Construction Of Highly Efficient Ni-Co-Mo Based Sulfide Electrodes For Electrocatalytic Hydrogen Evolution

Since the industrial revolution,human society has developed rapidly,and the demand for energy has been increasing,however the energy structure dominated by fossil fuels has led to serious environmental pollution and energy crisis,the development of new clean energy has become an urgent development issue.Hydrogen energy is an efficient and clean energy carrier with high energy density,and the combustion process is clean and pollution-free,so it is regarded as a new energy with broad application prospects.The electrocatalytic water splitting reaction is one of the main methods of hydrogen prodution at present.However,many complex multi-electron transfer processes are involved in the actual production process,and the sluggish reaction kinetics will greatly hinder the progress of the hydrogen evolution reaction.The efficient hydrogen evolution catalysts can reduce the overpotential and decrease the energy consumption during the reaction.Precious metals such as Pt have high catalytic activity,but their high cost and low reserves greatly limit the development and utilization of hydrogen energy.Therefore,the exploitation of high-efficiency,stable,and low-cost non-precious metal catalysts is crucial for the application of electrocatalytic water splitting reaction.The transition metal elements on earth are abundant in reserves and relatively cheap,which are potential hydrogen evolution electrode materials.Various explorations have been carried out by researchers,among which transition metal sulfides have received extensive attention due to their abundant active sites and noble metal-like electronic band gaps.Studies have shown that the synergistic effect of different transition metal elements can effectively reduce the overpotential during the hydrogen evolution reaction and improve its catalytic hydrogen evolution performance.In this paper,transition metals were alloyed by arc melting and induction melting,followed by dealloying and sulfuration,the Ni-Co-Mo-based sulfides as hydrogen evolution electrodes were prepared,then various phase characterizations and electrochemical tests were carried out on it.The hydrogen evolution reaction mechanism was deeply analyzed through density functional theory（DFT）calculations,and the changes in the microstructure and their effects on the hydrogen evolution performance of metal sulfides with different atomic ratios were explored.（1）Al₈₅Ni_xMo_15-x（x=15、10、7.5）ternary alloys with different atomic ratios were smelted in an arc melting furnace,and Al was used as the sacrificial component of dealloying in 6 M NaOH solution to obtain porous NiMo alloy precursor.Subsequent vapor sulfuration was carried out in the tube furnace constructed the microstructure of cauliflower-like nanospheres,which provided more active sites for the hydrogen evolution reaction.Electrochemical tests were carried out in an acidic environment（0.5 M H₂SO₄）,and the results showed that when the atomic ratio of Ni:Mo was 2:1,the Ni₁₀Mo₅-S electrode exhibited the most excellent hydrogen evolution performance,which can reach current densities of 10 mA cm^-2 and 100 mA cm^-2 at only 91 mV and 203 mV of overvoltage with a low Tafel slope of 66 mV dec^-1.DFT calculations show that the heterostructure of NiS and MoS₂ reduces the Gibbs free energy ΔG_H* of the reaction,improves the intrinsic catalytic activity of the catalyst,which is favorable for the hydrogen evolution reaction.This chapter combines experiments and theoretical calculations to explore the effects of different Ni-Mo atomic ratios on the phase morphology and hydrogen evolution performance of bimetallic sulfide electrodes.The results show that the synergistic effect of NiMo bimetallic sulfides reduces the energy barrier of hydrogen evolution reaction,the unique cauliflower-like micromorphology provides more active sites for the adsorption of H^*,and the self-supporting structure has good electrical conductivity,which is conducive to the release of bubbles,so that the Ni₁₀Mo₅-S electrode exhibits excellent catalytic performance.（2）In this chapter,the porous CoMo alloy precursor was prepared by combining arc melting technology and dealloying method,and then vapor sulfuration in a tube furnace to prepare CoMo bimetallic sulfide.The phase composition and microscopic morphology of the materials were characterized by X-ray diffractometer（XRD）,scanning electron microscope（SEM）,etc.The hydrogen evolution performance and stability of the catalytic electrode were tested by linear scanning voltammetry and chronopotentiometry.The results show that the addition of an appropriate amount of Mo promotes the dense growth of CoMo sulfide nanowires,increases the specific surface area,and facilitates electron transport during the hydrogen evolution reaction.Electrochemical tests show that the catalyst exhibits excellent hydrogen evolution performance in acidic media,and the overpotential of Co₁₃Mo₂-S electrode is only94 mV and 172 mV at current densities of 10 mA cm^-2 and 100 mA cm^-2 during cathodic hydrogen evolution,the Tafel slope is only 59 mV dec^-1,besides it has good hydrogen evolution stability and durability.