Oxygen Evolution Reaction Catalysts Based On First Transition Metals:Simple Preparation And OER Performance

The oxygen evolution reaction（OER）,as a half-reaction of the water splitting reaction,involves a proton coupled four-electron transfer process and the formation O-O bonds with a higher energy barrier.Compared with the two-electron transfer process of the hydrogen evolution reaction（HER）at the cathode,OER needs more energy consumption and is generally considered to be a bottleneck for water splitting.Looking for an efficient,stable,and inexpensive OER catalyst to reduce OER overpotential is conducive to improving the efficiency of water splitting for wide applications.This study aims to further improve the performance of iron-cobalt-based oxygen evolution catalyst,simplify the catalyst preparation steps,reduce energy consumption.With the aim of developing simple preparation methods for high-performance catalytic oxygen evolution electrodes,we designed and prepared porous carbon material-supported iron-cobalt-based catalyst,cobalt ion-loaded ferrous sulfide/iron foam catalytic electrode,copper@nitride carbon/copper foam electrode.Various methods were used to systematically characterize the obtained catalysts or catalytic electrodes.On this basis,in-depth investigation of the electrocatalytic properties of the obtained materials was performed.The study laid a foundation for the development of catalyst materials used in OER.1.A one-step method was used to prepare a mixed slurry consisting of Nafion,commercial carbon black,and Fe³⁺/Co²⁺ions.In alkaline electrolytes,the slurry adsorbed on the surface of carbon black was in situ transferred into hydroxides,and further evolved into electrocatalytic active species under certain potential conditions,which effectively catalyzes the oxygen evolution reaction.The electrochemically active material formed in situ in the electrocatalytic process can achieve a catalytic current density of 10 m A cm^-2at a lower overpotential（330 m V）in 1 M KOH.The Tafel slope is only 55 m V dec^-1.The method only needs simple adsorption and electrochemical activation process and does not require special equipment.It is easy for scale-up and presents a great application prospect.2.Iron-based sulfides were firstly prepared on commercial iron foam through a solvothermal route.Introducing Co species on the sulfide by a simple impregnation route will get an effective catalytic oxygen evolution electrode.In 1 M KOH solution,the overpotential of the catalytic oxygen evolution electrode at a current density of 10 m A cm^-2is 262 m V,which is 52 m V less than that of iron-based sulfides without Co species.At a current density of 50 m A cm^-2,the optimized catalytic electrode only needs an overpotential of 340 m V.At the same time,thanks to the good conductivity of the iron foam,the Tafel slope of the optimized catalytic electrode is lower to 32 m V dec^-1.In addition,the thus obtained sulfide catalytic oxygen evolution electrode also has excellent sustainable catalytic performance.3.A one-step high-temperature calcination method was used for the preparation of copper@nitride carbon/copper foam electrode with copper foam and melamine as raw materials.During the high-temperature calcination process,copper atoms escaping from the copper foam are captured by vacancy sites on nitrogen-containing carbon substrate,forming catalytic active sites.The obtained electrocatalytically active electrode prepared by this method can drive a current density of 50 m A cm^-2in 1 M KOH solution with an overpotential of 320 m V.The experimental results were further verified with copper foil as the substrate.The catalytic electrode also shows excellent catalytic stability.In addition,the catalysts after OER were collected and the possible changes of the catalyst during the catalysis process were analyzed.