La-Ni-MOF(BDC) composite with graphene oxide for enhanced bifunctional electrocatalysis in electrochemical water splitting

Abstract

Highly efficient electrocatalysts use graphene sheets that are abundant in nature create considerable importance during the complete process of water splitting because they enable sustainable energy conversion and storage. Study presents metal-organic frameworks (MOFs) which researchers synthesize through hydrothermal methods together with graphene oxide (GO) to use in electrochemical water splitting as an electrocatalytic material. The research aims to create non-precious metal bifunctional catalysts which will operate successfully through both anodic oxygen evolution reaction (OER) and cathodic hydrogen evolution reaction (HER) processes. The researchers produced La-Ni based MOFs through synthesis which they combined with GO to enhance their electrocatalytic performance. The La-Ni-MOF/GO material achieved dual performance through its superior output to produce hydrogen at 0.39 V and 93 mV at 10 mA cm^− 2 and its superior output to produce oxygen at 2.31 V and 184 mV at 10 mA cm^− 2. The electrochemical analysis revealed faster reaction kinetics because the Tafel slope measured 51 mV dec^− 1 during HER and 47 mV dec^− 1 during OER. The composite material reached its minimum charge transfer resistance at Rct = 4.3 Ω for OER and 556 Ω for HER while showing its highest turnover frequency at TOF = 1.34 s^− 1 and maintaining excellent long-term stability throughout 50 h. The excellent properties in La-Ni-MOF/GO occur because the combination of Ni, La and GO promotes the optimal charge transfer, increased active site exposure and enhanced electrical conductivity through multiple mechanisms. The presence of the organic linker, terephthalic acid incorporation, adds also increased separation between the metal ions as well as increased active site availability whilst maintaining the structural integrity of the composite compound. In this work, we present the potential for using La-Ni MOFs combined with Graphene Oxide to create an innovative bifunctional electrocatalytic material with enhanced charge transfer, increased number of available active sites and increased stability over time. This new low-cost scalable strategy will provide an exceptionally high-performance long-term catalyst for producing hydrogen from water using electrocatalytic water-splitting processes to support future developments in renewable energy conversion technologies.

Supplementary Information

The online version contains supplementary material available at 10.1038/s41598-026-42345-x.

Introduction

Modern society is driven by energy, which runs everything from daily living to industry to transportation. Generally non-renewable and renewable sources of energy define each other¹. For decades, non-renewable energy sources including coal and oil and natural gas have served as the primary energy sources. But their excessive use causes immense damage to the environment, which includes air pollution and global warming along with greenhouse emissions². The depletion of fossil fuels creates an acute necessity for sustainable alternatives for energy production³. Contrary to that, clean and sustainable alternatives are provided by renewable resources, which include solar, wind, hydrogen, and hydro energies⁴. Among those various advantages of hydrogen energy include high density, less carbon content, and usage capabilities for fuel cells and industrial processes⁵. Turning to hydrogen energy will help us greatly our reliance on fossil fuels, slow down environmental harm, and a sustainable energy⁶. Water splitting generates hydrogen, but to improve the reaction rate and lower energy consumption, effective catalysts also known as electrocatalysts are needed⁷. Large-scale hydrogen generation is still difficult, although, mostly because of the high energy barrier connected with the oxygen evolution reaction (OER)⁸. Cost-effective, highly active electrocatalysts capable of lowering the overpotential and quickening the kinetics of the water splitting process will help us overcome this hurdle⁹. Because of their exceptional catalytic activity and low Tafel slope values, Noble metal-based catalysts like RuO₂, IrO₂, and Pt are now extensively applied for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER)^1,10. Their great expense and rarity, however, greatly limit their general utilization. Consequently, development of non-precious, bifunctional catalysts able to effectively catalyze HER and OER in water electrolysis is quite urgently needed¹¹. Cost-effective, strong catalytic activity, and stability have made transition metal (TM)-based catalysts including oxides, nitrides, chalcogenides, phosphides, and hydroxides interesting substitutes¹². These catalysts’ general performance in water splitting is hampered, nonetheless, by their low electrical conductivity and restricted number of active sites¹³. Researchers have looked at Metal-Organic Frameworks (MOFs) as a potential water splitting option to solve the restrictions of noble metal-based catalysts and transition metal-based substitutes¹⁴. Because of their high surface area, variable porosity, and structural adaptability, metal-organic frameworks (MOFs) have attracted great interest as next-generation electrocatalysts for water splitting. Highly porous structures created by metal ions coupled with organic ligands can be tailored at the molecular level to improve catalytic efficiency in MOFs^15,16. MOFs’ capacity to offer a lot of active sites for HER and OER helps to improve reaction kinetics by thus enhancing their main benefit¹⁷. Nickel-based metal-organic frameworks which exist as Ni-MOFs demonstrate high efficiency for water splitting electrocatalysis because they possess excellent catalytic performance and different porosity levels and exceptional stability properties¹⁸. MOFs’ microporosity provides multiple active sites, which will extend the electrochemical surface area and increase electrochemical performance of OER and HER¹⁹.

