Ni3S2/ZrCoFe-LDH@NF heterojunction catalysts for efficient Overall water Splitting

doi:10.21203/rs.3.rs-3347885/v1

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Ni3S2/ZrCoFe-LDH@NF heterojunction catalysts for efficient Overall water Splitting

https://doi.org/10.21203/rs.3.rs-3347885/v1

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With the continuous depletion of traditional energy sources, the development of sustainable energy sources has become one of the important tasks today. A two-step synthesis method was employed to construct Ni₃S₂/ZrCoFe-LDH@NF heterostructured electrocatalysts on nickel grid (NF) in situ. X-ray diffractometer, scanning electron microscope, transmission electron microscope and X-ray electron spectroscopy were employed to characterize the Ni₃S₂/ZrCoFe-LDH@NF heterostructure, and the HER, OER and total hydrolysis properties of this electrocatalyst were tested in 1 mol·L^− 1 KOH electrolyte. It was shown that Ni₃S₂/ZrCoFe-LDH@NF was a lamellar stacked heterostructure with an overpotential of 330 mV and a Tafel slope of 90.9 mV·dec^− 1 at a current density of 100 mA·cm^− 2 in the OER reaction and 159.2 mV at a current density of 10 mA·cm^− 2 in the OER reaction. Tafel slope was 96 mV·dec^− 1, and the catalyst exhibited good structural stability in the 100 h total hydrolysis stability test. The successful construction of this heterostructured electrocatalyst provides a good idea and research basis for the subsequent heterojunction and its application in electrocatalysis.

Ni3S2/ZrCoFe-LDH@NF

heterostructure

HER

OER

overall water splitting

The continuous development of the economy promotes the progress of society, but also makes all walks of life more and more dependent on fossil energy, and the demand for energy is becoming more and more drastic [1]. However, renewable energy sources such as solar energy and biomass are constrained by the environment [2], limiting their large-scale application. Hydrogen (H₂), as a non-polluting, renewable and clean energy source, has been attracting much attention. However, there is no natural H2 in nature, and it needs to be obtained by other means. Hydrogen production by electrolysis of water, as a zero-pollution and high-purity hydrogen production technology, can fundamentally get rid of the dependence on traditional fossil fuels for hydrogen production, and avoid causing environmental pollution problems [3–6]. To date, platinum-based noble metals are the most advanced hydrogen-extraction reaction (HER) catalysts, and ruthenium, iridium, and their oxides exhibit high oxygen-extraction reaction (OER) performance [7, 8]. However, their scarcity, high price, and poor stability have severely limited their large-scale applications [9]. Therefore, how to develop inexpensive bifunctional catalysts that promote both HER and OER is an urgent problem to be solved.

