Preparation And Electrocatalytic Hydrogen Evolution Properties Of Carbon Supported Mo-based Electrocatalyst

Hydrogen energy is a clean and non-polluting energy sources,and the hydrogen element mainly exists in the form of water with abundant reserves on the earth.Therefore,the hydrogen evolution by electrolytic water splitting is a promising method for hydrogen production.Precious metal platinum?Pt?is considered to be the best catalyst for hydrogen evolution,but the practical use is limited due to its low reserves and high cost.Therefore,exploring low-cost and high-efficiency non-precious metal catalysts for hydrogen evolution is of great significance for the development of hydrogen energy.As a hydrogen evolution electrocatalyst,molybdenum-based composite materials have the advantages of good structural stability and excellent catalytic performance.In this thesis,carbon nitride?g-C₃N₄?was used as a self-sacrificial template to prepare a two-dimensional carbon-supported molybdenum-based material as a hydrogen evolution electrocatalyst.The main research contents are as follows:1. The catalyst precursors are first synthesized by using hydrothermal method with g-C₃N₄ as a self-sacrificing template,glucose as the carbon source and ammonium molybdate as the molybdenum source,which is further calcined at high temperature to prepare two-dimensional nanostructured nitrogen-doped molybdenum carbide decorated carbon nanosheets.We have evaluated the hydrogen evolution performances of the electrocatalysts prepared at different calcination temperatures,and explored the effects of nitrogen doping and two-dimensional structure on the hydrogen evolution performance of electrocatalysts.The results show that the electrocatalyst calcine at 800?exhibits more excellent hydrogen evolution performances.In a 1.0 M KOH solution,the resulting electrocatalyst presents an overpotential of 185 m V at a current density of 10 m A cm^-2 and a Tafel slope of 69 m V dec^-1,and the electrocatalyst could maintain a stable hydrogen evolution potential over 20 hours.The electrocatalyst with a two-dimensional structure possesses a larger specific surface area and thus exposes more active sites,which is beneficial to improve the hydrogen evolution performance of molybdenum carbide.The formation of Mo-N bonds in nitrogen-doped molybdenum carbide can significantly change the electronic structure of adjacent Mo and C atoms to improve the desorption ability of H from the Mo-H bond and promote the HER reaction process.2. The catalyst precursors are first synthesized by using hydrothermal method with g-C₃N₄as a self-sacrificing template,glucose as the carbon source and ammonium thiomolybdate as the molybdenum source,which is further calcined at high temperature to prepare two-dimensional nanostructured sulfur-doped molybdenum phosphide decorated carbon nanosheets.The effect of sulfur doping on the hydrogen evolution performance of Mo P is studied.The results show that sulfur-doped molybdenum phosphide exhibits more excellent hydrogen evolution performance.In a 1.0 M KOH solution,the resulting electrocatalyst presents an overpotential of 97 m V at a current density of 10 m A cm^-2 and a Tafel slope of 63m V dec^-1.After a 60-hour cycle,the hydrogen evolution overpotential only decay slightly.The doping of S could reduce the energy barrier of the electrochemical reaction,which is beneficial to the adsorption of hydrogen atoms on the surface of the catalyst,and could further strengthen the interaction between the catalyst and the electrolyte,and thereby increases the HER activity.