Regulating The Oxygen Electrocatalytic Activity Of Co/Mn-based Oxides By Double Exchange Interaction

Oxygen electrocatalytic reactions,including oxygen reduction reaction（ORR）and oxygen evolution reaction（OER）,are key parts in clean and renewable energy technologies such as fuel cells and metal-air batteries,which are of great significance for addressing energy and environmental issues.However,ORR/OER usually has a high over-potential,which limits the overall efficiency of the device.Therefore,it is important to develop efficient and cost-effective oxygen electrocatalysts.Transition metal oxides are considered to be ideal catalyst materials due to their low cost and flexibility in adjustment of composition and crystal structure.Exploring effective strategies to control the electronic structure of transition metal oxides and enhance the oxygen electrocatalytic activity has become a research hotspot.In this work,the electronic structures of Co/Mn-based oxides are regulated by double exchange interaction to improve their ORR/OER performance.The specific research contents are as follows.（1）Using a CoO nanorod as a design platform,we systematically evaluate the effect of V,Mn and Ni with varied d-electron numbers as substitutional dopants by electron paramagnetic resonance spectroscopy（EPR）and X-ray photoelectron spectroscopy（XPS）.Combined with electrochemical tests,it is proved that the double exchange interaction between the dopant and Coions can promote the generation of high-valence Co（IV）,thereby enhancing the neutral OER activity;and demonstrated that the d electron-poor dopant exhibits more significant double exchange interaction with the transition metal ions.（2）We synthesized Mn₂V₂O₇ nanosheets by a cation exchange method to construct a material system with local structure of Mn-O-V;double exchange effect is introduced through V to enhance its ORR activity.Electrochemical tests show that the half-wave potential of Mn₂V₂O₇ is 0.88 V relative to the reversible hydrogen electrode,which is equivalent to Pt/C catalyst;and exhibits a peak power density of 408 m A cm^-2 in zinc-air batteries.In-situ X-ray absorption near-edge spectroscopy（XANES）analysis of the electronic structure of Mn₂V₂O₇ demonstrated that the excellent ORR activity of Mn₂V₂O₇ could be attributed to the double exchange interaction between Mn and V,which optimizes the e_g electron filling of the active Mn sites（e_g=0.7）.