In recent years, non-precious metal catalysts have shown great potential, including transition metal oxides [10], hydroxides [11], hydroxyl oxides [12, 13], phosphides [14, 15] and sulphides [16, 17]. Among them, layered double hydroxides (LDHs) have been widely studied as electrocatalytic water decomposition catalysts [18, 19].LDHs are two-dimensional layered materials based on metal hydroxides [20].LDHs are characterised by adjustable anions and valence states between layers. However, their catalytic mechanism needs to be improved for practical applications. Therefore, the development of universal reaction methods is of great importance for the development of highly efficient and selective bifunctional catalysts. The bifunctional properties of materials can be effectively improved through a series of optimisation tools, including deposition on conductive substrates, component optimisation and defect modulation [21–24]. Specifically, cation modulation can change the three-dimensional energy levels of electrocatalysis and enhance the electronic interactions, which in turn modulate the surface adsorption energy of intermediates [25–27]. Notably, the doping of high valence Mo⁶⁺ [28], Cr³⁺/⁶⁺ [29] and V⁵⁺ [30] into LDH has attracted extensive attention from scholars. Zirconium (Zr) is an abundant earth element with abundant valence states (+ 2, + 3, +4) and Zr⁴⁺ is a stable valence state, which can be used as a doping element to improve the performance of catalysts.Kurungot et al [23] doped Zr⁴⁺ in spinel oxides can optimize the electronic structure and improve the ORR and OER performance.Huang et al [31] improved the catalyst performance by doping Zr⁴⁺ in Zr doping in CoFe₂O₄, the morphology and electronic structure of the intermediates were tuned and the surface adsorption energy of the intermediates was optimised to further enhance the catalytic performance. Excess metal sulfides have been widely studied due to their abundant raw material reserves, simple preparation process and environmental friendliness [32]. In general, Ni₃S₂ can provide more active sites for electrocatalysis than other electrocatalysts due to its layered structure at the macroscopic scale, increasing the catalytically active surface area actually involved in the reaction, and thus greatly enhancing the catalytic performance. Ni₃S₂ is often chosen as a heterojunction electrocatalyst because of its high theoretical specific heat capacity, low raw material cost, simple synthesis method, and easy preparation, and so on. Materials [33].Zhang et al [34] firstly proposed the interfacial engineering of novel MoS₂/Ni₃S₂ heterostructures, in which abundant interfaces were formed. For OER, this MoS₂/Ni₃S₂ heterostructure exhibits a very low overpotential of about 218 mV at a current density of 10 mA·cm^− 2.Yang et al [35] prepared MoS₂-Ni₃S₂ heterostructured nanorods on nickel foam by a one-pot hydrothermal method, achieving HER and OER current densities of 10 mA·cm^− 2 in 1.0 M KOH, respectively. Zeng et al [36] coupled and combined Ni₂P and Ni₃S₂ and grew them in situ on nickel foam, which resulted in good catalytic performance due to its strong interfacial coupling effect and large surface area, reaching very low overpotentials of 80 and 210 mV for HER and OER, respectively, at a current density of 10 mA·cm^− 2 in 1.0 M KOH solution. In addition, in order to further enhance the catalytic activity of the catalysts, efforts have been devoted to the development of nanomaterials grown directly on conducting substrates such as nickel foam (NF), iron foam (Fe), etc.[37] NF is a new type of conductive material that is highly promising for applications. In particular, the introduction of a three-dimensional framework structure can not only increase the conductivity of the material, but also increase the specific surface area of the material, which in turn accelerates the catalytic reaction rate [38]. If N_i3S₂ and ZrCoFe-LDH can be heterogeneously combined by a simple preparation technique, the synergistic effect between the heterostructures is expected to significantly improve the total decomposition of water performance.

Based on the above study, our group used a two-step method to prepare Ni₃S₂/ZrCoFe-LDH@NF catalysts, and regulated the structure and morphology of the heterojunction catalysts by changing the concentration of Fe element in the reactants to increase the density of active sites on the surface of the catalysts, which effectively improved the catalytic performance of Ni₃S₂/ZrCoFe-LDH@NF catalysts.

Nickel foam (d = 1.5 mm) was cut into 10 mm×40 mm and was ultrasonically cleaned in 1 mol/L HCl, anhydrous ethanol, and deionized water for 0.5 h, respectively, and then dried at a constant temperature of 60°C for 6 h, which was recorded as NF.0.606 g (1.5 mmol) of Fe(NO₃)₃·9H₂O, respectively, and 0.582 g (2.0 mmol) Co(NO₃)₂·6H₂O, 0.466 g (2.0 mmol) ZrCl₄, and 3.03 g (0.03 mol) KNO₃ as Fe, Co, and Zr sources, respectively, were dissolved in 100 mL of deionized water and stirred at a low speed for 60 min, and the above solutions were used to perform ZrCoFe- LDH/NF electrodeposition. a Pt sheet, saturated calomel electrode (SCE) and NF were used as auxiliary, reference and working electrodes, respectively. A constant voltage of -1.1 V was used in the experimental process, and the electrodeposition time was 800 s. After the reaction, the NF was washed with deionized water and anhydrous ethanol alternately for three times, and the cleaned NF was dried at a constant temperature of 60 ℃ for 2 h. 30 mg of TAA was dissolved in 30 mL of deionized water, and then poured into 50 mL of polytetrafluoroethylene inner liner after complete dissolution, and then put into the ZrCoFe-LDH/NF. The stainless steel autoclave was sealed, heated to 140 ℃ for 30 min, washed with deionized water and anhydrous ethanol alternately for 3 times, and the cleaned NF was dried at a constant temperature of 60 ℃ for 6 h, which was recorded as Ni₃S₂/ZrCoFe-LDH@NF.

