Preparation And Water Electrolysis Performance Of Transition Metal Nitride(M_xN,M=Ni,Mo,Co)-Based Catalysts

In recent years,due to the continuous consumption of fossil fuels and the intensification of Greenhouse Effect,we are facing an unprecedented energy and environmental crisis.Therefore,clean energy sources that can replace fossil fuels must be found as soon as possible.As one of the most ideal clean energy sources at present,hydrogen energy not only has the characteristics of high energy density and environment-friendly,but also can be produced continuously by simple electrolysis of water.However,at present,low activity,poor stability and the high cost of catalysts for hydrogen production from electrolytic water seriously hinder the large-scale development of hydrogen production from electrolytic water.In this regard,the development of efficient,stable and low-cost electrolytic water catalyst is the key to solve the problem.Transition metal nitride（M_xN）has attracted more and more attention of researchers because of its unique physical,chemical and electronic properties.It is one of the most promising new non-precious metal catalysts for hydrogen production from water electrolysis.Based on M_xN,this paper adopts the strategies of carrier recombination,precise regulation,heterogeneous interface construction and defect engineering to design,regulate and prepare related M_xN-based catalysts.The catalytic activity and reaction mechanism of Ni,Mo,Co-based transition metal nitride catalysts for hydrogen evolution and oxygen evolution reaction and its application as bifunctional catalyst in overall water splitting were studied.The specific research contents are as follows:（1）Ni₃N nanoparticles were successfully loaded onto nitrogen-doped carbon microspheres（N-CMSs）（Ni₃N@N-CMSs）by two-step hydrothermal and two-step annealing methods.The electrochemical test of Ni₃N@N-CMSs electrode under alkaline condition shows that it shows certain hydrogen and oxygen evolution activity and good long-term stability:when the hydrogen evolution overpotential is 126/261 m V,it can reach the current density of 10/100 m A cm^-2,and when the oxygen evolution overpotential is 329/467 m V,it can reach the current density of 10/100 m A cm^-2.And the 12-hour chronopotentiometric test and 2000 cyclic voltammetry（CV）cycle stability tests show good stability.The voltage of Ni₃N@N-CMSs catalyst,which acts as both cathode and anode,is 1.661/1.972 V when the current density is 10/100 m A cm^-2,and shows good stability.Compared with the Ni₃N unloaded on N-CMSs,its catalytic performance is further improved.This is because the loading of Ni₃N nanoparticles into N-CMSs increases the contact area between the catalyst and the electrolyte and provides more reaction active sites.The combination of the two is also more conducive to the charge transfer of the catalyst.This study shows that using N-CMSs as a supporting material and loading Ni₃N nanoparticles on its surface can enhance the catalytic performance of hydrogen and oxygen evolution.（2）MoN/MoO₂ heterojunction nanosheet array was synthesized in situ on nickel foam（NF）by precise control strategy.The electrochemical test of MoN/MoO₂electrode under alkaline condition shows that it shows excellent hydrogen and oxygen evolution activity and good long-term stability:the current density of 10/100 m A cm^-2can be reached when the hydrogen evolution overpotential is 30/118 m V and the current density of 10/100 m A cm^-2 can be reached when the oxygen evolution overpotential is292/370 m V.And the 20-hour chronopotentiometric test and 3000 CV cycle stability tests show good stability.Compared with pure Mo O₂,its catalytic performance is further improved.This is because the coupling between Mo N and Mo O₂ not only ensures the rapid transport of electrons,but also exposes more catalytic active sites.When the current density is 10/100 m A cm^-2,the voltage of MoN/MoO₂ catalyst,which is both cathode and anode,is only 1.565/1.843 V,and shows good stability.This study shows that the MoN/MoO₂ nanosheet array material prepared by using NF as the reaction substrate,with the help of template and precise temperature control is expected to be a catalyst for hydrogen production from overall water splitting.（3）The precursor of CoMoO₄ nanosheet array was grown in situ on NF and reduced by nitridation under one-step annealing to obtain Co_5.47N/Mo N composite porous nanosheet array.The electrochemical test of Co_5.47N/Mo N electrode under alkaline condition shows that it shows excellent hydrogen and oxygen evolution activity and good long-term stability:the current density of 10/100 m A cm^-2 can be reached when the hydrogen evolution overpotential is 81/198 m V and the current density of10/200 m A cm^-2 can be reached when the oxygen evolution overpotential is 290/413m V.And the 10-hour chronopotentiometric test and 2000 CV cycle stability tests showed good stability.Compared with pure Co_5.47N and Mo N,its catalytic performance is further improved.On the one hand,the combination of Co_5.47N and Mo N promotes electron exchange and reduces the reaction energy barrier;on the other hand,the porous structure of Co_5.47N/Mo N provides a favorable channel for gas emission in time.When the current density is 10/50/100 m A cm^-2,the voltage of Co_5.47N/Mo N catalyst,which is both cathode and anode,is only 1.596/1.698/1.788 V,and shows good stability.This study shows that the Co_5.47N/Mo N porous nanosheet array material prepared by using foamed nickel as reaction substrate and annealing nitridation reduction“pore”is expected to produce hydrogen through overall water splitting at high current density.