contrary, Hc values of ferrites grow bigger as a result of the larger ion radius of Co2+ (0.78 A) as opposed to Ni2+ (0.7 Å), giving rise to the lattice expansion (refer to Figure 1b). Thus, the widening of both interplanar spatial spacings of the particles impedes the response of particles to the external magnetic field.

Figure 5.

Figure 5

Open in a new tab

Magnetization curve of the magnetic nanoparticles.

Table 1. Variation of Ms, Hc, and Mr of Spinel CoxNi1-xFerrite Nanoparticles.

sample Ms Hc Mr
NiFerrite 41.5 –129.6 13
Co0.1Ni0.9Ferrite 47.2 –294.2 18.2
Co0.3Ni0.7Ferrite 51.3 –639.7 23.8
Co0.5Ni0.5Ferrite 55 –863.7 27
Co0.7Ni0.3Ferrite 55.7 –1004.8 27
Co0.9Ni0.1Ferrite 62.8 –1019.9 30.5
CoFerrite 66.4 –1174.5 32.5
Open in a new tab

2.2. Electrochemical Studies

The electrochemical properties of prepared catalysts for HER and OER were evaluated on GC = with 0.125 mg cm–2 catalyst loading as a working electrode in 1 M KOH solution. Figure 6a demonstrates the linear sweep voltammetry (LSV) polarization curves of electrocatalysts toward HER inclusive of GC and 10% Pt/C. As it can be seen, GC shows insignificant electrochemical activity, verifying its inertness. On the contrary, 10% Pt/C reveals a low onset potential of 198 mV to achieve 10 mA cm–2. The overpotential values of the as-synthesized samples are tabulated in Table 2. A glance at this table discloses the fact that NiFerrite suffers from low performance (600 mV at 10 mA cm–2), whereas CoFerrite enjoys the highest performance (422 mV at 10 mA cm–2) relative to other samples. Not to mention that HER performance and Co concentration are roughly in direct relation, suggesting that increasing Co content leads to a positive effect on HER activity. In fact, the Co element is believed to be a favorable factor in improving HER due to its moderate H-bonding energy. Incorporation of trace amount of Co into the lattice of catalysts can substantially alter the electronic structure.49−51 The earlier studies manifested that the catalytic performance is strongly dependent on the Co doping levels, and thus only a proper concentration of Co can boost the inherent conductivity and decline the adsorption energy of H atoms (ΔGH*). For an instance, for Co-doped FeS2 nanosheets, it was found that a Co/Fe ratio of 1:9 resulted in the highest HER activity. The density functional theory calculations revealed that the Co doping greatly decreased the energy barrier of H adsorption on the FeS2 surface. Considering the points mentioned above, the same scenario can be developed for the present work—in that—adsorption energy of H atoms on the surface has gradually decreased with increasing Co concentration, giving rise to the best HER performance for the case of CoFerrite.50,52

Figure 6.

Figure 6

Open in a new tab

Electrochemical studies of CoxNi1–xFerrite nanoparticles. (a) Polarization curves toward HER and (b) corresponding Tafel plots. (c) Polarization curves toward OER and (d) corresponding Tafel plots.

Table 2. Overpotential Values of As-prepared Catalysts for HER and OER in 1 M KOH Medium and Corresponding Brunauer–Emmett–Teller (BET) Surface Area.

sample HER overpotential (mV) OER overpotential (mV) BET surface area (m2/g)
Pt/C 198    
RuO2   290  
NiFerrite 600   4.66
Co0.1Ni0.9Ferrite 566   7.08
Co0.3Ni0.7Ferrite 541 467 5.88
Co0.5Ni0.5Ferrite 495 451 7.12
Co0.7Ni0.3Ferrite 446 467 9.45
Co0.9Ni0.1Ferrite 451 419 12.10
CoFerrite 422 434 11.35
Open in a new tab

Catalysts based on earth-abundant Co have received tremendous research interest owing to their intrinsic electrocatalytic capacity toward HER and/or OER.53−56 Previous studies have validated that spinels of cobalt can contribute to higher electronic conductivity as well as the number of active sites, which in turn reflect in greater electrochemical features.57 Previously, it has been proven that the electronic structure of a catalyst can be modulated and thereby promoted by the incorporation of more cations. Comparing bimetallic spinels of Co and Ni in this work, we can notice the positive impact of cation introduction in both cases of HER and OER. Compared to HER, NiFerrite still holds inferior performance for OER. However, Co0.9Ni0.1Ferrite is the best performing catalyst (419 mV at 10 mA cm–2), exceeding the performance of CoFerrite (434 mV at 10 mA cm–2), thanks to optimized charge transfer between bimetals of Co and Ni (Figure 6c). In many cases, the incorporation of more metal atoms can modify the adsorption energy of reaction intermediates and improve catalytic activity.58,59 In addition, according to the calculated particle size in Table S1, the smallest size corresponds to Co0.9Ni0.1Ferrite (26.71 nm), a beneficial contribution to OER electrocatalytic activity.34 It should be pointed out that benchmark RuO2 was also evaluated toward OER, implying that as-synthesized catalysts are less efficient, yet fairly promising regarding their economic precursors, green fabrication method, and easily scalable procedure.

In principle, Co-containing ferrites are preferably viewed as favorable electrocatalysts toward OER,34,60,61 in which their activities can be altered by size, morphology,62 and hybrid forming.63,64 The surface of Co-bearing catalysts under alkaline conditions transforms to thermodynamically stable species such as Co-(oxy) hydroxide (CoOOH) which can function as active sites for the oxygen-evolving reaction.2 It is believed that the OER mechanism is subject to the occurrence of four successive steps.

2.2.
2.2.
2.2.
2.2.