Nickel provides redox properties that are vital for its electrocatalytic activity and electronic connection to electronegativity and fabricating Ni-MOFs with high electrical conductivity and stability²⁰. La electrons charge transfer kinetics and decreases the energy barriers to permit fast water-splitting reactions²¹. La enhances charge transfer kinetics through its electron-donating ability which reduces reaction energy barriers for faster water splitting²². The material exhibits oxophagic properties which create a strong bond with oxygen-based intermediates that preserve OER process stability while decreasing overpotential²³. Lanthanum creates electronic contact with Nickel which transforms its electronic structure into optimal electronic properties that enhance its catalytic performance²⁴. Graphene oxide (GO) demonstrates high conductivity which makes it an effective supporting material because it improves the performance of the catalytic system. Its great electrical conductivity effective electron transmission between the active sites and the electrode, therefore reducing charge recombining losses²⁵. O provides Ni-MOFs with additional anchoring points through its extensive surface area and 2D layout which prevents catalyst agglomeration and maintains its stability during lengthy electrochemical experiments²⁶. The oxygen-containing functional groups in GO enhance the bonding between Ni-MOF and La, which creates vital structural attributes and corrosion resistance that ensure lasting catalytic efficiency. The combination of Ni with La-MOF and GO creates an advanced bifunctional electro catalyzer for water splitting applications. La improves electronic structure and charge transfer; Ni-MOFs contribute great catalytic activity and stability; GO offers effective conductivity and structural support²⁷. By improving charging processes and thereby stabilizing metal sites and reducing activation barriers, the La-Ni-MOF/GO hybrid fast electrolytic activity together with longer operational stability. Because of its affordable durability, La-Ni-MOF/GO results in a low-overpotential, high-efficiency, and durable electrocatalyst, providing a sustainable and reasonably priced alternative for hydrogen production via water splitting when replacing noble-metal-based systems²⁸. The interaction mechanism between GO and La/Ni-based MOF in our composite system is predominantly chemical, specifically through coordination bonding. The oxygen-containing functional groups on GO (e.g., –OH and –COOH) serve as donor sites to the La³⁺ and Ni²⁺ ions in the MOF framework, forming La–O and Ni–O linkages. La/Ni bimetallic MOF/GO hybrid catalyst that combines La (as second metal), Ni-MOF active sites, and conductive graphene oxide (GO) to achieve synergistic electronic modulation for efficient bifunctional water splitting. This demonstrates structural composition performance, where La modulates electronic structure, Ni serves as the primary catalytic center, and GO improves electron transport and active site dispersion, resulting in superior HER/OER kinetics and stability compared to single- or binary-component systems²⁹. Ming Zhou and his research team focused on developing a method to produce MOF-derived co-nanoparticles/nitrogen-doped porous graphene through a simple process which requires no special equipment and can be done at room temperature in open air. The electrocatalytic tests of Co/PNG demonstrate that this material provides effective performance together with long-lasting durability for water electrolysis. The hydrogen evolution reaction and oxygen evolution reaction and water splitting reaction of the flexible electrode exhibit different overpotential values because its Co–Nx active sites and porous structure enable various reaction functions³⁰. Shreyanka and his team created three-dimensional metal-organic frameworks by using PLAL to build metal-organic frameworks which include M-BTC materials with M representing the metals Cu and Co and Ni to create bifunctional electrocatalysts that enable complete water splitting. The Co-BTC electrocatalyst reached a low overpotential value of 437 mV while performing HER at a 10 mA cm⁻² current density during 1.0 M potassium hydroxide testing. The Tafel slope value measures 2.77 Ω cm⁻² while the Rct value shows 115.1 mV dec⁻¹. The Co-BTC metal-organic framework shows excellent performance for OER research because it achieves 10 mA cm⁻² while maintaining low overpotential of 370 mV³¹. Ji, Xian-Xian and his team used molybdenum to create a hybrid electrocatalyst which combines Co-MOF with their created hybrid electrocatalyst for hydrogen production. The material demonstrates outstanding electrocatalytic performance through an overpotential value of 120 mV at 10 mA cm⁻² and a Tafel slope measurement of 69 mV which is based on HER activity in 0.5 M H₂SO₄ solution³². The researchers Li and Xiao created graphene-coated hybrid electrocatalysts which used bimetallic metal-organic frameworks to produce efficient hydrogen generation. The Ni and Mo2C nanocomposite material demonstrates excellent electrocatalytic performance which lasts for 10 h while exposed to both acidic and basic environments. The overpotentials required to reach a current density of 10 m A cm^− 2 stand at 169 mV and 181 mV²⁴.

Here we synthesized a La-Ni-MOF/GO composite to evaluate its electrocatalytic performance for water splitting. Graphene oxide (GO) was included into the La-Ni-MOF framework to maximize structural integrity, catalytic characteristics, and shape. La-Ni-MOF/GO composite, which combines the synergistic effects of La for active site stabilization, Ni for catalysis, and GO for enhanced electron transport, resulting in exceptional electrocatalytic performance for HER and OER. La-Ni-MOF/GO combination had an low overpotential at a current density of 10 mA cm^− 2, overpotentials were 184 mV for the OER and 93 for the HER. Furthermore, the La-Ni-MOF/GO combination had favourable reaction kinetics, as evidenced by low Tafel slopes of 47 mV dec^− 1 for the OER and 51 mV dec^− 1 for the HER. La-Ni-MOF/GO composite also exhibited good corrosion resistance, demonstrating substantial long-term electrochemical stability in an alkaline medium over a period of more than 50 h. These results emphasize the possibilities of La-Ni-MOF/GO composites as effective, durable, and reasonably priced electrocatalysts for sustainable hydrogen generation by water electrolysis.

Experimental

Chemicals

Lanthanum nitrate hexahydrate (La(NO₃)₃·6H₂O, 98%, Sigma Aldrich), N,N-dimethylformamide (DMF, 98%, Sigma Aldrich) and terephthalic acid (C₈H₆O₄, BDC, 98%, Sigma Aldrich) Nickel nitrate hexahydrate (Ni(NO₃)₃·6H₂O, 98%, Sigma Aldrich) as a metal precursor, Triethylamine (TEA) (99%, C₆H₁₅N Sigma Aldrich), sodium nitrate (99%, NaNO₃, Sigma Aldrich), graphite powder (99%, Merck), sulphuric acid (58.5%, H₂SO₄, Merck), hydrogen peroxide (30%, H₂O₂, Merck), potassium permanganate (97%, KMnO₄, Emplura) methanol (99%, CH₃OH, Sigma Aldrich) and double distilled water were obtained from China Medicine. Since every reagent was of analytical variety, no additional purification was necessary.

Synthesis of GO

Hummer methods have changed significantly to obtain graphene oxide. The 120 mL of pure sulfuric acid was mixed with one gram of graphite powder and stirred until the mixture merged to a homogenate. One gram of sodium nitrate was then gradually introduced into mixture and continues stirring. Finally, 6 g of potassium permanganate was added to the solution by mixing it using a mixer. The solution was incubated at room temperature (until 72 h) and then diluted with 600 mL of deionized water (DIW) in an ice under mixed 30 min. The last step involved the drop-by-drop addition of the hydrogen peroxide to the diluted solution to prevent the oxidation reactions and obtain a dark yellow mixture. The solution was to keep the solution at 24 h to get the precipitation. Graphite oxide sheets by repeated sonication and centrifugation by using 1 M hydrochloric acid solution and DIW were repeated three times, respectively. Afterwards the product will be graphene oxide.

Preparation of La-MOF

The preparation of La-MOFs involved dissolving 3 mmol of a BDC and 5 mmol of La (NO₃)₃·6H₂O in 60 mL of DMF, which was then subjected to ultrasonication for 30 min. The filtered solution was then placed in an 80 mL Teflon lined autoclave and reacted at 130 °C for 48 h. The liner was pulled off after the temperature fell to room temperature. The mixture then was put in a centrifuge tube and repeatedly rinsed with DMF and methanol many times to eliminate unreacted chemicals. To get the samples, they were then dried at 90 °C for 12 h.

Synthesis of Ni-MOF

First, using constant stirring, 1.36 grammes of terephthalic acid was dissolved in 100 mL of DMF. After 30 min, the solution included a few drops of triethylamine (TEA). Under constant stirring, 1.84 g of nickel nitrate hexahydrate was then also added into the linker solution. The solids dissolved and the fluid turned homogeneous after constant stirring. Then, the homogeneous solution was transferred to a Teflon-lined autoclave, which was then heated in a hydrothermal reactor at 120 °C for 24 h. After filtering and washing three times using ethanol, the green colored crystal of Ni-MOF(BDC) dried in vacuum oven at 80 °C.

