The Catalytic Mechanism Of Co(Ni)/Carbon Nitride Composites For Hydrogen Production From Hydrolysis

The efficient development,utilization and storage of clean energy are an effective way to solve the energy problem.Hydrogen is the energy material with the highest energy per unit mass.The efficient preparation of hydrogen energy has attracted widespread attention in recent years.The use of solar energy and electrical energy to decompose water to produce hydrogen is currently two important methods for producing hydrogen energy.As an emerging non-metallic photo/electrocatalyst,carbonitrides have attracted extensive attention from researchers in the field of photocatalysis or electrocatalysis due to their green,abundant sources and excellent performance.Among them,g-C₃N₄ and N doping carbon?N-C?are very popular.However,the shortcomings of g-C₃N₄ such as low specific surface area,easy recombination of photogenerated carriers,and poor conductivity severely hinder it's photocatalytic performance for hydrogen production from water.Although N-C has good conductivity and abundant active sites,it has a weak Gibbs free energy for hydrogen adsorption,resulting in poor adsorption of hydrogen,and its electrocatalytic hydrogen evolution performance still needs to be improved.To this end,transition metal elements?Co,Ni?are introduced to modify carbonitrides to improve their catalytic activity.The morphology,structure,and hydrogen evolution properties of materials are characterized.The relevant research results are as follows:?1?Organic-inorganic hybrid precursors were synthesized by a hydrothermal method and the in-situ cobalt-doped tubular g-C₃N₄?Co-CN?was generated during heat treatment.The study found that the photocatalytic hydrogen production performance of the sample with the best doping ratio has been improved compared to pure g-C₃N₄.The incorporation of Co²⁺can effectively improve the photogenerated electron-hole separation efficiency.The band gap of Co-CN became narrower and the conduction band potential shifted forward,resulting reducing reduction ability.Therefore,although the specific surface area of the prepared Co-CN sample was significantly improved,the catalytic activity of the sample was not significantly improved.?2?Co and Ni double transition metal elements were introduced to obtain Co and Ni double doped g-C₃N₄ through heat treatment.The doping of bimetal elements effectively inhibited the recombination of photogenerated carriers.The conduction band potential of 2 wt.%CoNi-CN shifted negatively,the reducing ability was enhanced,and the photocatalytic activity of the sample was also enhanced.?3?Organic-inorganic hybrid precursors were synthesized by hydrothermal method with increased addition ratio of cobalt salts,and then the metal cobalt nano-particles supported by nitrogen-doped carbon nano flakes were obtained by low temperature carbonization during the heat treatment process.There are carbon nanotubes appearing in some samples.They all exhibited good electrocatalytic hydrogen evolution?HER?activity in acidic media.After electrochemical etching,cobalt nanoparticles in the sample of 4.55%Co-N/C became smaller and more uniform in size,and HER performance was further improved.At a current density of 10 m A cm^-2,the required overpotential is only 168 mV and the Tafel slope is 108 mV dec^-1,and the stability is relatively good.