Synthesis Of Cobalt-based And Nickel-based Compounds As Electrocatalyts For Water Spiltting

It is of great practical significance to develop economical and efficient bifunctional water-splitting catalysts which can replace precious metalstoward oxygen and hydrogen evolution reactions(OER and HER).In recent years,the preparation of heterogeneous nanostructures between metal compounds has become an economical and efficient way to synthesis an electrocatalyst with high performance.The introduction of heterogeneous interface between compounds can reduce the gibbs adsorption free energy of catalyst to hydrogen or oxygen,and provide a large number of active sites for catalytic reaction,so as to improve catalytic activity.Therefore,the synthesis of efficient,stable and low-cost electrolytic water catalyst with rich heterogeneous interface has a high application value.For this reason,we carried out the following two parts of work:(1)We present interface engineering of Co₉S₈ nanoflakes decorated Co₃O₄nanoarrays with enriched heterointerfaces on Ni foam(Co₉S₈@Co₃O₄/NF)via a novel step-wise approach,and used it as a water splitting catalyst for the first time.This kind of core-shell structure shows excellent bifunctional catalytic performance.For HER,the current density of 10 m A cm^-2 can be achieved only by a overpotential of 130 m V.For OER process,under the current density of 100 m A cm^-2,the overpotential only needs 331 m V.In addition,when Co₉S₈@Co₃O₄/NF is used as cathode and anode at the same time at the current density of 10 m A cm^-2,it deliver a very small voltage of1.52 V for water splitting,which even surpass the precious metals of Pt/C-Ru O₂and previously reported earth-abundant nanocatalysts.Meanwhile,the stability of Co₉S₈@Co₃O₄/NF catalyst is extremely high,and it can steadily work for more than 50hours continuously.The results of further study and density functional theory(DFT)calculation show that the excellent catalytic performance of Co₉S₈@Co₃O₄/NF is attributed to:(i)highly conductive Ni facilitates the efficient charge transfer;(ii)porous core-shell nanoarchitecture benefits the infiltration and transportation of gases/ions,and increases the contact area between the catalyst and the reaction solution;(iii)heterointerface synergistically lowers chemisorption energy of hydrogen/oxygen intermediates,and provides a large number of active sites for the reaction.This work can be used as a reference for the development of high-performance bifunctional materials in the future.(2)Using the same experimental method,a Ni@NiO/NF catalyst rich in interface was synthesized.OER overpotential at the current density of 100 m A cm^-2 is 319 m V,and HER overpotential at 10 m A cm^-2 is 150 m V.Moreover,at the current density of10 m A cm^-2,the overall water splitting voltage can be as low as 1.54 V.This work will provide reference for controllable synthesis and interface engineering of heterogeneous structure nanomaterials in clean energy technology.