Preparation Of Transition Metal Hydroxide Materials With Oxygen Deficiency And Their Electrocatalytic Oxygen Evolution Performance

Water-splitting is one of the most important ways for the clean energy conversion and has received wide attention.It mainly includes hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）.Compared with the cathode reaction HER,it is found that the OER reaction occurring at the anode has a complicated multi-electron transfer process and the reaction kinetics are slow,which is the key bottleneck for further improving the water-splitting efficiency.At present,most of the commercial materials are precious metal-based materials,which are not only expensive but also have poor stability and cannot be widely used on a large scale.Transition metal hydroxides have been discovered and used in electrocatalytic oxygen evolution because of their advantages of abundant yield and low price.Especially in alkaline electrolytes,transition metal hydroxides have potential application value.As the research goes further,the important role of oxygen defects in OER electrocatalysis is highlighted.The presence of oxygen vacancies can effectively adjust or change the distribution of electrons on the surface of the material,thereby adjusting the intrinsic activity of the material.Therefore,this paper summarizes and discusses the oxygen vacancies in transition metal hydroxides and their positive effects on the surface electron distribution of transition metal materials,including the following two work:1.Ultralong needle-like nitrogen-doped Co（OH）F material was prepared by one-step hydrothermal synthesis and loaded on the conductive carbon fiber paper.In the experiment,sodium fluoride and urea were used as materials to provide anion F and hetero atom N.Scanning electron microscopy（SEM）and transmission electron microscopy（TEM）were used to highlight the importance of ultra-long needle-like morphology for improving the catalytic properties of OER.At the same time,X-ray photoelectron spectroscopy（XPS）was used to characterize the oxygen holes on the surface of nitrogen-doped Co（OH）F supported on carbon fiber paper（N:Co（OH）F-CFP）.The test results further illustrate the excellent catalytic activity of ultralong needle-like N:Co（OH）F-CFP material for the oxygen evolution reaction.In1 M KOH solution,its OER catalytic activity is higher than that of the commercial IrO₂-CFP.2.Manganese-doped F-containing Ni（OH）₂ with multi-level nanostructures was synthetised by a one-step hydrothermal method on the nickel foam substrate（Mn-F/Ni（OH）₂-NF）.X-ray powder diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,X-ray photoelectron spectroscopy（XPS）and other characterization methods further illustrate the difference in internal and external structure of the Mn-F/Ni（OH）₂-NF and F-containing Ni（OH）₂（F/Ni（OH）₂-NF）.The atomic radius of manganese is bigger than that of nickel,so Mn will occupy the position of part of nickel in the molecule during the doping process,causing a change in the crystallinity and the amount of oxygen vacancies of the Mn-F/Ni（OH）₂-NF material.At the same time,such doping can improve the stability of Mn-F/Ni（OH）₂-NF composites.The multilevel nanostructure of Mn-F/Ni（OH）₂-NF can facilitate the transport of electrons and improve its own OER catalytic activity.In the solution of 1 M KOH,the overpotential and Tafel slopes were better than that of the same loading of IrO₂ on nickel foam.