From a thermodynamic point of view, the last step is irreversible (ΔG4< 0). Thus, one of three remaining reversible steps is the rate-controlling step. During OER, CoII/CoIII/CoIV mixed states are the dominating cobalt species. Here, CoIIIOOH, CoOIV(OH)2, and CoIVOO2 represent the adsorbed intermediates on the surface-active sites, and (l) and (g) denote liquid and gas phases, individually. Concerning the investigated samples and particularly the best-performing one, Co0.9Ni0.1Ferrite, the catalyst goes under partial oxidation, converting to CoIIIOOH followed by an electron release (step 1). Nest, CoIIIOOH reacts with another OH–, producing CoIVO(OH)2and an electron (step 2). Afterward, CoIVO(OH)2 reacts with two other OH–, generating CoIVOO2, two water molecules, and two electrons (Step 3). Finally, CoIVOO2 combines with another OH– to form O2 gas, a CoIIIOOH, and an electron (Step 4). As a whole, mixed cobalt states on the catalyst surface create more active sites and hence encourage the charge transfer.53,65,66

From Figure 6b, calculated Tafel slopes can be seen. The Tafel slope is a key indicator to ascertain the HER kinetics, establishing the rate-controlling step during the reaction.24,67 The two general routes reported in the literature68−70 for hydrogen evolution under basic conditions are as follows

2.2.
2.2.
2.2.
2.2.

Therefore, the adsorption–desorption process either takes place via the Volmer–Heyrovsky mechanism (a,b) or the Volmer–Tafel mechanism (c,d). Here, ° and H° stand for available active sites and hydrogen atoms adsorbed on the active sites, respectively. The estimated Tafel slopes for the Volmer reaction, Heyrovsky reaction, and Tafel reaction are respective values of ∼120 mV dec–1, ∼40 mV dec–1, and ∼30 mV dec–1,68 The results exhibit that commercial 10% Pt/C as a reference material has a slope of 86.5 mV dec–1 which is in the region of 40–120 mV dec–1, suggesting the Volmer–Heyrovsky mechanism. Among the prepared samples, CoFerrite and Co0.9Ni0.1Ferrite display the smallest Tafel slopes (72.7 mV dec–1 and 81.1 mV dec–1) compared to other catalysts and reference material, suggesting the Volmer–Heyrovsky path. The corresponding Tafel plots for OER are shown in Figure 6d. According to this figure, RuO2 owns the smallest Tafel slope (68.4 mV dec–1) and hence enjoys the fastest kinetics. Amidst the as-synthesized electrocatalysts, Co0.9Ni0.1Ferrite holds the lowest slope value (89.1 mV dec–1), which is in line with its OER performance. The preceding statements accord with the BET results, meaning that the sample endowing with the highest BET surface area enjoys the best OER activity (Table 2). It should be noted that the comparison of present results with those of previously reported spinel catalysts in OER and HER has been tabulated in Table S3.

Because catalytic sustainability has a central role in water splitting applications, the longevity of the best-performing catalysts in OER (Co0.9Ni0.1Ferrite) and HER (CoFerrite) were also measured and recorded at a current density of 10 mA cm–2 (Figure 7). Moreover, the microstructure of these materials after electrochemical operations was studied (see Figure S3). According to the SEM images, no pronounced alteration was detected after OER and HER experiments on the surface of electrodes in terms of morphology. In addition, the EDS elemental analyses confirmed the presence of initial elements in the matrices of as-obtained electrocatalysts.

Figure 7.

Figure 7

Open in a new tab

Chronopotentiometric curves recorded at a current density of 10 mA cm–2 of the best-performing catalysts.

The electrochemical impedance spectroscopy (EIS) experiments were performed to inspect the charge transfer resistance. Figure 8 presents the Nyquist plots along with equivalent circuits once the samples were placed in contact with electrolyte. Re indicates the resistance of the solution between the working and reference electrodes. CPE and Rct stand for the impedances of the interfacial reactions on the surface, namely, capacitive component and Faraday resistance, individually. Finally, Warburg impedance (W) was added to the equivalent circuit, indicating that diffusion is the controlling step on the surface.

Figure 8.

Figure 8

Open in a new tab

Nyquist plots of CoxNi1–xFerrite nanoparticles.

Table 3 summarizes the calculated values of the equivalent circuit parameters using ZView software. The results exhibit two types of behavior based on the cobalt content. Those with low Co loadings (x = 0, 0.1, 0.3, and 0.5) display a completely diffusion controlling manner on account of their high Warburg resistance. In this context, the ionic diffusion is suppressed, resulting in a severe decline in the diffusion of ions from the electrolyte to the electrode surface. On the contrary, those with high Co concentrations (x = 0.7, 0.9, and 1.0) enjoy a low Warburg resistance, manifesting a more capacitive manner than the other samples. Consequently, the ion diffusion path is alleviated more efficiently, and capacitive current can be improved. It is worth noting that the Co0.9Ni0.1Ferrite showed the lowest Rct and Warburg resistance among the second group of samples, providing more efficacious capacitive current and therefore enhanced electrocatalytic activity.