Synthesis of La-Ni-MOF

The standard procedure involved dissolving 0.15 mmol of terephthalic acid in a mixture of 100 mL of DMF. After then, 0.4 mmol of Ni (NO₃)₂·6H₂O and 0.4 mmol of La (NO₃)₃·6H₂O were introduced and stirrer for 1 h. The resulting mix was then put into an autoclave lined with Teflon. The autoclave was then sealed and held at 120 °C for 12 h. The products were collected, washed, and stored in ethanol when they had cooled to room temperature naturally. The output products are listed as La-Ni-MOF.

Synthesis of La-Ni MOF/GO composites

Two distinct composites were made using the stated hydrothermal technique 1.36 g of terephthalic acid added to DMF with few drops of triethylamine and constant stirring produced a solution. 0.4 mmol of La (NO₃)₃·6H₂O and Ni (NO₃)₂·6H₂O then was added. Stirring went on until every bit of solid stuff dissolved. GO was then included into the mixture, which was sonicated for additional homogeneous mixing following half an hour of stirring. The solution was then firmly closed, heated at 120 °C for 36 h in Teflon walled autoclave. The precipitates’ color matched the level of GO injected. Collected crystals were cleaned and dried under vacuum all the schemes shown in Fig. 1.

Fig. 1.

Synthesis of La-Ni-MOF/GO.

Electrode preparation

The electrochemical catalytic properties of La-Ni-MOF/GO composite and other materials (La-MOF, Ni-MOF, GO, La-Ni-MOF) were investigated on a Nickel Foam (NF) substrate. Combining 330 mL of ethanol, 90 mL of Nafion reagent, and 10 mg of each synthesized component produced a homogeneous ink using sonication. The mixture was sonicated for thirty minutes to ensure that everything blended evenly. Following that, precisely 10 mL of the produced material ink was laid over the NF substrate and let to air-dry for about half an hour. Using all electrochemical testing techniques in a 13.6 pH alkaline solution of KOH (1.0 M KOH) produced a suitable environment for evaluating the catalytic performance of the composite material. From ink manufacture to testing settings, this rigorous process consistent and dependable electrochemical evaluation and offers valuable information for the practical application of synthetic materials.

Physical characterization

The Kα emission was measured in the 2θ range of 10–70° using a Bruker D2 PHASER powdered diffractometer, operating at a current of 10 mA and a voltage of 30 kV. Powder X-ray diffraction (XRD) was utilized to validate the crystalline and structural properties of hydrothermally fabricated La-MOF, Ni-MOF, GO, La-Ni-MOF, and La-Ni-MOF/GO nanocomposite. A scanning electron microscope (TESCAN MIRA3, Czech Republic) was utilized to analyze the external morphological characteristics of the materials. An Agilent spectrometer (Cary 360, FTIR, Malaysia) was utilized to analyze the infrared spectra of materials within the 400–4000 cm^− 1 range. The Brunauer–Emmett–Teller (BET) method and the Barrett–Joyner–Halenda (BJH) technique were utilized to calculate the surface area and pore volume, respectively.

Electrochemical activity

The study examined the standard method for breaking down water into its component elements using an electrochemical system that operated with three separate electrodes. The system contained three elements which included an Ag/AgCl reference electrode and a Pt wire that functioned as the counter electrode and an electrocatalyst that had been applied to the working electrode area. The study used the AUTOLAB PGSTAT-204 electrochemical workstation to tests that required 1.0 M KOH as their testing solution. The cyclic voltammetry and linear sweep voltammetry tests with a 1.0 M KOH electrolyte solution while implementing iR correction at room temperature and using a 5 mV/s sweeping speed. The researchers applied Eq. (1) to change the Ag/AgCl potential value into RHE standard measurements.

1

The Ag/AgCl electrode measures E_Ag/AgCl for its potential value which Ag/AgCl electrode displays while Eo represents the complete thermodynamic potential for the Ag/AgCl standard electrode which has a value of 0.197 V and 0.059 serves as the correct factor which calculates the pH of the electrolyte that was first used.

To determine the overpotential (η), the given equation is used

2

The Tafel value was determined from the linear section of the CV graph which shows how overpotential relates to the OER onset potential³³. The Tafel slope values which explain the speed of OER electrocatalytic reactions were derived from this equation

3

The formula requires n to define the OER response’s electron requirement while η represents the overpotential measurement that connects to the RHE potential. The formula requires n to define the OER response’s electron requirement while η represents the overpotential measurement that connects to the RHE potential. The ECSA measurement was performed through Cdl assessment which is a method that assesses electrochemical double layer capacitance. The external voltametric method allowed researchers to derive electrocatalytic double-layer capacitance value Cdl from the CV plot which spanned multiple voltage levels. The subsequent formula was employed to ascertain ECSA:

4

5

In this context, Cs stands for specific capacitance as measured in mF cm^− 2, and Cdl is the double-layer capacitance of the electrocatalyst material that is prepared. Theoretical calculation of the turnover frequency for the OER was calculated via the following equation:

6

7

The processes involved in water oxidation were analyzed through EIS calculations, linking the EIS values to the dynamics of the OER. The semicircle in the lower-frequency zone demonstrates efficient OER outcomes due to its robust electrical properties and minimal electron transportation resistance. Chronoamperometry serves as a crucial element in assessing the durability of the produced MOFs.

Results and discussion

Physical characteristics

Using Fourier Transform Infrared Spectroscopy (FTIR), functional groups and bonding interactions in the produced samples GO, Ni-MOF, La-MOF, Ni-La-MOF, and Ni-Li-MOF/GO were investigated and shown in Fig. 2. Confirming the effective coordination of the organic linker with Ni²⁺ ions, the FTIR spectrum of Ni-MOF exposes discrete vibrational bands corresponding to the functional groups present in the framework. O–H stretching vibrations are responsible for the broad absorption peak at 3239 cm^{− 1}, therefore showing the existence of water molecules and hydroxyl groups³⁴. The asymmetric and symmetric stretching modes of carboxylate (–COO⁻) groups match the observed characteristic peaks at 1617 cm^{− 1} and 1428 cm^{− 1}, therefore verifying the coordination of the BDC (benzene-1,4-dicarboxylate) linker to Ni²⁺³⁵. Whereas the peaks at 1364 cm^{− 1} and 1015 cm^{− 1} are ascribed to C–O stretching from carboxylate groups, the band at 1554 cm^{− 1} is given to the C=C stretching vibrations of the aromatic benzene ring. Furthermore, verifying the conservation of the aromatic structure inside the MOF framework, the peaks at 755 cm^{− 1} and 715 cm^{− 1} match out-of-plane C–H bending vibrations. Ni-MOF, La-MOF, La-Ni-MOF/GO FTIR spectra showed similar distinctive peaks in the same range as Ni-MOF, therefore preserving the essential framework and functional groups. GO’s (graphene oxide) FTIR spectrum shows clear peaks matching the presence of oxygen-containing functional groups, therefore verifying its successful oxidation. Attributed to the O–H stretching vibration, the broad signal at 3239 cm^{− 1} indicates the presence of hydroxyl (–OH) groups and adsorbed water molecules. While the peak at 1428 cm^{− 1} indicates the C–OH bending mode, therefore verifying the presence of hydroxyl functionalities, the characteristic peak at 1617 cm^{− 1} corresponds to the C=O stretching vibration from carboxyl (–COOH)³⁶. The band seen at 1364 cm^{− 1} is allocated to C–O stretching from epoxy (–C–O–C) and carboxylate groups; the peak at 1015 cm^{− 1} is linked to alkoxy (–C–O) stretching vibrations.