Synthesis of Ni₃S₂/ZrCoFe-LDH@NF electrode

The Ni₃S₂/ZrCoFe-LDH@NF catalysts were prepared by a two-step method and optimized by modulating the initial concentration of Fe elements (1.0 mmol and 2.0 mmol). Figure 1 shows a schematic diagram of the synthesis process. The three-dimensional porous NF structure (Fig. S 1a) can be used as a catalyst carrier due to its good electrical conductivity and provides a source of Ni. A layer of ZrCoFe-LDH structure was first formed on the NF by electrodeposition, and then the obtained product was sulfurized to finally obtain the Ni₃S₂/ZrCoFe-LDH@NF heterojunction catalyst.

Physical and structural analysis

Scanning electron microscopy (SEM) was used to analyze the indicated morphology and structure of the catalysts.The SEM image of the ZrCoFe-LDH@NF catalysts showed a uniform lamellar stacking structure (Fig.S1).After the introduction of Ni₃S₂, the morphology and structure changed, as shown in Fig.S2, with some particles stacked on top of the original lamellae.As the concentration of elemental Fe gradually increased, the particles become fine and uniform, but when the Fe element concentration is 0.2 mmol, the particles are fine and uniform, as shown in Fig. 2a. The results show that the introduction of Ni₃S₂ can effectively affect the specific surface area of the catalyst. In addition, the NF surface was initially smooth as can be seen from the low-resolution SEM image in Fig. S1. However, after Ni₃S₂/ZrCoFe-LDH synthesis, the structure of the NF scaffold became rough due to the increase of active adsorption sites on the catalyst (Fig. S2a). The internal structural features of Ni₃S₂/ZrCoFe-LDH@NF were further analyzed using transmission electron microscopy (TEM). Figure 2b shows the TEM image, from which it can be seen that Ni₃S₂/ZrCoFe-LDH@NF is a stacking of small particles on lamellae, which is in perfect agreement with Fig. 2a. Figure 2c shows the HRTEM image, in which the lattice spacing of 0.2 nm is attributed to the (202) crystallographic plane of Ni₃S₂ (JCPDS No. 44-1418), and the lattice spacing of 0.26 nm is attributed to the (102) crystallographic plane of ZrCoFe-LDH (JCPDS No. 46–0605), which indicates that the Ni₃S₂/ZrCoFe -LDH heterostructure. This heterostructure can form more electron holes, increase the active sites for electrocatalysis, and improve the catalyst conductivity and electron migration, thus accelerating the reaction rate. The EDS data of Fig. 2d-j and Fig. S3 show that Ni₃S₂/ZrCoFe-LDH@NF consists of the elements Co, Fe, Ni, S, O, and Zr with a uniform distribution of each element.

The lattices of the prepared Ni₃S₂/ZrCoFe-LDH@NF catalysts were characterized by X-ray diffraction (XRD) and the results are shown in Fig. 3. The XRD of Ni₃S₂/ZrCoFe-LDH@NF, ZrCoFe-LDH@NF and Ni₃S₂@NF catalyst electrodes are shown in Fig. 3. The diffraction peaks located at 2θ = 44.5°, 51.8° and 76.3° in the XRD patterns of all electrodes correspond to each other with the (111), (200) and (220) crystal planes of Ni (JCPDS No. 04-0850), all of which are diffraction peaks of NF. Ni₃S₂/ZrCoFe-LDH@NF at 2θ = 11.5°, 23.2° and 34.4 The diffraction peaks at 2θ = 27.1°, 31.1°, and 49.7° correspond to the (003), (006), and (102) crystal planes (JCPDS No. 46–0605) of ZrCoFe-LDH@NF, and the diffraction peaks at 2θ = 27.1°, 31.1°, and 49.7° correspond to the (101), (110), and (113) crystal planes (JCPDS No. 44- 1418) correspond to each other. The decrease of the diffraction peaks in the Ni₃S₂/ZrCoFe-LDH@NF electrode in the figure with respect to the single electrode is due to the formation of a heterojunction, which leads to a decrease in crystallinity. It can be seen that the Ni₃S₂/ZrCoFe-LDH@NF composite electrode can be prepared by two-step synthesis.