Table 3. Calculated Values of the Equivalent Circuit Elements for the Samples.

sample Re (Ω) CPE-T (mFsp–1) CPE-P Rct (Ω) W–R (Ω)
NiFerrite 12.5 8.6 × 10–6 0.8 218 17365
Co0.1Ni0.9Ferrite 10.85 7.56 × 10–6 0.86 191.3 9891
Co0.3Ni0.7Ferrite 12.14 1.23 × 10–6 0.91 184.6 8617
Co0.5Ni0.5Ferrite 11.9 1.14 × 10–7 0.78 172.9 35871
Co0.7Ni0.3Ferrite 13.17 7.74 × 10–5 0.70 10391 410.2
Co0.9Ni0.1Ferrite 12.6 8.4 × 10–5 0.83 7365 152.4
CoFerrite 12.1 3.8 × 10–5 0.79 9538 161.7
Open in a new tab

3. Conclusions

In summary, CoxNi1–xFerrite (x = 0.0, 0.1, 0.3, 0.5, 0.7 and 1.0) nanoparticles with varying compositions were successfully prepared using a microwave auto-combustion method. The adopted combustion approach is a facile, highly affordable, and readily adaptable route to synthesize non-polluting materials. The resultant products were manipulated as HER and OER electrocatalysts in a 1 M KOH medium. The electrochemical experiments proved that CoFerrite (422 mV at −10 mA cm–2) and Co0.9Ni0.1Ferrite (419 mV at 10 mA cm–2) possess the best electrocatalytic activities for HER and OER, separately. From the Tafel slope point of view, Co0.9Ni0.1Ferrite holds the smallest value for OER, 89.1 mV dec–1, suggesting alleviated kinetics compared to other samples. The same behavior was observed for HER kinetics except that, Co0.9Ni0.1Ferrite has slower kinetics than CoFerrite (81.1 mV dec–1 vs 72.7 mV dec–1). Our findings pave the path for developing green electrocatalysts by the virtue of highly economical precursors.

4. Experimental Section

4.1. Preparation of Catalysts

The reaction process was elaborated in our previous work.48 In brief, for a normal synthesis procedure, Fe(NO3)3.9H2O, Ni(NO3)2.5H2O, and Co(NO3)2.6H2O were employed as metal sources, and NH2CH2COOH and NH4NO3 were utilized as the fuel and oxidizer, respectively. In order to prepare CoxNi1–xFe2O4 (x = 0.0, 0.1, 0.3, 0.5, 0.7 and 1.0) nanoparticles, first Fe(NO3)3·9H2O (2 mmol), Co(NO3)2·6H2O, and Ni(NO3)2·5H2O with certain molar ratios, NH2CH2COOH (3 mmol), and NH4NO3(6 mmol) were mixed. The mixture was then transferred into an alumina crucible covered by a jacket layer of CuO to draw the microwave energy and generate calcination heat. For thermal treatment, the alumina crucible was placed in a domestic microwave oven with a power of 450 W for 30 min. The resulting powder was collected, washed several times with distilled water and ethanol to remove the residual initial materials, and dried in a hot air oven at 80 °C for 24 h. The final products were labeled as CoxNi1–xFerrite (refer to Figure 9).

Figure 9.

Figure 9

Open in a new tab

Schematic illustration of synthesis procedure.

4.2. Apparatus and Procedure

4.2.1. Apparatus

To examine the structural aspects of the as-synthesized materials, a Rigaku Mini Flex 600; Cu Kα (λ = 1.5418 Å) XRD was used. XRD patterns were recorded in the 2θ ranging from 10 to 90°. A zero-background powder specimen holder was utilized for the XRD analysis of all samples. To identify the functional groups a JASCO 6800 FTIR FULL VACUUM & FTIR MICROSCOPE FT-IR apparatus was employed and the spectra were collected in the wavenumber region of 4000–400 cm–1 with the aid of the KBr pellet approach. Field emission scanning electron microscopy (FESEM) images were achieved on a TESCAN MIRA3 microscope, operated at 15 kV. In addition, EDS was carried out by Zeiss Ultra Plus FESEM at an accelerating voltage of 5 kV. Further examination on morphology was accomplished through TEM images, taken by a Hitachi HT7700 TEM instrument, functioning at the accelerating voltage of 120 kV. The high-resolution transmission electron microscope images were obtained by the Thermo Scientific Talos F200S 200 kV TEM. The magnetic tests were implemented at ambient conditions employing a vibrating sample magnetometer, model VSM, LBKFB, with a maximum magnetic field of 10 kQe. Finally, to determine the BET specific surface area of the powder products, a Micromeritics ASAP 2010 instrument was exploited.

4.2.2. Electrode Fabrication

The catalysts inks were made by thoroughly mixing 1 mg of resulting powders in a 480 μL pure ethanol–deionized water mixture (380:100) under ultrasonication for 20 min, followed by the addition of 5% wt Nafion solution (5 μL) to the mentioned mixture, accompanied by another 20 min of ultrasonication. 10 μL of the homogeneous catalyst ink was pipetted out on the - fresh surface of cleaned glassy carbon (GC). Finally, the drying process of the catalyst-coated surface of the GC electrode was carried out in the presence of an air atmosphere at 80 °C for 120 min. To construct the working electrodes of reference commercial materials, 10% Pt/C and RuO2, identical steps were followed. The loading amount of catalysts for each run was about ∼0.125 mg/cm2.

4.2.3. Electrochemical Measurements

To evaluate the electrochemical characteristics of the prepared electrocatalysts, we followed a similar strategy to our earlier report 19. Succinctly, the electrochemical tests were performed on a VersaSTAT Potentiostat Galvanostat by means of a normal three-electrode cell containing reversible hydrogen electrode (RHE; HydroFlex) and Pt wire as reference and counter electrodes, respectively, under 1 M KOH medium. A 3 mm-diameter GC was employed as a working electrode, polished with = Al2O3 slurry (0.3 μm) and ultrasonically washed with distilled water and ethanol each for 10 min prior to each run. To this end, the LSV curves were recorded from 0 to −1.2 V and 0 to +1.8 V toward HER and OER, separately. The required overpotential for water reduction and oxidation were calculated at a current density of 10 mA cm–2. Furthermore, a frequency ranged from 100 kHz and 0.1 Hz with a 10 mV RMS sinusoidal modulation at 0 V was considered to obtain the EIS curves.