Fig. 2.

FTIR pattern of GO, Ni-MOF, La-MOF, La-Ni-MOF and La-Ni-MOF/GO.

Furthermore, confirming conservation of aromatic sp² domains in GO structure, peaks at 755 cm^{− 1} and 715 cm^{− 1} match out-of-plane C–H bending vibrations³⁷. In Ni-Li-MOF/GO nanocomposite, these functional groups are essential for improving the contact between GO and MOF, hence promoting structural stability and electrochemical performance. Strong interfacial contacts between GO and the MOF structure are shown by a little broadening of the O–H peak and an increase in C–O stretching intensity, therefore indicating the presence of GO in Ni-La-MOF/GO. These results validate the effective production of a stable nanocomposite with possible synergistic capabilities for electrocatalytic uses together with retained structural integrity.

The SEM images expose different morphologies affecting the electrochemical water splitting performance. Though it has low conductivity, GO (Graphene Oxide) Fig. 3a shows a wrinkled, sheet-like structure that offers great surface area and enhanced electron transport. Despite its limited conductivity, Ni MOF (Nickel-Based MOF) Fig. 3b exhibits a crystalline, porous structure with a well-defined cubic morphology, which improves ion transport and Ni²⁺/Ni³⁺ redox activity for OER.

Fig. 3.

SEM images of (a) GO, (b) Ni-MOF, (c) La-MOF, (d) La-Ni-MOF and (e) La-Ni-MOF/GO (f) EDX of the La-Ni-MOF/GO.

Improving stability and electron transport, the lanthanum-based MOF Fig. 3c shows a rod-like, porous framework with aggregated particles. With a hybrid crystalline structure, the La-Ni MOF (Bimetallic MOF) Fig. 3d gains from synergistic interactions between Ni and La, so improving catalytic efficiency and stability. The highly porous, linked network formed by the MOF particles anchored on GO sheets shown in the La-Ni-MOF/GO nanocomposite Fig. 3e. In the La-Ni-MOF/GO composite Fig. 3e, the characteristic cubic morphology of Ni-MOF and La-Ni-MOF Fig. 3b,d is less evident after the addition of GO. This is attributed to the strong anchoring and partial encapsulation of the cubic domains of Ni-MOF by the GO sheets, making the individual domains less distinguishable. In contrast, the rod-like morphology of La-MOF is still partly evident in the composite, likely due to its anisotropic nature and larger size, which make it less likely to be fully covered by the GO sheets. The coexistence of La-MOF rods on the surface and Ni-MOF domains inside the composite indicates a strong interface in the hybrid material. The EDX spectrum Fig. 3f shows that La-Ni-MOF/GO composite element composition contains C, O, La, and Ni elements which match the material’s expected phase. The absence of additional peaks demonstrated that the composite maintained complete purity. The EDX spectrum shows that C, O, La, and Ni exist in the atomic ratio which matches the expected stoichiometric ratio therefore this result confirms that the La-Ni-MOF/GO composite material successfully achieved its desired formation.

The materials’ BET surface area and BJH pore size together with pore volume measurements enable researchers to assess their structural features which affect their capacity to produce electrochemical water splitting are shown in Fig. 4a,b. The specific surface area increases from 184.81 m²/g of GO to 298.49 m²/g of La-Ni-MOF/GO which indicates that the nanocomposite developed a highly porous structure that suits catalytic applications. The pore size reduction from GO (41.35 nm) to La-Ni-MOF/GO (33.44 nm) demonstrates that mesopores emerged which help with ion transport while maintaining extensive surface area. Likewise, the pore capacity rises dramatically from GO (8.52 cm²/g) to La-Ni MOF/GO (16.69 cm¹/g), so the composite’s enhanced porosity that improves reactant accessibility and gas evolution during water splitting values are shown in Table 1. La-Ni-MOF and La-Ni MOF/GO follow a Type IV isotherm, but with an H1/H2 hysteresis loop, unique of well-formed mesoporous frameworks with homogeneous pore topologies. For electrocatalysis in water splitting, the porosity and mass transfer characteristics are improved by GO inclusion. La-Ni-MOF/GO’s increasing surface area and controlled pore size assurances more active sites for electrocatalysis, effective charge transfer, and lowered diffusion resistance. Excellent catalytic activity and stability for general water splitting applications depend on the mass transport of reactants and electrolytes being improved by the hierarchical porosity of the composite. This study demonstrates that GO is a perfect electrocatalyst since its inclusion into La-Ni-MOF improves surface characteristics efficiently.

Fig. 4.

BET isotherms (a) SSA and (b) Pore size of GO, Ni-MOF, La-MOF, La-Ni-MOF and La-Ni-MOF/GO.

Table 1.

Comparative table of BET surface area, BJH pore size, and pore volume.

Material	Specific surface area (mA2/g)	Pore size (nm)	Pore volume (cmA3/g)
GO	184.81	41.35	8.52
Ni-MOF	209.8	37.35	9.14
La-MOF	246.02	36.39	10.6
La-Ni-MOF	265.03	35.75	12.71
La-Ni-MOF/GO	298.49	33.44	16.69