The Ni₃S₂/ZrCoFe-LDH@NF electrode was analyzed for its chemical composition valence using X-ray electron spectroscopy (XPS). The full spectrum shows the presence of the elements Ni, S, Zr, Co and Fe (Fig. 3b), which is consistent with the EDX analysis. Figure 3c shows the high-resolution XPS spectrum of Ni 2p, Ni₃S₂/ZrCoFe-LDH@NF Strong Ni 2p_3/2 and Ni 2p_1/2 peaks were observed at binding energies of 855.90 eV and 873.74 eV. The energy difference of 17.84 eV between the two peaks indicates the coexistence of Ni²⁺ and Ni³⁺ oxidation states [39]. Where "Sat." is the satellite peak [40]. It is clearly seen in the figure that the Ni 2p_3/2 and Ni 2p_1/2 peaks of Ni₃S₂/ZrCoFe-LDH@NF-after electrochemical testing are shifted by -0.19 eV and − 0.33 eV, respectively. The high-resolution XPS spectra of Fe 2p are shown in Fig. 3d. The peaks at 717.27 eV and 724.83 eV are the peaks of Fe 2p_3/2 and Fe 2p_1/2 peaks, in which the ZrCoFe-LDH@NF peak position is significantly shifted, probably due to the complexation of Ni₃S₂ and ZrCoFe-LDH. Figure 3e shows the XPS map of Co 2p, in which the Co 2p_3/2 and Co 2p_1/2 peaks of Co³⁺ are shown to be centered at 780.79 eV and 797.13 eV, and the peaks located at 782.30 eV and 803.05 eV correspond to Co²⁺ with satellite peaks [41, 42]. Compared with ZrCoFe-LDH@NF, the Co 2p peaks in Ni₃S₂/ZrCoFe-LDH@NF electrodes are significantly shifted, which may be consistent with the shift of the Fe 2p peaks, due to the complexation of Ni₃S₂ and ZrCoFe-LDH. Figure 3f shows the XPS map of Zr 3d with peaks out at 182.15 eV and 184.65 eV corresponding to Zr 3d_5/2 and Zr 3d_3/2 [43]. As with Co and Fe, the single electrodes have peak shifts. Fig. S4b shows the S 2p XPS map of the Ni₃S₂/ZrCoFe-LDH@NF features S 2p_3/2 and S 2p_1/2 peaks with binding energies at 162.8 eV and 164.0 eV, indicating the electrical formation of metal sulfides at the Ni-S bonding site corresponding to S²⁻ [44]. The target electrode exhibited some peak shifts compared to the single motor.

