Design,Synthesis Of Nickel-Based Core-Shell Structure Bi-Functional Electrocatalyst For Overall Water Splitting

The development of low-cost bi-functional electrocatalysts with high activity for both Hydrogen Evolution Reaction（HER）and Oxygen Evolution Reaction（OER）is one of the research hotspots in the field of water electrolysis.Ni₃S₂-Mo S₂/Ni Foam supported by nickel foam,with 3D structure and high conductivity,contains a large number of heterogeneous interfaces and has a good application prospect.In this paper,Ni₃S₂-Mo S₂/Ni Foam with core-shell structure was used as the research object,and its structure and performance were optimized by regulating p H value and doping graphene.The specific research contents are as follows:（1）Ni₃S₂-Mo S₂/Ni Foam was prepared in situ with thioacetamide as sulfur source and ammonium heptadecolybdate tetrahydrate as molybdenum source by a one-pot hydrothermal method.The effects of p H values（2.0,7.0,9.2,9.4 and 9.6）on the morphology,HER,OER and catalytic properties of the composite were investigated.When p H value is 9.4,the composite morphologies are nanorods with a diameter of about200 nm and a length of about 1 um.Ni₃S₂ nanorods grow on the foam nickel skeleton,and Mo S₂ nanorods are uniformly covered on the nanorods.The high resolution transmission and XPS show that the electron rearrangement is caused by the lattice mismatch at the interface,resulting in the formation of a rich heterogeneous interface.At the same time,the composite has the best water electrolytic performance in 1 M KOH.In HER,the current density of 10 and 100 m A cm^-2 is generated,which requires only 102 and 172 m V of overpotential,respectively.The Tafel slope is 72 m V dec^-1.In OER,the current density of 100 and 200 m A cm^-2 is generated,which requires only 347 and 399 m V of overpotential,respectively,and the Tafel slope is 159 m V dec^-1.In OWS（Overall Water Splitting）,only 1.57 V applied voltage can produce a current density of 10 m A cm^-2,and under this current density,after 50 h long catalytic reaction,the current density retention rate reaches 91.7%.（2）Based on the Ni₃S₂-Mo S₂/Ni Foam mentioned above,reduced graphene oxide（r GO）was introduced to improve the catalytic performance.The effects of mesh number（5000,10000,15000,20000）and concentration(0.25,0.50,0.75,1.00 mg m L^-1)of r GO were studied.The results showed that the optimal catalytic performance（1 M KOH）was obtained when the r GO mesh number was 15000 and the concentration was 0.75 mg m L^-1.In the composite,Ni₃S₂ nanorods are grown on nickel foam,and r GO is assembled with Mo S₂ nanosheets to form a nanonetwork that uniformly covers the nanorods.After the introduction of r GO,the diameter of the composite material increases to about 400 nm.According to the electrochemical characterization,both R_s and R_ct of the composite are reduced,and the double electric layer capacitance(249 m F cm^-2)is increased,which indicates that the introduction of r GO can optimize the conductivity of the material,and stimulate the material activity,and increase the active specific surface area.In HER,the current density of 10 and 100 m A cm^-2 was generated,which requires only 83 and 159 m V of overpotential,respectively and the Tafel slope is 65 m V dec^-1.In OER,the current density of 100 and 200 m A cm^-2 is generated,and only 331 and 359 m V of overpotential is required,respectively.The Tafel slope is only 55 m V dec^-1.In OWS,only needed 1.52 V of applied voltage to produced a current density of 10 m A cm^-2,and under this current density,after 70 h long reaction,current density retention rate can reach 90.1%.