Acknowledgments

U.A. acknowledges the funding support provided by the Turkish Academy of Sciences - Outstanding Young Scientist Award Program. M. KH. thanks the University of Tabriz and IRAN Nanotechnology Innovation Council (INIC) for their help and support. The authors would like to show their gratitude to Dr. Barış Yağcı and Dr. Amir Motallebzadeh from Koç University Surface Science and Technology Center (KUYTAM) as well as Zafer Eroğlu from Koç University for their help with chemical characterizations. We acknowledge Dr. Suleyman Tekmen from Bayburt University Central Research Laboratory (BUMER) for the HRTEM measurement.

Supporting Information Available

The Supporting Information is available free of charge at https://pubs.acs.org/doi/10.1021/acsomega.1c05183.

  • Data of SEM images, EDS elemental mappings, crystallite size table, table of the HER and OER performances of previous works, and SEM images and EDS graphs after electrochemical experiments (PDF)

Author Contributions

S.C. synthesized and characterized the electrocatalysts. N.S.P. prepared the electrodes and conducted the electrochemical experiments. M.K. and U.A. supervised the whole project from synthesis to interpretation of the results. All authors contributed to the writing of the manuscript and approved its final version.

The authors declare no competing financial interest.

Supplementary Material

ao1c05183_si_001.pdf (1MB, pdf)

