Preparation Of Mn₂V₂O₇ Nanosheets For Oxygen Reduction Reaction And Zinc-air Batteries

The development of high-efficiency oxygen reduction（ORR）catalysts is critical to the further development of metal zinc-air batteries.Zinc-air batteries are widely concerned by researchers for their high energy density and high safety,but lower power density always limits its development.In this paper,a Mn/V mixed bimetal oxide was successfully synthesized by gas phase cation exchange method.The excellent ORR activity was obtained and applied to the zinc-air battery.The specific research results and innovation are as follows:（i）In addition to the intrinsic activity of the catalyst,various factors affecting the activation polarization,ohmic polarization and concentration polarization of the zinc-air battery are discussed,including electrode spacing,electrolyte concentration,oxygen flux,carbon material,addition amount of polytetrafluoroethylene（PTFE）.（ii）Gas phase cation exchange method synthesizes Mn₂V₂O₇ nanosheets in one step.The synthesized Mn₂V₂O₇ nanosheets are a porous two-dimensional structure with a thickness of about 60-90 nm.{20 （?）}crystal plane is the largest exposed surface of the nanoparticle.There are three valence states of Mn,+2,+3,and+4 in the system,and V has two valence states of+4 and+5.The material has excellent ORR performance,a half-wave potential of 870 m V（vs RHE）,a current density of 4.5 m A cm^-2,and no change in the phase after 1000 cycles of CV.And the intrinsic conductivity of the material is as high as 7.72 S cm^-1,which is several orders of magnitude higher than that of Mn oxide.（iii）Applying this highly efficient ORR catalyst to a zinc-air battery,the power density of the battery can reach 380 m W cm^-2 when discharged,which is the highest value of the existing reported zinc-air battery.The cycle efficiency of the battery for long-term cycle charge and discharge(charge current density is 2 m A cm^-2,discharge current density is 20 m A cm^-2)is only 6%attenuated,which is better than Pt/C catalyst,and the open circuit voltage of the battery is 1.45 V,it is equivalent to Pt/C.