The XRD patterns support the catalysts’ effective production and phase purity, and his graph are shown in Fig. 5. GO shows a comparable (002) plane characteristic peak at 2θ = 15.8°. The well-ordered diffraction peaks of Ni-MOF at 18.05°, 19.14°, 42.07°, 45.42°, 52.59°, and 58.98° are due to its crystalline structure, which transforms into porous structures with active metal species during electrochemical activation³⁸. Confirming phase purity, La-MOF shows peaks at 10.76°, 13.71°, 15.02°, 21.82°, 23.52°, 25.52°, 27.27°, and 31. 42°³⁹. Indicating the creation of a bimetallic framework, the La-Ni-MOF pattern exhibits peaks at 10.96°, 13.91°, 15.22°, 17.52°, 22.05°, 23.73°, 25.69°, 27.47°, and 31.59°. Peak values at 13.64°, 17.73°, 24.65°, 27.73°, 29.21°, 29.74°, 31.04°, 35.35°, 41.45°, and 66.85° in La-Ni-MOF/GO demonstrate the effective integration of GO, with minor peak shifts suggesting robust interfacial interactions. The shift of the GO characteristic peak from around 15.8° to 17.7° in the La-Ni-MOF/GO composite can be attributed to a few factors. The current study shows that GO and La-Ni-MOF both exhibit substantial binding strength through their interfacial connections, which results in changes to the GO interlayer distance and its crystal structure. The composite synthesis process leads to two effects which decrease the interlayer distance because partial reduction and restacking of GO layers lead to oxygen group changes that create more ordered structures which result in peak shifts towards higher angles. The distinct peaks from both Ni-MOF and La-MOF confirm the preservation of their individual crystalline phases within the composite, that improve electron transfer and catalytic activity, thereby enhancing overall efficiency. The combination of Ni-MOF and La-MOF provides a stable crystalline framework with active sites for catalysis, while GO increases conductivity and surface area; their combined effect creates an enhanced composite which improves water splitting through better electron transfer and structural stability and catalytic efficiency. The sharper Ni-MOF peak in the composite indicates enhanced crystallinity and better structural ordering due to the interaction with GO. Crucially for the electrocatalytic performance in water splitting, these XRD measurements confirm the structural stability and improved crystallinity of the materials.

Fig. 5.

XRD pattern of GO, Ni-MOF, La-MOF, La-Ni-MOF and La-Ni-MOF/GO.

The average crystallite size of La-MOF, Ni-MOF, GO, La-Ni-MOF, and La-Ni-MOF/GO nanocomposite corresponds to 2.8, 11.28, 18.05, 19.23 and 30.29 nm, respectively, as evaluated by the Debye–Scherrer equation:

8

Here, β denotes full width at half maximum of the diffraction peaks, λ is the X-ray wavelength, and θ is the diffraction angle. And XRD parameters like Lattice constants, d-spacing, Lattice Strain, Crystalline size and Dislocation density for GO, La-MOF, Ni-MOF, La-Ni-MOF, and La-Ni-MOF/GO are shown in Table 2 which is calculated by applying following Eqs. (9), (10), and (11). The observed shift of XRD peaks to higher 2θ values is a direct consequence of increased lattice strain⁴⁰. As the strain increases, the lattice parameter decreases, causing peak shifting according to Bragg’s law.

9

10

11

Table 2.

Calculated XRD parameters for La-MOF, Ni-MOF, GO, La-Ni-MOF, and La-Ni-MOF/GO.

Sr. no.	Material	d-spacing (Å)	Lattice strain	Crystalline size (nm)	Dislocation density (m-2)
1	Go	0.62	0.019	2.8	0.011
2	Ni-MOF	0.58	0.087	11.28	0.261
3	La-MOF	0.47	0.098	18.05	1.48
4	La-Ni-MOF	0.45	0.15	19.23	2.76
5	La-Ni-MOF/GO	0.33	1.09	30.29	12.16

The researchers used Raman spectroscopy to analyze carbon samples through measurements taken between 200 cm^{− 1} and 3200 cm^{− 1} which they displayed in Fig. 6. The D and G bands of graphene show two main peaks at 1339 and 1571 cm^{− 1} which represent its two fundamental characteristics. The G band originates from the E2 g mode which exists at the zone center and corresponds to ordered sp2-bonded carbon while structural defects and graphene disorders produce the D band. The D band and G band appear at 1435 cm^{− 1} and 1597 cm^{− 1} in the Ni-MOF spectrum which matches the Ni-MOF D band and G band positions documented in previous studies. The La-Ni-MOF/GO spectrum contains all essential characteristic peaks which exist in its spectrum. The D and G bands of the composite spectrum show characteristic graphene peaks which prove that the La-Ni-MOF/GO nanocomposite contains both graphene and La-MOF and Ni-MOF materials. The D band to G band intensity ratio (ID/IG) provides a measurement of sp3 carbon domain disorganization which results from the experimental measurements. The ID/IG ratio for Ni-MOF/G shows an increase which indicates that graphene defects developed and Ni-MOF network experienced disarray. The aromatic ring C–C and C–H bending regions have been confirmed at 1167 cm^{− 1} and 1849 cm^{− 1} while the –COO⁻ group appears at 654 cm^{− 1}. HBTC exhibits multiple intricate vibration patterns which include in-plane vibrations at 1004 cm^{− 1} and out-of-plane vibrations at 864 cm^{− 141}.

Fig. 6.

Raman spectrum of the La-Ni-MOF/GO.