Electrocatalytic OER performance

The OER performance of Ni₃S₂/ZrCoFe-LDH@NF electrocatalysts was evaluated using a three-electrode system in a 1 M KOH alkaline electrolyte, with the catalysts, carbon rods, and Hg/HgO serving as the working electrode, auxiliary electrode, and reference electrode, respectively. The OER performance of the electrodes prepared with different Fe concentrations was firstly evaluated (Fig.S5), and it was observed that Ni₃S₂/ZrCoFe-LDH@NF-2 had a good OER performance, and the OER performance of Ni₃S₂@NF, ZrCoFe-LDH@NF, IrO₂@NF and NF were compared. Figure 4a shows the linear scanning voltammetric curves (LSV) of various catalyst electrodes after IR correction. The optimized Ni₃S₂/ZrCoFe-LDH@NF has the lowest negative current, and the anodic current increases sharply with the increase of driving voltage, even exceeding the performance of the noble metal IrO₂@NF catalyst. The Tafel slope is an important parameter for evaluating the fast and slow HER kinetics[45], and the smaller the Tafel slope is, the better the catalytic kinetics of the electrode is. The Tafel slope was obtained by fitting the polarization curves of the catalytic electrodes to evaluate the reaction kinetics of the catalysts in the OER process, and the results are shown in Fig. 4b. Ni₃S₂/ZrCoFe-LDH@NF, ZrCoFe-LDH@NF, Ni₃S₂@NF and IrO₂@NF The Tafel slopes of 90.9 mV·dec^− 1, 108.2 mV·dec^− 1, 130.2 mV·dec^− 1, and 125.4 mV·dec^− 1 were all lower than that of the basal NF (168.9 mV·dec^− 1) in that order. Based on the polarization curves, the overpotentials of different catalytic electrodes with a current density of 100 mA·cm^− 2 were compared, and the results are shown in Fig. 4c. Compared with Ni₃S₂@NF (460 mV), ZrCoFe-LDH@NF (392 mV), IrO₂@NF (470 mV) and NF (620 mV), the Ni₃S₂/ZrCoFe-LDH@NF has the lowest overpotential of 330 mV. To characterize the charge transfer ability of the catalytic electrodes, different catalytic electrodes were fitted with electrochemical impedance Nyquist curves of -1.3 V vs. RHE using ZSimp Win software. The fitted semicircle is a result of interfacial charge transport between the catalyst and the electrolyte, with smaller diameters resulting in lower resistivity. Figure 4d shows the EIS curves obtained for the electrodes at the same test potentials, and the internal inset shows the equivalent circuit diagram consisting of ohmic resistance (Rs), charge transfer impedance (Rct), and double layer capacitance (C_dl). Generally, the lower the value of charge transfer resistance (Rct), the lower the resistance to charge transfer between the solid-liquid; the smaller the value of full contact resistance (Rs), the closer the contact between the substrate and the catalyst[46].The smallest fitted semicircle diameter for the Ni₃S₂/ZrCoFe-LDH@NF catalytic electrode suggests that the interfacial charge transfer between the laminar heterostructures and the electrolyte is more convenient, which can accelerate the charge transfer kinetic process, thus accelerating the rate of the reaction and enabling the catalytic performance of the electrode to be improved. The durability and stability of electrodes is an important index for the industrial application of electrodes, so the stability and multistep current tests of Ni₃S₂/ZrCoFe-LDH@NF electrodes and IrO₂@NF electrodes were carried out in 50 h constant current (10 mA·cm^− 2) alkaline (1 mol·L^− 1 KOH) electrolyte as shown in Fig. 4e. The Ni₃S₂/ZrCoFe-LDH@NF Voltage changed from 1.49 V vs. RHE to 1.5 V vs. RHE, and the voltage was reduced to 1.5 V vs. RHE. while the IrO₂@NF electrode showed a rapid voltage drop from 1.49 V vs. RHE to 1.47 V vs. RHE only under the 20 h constant current (10 mA·cm^− 2) test, and the inset graph shows the multistep currents of Ni₃S₂/ZrCoFe-LDH@NF electrode, from which it can be seen that the curve is relatively smooth and without up and down fluctuations in each test current interval, indicating that Ni₃S₂/ZrCoFe-LDH@NF has relative stability in both increasing and decreasing currents. In order to further explore the effect of electrocatalytic active sites of Ni₃S₂/ZrCoFe-LDH@NF, electrochemically active surface area (ECSA) tests were carried out (Fig. S6), and the double-layer capacitance (C_dl) values were obtained by computational fitting as shown in Fig. 4f, which were comparable to those of ZrCoFe-LDH@NF (4.6 mF·cm^− 2), Ni₃S₂@NF (2.4 mF·cm^− 2), IrO₂@NF (2.3 mF·cm^− 2) and NF (2.2 mF·cm^− 2), Ni₃S₂/ZrCoFe-LDH@NF has a larger double-layer capacitance value of C_dl = 19.2 mF·cm^− 2 compared to Ni₃S₂/ZrCoFe-LDH@NF, as shown by the combination of SEM and TEM, which shows that a large number of laminar stacks were formed on the surface of the catalysts, which increased the exposed interfacial active site number and enlarged the active region. In summary Ni₃S₂/ZrCoFe-LDH@NF exhibits excellent OER performance.