References

  1. Alshehri S. M.; Alhabarah A. N.; Ahmed J.; Naushad M.; Ahamad T.; science i. An efficient and cost-effective tri-functional electrocatalyst based on cobalt ferrite embedded nitrogen doped carbon. J. Colloid Interface Sci. 2018, 514, 1–9. 10.1016/j.jcis.2017.12.020. [DOI] [PubMed] [Google Scholar]
  2. Wang S.; Bendt G.; Saddeler S.; Schulz S. Synergistic Effects of Mo2C-NC@ CoxFey Core–Shell Nanoparticles in Electrocatalytic Overall Water Splitting Reaction. Energy Technol. 2019, 7, 1801121. 10.1002/ente.201801121. [DOI] [Google Scholar]
  3. Abbaspour A.; Mirahmadi E. Electrocatalytic hydrogen evolution reaction on carbon paste electrode modified with Ni ferrite nanoparticles. Fuel 2013, 104, 575–582. 10.1016/j.fuel.2012.07.016. [DOI] [Google Scholar]
  4. Zhao X.; Yang Z.; Wang W.; Li Y.; Zhou X.; Zhang H. Highly dispersed ultrafine shell-like nano-Pt with efficient hydrogen evolution via metal boron organic polymers. J. Mater. Chem. A 2020, 8, 7171–7176. 10.1039/d0ta02110e. [DOI] [Google Scholar]
  5. Yuan F.; Cheng X.; Wang M.; Ni Y. Controlled synthesis of tubular ferrite MFe2O4 (M= Fe, Co, Ni) microstructures with efficiently electrocatalytic activity for water splitting. Electrochim. Acta 2019, 324, 134883. 10.1016/j.electacta.2019.134883. [DOI] [Google Scholar]
  6. Yang Y.; Fei H.; Ruan G.; Tour J. M. Porous cobalt-based thin film as a bifunctional catalyst for hydrogen generation and oxygen generation. Adv. Mater. 2015, 27, 3175–3180. 10.1002/adma.201500894. [DOI] [PubMed] [Google Scholar]
  7. Liu J.; Zhao S.; Wang C.; Ma Y.; He L.; Liu B.; Zhang Z. Catkin-derived mesoporous carbon-supported molybdenum disulfide and nickel hydroxyl oxide hybrid as a bifunctional electrocatalyst for driving overall water splitting. J. Colloid Interface Sci. 2022, 608, 1627–1637. 10.1016/j.jcis.2021.10.069. [DOI] [PubMed] [Google Scholar]
  8. Septiani N. L. W.; Kaneti Y. V.; Fathoni K. B.; Kani K.; Allah A. E.; Yuliarto B.; Nugraha; Dipojono H. K.; Alothman Z. A.; Golberg D.; Yamauchi Y. Self-assembly of two-dimensional bimetallic nickel–cobalt phosphate nanoplates into one-dimensional porous chainlike architecture for efficient oxygen evolution reaction. Chem. Mater. 2020, 32, 7005–7018. 10.1021/acs.chemmater.0c02385. [DOI] [Google Scholar]
  9. Debnath B.; Parvin S.; Dixit H.; Bhattacharyya S. Oxygen-Defect-Rich Cobalt Ferrite Nanoparticles for Practical Water Electrolysis with High Activity and Durability. ChemSusChem 2020, 13, 3875–3886. 10.1002/cssc.202000932. [DOI] [PubMed] [Google Scholar]
  10. Jian J.; Chen W.; Zeng D.; Chang L.; Zhang R.; Jiang M.; Yu G.; Huang X.; Yuan H.; Feng S. Metal-ionic-conductor potassium ferrite nanocrystals with intrinsic superhydrophilic surfaces for electrocatalytic water splitting at ultrahigh current densities. J. Mater. Chem. A 2021, 9, 7586–7593. 10.1039/d1ta00693b. [DOI] [Google Scholar]
  11. Liu J.; Zhu D.; Ling T.; Vasileff A.; Qiao S.-Z. S-NiFe2O4 ultra-small nanoparticle built nanosheets for efficient water splitting in alkaline and neutral pH. Nano Energy 2017, 40, 264–273. 10.1016/j.nanoen.2017.08.031. [DOI] [Google Scholar]
  12. Wang X.; Su R.; Aslan H.; Kibsgaard J.; Wendt S.; Meng L.; Dong M.; Huang Y.; Besenbacher F. Tweaking the composition of NiMoZn alloy electrocatalyst for enhanced hydrogen evolution reaction performance. Nano Energy 2015, 12, 9–18. 10.1016/j.nanoen.2014.12.007. [DOI] [Google Scholar]
  13. Yang Y.; Lin Z.; Gao S.; Su J.; Lun Z.; Xia G.; Chen J.; Zhang R.; Chen Q. Tuning electronic structures of nonprecious ternary alloys encapsulated in graphene layers for optimizing overall water splitting activity. ACS Catal. 2017, 7, 469–479. 10.1021/acscatal.6b02573. [DOI] [Google Scholar]
  14. Zeng M.; Chen Y.; Li J.; Xue H.; Mendes R. G.; Liu J.; Zhang T.; Rümmeli M. H.; Fu L. 2D WC single crystal embedded in graphene for enhancing hydrogen evolution reaction. Nano Energy 2017, 33, 356–362. 10.1016/j.nanoen.2017.01.057. [DOI] [Google Scholar]
  15. Zhu J.; Sakaushi K.; Clavel G.; Shalom M.; Antonietti M.; Fellinger T.-P. A general salt-templating method to fabricate vertically aligned graphitic carbon nanosheets and their metal carbide hybrids for superior lithium ion batteries and water splitting. J. Am. Chem. Soc. 2015, 137, 5480–5485. 10.1021/jacs.5b01072. [DOI] [PubMed] [Google Scholar]
  16. Zhang B.; Xiao C.; Xie S.; Liang J.; Chen X.; Tang Y. Iron–nickel nitride nanostructures in situ grown on surface-redox-etching nickel foam: efficient and ultrasustainable electrocatalysts for overall water splitting. Chem. Mater. 2016, 28, 6934–6941. 10.1021/acs.chemmater.6b02610. [DOI] [Google Scholar]
  17. Wang Y.; Liu D.; Liu Z.; Xie C.; Huo J.; Wang S. Porous cobalt–iron nitride nanowires as excellent bifunctional electrocatalysts for overall water splitting. Chem. Commun. 2016, 52, 12614–12617. 10.1039/c6cc06608a. [DOI] [PubMed] [Google Scholar]