OER activity

Using CV, LSV, Tafel slope analysis, electrochemical impedance spectroscopy (EIS), and stability tests in 1.0 M KOH solution, the electrocatalytic activity of the produced materials toward the oxygen evolution process (OER) was thoroughly assessed. By means of a comparison of GO, Ni-MOF, La-MOF, La-Ni-MOF, and La-Ni-MOF/GO, material composition, crystallinity, and electrical interactions were shown as factors influencing OER efficiency. Cyclic voltammetry (CV) was conducted at a scan rate of 10 mV/s, while Linear sweep voltammetry (LSV) measurements were performed at a scan rate of 5 mV/s for OER. Figure 7a illustrates the cyclic voltammetry (CV) OER polarization curves for the La-Ni-MOF/GO composite together with other materials. The CV curves emphasis the oxidation and reduction peaks, illustrating the electrochemical activity of each substance. These peaks show the efficiency of charge transfer and catalytic activity, with La-Ni-MOF/GO demonstrating higher electrocatalytic behavior. Figure 7b illustrates the GO (2.47 V), Ni-MOF (2.45 V), La-MOF (2.44 V), La-Ni-MOF (2.37 V), and La-Ni-MOF/GO (2.31 V), the onset potential which denotes the voltage needed to start OER gradually drops: Fig. 7d illustrates the overpotential a crucial metric showing energy efficiency is 248 mV (GO), 231 mV (Ni-MOF), 218 mV (La-MOF), 201 mV (La-Ni-MOF/GO), and 184 mV (La-Ni-MOF/GO) at a current density of 10 mA cm⁻². The lower overpotential values suggest that La-Ni-MOF/GO needs the least energy for oxygen evolution, which is important for useful applications. Strong interaction between Ni, La, and GO alters the electronic structure and increases oxygen intermediate adsorption and desorption rates, thereby explaining the great performance of La-Ni-MOF/GO. While La insertion stabilizes the structure and hence improves electronic interactions, Ni active centers help the oxidation from Ni(II) to Ni(III), so improving the catalytic process. Figure 7c illustrates the Tafel slope exhibit a considerable drop from 113 mV dec⁻¹ (GO), 97 mV dec⁻¹ (Ni-MOF), 89 mV dec⁻¹ (La-MOF), 73 mV dec⁻¹ (La-Ni-MOF), to 47 mV dec⁻¹ (La-Ni-MOF/GO). Rapid reaction kinetics suggested by a smaller Tafel slope confirm that La-Ni-MOF/GO shows the most effective charge transfer for OER. Ni and La synergy inside the MOF framework is credited for the improvement in reaction kinetics since it maximizes Ni redox states and promotes electron mobility. GO material demonstrates improved electrical conduction because it enhances the movement of electrons through the material. The stability assessment of catalysts through testing showed that their performance remained unchanged during 50 h of constant overpotential testing which produced chronoamperometry results are shown in Fig. 7e. The La-Ni-MOF/GO system maintained its catalytic performance because La-Ni-MOF/GO maintained its original structural form through multiple structural tests which confirmed its extended operational ability. The combination of strong La-Ni metal bonding with a rigid MOF framework and GO’s shielding effect which prevents damage during long electrochemical tests results in enhanced stability. The current decrease which occurred during chronoamperometry after 2 h of OER testing indicates that the catalyst experienced partial degradation while its surface underwent transformation thus showing paths for better stability development. The Faster electron movement through the catalysts gets proved by the Nyquist plots which EIS measurements recorded because the charge transfer resistance (Rct) showed a decrease across the catalysts. From 10.54 Ω (GO), 8.61 Ω (Ni-MOF), 6.31 Ω (La-MOF), 5.9 Ω (La-Ni-MOF), to 4.3 Ω (La-Ni-MOF/GO) are shown in Fig. 7f. The low charge transfer resistance in La-Ni-MOF/GO shows that strong interfacial contacts between MOF and GO enhance charge transport which leads to better OER performance. The conductivity findings from Fig. 7g provide additional evidence that La-Ni-MOF/GO exhibits improved electronic properties. From 0.28 Ω⁻¹ cm^− 1 (GO), 0.35 Ω⁻¹ cm^− 1 (Ni-MOF), 0.47 Ω⁻¹ cm^− 1 (La-MOF), 0.51 Ω⁻¹ cm^− 1 (La-Ni-MOF), to 0.71 Ω⁻¹ cm^− 1 (La-Ni-MOF/GO), so verifying better electron transport. The combination of highly conductive GO material which serves as an electron-conducting matrix together with improved metal-ligand charge transfer from La-Ni-MOF produces this amplification effect. The introduction of La into Ni-MOF structure decreases charge recombination rates while it increases carrier density and improves electronic band structure which results in better catalytic performance. Figure 7h shows TOF values which demonstrate how efficiently catalytic sites function, ranging from 0.91 s^− 1 (GO) to 0.98 s^− 1 (Ni-MOF) to 1.13 s^− 1 (La-MOF) to 1.25 s^− 1 (La-Ni-MOF) and finally to 1.34 s^− 1 (La-Ni-MOF/GO). This improvement results from better access to Ni active centers and increased density of active sites which can be reached. The combination of La and Ni improves metal ion distribution which creates additional catalytic sites for the process. GO prevents MOF particles from sticking together which results in steady catalytic activity. The La-Ni-MOF/GO composite achieves exceptional OER and HER performance through multiple synergistic effects. The combination of Ni, La, and terephthalic acid linkers creates a customized electronic structure which enhances charge transfer while providing more active sites.

Fig. 7.

(a) CV curves, (b) LSV curves (c) Tafel slope (d) Overpotential (e) Chronoamperometry (f) EIS (g) Conductivity (h) TOF of GO, Ni-MOF, La-MOF, La-Ni-MOF and La-Ni-MOF/GO in basic media.

The Ni–La interaction enables the oxidation of Ni(II) to Ni(III) as GO enhances electron transport according to results which show a low Tafel slope and high conductivity. The high TOF values together with EIS data demonstrate that better surface area results in increased active site exposure and improved charge transfer. The BDC linker in the MOF system provides both stability and maintenance of metal ion coordination which results in better electrocatalytic performance. The La-Ni-MOF/GO catalyst outperforms both single-component and binary catalysts because it shows better overpotential, Tafel slope, conductivity, and charge-transfer characteristics which result from Ni, La, and GO working together in synergy. This design optimizes electron transfer, maximizes active sites, and reduces charge transfer resistance, making it an ideal candidate for high-performance water-splitting systems.

Mechanism of OER

Beginning the adsorption of water molecules, the OER is a complex process that proceeds to produce reaction intermediates and culminates in the release of oxygen molecules. Since they increase the rate of every individual step and lower the total energy consumption of the reaction, catalysts are crucial for raising OER efficiency. Below is a diagram illustrating the oxygen evolution reaction (OER) catalyzed on MOF surfaces in an alkaline environment.

When OH⁻ ions are attracted to the catalyst’s active sites, it releases an electron. This causes MOH intermediates to be formed.

12

Adsorbed MOH species must dissociate, releasing a proton and losing an electron to create MO intermediates.

13

14

When OH⁻ ions attack MO intermediates, they remove the third electron and create MOOH intermediates.

15

As OH⁻ attacks the adsorbed MOOH intermediates, it frees O₂ from the active sites and simultaneously gives up the fourth electron⁴².

16

The oxygen evolution reaction (OER) mechanism which is shown in Fig. 8 starts when OH⁻ ions adsorb onto the active sites of the catalyst. The reaction produces MOH intermediates according to Eq. (12). The intermediates dissociate into MO intermediates while they emit one electron according to Eq. (13). The OER proceeds when La³⁺/Ni²⁺–O intermediates transform into MOOH intermediates according to Eq. (15) which leads to oxygen release and catalyst regeneration according to Eq. (16). This mechanism serves as an essential component which helps scientists understand how the La-incorporated Ni-MOF/GO hybrid catalyst performs electrocatalytically.

Fig. 8.

Mechanism of OER.