Electrocatalytic HER performance

The HER performance of Ni₃S₂/ZrCoFe-LDH@NF electrocatalysts was evaluated under the same conditions, and the HER performances of Ni₃S₂@NF, ZrCoFe-LDH@NF, Pt/C@NF, and NF were further investigated, and the results are shown in Fig. 5, and the HER performances of the electrodes prepared with different Fe concentrations were evaluated as in Fig. S5. Figure 5a is a comparison plot of the electrodes' LSV comparison plots, except for the Pt/C@NF electrode, the optimized Ni₃S₂/ZrCoFe-LDH@NF electrode not only exhibits the best HER performance, but also exhibits significant HER activity, with the lowest applied driving voltage and a sharp increase in current density when the same cathodic current is reached. Figure 5b shows a comparison of Tafel slopes, with Ni₃S₂/ZrCoFe-LDH@NF having the closest slope of 96 mV·dec^− 1 compared to Ni₃S₂@NF (106 mV·dec^− 1), ZrCoFe-LDH@NF (113 mV·dec^− 1), and NF (116 mV·dec^− 1), but the slope is not significant in comparison with that of the Pt/C@ NF (29 mV·dec^− 1) is yet to be optimized. The required overpotentials for each electrode at a current density of 10 mA·cm^− 2 are shown in Fig. 5c. Ni₃S₂/ZrCoFe-LDH@NF has a lower overpotential of 159.2 mV, which is lower than Ni₃S₂@NF (214.9 mV), ZrCoFe-LDH@NF (225.5 mV), and NF (234.5 mV), indicating that the that the synergistic effect between Ni₃S₂ and ZrCoFe-LDH can significantly improve the HER performance. The electrochemical impedance spectroscopy (EIS) curves shown in Fig. 5d show the charge transfer resistance (R_ct) of different catalysts. From the semicircle diameters of the fitted curves, it can be seen that the fitted diameters of Ni₃S₂/ZrCoFe-LDH@NF are the smallest except for Pt/C@NF, indicating that the charge transfer resistance of this catalyst is the smallest, which is the more favorable for the HER reaction to proceed. Figure 5e shows the stability test carried out at a current density of 10 mA·cm^− 2 for 50 h. The voltage was decreased from − 0.22 V vs. RHE to -0.26 V vs. RHE, and the inset is a multistep current plot, in which Ni₃S₂/ZrCoFe-LDH@NF showed relative stability during the process of decreasing and increasing currents, which indicates that Ni₃S₂/ZrCoFe- LDH@NF can withstand the impact brought by the alkaline solution and gas escape with good stability and durability. Figure 5f shows the LSV curves of Ni₃S₂/ZrCoFe-LDH@NF before and after 3000 cycles of CV. When the driving current density reaches 100 mA·cm^− 2, the η₁₀₀ value of the polarization curve varies from 270 mV to 266 mV, with a very small potential difference, and the curves are highly coincident, which further illustrates that Ni₃S₂/ZrCoFe-LDH@NF has a good stability. In summary Ni₃S₂/ZrCoFe-LDH@NF exhibits excellent HER performance.

Total Hydrolysis Performance

Based on the results of electrocatalytic HER and OER performance evaluation, the Ni₃S₂/ZrCoFe-LDH@NF catalyst exhibited excellent hydrogen and oxygen precipitation activities, and thus its overall water decomposition performance as a bifunctional catalyst was investigated in a two-electrode system with 1 M KOH alkaline electrolyte. The Ni₃S₂/ZrCoFe-LDH@NF||Ni₃S₂/ZrCoFe-LDH@NF coupled electrodes were used as the cathode and anode in the experiments. During the water decomposition process at the applied voltage, a large amount of H₂ and O₂ were produced at the cathode and anode, respectively.As shown in Fig. 6a, the full hydrolysis polarization curve of Ni₃S₂/ZrCoFe-LDH@NF reached 10 mA·cm^− 2 at a driving voltage of 1.57 V. This indicates that the Ni₃S₂/ZrCoFe-LDH@NF catalyst promoted the HER and OER reaction kinetics. Figure 6b shows the chronoamperometric voltage profile of the Ni₃S₂/ZrCoFe-LDH@NF electrode operating at a current density of 10 mA·cm^− 2 for 100 h. The results show that the electrolytic cell provided a stable current, and the cathode and anode voltages were changed from 0.56 V to 0.57 V with a change of only 0.01 V during the long-term water decomposition process, and, in summary, the Ni₃S₂/ZrCoFe -LDH@NF has good total hydrolysis performance and stability in alkaline solution.