  18. Ou G.; Fan P.; Zhang H.; Huang K.; Yang C.; Yu W.; Wei H.; Zhong M.; Wu H.; Li Y. Large-scale hierarchical oxide nanostructures for high-performance electrocatalytic water splitting. Nano Energy 2017, 35, 207–214. 10.1016/j.nanoen.2017.03.049. [DOI] [Google Scholar]
  19. Gao X.; Zhang H.; Li Q.; Yu X.; Hong Z.; Zhang X.; Liang C.; Lin Z. Hierarchical NiCo2O4 hollow microcuboids as bifunctional electrocatalysts for overall water-splitting. Angew. Chem., Int. Ed. 2016, 55, 6290–6294. 10.1002/anie.201600525. [DOI] [PubMed] [Google Scholar]
  20. Peighambardoust N. S.; Khameneh Asl S.; Maghsoudi M. The effect of doping concentration of TiO2 nanotubes on energy levels and its direct correlation with photocatalytic activity. Thin Solid Films 2019, 690, 137558. 10.1016/j.tsf.2019.137558. [DOI] [Google Scholar]
  21. Ha D.-H.; Han B.; Risch M.; Giordano L.; Yao K. P. C.; Karayaylali P.; Shao-Horn Y. Activity and stability of cobalt phosphides for hydrogen evolution upon water splitting. Nano Energy 2016, 29, 37–45. 10.1016/j.nanoen.2016.04.034. [DOI] [Google Scholar]
  22. Huang Z.; Chen Z.; Chen Z.; Lv C.; Humphrey M. G.; Zhang C. Cobalt phosphide nanorods as an efficient electrocatalyst for the hydrogen evolution reaction. Nano Energy 2014, 9, 373–382. 10.1016/j.nanoen.2014.08.013. [DOI] [Google Scholar]
  23. Septiani N. L. W.; Kaneti Y. V.; Fathoni K. B.; Guo Y.; Ide Y.; Yuliarto B.; Jiang X.; Nugraha H. K.; Dipojono H. K.; Golberg D.; Yamauchi Y. Tailorable nanoarchitecturing of bimetallic nickel–cobalt hydrogen phosphate via the self-weaving of nanotubes for efficient oxygen evolution. J. Mater. Chem. A 2020, 8, 3035–3047. 10.1039/c9ta13442e. [DOI] [Google Scholar]
  24. Mete B.; Peighambardoust N. S.; Aydin S.; Sadeghi E.; Aydemir U. J. E. A. Metal-Substituted Zirconium Diboride (Zr1-xTMxB2; TM= Ni, Co, and Fe) as Low-Cost and High-Performance Bifunctional Electrocatalyst for Water Splitting. Electrochim. Acta 2021, 389, 138789. 10.1016/j.electacta.2021.138789. [DOI] [Google Scholar]
  25. Chen Z.; Duan X.; Wei W.; Wang S.; Zhang Z.; Ni B.-J. Boride-based electrocatalysts: Emerging candidates for water splitting. Nano Res. 2020, 13, 293–314. 10.1007/s12274-020-2618-y. [DOI] [Google Scholar]
  26. Konkena B.; Masa J.; Xia W.; Muhler M.; Schuhmann W. MoSSe@ reduced graphene oxide nanocomposite heterostructures as efficient and stable electrocatalysts for the hydrogen evolution reaction. Nano Energy 2016, 29, 46–53. 10.1016/j.nanoen.2016.04.018. [DOI] [Google Scholar]
  27. Gao M.-R.; Liang J.-X.; Zheng Y.-R.; Xu Y.-F.; Jiang J.; Gao Q.; Li J.; Yu S.-H. An efficient molybdenum disulfide/cobalt diselenide hybrid catalyst for electrochemical hydrogen generation. Nat. Commun. 2015, 6, 5982. 10.1038/ncomms6982. [DOI] [PMC free article] [PubMed] [Google Scholar]
  28. Cao L.; Li Z.; Su K.; Zhang M.; Cheng B. Rational design of hollow oxygen deficiency-enriched NiFe2O4@ N/rGO as bifunctional electrocatalysts for overall water splitting. J. Energy Chem. 2021, 54, 595–603. 10.1016/j.jechem.2020.06.053. [DOI] [Google Scholar]
  29. Navadeepthy D.; Rebekah A.; Viswanthan C.; Ponpandian N. Boosting the kinetics of oxygen and hydrogen evolution in alkaline water splitting using nickel ferrite/N-graphene nanocomposite as a bifunctional electrocatalyst. Int. J. Hydrogen Energy 2021, 46, 21512–21524. 10.1016/j.ijhydene.2021.03.244. [DOI] [Google Scholar]
  30. Zhang C.; Bhoyate S.; Zhao C.; Kahol P.; Kostoglou N.; Mitterer C.; Hinder S.; Baker M.; Constantinides G.; Polychronopoulou K.; Rebholz C.; Gupta R. Electrodeposited nanostructured CoFe2O4 for overall water splitting and supercapacitor applications. Catalysts 2019, 9, 176. 10.3390/catal9020176. [DOI] [Google Scholar]
  31. Hu H.; Guan B.; Xia B.; Lou X. W. Designed formation of Co3O4/NiCo2O4 double-shelled nanocages with enhanced pseudocapacitive and electrocatalytic properties. J. Am. Chem. Soc. 2015, 137, 5590–5595. 10.1021/jacs.5b02465. [DOI] [PubMed] [Google Scholar]
  32. Fu W.; Zhao C.; Han W.; Liu Y.; Zhao H.; Ma Y.; Xie E. Cobalt sulfide nanosheets coated on NiCo 2 S 4 nanotube arrays as electrode materials for high-performance supercapacitors. J. Mater. Chem. A 2015, 3, 10492–10497. 10.1039/c5ta00742a. [DOI] [Google Scholar]
  33. Chauhan M.; Reddy K. P.; Gopinath C. S.; Deka S. Copper cobalt sulfide nanosheets realizing a promising electrocatalytic oxygen evolution reaction. ACS Catal. 2017, 7, 5871–5879. 10.1021/acscatal.7b01831. [DOI] [Google Scholar]
  34. Chakrapani K.; Bendt G.; Hajiyani H.; Schwarzrock I.; Lunkenbein T.; Salamon S.; Landers J.; Wende H.; Schlögl R.; Pentcheva R.; Behrens M.; Schulz S. Role of composition and size of cobalt ferrite nanocrystals in the oxygen evolution reaction. ChemCatChem 2017, 9, 2988–2995. 10.1002/cctc.201700376. [DOI] [Google Scholar]
  35. Sahoo P.; Tan J.-B.; Zhang Z.-M.; Singh S. K.; Lu T.-B. Engineering the Surface Structure of Binary/Ternary Ferrite Nanoparticles as High-Performance Electrocatalysts for the Oxygen Evolution Reaction. ChemCatChem 2018, 10, 1075–1083. 10.1002/cctc.201701790. [DOI] [Google Scholar]