HER activity

The study evaluated five different synthesized catalysts (GO, Ni-MOF, La-MOF, La-Ni-MOF, and La-Ni-MOF/GO) performed in the hydrogen evolution reaction test through three testing methods which included linear sweep voltammetry (LSV) Tafel slope analysis, and electrochemical impedance spectroscopy (EIS) and stability tests which took place in a 1.0 M KOH solution. The La-Ni-MOF/GO composite demonstrates superior hydrogen evolution reaction activity to its separate components because the combination of nickel, lanthanum, and graphene oxide creates stronger combined effects which enhance their electrocatalytic abilities. The conducted linear sweep voltammetry (LSV) tests for hydrogen evolution reaction (HER) at a 5 mV/s scan speed. The LSV curves in Fig. 9a show how the samples demonstrate their electrocatalytic abilities through the relationship between current density and applied potential, which demonstrates better catalytic performance with lower onset potential. The onset potential shows a progressive decrease from 0.47 V (GO) to 0.39 (La-Ni-MOF/GO), indicating enhanced catalytic efficiency. Figure 9b displays Tafel slope values which demonstrate a significant decrease in HER from 165 mV dec^− 1 (GO) to 51 mV dec^− 1 (La-Ni-MOF/GO). The Tafel slope reduction shows how La-Ni-MOF/GO speeds up electron flow during the hydrogen evolution reaction because it boosts the rate of chemical reactions. The Tafel slope values for La-Ni-MOF (73 mV dec^− 1), La-MOF (97 mV dec^− 1), and Ni-MOF (113 mV dec^− 1) exhibit a clear progression which shows how La-Ni-MOF/GO improves its reaction speed performance. The Tafel slope reduction indicates that the La-Ni-MOF/GO composite follows a more efficient hydrogen evolution reaction process, which uses Ni-La interaction to enhance hydrogen intermediate adsorption and fast track chemical reactions. Figure 9c shows the overpotential value which measures the energy requirements for hydrogen evolution reaction (HER) to decrease from 171 mV (GO) to 93 mV (La-Ni-MOF/GO). The overpotential values for the additional catalysts 153 mV (Ni-MOF), 138 mV (La-MOF), and 118 mV (La-Ni-MOF). The reduction in overpotential can be ascribed to the synergistic interaction among Ni, La, and GO. The active centers of Ni facilitate hydrogen adsorption and desorption while La improves the electronic structure of the catalyst to enhance charge transfer. GO serves as a matrix which conducts electrons to boost electronic conductivity and permits quick electron transfer essential for effective hydrogen evolution reaction. The turnover frequency (TOF) values in Fig. 9d show the catalytic activity of each catalyst which was measured at 1.2 s^− 1 for GO and 1.27 s^− 1 for Ni-MOF and 1.33 s^− 1 for La-MOF and 1.4 s^− 1 for La-Ni-MOF and 1.54 s^− 1 for La-Ni-MOF/GO. The La-Ni-MOF/GO composite showed the highest TOF which demonstrates better active site usage and better intrinsic performance. The combination of Ni and La creates more active sites for hydrogen evolution while graphene oxide prevents MOF particles from clustering, which results in constant catalytic activity. The La-Ni-MOF/GO TOF increase shows that it makes hydrogen evolution happen more effectively at all active sites, which results in better catalytic performance. The first current density reduction which occurs in Fig. 9e represents a standard pattern for catalyst activation because it establishes permanent active sites through structural modifications. The current density stabilizes which demonstrates that the La-Ni-MOF/GO catalyst maintains its electrochemical performance and permanent operational capacity throughout 150 h of testing under HER conditions. The improved stability results from two factors which include strong La-Ni coordination and the protective function of GO that stops major material losses during prolonged system operation. The study measures charge transfer resistance through EIS testing as shown in Fig. 9f which displays the Rct values for various materials including GO at 687 Ω and Ni-MOF at 909 Ω and La-MOF at 799 Ω and La-Ni-MOF at 743 Ω and La-Ni-MOF/GO at 556 Ω. The lowest Rct value for La-Ni-MOF/GO shows improved electron movement through the material which allows better charge distribution throughout the system. The La-Ni-MOF/GO composite material shows a low Rct value because it enhances electron transport between the electrode and electrolyte interface which serves as a critical element for efficient HER performance. The conductivity values demonstrate that GO has a conductivity of 0.0043 Ω⁻¹ cm^− 1 and Ni-MOF has 0.0032 Ω⁻¹ cm^− 1 and La-MOF has 0.037 Ω⁻¹ cm^− 1 and La-Ni-MOF has 0.0041 Ω⁻¹ cm^− 1 and La-Ni-MOF/GO has 0.0054 Ω⁻¹ cm^− 1 are shown in Fig. 9g. The La-Ni-MOF/GO material shows the highest conductivity among all tested samples because its GO content significantly boosts electron transport which serves as a crucial element for effective HER performance. The conductivity increase in La-Ni-MOF/GO creates faster charge movement while enhancing HER performance through decreased resistance during charge transfer. Graphene oxide functions as an electron-conductive matrix that enhances bulk electronic conductivity while supporting efficient electron movement toward active sites which serve as essential requirements for effective hydrogen evolution reaction (HER) operation. The layered structure of GO together with its contact resistance produces high interfacial charge transfer resistance (Rct) which does not impact hydrogen evolution reaction (HER) kinetics. The results demonstrate that La-Ni-MOF composites designed with GO through deliberate planning show significant improvements in electrocatalytic performance which will benefit water-splitting technologies. A comparison with previously reported materials is given in Table 3.

Fig. 9.

(a) LSV curves (b) Tafel slope (c) Overpotential (d) TOF (e) Chronoamperometry (f) EIS (g) Conductivity of GO, Ni-MOF, La-MOF, La-Ni-MOF and La-Ni-MOF/GO in basic media.

Table 3.

Comparison table between designed electrode material and published literature.

Sample	Overpotential at 10 mA/cm2 (mV)	Tafel slope (mV/dec)	Activity	References
La-doped CoMoP	49 250	127.7 88.9	HER OER	45
Co/La2O3-NC	75 284	98 71	HER OER	46
CoP/rGO	105 340	50 66	HER OER	47
NiCoZnP/NC	74 228	47.51 60.12	HER OER	48
Co(Ni)Ox:CoPx	97 309	9.12 108.42	HER OER	49
FeNi@N-CNT	77 300	68 47.7	HER OER	50
NiCo-UMOFNs	128 250	87 42	HER OER	51
Ni1-xFex-HP	215 280	133 79	HER OER	52
NiMOF	209 297	138.8 178.8	HER OER	53
Ni/(α,β)-NiS MOF@CNT	123 244	50.8 47.2	HER OER	54
Ni2P/rGO	142 260	58 62	HER OER	55
Ni-MOF-74/Ni3N	73 222	109 58	HER OER	56
NiCoSe	170 278	88.8 92	HER OER	[57]
La-Ni-MOF/GO	184 93	51 47	OER HER	Current study

Mechanism of HER

The Hydrogen Evolution Reaction (HER) involves a two-step process, with each step contributing to the formation of H₂. The two steps of the process begin with the Volmer step and continue through the Heyrovsky or Tafel steps as pr shown in Fig. 10. The process operates through the following steps:

Fig. 10.

Mechanism of HER.

1. Volmer step (hydrogen adsorption):

The Volmer step involves the transfer of an electron (e⁻) to the electrode and the interaction of H⁺ ions from the solution with the unoccupied active site of the catalyst. Adsorbed hydrogen atoms () are formed on the catalyst surface as a result of this step. This process lowers the concentration of protons in solutions.

17

• 2.Heyrovsky step (hydrogen evolution):

In the Heyrovsky step, interacts with another proton () in the solution, and gains an electron () to form . This occurs due to the minimal presence of on the catalyst surface.

18

• 3.Tafel step (hydrogen evolution):

The Tafel step occurs when atoms on the catalyst surface interact with each other, leading to the formation of . This process is more prevalent as the concentration of on the surface increases⁴³.

