Oxygen Evolution Behavior And Valence Evolution Of Transition Metal Oxides

Social development is inseparable from energy.Fossil energy being the main supply of natural energy not only has limited reserves,but also causes pollution.To provide a solution to this,a new and renewable clean energy is required,though its development is the main challenge the world is facing.Hydrogen is clean and renewable,hence attracting the attention of researchers.Electrolyzed water,which involves oxygen evolution reaction（OER）,is one of the most mature hydrogen energy preparation techniques used today.OER is a key semi-reaction that involves complex reaction steps and unclear mechanism.It is a"stuck neck"factor for efficiently electrolyzing water.Due to this reason,it is worth to develop a highly efficient electrocatalytic oxygen evolution catalyst and clarify its reaction mechanism.At present,the best performing catalysts are Ir O₂and Ru O₂,however,due to their limited reserves and high prices,it is difficult to achieve large-scale applications.As a result,alternative catalysts are required.Transition metals and their oxides,which are rich in their reserves and diverse in valence,gradually come into the eyes of researchers,not excluding the research work presented here.In this work,Ni（OH）₂and CoMoO₄nanosheets were grown on nickel foam substrates to study their electrocatalytic OER performance and valence state changes during the OER process.The following were the results obtained:（1）A simple one-step hydrothermal method was used to prepare the foamed Ni/Ni（OH）2 nanosheet array composite electrode（abbreviated as NF/Ni（OH）₂）.It was processed by continuous linear scanning to make the electrode electrically.Catalytic oxygen evolution energy absorption was improved:both the overpotential and the Tafel slope were reduced by 30 m V and 118.5 m V dec^-1respectively.The reason for the performance improvement is mainly attributed to the electrochemical treatment process.A surface reconstruction phenomenon occurred on the surface of the electrode,thereby forming a Ni OOH shell layer,which can promote the oxygen evolution reaction,hence improving the conductivity of the electrode to promote the charge transport and mass transfer process;（2）Hydrothermal and calcination methods were used to grow uniform and dense CoMoO₄nanosheets on a nickel foam substrate to form a foamed Ni/CoMoO₄nanosheet composite electrode（NF/CoMoO₄）.The electrocatalytic oxygen evolution performance test was carried out.When the current density reached 100 m A cm^-2,the overpotential was 409 m V and the Tafel slope was 67.2 m V dec^-1.Comparing the results with other cobalt-based oxygen evolution catalysts showed that The NF/CoMoO₄electrode is a promising oxygen evolution catalyst.