  36. Liu Y.; Bai Y.; Han Y.; Yu Z.; Zhang S.; Wang G.; Wei J.; Wu Q.; Sun K. Self-supported hierarchical FeCoNi-LTH/NiCo2O4/CC electrodes with enhanced bifunctional performance for efficient overall water splitting. ACS Appl. Mater. Interfaces 2017, 9, 36917–36926. 10.1021/acsami.7b12474. [DOI] [PubMed] [Google Scholar]
  37. Yin J.; Zhou P.; An L.; Huang L.; Shao C.; Wang J.; Liu H.; Xi P. Self-supported nanoporous NiCo 2 O 4 nanowires with cobalt–nickel layered oxide nanosheets for overall water splitting. Nanoscale 2016, 8, 1390–1400. 10.1039/c5nr06197k. [DOI] [PubMed] [Google Scholar]
  38. Wu Z.; Wang X.; Huang J.; Gao F. A Co-doped Ni–Fe mixed oxide mesoporous nanosheet array with low overpotential and high stability towards overall water splitting. J. Mater. Chem. A 2018, 6, 167–178. 10.1039/c7ta07956g. [DOI] [Google Scholar]
  39. Osgood H.; Devaguptapu S. V.; Xu H.; Cho J.; Wu G. Transition metal (Fe, Co, Ni, and Mn) oxides for oxygen reduction and evolution bifunctional catalysts in alkaline media. Nano Today 2016, 11, 601–625. 10.1016/j.nantod.2016.09.001. [DOI] [Google Scholar]
  40. Dhas C. R.; Monica S.; Jothivenkatachalam K.; Nathanael A. J.; Kavinkumar V.; Venkatesh R.; Arivukarasan D. Direct-grown nebulizer-sprayed nickel-copper mixed metal oxide nanocomposite films as bifunctional electrocatalyst for water splitting. Ionics 2021, 1–14. 10.1007/s11581-021-04285-6.33623185 [DOI] [Google Scholar]
  41. Naseri M. G.; Saion E. B.; Ahangar H. A.; Hashim M.; Shaari A. H. Simple preparation and characterization of nickel ferrite nanocrystals by a thermal treatment method. Powder Technol. 2011, 212, 80–88. 10.1016/j.powtec.2011.04.033. [DOI] [Google Scholar]
  42. Zi Z.; Sun Y.; Zhu X.; Yang Z.; Dai J.; Song W. Synthesis and magnetic properties of CoFe2O4 ferrite nanoparticles. J. Magn. Magn. Mater. 2009, 321, 1251–1255. 10.1016/j.jmmm.2008.11.004. [DOI] [Google Scholar]
  43. Mallesh S.; Srinivas V.; Vasundhara M.; Kim K. H. Low-temperature magnetization behaviors of superparamagnetic MnZn ferrites nanoparticles. Phys. B 2020, 582, 411963. 10.1016/j.physb.2019.411963. [DOI] [Google Scholar]
  44. Padmapriya G.; Manikandan A.; Krishnasamy V.; Jaganathan S. K.; Antony S. A. Spinel NixZn1– xFe2O4 (0.0≤ x≤ 1.0) nano-photocatalysts: synthesis, characterization and photocatalytic degradation of methylene blue dye. J. Mol. Struct. 2016, 1119, 39–47. 10.1016/j.molstruc.2016.04.049. [DOI] [Google Scholar]
  45. Sertkol M.; Köseoğlu Y.; Baykal A.; Kavas H.; Bozkurt A.; Toprak M. S. Microwave synthesis and characterization of Zn-doped nickel ferrite nanoparticles. J. Alloys Compd. 2009, 486, 325–329. 10.1016/j.jallcom.2009.06.128. [DOI] [Google Scholar]
  46. Mahmoud M. H.; Elshahawy A. M.; Makhlouf S. A.; Hamdeh H. H. Mössbauer and magnetization studies of nickel ferrite nanoparticles synthesized by the microwave-combustion method. J. Magn. Magn. Mater. 2013, 343, 21–26. 10.1016/j.jmmm.2013.04.064. [DOI] [Google Scholar]
  47. Kombaiah K.; Vijaya J. J.; Kennedy L. J.; Bououdina M.; Al-Najar B. Conventional and microwave combustion synthesis of optomagnetic CuFe2O4 nanoparticles for hyperthermia studies. J. Phys. Chem. Solids 2018, 115, 162–171. 10.1016/j.jpcs.2017.12.024. [DOI] [Google Scholar]
  48. Dehghani M.; Tadjarodi A.; Chamani S. Synthesis and Characterization of Magnetic Zeolite Y–Palladium–Nickel Ferrite by Ultrasonic Irradiation and Investigating Its Catalytic Activity in Suzuki–Miyaura Cross-Coupling Reactions. ACS Omega 2019, 4, 10640–10648. 10.1021/acsomega.9b00666. [DOI] [PMC free article] [PubMed] [Google Scholar]
  49. Zhang G.; Zheng X.; Xu Q.; Zhang J.; Liu W.; Chen J. Carbon nanotube-induced phase and stability engineering: a strained cobalt-doped WSe 2/MWNT heterostructure for enhanced hydrogen evolution reaction. J. Mater. Chem. A 2018, 6, 4793–4800. 10.1039/c8ta00163d. [DOI] [Google Scholar]
  50. Wang J.; Liao T.; Wei Z.; Sun J.; Guo J.; Sun Z. Heteroatom-Doping of Non-Noble Metal-Based Catalysts for Electrocatalytic Hydrogen Evolution: An Electronic Structure Tuning Strategy. Small Methods 2021, 5, 2000988. 10.1002/smtd.202000988. [DOI] [PubMed] [Google Scholar]
  51. Xiong Q.; Zhang X.; Wang H.; Liu G.; Wang G.; Zhang H.; Zhao H. One-step synthesis of cobalt-doped MoS 2 nanosheets as bifunctional electrocatalysts for overall water splitting under both acidic and alkaline conditions. Chem. Commun. 2018, 54, 3859–3862. 10.1039/c8cc00766g. [DOI] [PubMed] [Google Scholar]
  52. Wang D.-Y.; Gong M.; Chou H.-L.; Pan C.-J.; Chen H.-A.; Wu Y.; Lin M.-C.; Guan M.; Yang J.; Chen C.-W.; Wang Y.-L.; Hwang B.-J.; Chen C.-C.; Dai H. Highly active and stable hybrid catalyst of cobalt-doped FeS2 nanosheets–carbon nanotubes for hydrogen evolution reaction. J. Am. Chem. Soc. 2015, 137, 1587–1592. 10.1021/ja511572q. [DOI] [PubMed] [Google Scholar]
