Preparation Of Transition Metal Sulfide Composites And Their Hydrogen Evolution Performance In Electrolytic Water

Hydrogen energy is clean,renewable,environmentally friendly and easy to store and transport.It is expected to replace fossil fuels in the future.Among the various hydrogen production methods,electrolysis of water hydrogen production with good safety,high purity hydrogen production,high applicability is considered to be the optimal way of hydrogen production.However,at present,the process of hydrogen production by electrolytic water has high overpotential and slow reaction kinetics,resulting in high energy consumption and low conversion efficiency.Rational design of efficient and stable electrocatalysts for hydrogen evolution reaction（HER）is an effective strategy to reduce the cost of hydrogen production and improve the conversion of electric energy to hydrogen energy.Precious metal platinum（Pt）based material is the most effective HER catalyst at present,but its high price,small reserves and poor durability do not have economic and competitive advantages.Therefore,it has become an important direction for researchers to use low-cost and abundant reserves to replace expensive and rare Pt-based catalysts.The catalytic efficiency of transition metal sulfide is relatively low,so the electrocatalytic hydrogen evolution activity is not ideal.Therefore,how to further improve the catalytic activity of transition metal sulfide for its large-scale application is a hot topic for researchers.The key factors affecting electrocatalytic performance are the conductivity of electrocatalyst and exposed active sites.Therefore,this paper focuses on improving HER catalytic activity of transition metal cobalt-nickel sulfide through different modification strategies to study HER performance in electrolytic water.Specific research contents are as follows:（1）Ni（OH）₂/CoNi₂S₄/NF composites with nano-flower structure were prepared on nickel foam substrate by hydrothermal reaction and vulcanization method and used as catalysts for electrolytic water HER.The results showed that the prepared Ni（OH）₂/Co Ni₂S₄/NF catalyst showed good catalytic activity and stability of HER in acidic electrolyte solution.When the current density was 10 m A cm^-2,the overpotential of the catalyst in 0.5 M H₂SO₄solution was 124 m V,and the Tafel slope was 84 m V dec^-1.The catalytic performance of the catalyst was obviously better than that of the control materials.The excellent performance of Ni（OH）₂/Co Ni₂S₄/NF catalyst is due to the unique nanoflower structure of the material,which is conducive to increasing the specific surface area,thus increasing the active area,providing more active sites,and the synergistic effect of Co and Ni bimetallic sites will improve HER catalysis performance.（2）The self-supported Co₃S₄-Ni₃S₄/NF heterojunction material supported on nickel foam was prepared by hydrothermal reaction and hydrothermal vulcanization method and used as catalyst for electrolytic water HER.The electrocatalytic performance of HER was improved by constructing a heterojunction modification strategy.The effect of vulcanizing temperature on the electrocatalytic performance of the material was studied.The results showed that when the current density is 10 m A cm^-2,the overpotentials of Co₃S₄-Ni₃S₄/NF in the electrolyte of 0.5 M H₂SO₄and 1 M KOH were 80 and 83 m V,and the Tafel slope were 72 and 89 m V dec^-1,respectively.Compared with the control materials showed better HER catalytic activity and stability.This is mainly attributed to the fact that bimetallic sulfide improves the conductivity of the electrocatalyst by optimizing the electronic structure,and the coupling effect of the heterogeneous interface formed between Ni₃S₄and Co₃S₄improves the charge density at the S-site,which makes the electrocatalyst more easily capture the active substance in the solution and thus improves the catalytic performance of the hydrogen evolution reaction（HER）.In addition,the design of the self-supporting structure on the nickel foam avoids the use of binders and facilitates the exposure of more reactive sites and the rapid transport of electrons and reactants.（3）Vanadium-doped Co₉S₈-Ni₃S₂/NF nano-flower-electrocatalyst was synthesized in situ by a simple two-step hydrothermal method and used as a catalyst for electrolytic water HER.The structure,composition,morphology and HER properties of the materials were controlled by adjusting the amount of vanadium doping.The results showed that the prepared V-Co₉S₈-Ni₃S₂/NF catalyst showed better HER catalytic performance than Co₉S₈-Ni₃S₂/NF in both acidic and alkaline electrolytes.The doping of vanadium can significantly improve HER performance of Co₉S₈-Ni₃S₂/NF material.When the doping amount of vanadium is 5%,the material V_5%-Co₉S₈-Ni₃S₂/NF showed the best HER catalytic activity and stability.This is attributed to the fact that a small amount of vanadium doping regulates the electronic structure of Co₉S₈-Ni₃S₂/NF and thus improves the intrinsic catalytic activity of the material.At the same time,the presence of heterogeneous interfaces in V-Co₉S₈-Ni₃S₂/NF materials is conducive to improving the electronic structure and generating more active sites.In addition,the unique nanoflower structure formed by vanadium doping helps to increase the surface area for electrocatalytic activity,which can provide more catalytic active sites and thus enhance the HER catalytic activity of the material.