Research On Electrochemical Hydrogen Production Based On Transition Metal Phosphates/Carbides

Hydrogen,as a clean fuel with high calorific value and affluent source,has caused extensive research by scientists.Electrocatalytic water splitting or urea electrolysis to hydrogen production is a simple,environmental-friendly and sustainable technology.Unfortunately,the high overpotential of electrocatalytic water splitting or urea electrolysis to hydrogen production during the reaction results in a large amount of energy loss.Although commercial precious metal catalysts have highly efficient catalytic activity,their large-scale applications are limited due to its high-cost,poor stability and shortage of raw materials.Transition metal materials have the advantages of low price and wide sources,which makes them large number of applications in energy,catalysis and other aspects.Therefore,people need to find an efficient transition metal catalyst to improve the efficiency of electrocatalytic water splitting or urea electrolysis to hydrogen production.Herein,the transition metal molybdenum vanadium cobalt material with high catalytic activity was synthesized.The specific work is as follows:（1）With ammonium molybdate tetrahydrate as the molybdenum source and polypyrrole and dicyandiamide as carbon and nitrogen sources,a nitrogen-doped carbon material loaded with molybdenum carbide（Mo₂C/NC）was prepared by high temperature pyrolysis.Mo₂C/NC both show excellent catalytic activity for hydrogen evolution reaction（HER）under alkaline and acidic conditions.We explored the effect of calcination temperature on the catalytic performance of the materials,and the optimized catalyst Mo₂C/NC-850 was obtained at 850℃.Under acidic conditions,Mo₂C/NC-850 only needs 107 m V HER overpotential to reach a current density of 10m A/cm²,while under alkaline conditions,the corresponding HER overpotential is 135m V at a current density of 10 m A/cm².（2）We synthesized a V/Co metal-organic framework compound（V/Co-MOF）through a simple solvothermal reaction.with V/Co metal–organic framework（V/Co-MOF）as a template and precursor,a series of V₈C₇ decorated Co P microspheres composed of nanosheets（V₈C₇/Co P）is first synthesized via pyrolysis and a subsequent low-temperature phosphidation.Due to the synergy between V₈C₇ and Co P,V₈C₇/Co P not only shows good catalytic performance for hydrogen evolution reaction under alkaline and acidic conditions,but also shows excellent catalytic activity for oxygen evolution reaction and urea oxidation reaction under alkaline conditions.In addition,with the optimized trifunctional catalyst V₈C₇/Co P-0.18 as the cathode and anode,we built an acid-base asymmetric-electrolyte electrolyzer and an acid-base asymmetric-electrolyte urea electrolyzer to produce hydrogen.The study found that the acid-base asymmetric-electrolyte urea electrolyzer only need an applied voltage of 0.8 V to achieve a current density of 10 m A/cm²,which saves 200 m V of electrical energy compared to the acid-base asymmetric-electrolyte electrolyzer.These results are attributed to the assistance of electrochemical neutralization energy and electrocatalytic urea oxidation energy.This work provides a shortcut for the energy-saving electrolytic hydrogen production.