  53. Loni E.; Shokuhfar A.; Siadati M. H. Cobalt-Based Electrocatalysts for Water Splitting: An Overview. Catal. Surv. Asia 2021, 25, 114–147. 10.1007/s10563-021-09329-5. [DOI] [Google Scholar]
  54. Wang X.; Huang X.; Gao W.; Tang Y.; Jiang P.; Lan K.; Yang R.; Wang B.; Li R. Metal–organic framework derived CoTe 2 encapsulated in nitrogen-doped carbon nanotube frameworks: a high-efficiency bifunctional electrocatalyst for overall water splitting. J. Mater. Chem. A 2018, 6, 3684–3691. 10.1039/c7ta10728e. [DOI] [Google Scholar]
  55. Gao J.; Liu L.; Qiu H.-J.; Wang Y. Engineering phase transformation of cobalt selenide in carbon cages and the phases’ bifunctional electrocatalytic activity for water splitting. Nanotechnology 2017, 28, 315401. 10.1088/1361-6528/aa788b. [DOI] [PubMed] [Google Scholar]
  56. Fan H. J.; Gösele U.; Zacharias M. Formation of nanotubes and hollow nanoparticles based on Kirkendall and diffusion processes: a review. Small 2007, 3, 1660–1671. 10.1002/smll.200700382. [DOI] [PubMed] [Google Scholar]
  57. Kumbhar V. S.; Jagadale A. D.; Shinde N. M.; Lokhande C. D. Chemical synthesis of spinel cobalt ferrite (CoFe2O4) nano-flakes for supercapacitor application. Appl. Surf. Sci. 2012, 259, 39–43. 10.1016/j.apsusc.2012.06.034. [DOI] [Google Scholar]
  58. Hu C.; Zhang L.; Zhao Z.-J.; Li A.; Chang X.; Gong J. Synergism of geometric construction and electronic regulation: 3D Se-(NiCo) Sx/(OH) x nanosheets for highly efficient overall water splitting. Adv. Mater. 2018, 30, 1705538. 10.1002/adma.201705538. [DOI] [PubMed] [Google Scholar]
  59. Zhang H.; Qian G.; Chen X.; Jiang W.; Yu T.; Wang Y.; Luo L.; Yin S. Engineering, V2O3-decorated spinel CoFe2O4 with carbon-encapsulated mesoporous nanosheets for efficient water splitting. ACS Sustainable Chem. Eng. 2021, 9, 980–986. 10.1021/acssuschemeng.0c08477. [DOI] [Google Scholar]
  60. Li T.; Lv Y.; Su J.; Wang Y.; Yang Q.; Zhang Y.; Zhou J.; Xu L.; Sun D.; Tang Y. Anchoring CoFe2O4 nanoparticles on N-doped carbon nanofibers for high-performance oxygen evolution reaction. Adv. Sci. 2017, 4, 1700226. 10.1002/advs.201700226. [DOI] [PMC free article] [PubMed] [Google Scholar]
  61. Kargar A.; Yavuz S.; Kim T. K.; Liu C.-H.; Kuru C.; Rustomji C. S.; Jin S.; Bandaru P. R. Solution-processed CoFe2O4 nanoparticles on 3D carbon fiber papers for durable oxygen evolution reaction. ACS Appl. Mater. Interfaces 2015, 7, 17851–17856. 10.1021/acsami.5b04270. [DOI] [PubMed] [Google Scholar]
  62. Li S.; Sirisomboonchai S.; Yoshida A.; An X.; Hao X.; Abudula A.; Guan G. Bifunctional CoNi/CoFe 2 O 4/Ni foam electrodes for efficient overall water splitting at a high current density. J. Mater. Chem. A 2018, 6, 19221–19230. 10.1039/c8ta08223e. [DOI] [Google Scholar]
  63. Jin H.; Wang J.; Su D.; Wei Z.; Pang Z.; Wang Y. In situ cobalt–cobalt oxide/N-doped carbon hybrids as superior bifunctional electrocatalysts for hydrogen and oxygen evolution. J. Am. Chem. Soc. 2015, 137, 2688–2694. 10.1021/ja5127165. [DOI] [PubMed] [Google Scholar]
  64. Li P.; Ma R.; Zhou Y.; Chen Y.; Zhou Z.; Liu G.; Liu Q.; Peng G.; Liang Z.; Wang J. In situ growth of spinel CoFe 2 O 4 nanoparticles on rod-like ordered mesoporous carbon for bifunctional electrocatalysis of both oxygen reduction and oxygen evolution. J. Mater. Chem. A 2015, 3, 15598–15606. 10.1039/c5ta02625c. [DOI] [Google Scholar]
  65. Feng Y.; Li Y.; Hou F. Preparation and electrochemical properties of Cr doped LiV3O8 cathode for lithium ion batteries. Mater. Lett. 2009, 63, 1338–1340. 10.1016/j.matlet.2009.03.009. [DOI] [Google Scholar]
  66. Masa J.; Barwe S.; Andronescu C.; Sinev I.; Ruff A.; Jayaramulu K.; Elumeeva K.; Konkena B.; Roldan Cuenya B.; Schuhmann W. Low overpotential water splitting using cobalt–cobalt phosphide nanoparticles supported on nickel foam. ACS Energy Lett. 2016, 1, 1192–1198. 10.1021/acsenergylett.6b00532. [DOI] [Google Scholar]
  67. Sadeghi E.; Peighambardoust N. S.; Khatamian M.; Unal U.; Aydemir U. Metal doped layered MgB 2 nanoparticles as novel electrocatalysts for water splitting. Sci. Rep. 2021, 11, 3337. 10.1038/s41598-021-83066-7. [DOI] [PMC free article] [PubMed] [Google Scholar]
  68. Kuang P.; Tong T.; Fan K.; Yu J. In situ fabrication of Ni–Mo bimetal sulfide hybrid as an efficient electrocatalyst for hydrogen evolution over a wide pH range. ACS Catal. 2017, 7, 6179–6187. 10.1021/acscatal.7b02225. [DOI] [Google Scholar]
  69. Zheng Y.; Jiao Y.; Zhu Y.; Li L. H.; Han Y.; Chen Y.; Du A.; Jaroniec M.; Qiao S. Z. J. N. c. Hydrogen evolution by a metal-free electrocatalyst. Nat. Commun. 2014, 5, 3783. 10.1038/ncomms4783. [DOI] [PubMed] [Google Scholar]
  70. Laursen A. B.; Kegnæs S.; Dahl S.; Chorkendorff I. Molybdenum sulfides—efficient and viable materials for electro-and photoelectrocatalytic hydrogen evolution. Energy Environ. Sci. 2012, 5, 5577–5591. 10.1039/c2ee02618j. [DOI] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

ao1c05183_si_001.pdf (1MB, pdf)

Articles from ACS Omega are provided here courtesy of American Chemical Society

RESOURCES