Study On Non-precious Metal Materials For Electrocatalytic Water Oxidation

Energy is an essential material for human survival and development.With the continuousexcessive consumption of fossil fuels,environmental pollution,global warming and other issues are becoming increasingly acute,people urgently need to develop clean and sustainable energy to alleviate the environmental and energy problems.Hydrogen energy is an ideal clean and renewable energy.In all kinds of hydrogen production methods,electrolysis of water is a more effective solution for producing large quantities of high-purity hydrogen,which includes the oxygen evolution reaction on the anode（OER）and hydrogen evolution reaction（HER）on the cathode.The OER is the bottleneck of the whole reaction because it involves the transfer of multiple protons and electrons.Currently,commonly used catalysts for OER are based on Ru and Ir materials.However,such materials are expensive and rare,limiting the large-scale production of hydrogen.Hence,it is an exigent need to develop high-performance OER electrocatalysts based on non-precious materials to promote the development in the field of electrolysis of water.Herein,two efficient and stable oxygen evolution catalysts based on inexpensive transition metals are developed.Firstly,bimetallic MOFs（Co Mn-MOF-74）based on Co and Mn were grown in situ on the surface of nickel foam（NF）by one-step solvothermal method.Compared with the Co Mn-MOF-74 Powder/NF electrode constructed with the assist of the extra binders,the as-prepared Co Mn-MOF-74/NF electrode is not only beneficial to the exposure of active sites,but also reduces the charge transfer impedance during the catalytic process.In alkaline solution（1 M KOH）,the Co Mn-MOF-74/NF exhibited superior catalytic activity toward OER with 10 m A·cm^-2 at a low overptential of 260 m V.At the same time,the Tafel slope of the Co Mn-MOF-74/NF is only 58.2m V·dec^-1,indicative of the favorable OER kinetics.After 20 h electrolysis,the required voltage has no obvious change,indicating that the catalyst has good stability.Secondly,to overcome the problems of MOFs being difficult to grow on conductive substrate and easy to aggregate,self-supported Co-MOF nanoplates grown on Ni foam（NF）were synthesized with cobalt carbonate hydroxide（Co CH）as a sacrificial template.In this approach,the resultant Co Ni-MOF/Co CH/NF electrodes have a higher catalytically active surface area and a smaller electrochemical impedance than that Co CH template-free electrodes（Co-MOF/NF）,which enable rapid electron transfer and mass transport during OER,thus showing more superior performance towards OER.Electrocatalytic water oxidation in alkaline solution showed that Co Ni-MOF/Co CH/NF delivered a current density of 50 m A cm^-2 with only 270 m V overpotential.After20 h electrolysis at 50 m A cm^-2,the required voltage remained basically unchanged,indicating that the catalyst has excellent stability.The developed approach may inspire further capability on constructing more promising catalysts for energy conversion and utilization.