In summary, Ni₃S₂/ZrCoFe-LDH@NF heterostructured electrocatalysts were synthesized by a two-step method. Various tests and characterization results showed that the lamellar formations of Ni₃S₂/ZrCoFe-LDH@NF exposed more active sites with larger specific surface area and abundant active centers. In addition, the synergistic interaction between the heterostructures optimizes the electronic structure, which in turn effectively improves the carrier transport rate in alkaline media. Ni₃S₂/ZrCoFe-LDH@NF can be used as an electrode in an electrolytic cell with an ultra-low driving voltage of only 1.57 V to carry out hydride composition at a current density of 10 mA·cm^− 2, which is superior to the majority of the bifunctional catalysts reported so far. This study provides a new idea for the design of efficient, stable and economical heterojunction electroelect rocatalysts.

Author Contributions: Yuchen Guo(first auther):conceptualization, analysis, writing—original draft, conducted the synthesis of the electrodes, and carried out corresponding characterizations, Xiangyu Zou. and Xueling Wei: funding acquisition, writing—review and editing, Weiwei Bao., Jie Han,and Feihong Jia: helped to conduct data analysis. All authors have read and agreed to the published version of the manuscript.

Funding: This research was supported by the National Natural Science Foundation of China (Grant Nos.51504147) and the Natural Science Basic Research Program of Department of Science and Technology of Shaanxi Province (2023-JC-YB-404).

Data Availability Statement: Data sharing is not applicable to this article as no new data were created or analyzed in this study.

Declaration of competing interest：The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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No competing interests reported.

supplementarymaterial.docx
Supplementary material: Figure S1: SEM images of ZrCoFe-LDH@NF catalysts prepared with different Fe concentrations (a) NF, (b) ZrCoFe-LDH@NF-1, (c) ZrCoFe-LDH@NF-2, (d) ZrCoFe-LDH@NF-3; Figure S2: SEM images of Ni3S2/ZrCoFe-LDH @NF catalysts with SEM images of (a) NF, (b) Ni₃S₂/ZrCoFe-LDH@NF -1, (c) Ni₃S₂/ZrCoFe-LDH@NF -2, and (d) Ni₃S₂/ZrCoFe-LDH@NF-3; Fig. S3: EDX spectra of Ni₃S₂/ZrCoFe-LDH@NF catalysts and corresponding atomic (Co, Fe, Ni, S, O and Zr) contents; Figure S4: XRD and XPS plots of (a) XRD comparison of Ni₃S₂/ZrCoFe-LDH@NF catalysts prepared with different Fe concentrations, (b) S 2pXPS plots; Figure S5: Comparison of the OER performance of ZrCoFe-LDH@NF catalysts prepared with different Fe concentrations (a) LSV comparison, (b) Tafel comparison, (c) overpotential comparison, and (d) EIS comparison; Figure S6. comparison of ECSA curves of different electrodes (a) Ni₃S₂/ZrCoFe-LDH@NF, (b) ZrCoFe-LDH@NF, (c) Ni₃S₂ @NF, (d) IrO₂@NF, (e) NF.

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Ni3S2/ZrCoFe-LDH@NF heterojunction catalysts for efficient Overall water Splitting

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Abstract

Figures

Introduction

Experimental materials and methods

Results and discussion

Synthesis of Ni₃S₂/ZrCoFe-LDH@NF electrode

Physical and structural analysis

Electrocatalytic OER performance

Electrocatalytic HER performance

Total Hydrolysis Performance

Conclusion

Declarations

References

Additional Declarations

Supplementary Files

Status:

Version 1

Ni3S2/ZrCoFe-LDH@NF heterojunction catalysts for efficient Overall water Splitting

Status:

Version 1

Abstract

Figures

Introduction

Experimental materials and methods

Results and discussion

Synthesis of Ni3S2/ZrCoFe-LDH@NF electrode

Physical and structural analysis

Electrocatalytic OER performance

Electrocatalytic HER performance

Total Hydrolysis Performance

Conclusion

Declarations

References

Additional Declarations

Supplementary Files

Status:

Version 1

Synthesis of Ni₃S₂/ZrCoFe-LDH@NF electrode