19

The Hydrogen Evolution Reaction (HER) mechanism consists of two main steps. In the Volmer step in Eq. (17), an electron is transferred to the electrode and reacts with H⁺ ions from the solution, forming adsorbed hydrogen atoms () on the catalyst surface. In the subsequent Heyrovsky step in Eq. (18), interacts with H and an electron to produce . Alternatively, the Tafel step in Eq. (19) occurs when two adjacent atoms combine to release . These steps contribute to the overall efficiency of the hydrogen evolution process on the catalyst.

The electrochemical active surface area (ECSA) of the synthesized catalysts was measured by measuring the electrochemical double-layer capacitance (Cdl) in the non-Faradaic region at different scan rates. The ECSA values indicate that higher values demonstrate more active sites which result in improved catalytic performance. The researchers used cyclic voltammograms to identify the non-Faradaic zone at scan rates of 10, 20, 30, 40, and 50 mV s^{− 1} which are shown in Fig. 11a–e. The Cdl value was determined by measuring the anodic and cathodic current densities (j) which were obtained from these plots and their differences were plotted against scan rates resulting in a straight-line relationship Fig. 11f–j. The slope of this line was utilized to calculate the Cdl values for the various catalysts, with GO, Ni-MOF, La-MOF, La-Ni-MOF, and La-Ni-MOF/GO nanocomposite demonstrating capacitance values of 2.0 mF, 2.5 mF, 11 mF, 13.5 mF, and 22 mF, respectively. The ECSA values for GO, Ni-MOF, La-MOF, La-Ni-MOF, and La-Ni-MOF/GO nanocomposite were calculated as 50 cm², 62.5 cm², 275 cm², 337.5 cm², and 550 cm² respectively. The nanocomposite exhibits higher ECSA values because it provides more active sites which enables essential electron-proton transport to occur at the interface between the electrolyte and the electrode thus enhancing its electrochemical performance during electrolysis⁴⁴.

Fig. 11.

(a–e) ECSA and (f–j) Cdl values of GO, Ni-MOF, La-MOF, La-Ni-MOF and La-Ni-MOF/GO in basic media at different current density.

Electrode system

The two-electrode water splitting experiment uses Various electrochemical methods to assess how effectively electrode materials function during Hydrogen Evolution Reaction and Oxygen Evolution Reaction testing. The process starts with cyclic voltammetry (CV) in Fig. 12a which shows how electrodes behave electrically by displaying their current response to different voltage levels. The CV curve shows when OER and HER reactions start because the curve has specific peaks which show how quickly the material reacts and how well it performs. The OER performance of the anode gets evaluated through anodic linear sweep voltammetry (LSV) testing. Figure 12b exhibits the anodic LSV curve which shows how current density changes with increasing applied voltage. The onset potential and current density serve as essential metrics which measure how effectively the electrode performs during the oxygen evolution reaction. The researchers use Cathodic LSV to evaluate the HER performance on the cathodic electrode are shown in Fig. 12c. The cathodic curve provides information similar to the anodic LSV but specifically for hydrogen evolution. The researchers present Tafel slopes in Fig. 12d which show how OER and HER reactions proceed through their reaction kinetics. The Tafel slope for OER measures 101 mV dec^− 1 while HER has a slightly lower value of 93 mV dec^− 1. HER show faster reaction rates because its smaller Tafel slope indicates that the electrochemical reaction needs less activation energy to proceed. The two reactions have different kinetic profiles which become evident through their Tafel slope differences because HER typically shows more efficient reaction rates than OER at common operating conditions. Electrode performance evaluation relies on overpotential values which reveal electrode’s working. The OER reaction at a specific current density needs a 535 mV overpotential because this value shows the energy barrier which needs to be eliminated for the reaction are shown in Fig. 12e. The overpotential for HER demonstrates that energy requirements for hydrogen evolution are lower than those needed for oxygen evolution. The material demonstrates higher efficiency for hydrogen evolution because it needs lower voltage to produce hydrogen. The electrochemical impedance spectroscopy EIS results shown in Fig. 12f, g produce charge transfer resistance Rct measurements for both chemical reactions. The Rct for OER shows a value of 26.32 Ω which proves the material enables effective charge transfer during oxygen evolution. The Rct for HER shows a value of 1586 Ω which proves hydrogen evolution faces greater resistance than other processes. The study indicates that researchers must work on further optimization efforts to achieve better HER performance through lower resistance. The results from Fig. 12h, i show that the material shows consistent performance results for both OER and HER during a 50-h testing period. The material demonstrates long-term stability through its ability to maintain operational capacity for extended periods which makes it suitable for applications that require catalysts to perform their functions without prolonged usage.

Fig. 12.

Two electrode analysis of OER and HER (a,b) CV and LSV of OER (c) LSV of HER (d) Tafel slop of Her and OER, (e) Overpotential HER and OER, (f,g) EIS of HER and OER (h,i) Chronoamperometry of HER and OER.

Conclusion

The La-Ni-MOF/GO composite outperforms its constituent parts when used as an electrocatalyst for water splitting in general, showing increased efficiency in the HER and OER relative to their individual strengths. With the lowest onset potential (0.39 V) and overpotential (93 mV) for HER and the lowest onset potential (2.31 V) and overpotential (184 mV) for OER, the composite exhibits remarkable bifunctional catalytic performance and is highly efficient for both reactions. The La-Ni-MOF/GO composite displays its reaction kinetics through a low Tafel slope which measures 51 mV dec^− 1 for HER and 47 mV dec^− 1 for OER while demonstrating effective electron transfer capabilities. The system displays excellent charge mobility and minimal energy loss through its lowest charge transfer resistance Rct which measures 4.3 Ω, while high conductivity reaches 0.71 Ω⁻¹ cm^− 1 and exceptional turnover frequency achieves TOF of 1.34 s^− 1, which results in a substantial boost to electrocatalytic performance. The composite achieves its sustainability for practical applications through its ability to maintain high performance levels throughout 50 h of chronoamperometry. The composite requires the interactive functions between Ni, La, and GO to achieve its full electrocatalytic performance improvements. The combination of La and GO enables efficient electron transport through La’s enhancement of electronic properties which increases available active sites while improving the absorption and release of intermediate reaction substances. The results demonstrate that La-Ni-MOF/GO functions as an extremely stable and highly effective water-splitting catalyst, which advances the development of sustainable energy conversion systems.

Supplementary Information

Below is the link to the electronic supplementary material.

Author contributions

F.N., A.J., K.-t.-K.: Investigation, methodology, writing-review and editing. A.F., A.K.A.: Validation, data curation, software. G.E., M.E.A.Z., S.M.G.: Investigation, validation, funding acquisition. S.I.A.S., Z.S.: Conceptualization, supervision, writing-review and editing.

Funding

The authors extend their appreciation to Deanship of Scientific Research and Graduate Studies at King Khalid University for funding this work through large research project under grant number (RGP2/489/46).

Data availability

All data generated or analyzed during this study are included in this published article [and its supplementary information files.

Declarations

Competing interests

The authors declare no competing interests.