Preparation And Performance Of Electrocatalysts For Water Splitting Based On Nickel Nitride Heterojunction Nanoarrays

With the deepening of industrialization,human production and lifestyles are requiring energy that are efficient,clean and safe.As a high energy efficiency energy carrier,hydrogen can effectively solve the problems of pollution emission and energy security.In recent years,hydrogen production from water splitting has attracted a lot of attention from researchers due to its simplicity and low cost.In the electrolysis of water for hydrogen production,a half-reaction occurs on the cathode and anode surfaces,respectively,with hydrogen evolved on the cathode surface（Hydrogen Evolution Reaction,HER）and oxygen evolved on the anode surface（Oxygen Evolution Reaction,OER）.Under standard conditions,only a thermodynamic potential of 1.23 V is required to drive electrochemical water splitting,but due to the slow kinetics,voltages greater than 1.23 V are usually required.The high cost and scarce reserves of noble metal-based electrocatalysts and the poor activity of non-precious metal electrocatalysts are limiting the development of electrocatalytic water splitting.Therefore,it is of great practical importance to develop cheap and efficient electrocatalysts.In this paper,Ni@Ni₃N andα-Co（OH）₂@Ni₃N electrocatalysts with highly efficient electrocatalytic performance are prepared by electrodeposition using Ni₃N nanosheet arrays as supports,respectively.In Chapter 3,homogeneous Ni₃N nanosheets are successfully grown on carbon cloth by hydrothermal reaction with subsequent thermal nitridation,and then Ni@Ni₃N heterostructure catalyst are prepared by electrodeposition.The HER performance of this catalyst is tested in 1 M KOH solution,driving a current density of 10 m A cm^-2 at only 91 m V with a Tafel slope of 115 m V dec^-1.The catalyst is then tested for stability at current densities of 10,20 and 50 m A cm^-2 for a total of 30 h.It is found that the performance does not show significant attenuation and is consistent before and after.This indicates that a high-performance HER catalyst is synthesized in situ by hydrothermal-thermal nitridation-electrodeposition.In Chapter 4 of this paper,α-Co（OH）₂@Ni₃N heterostructure catalysts are successfully prepared by electrodeposition using previously synthesized Ni₃N nanosheets as support.The OER performance of this catalyst is tested in 1 M KOH solution,it is found that theα-Co（OH）₂@Ni₃N catalyst drives a current density of 50m A cm^-2 with an overpotential of only 311 m V and a Tafel slope of only 64 m V dec^-1,indicating that the material has good reaction kinetics and continues to exhibit excellent electro catalytic activity after stability tests at different current densities for up to 30hours.This indicates that a highly efficient and stable OER catalyst is synthesized in situ by hydrothermal-thermal nitridation-electrodeposition.In summary,the successful synthesis of Ni@Ni₃N andα-Co（OH）₂@Ni₃N electrocatalysts illustrates that by constructing a reasonable heterojunction,the reaction activity can be effectively enhanced,leading to the design of highly efficient and stable electrocatalysts.