Co₂VO₄ Nanosheets For Highly Efficient Electrocatalytic Oxygen Reduction Reaction And Zinc-Air Batteries

In renewable energy technologies such as fuel cells and metal-air batteries,transition metal oxides are the most promising catalysts to replace precious metals.However,they are often limited by their catalytic and conductive capabilities.In this paper,spinel oxide Co₂VO₄ was prepared,combining highly active transition metal cobalt cations with highly conductive metallic vanadium atomic chains to achieve the common improvement of electrocatalytic activity and conductivity,and applied it to zinc-air batteries.The specific research results are as follows:(1)Co₂VO₄ nanosheets were successfully synthesized by gas-phase cation exchange method,using ZnO nanosheets as templates.Co₂VO₄ is an inverse spinel with half Co²⁺cations occupying octahedral and the other half Co²⁺cations taking tetrahedral sites.The experimental and simulated electron energy-loss spectroscopy(EELS)analyses reveal that Co²⁺cations at the octahedral sites take the low spin(LS)state,and the e_g orbital is filled with only one electron(t_2g⁶e_g¹).Theoretical calculations reveal that this LS state originates from the contracted Co-O octahedra in Co₂VO₄,which enhances the crystal field.The conductivity test results show that,compared with CoO and Co₃O₄,the conductivity of Co₂VO₄ is improved by 3 and 6 orders of magnitude,respectively.(2)Because of its good conductivity and optimized electronic structure,Co₂VO₄exhibits excellent oxygen reduction reaction(ORR)performance,with a half-wave potential(E_1/2)of 0.83 V_RHE,which is 80m V and 60 m V higher than CoO and Co₃O₄,respectively.Its Tafel slope is 59 m V dec^-1,which is less than 83 m V dec^-1 of CoO and85 m V dec^-1 of Co₃O₄.Co₂VO₄ was assembled into a zinc-air battery,and the peak discharge power density of 380 m W cm^-2 was obtained.This performance is superior to Pt/C-based device(244 m W cm^-2).