Study On Oxygen Evolution Reaction Performance Of Single Atom Supported NiFe Layered Double Hydroxide

With the rapid development of the world economy,the energy issue has become one of the important problems that bother people.Among them,fossil energy sources such as coal,oil and natural gas are widely used in industrial development,but due to the serious pollution caused to the environment after their use,people have to look for a sustainable,environmentally friendly,green and pollution-free clean energy source.With the advantages of high energy density and zero CO2 emission,hydrogen energy has become one of the clean energy sources of great interest.Since its discovery in the 18th century,hydrogen production from electrolytic water has become an important sustainable hydrogen production technology after more than two hundred years of technological development.The process of hydrogen production from electrolytic water consists of two halfreactions,the cathodic hydrogen evolution reaction(HER)and the anodic oxygen evolution reaction(OER).In contrast to HER,OER has a slow four-electron reaction kinetics,which is equivalent to the decisive step in the electrolytic water hydrogen production process.Currently,noble metal-based(RuO2/IrO2)is an effective OER catalyst,but its high cost hinders the development.Therefore,it is especially important to find an efficient and low-cost electrocatalyst to replace noble metals.NiFe layered double hydroxide(NiFe LDH)is considered as the most representative non-precious metal catalyst due to its unique layered structure and considerable catalytic performance.Therefore,in this paper,NiFe LDH is used as a base to prepare different metal single atoms for loading,which can reduce the cost of precious metals and optimize the electronic structure of NiFe LDH to enhance its intrinsic activity.The main studies are as follows:1.Single atom Ru loaded NiFe layered double hydroxide as a highly active electrocatalyst for oxygen evolution reaction.NiFe LDH was first produced as a carrier by a simple hydrothermal synthesis method,and then SARu/NiFe LDH was produced by a simple solvothermal method using NaBH4 as the reducing agent,NaOH as the solvent,and RuCl3 as the ruthenium source,and reacted at 120℃ for 2 h.Using sphere-difference corrected transmission electron microscopy(AC-STEM)and X-ray diffraction absorption fine structure spectroscopy(XAFS).The presence of Ru species in the form,specific oxidation state and local coordination environment were investigated.The results are that Ru exists as a single atom with a specific oxidation state of+1.6 and two coordination environments(Ru-O and Ru-O-M(M=Ni,Fe)).The twodimensional powder exhibits good OER catalytic performance with an overpotential(η10)of 251 mV,which is 65 mV lower compared to NiFe LDH(316 mV).It is demonstrated that the single atom Ru loading enhances the intrinsic activity of NiFe LDH.To investigate the reaction mechanism of the material during OER,the SARu/NiFe LDH Faraday efficiency of 99.3%was calculated by rotating ring-disk electrode test.It is demonstrated that the material selectively oxidizes water to oxygen instead of generating by-products(peroxides).Finally,the single atom Ru has a greater contribution to the OER process as an active site by density flooding theory calculations and differential charge density characterization.The difference in charge density before and after loading induces electron rearrangement,that is,electron transfer from Ru to Ni or Fe via Ru-O-M(M=Ni,Fe),optimizing the electronic structure of NiFe LDH and enhancing the intrinsic activity.2.Preparation of single atom Mo loaded NiFe layered double hydroxide and study of the performance of oxygen evolution reaction.SAMo/NiFe LDH was also produced by reducing Mo in Na2MoO4 to single atoms loaded on NiFe LDH by a simple solvothermal method using NiFe LDH as a carrier.AC-STEM and XAFS were used to probe the Mo species presence form,specific oxidation state,and local coordination environment.At this time,the Mo species is present as a single atom with a specific oxidation state of+1.9 and only one coordination environment,Mo-O.When Mo is present in the Mo-O coordination environment,an unsaturated coordination environment is added,which is believed to enhance the NiFe LDH intrinsic activity at the theoretical level.The SAMo/NiFe LDH possesses more excellent catalytic performance by electrochemical performance tests.The overpotential was as low as 228 mV at a current density of 10 mA cm-2.The OER reaction mechanism was investigated by rotating the ring-disk electrode,and it was calculated that SAMo/NiFe LDH has a high Faraday efficiency of 99.5%,which proves that the material undergoes a complete four-electron transfer and selectively oxidizes water to oxygen during the OER process.To further enhance the OER performance,SAMo/NiFe LDH was grown in situ on NF(SAMo/NiFe LDH@NF).The overpotential(η10)was only 158 mV,while the material was subjected to stability tests for up to 85 h with only 1.1%performance degradation.X-ray photoelectron spectroscopy(XPS)characterization of the material at the end of the stability test showed th at the SAMo/NiFe LDH was a stable catalyst.