Transition Metal Oxides As Bifunctional Oxygen Electrocatalysts For Metal-Air Batteries

The worldwide continued demand for energy sources and rising concerns of environmental issues greatly promote the progress of renewable energy storage and conversion devices.As one kind of new type of batteries,metal-air batteries have recently gained tremendous attention thanks to their high energy density,low price and environment-friendly.However,the slow kinetics of electrochemical oxygen reactions hinder their commercialization.Therefore,study and de velopment of bifunctional catalysts with oxygen reduction reaction?ORR?and oxygen evolution reaction?OER?catalytic activity become a key factor.Based on the above problems,the paper mainly prepared three kinds of transition metal oxide composite materials,and study their bifunctional electrocatalytic activity for metal-air battery,the main contents are as follows:First of all,Ag-CoFe₂O₄/C nanocomposites were synthesized by one-pot solvothermal method using carbon black as the substrate.The prepared Ag-CoFe₂O₄/C nanocomposites showed excellent ORR and OER catalytic activity in alkaline solution which is because of the addition of CoFe₂O₄ hinders the agglomeration of Ag nanoparticles and exposes more active sites on the composites surface.Meanwhile,the electron effect between Ag and CoFe₂O₄ also promoted the electrocatalytic activity of Ag-CoFe₂O₄/C nanocomposites.In addition,Ag-CoFe₂O₄/C catalyst also showed pretty good methanol tolerance and stability.Then,MnO₂-CoFe₂O₄/C nanocomposites were prepared by solvothermal method.The results of electrochemical tests reveal that MnO₂-CoFe₂O₄/C catalyst exhibits better ORR and OER catalytic activity than MnO₂/C,CoFe₂O₄/C and MnO₂/C + CoFe₂O₄/C?mechanical mixture?.In addition,comparing the catalytic activity of MnO₂-CoFe₂O₄/C with different mass ratios,it can be concluded that when the mass ratio of MnO₂ to CoFe₂O₄ is 1:1,the ?E value is the smallest,that is to say,the MnO₂-CoFe₂O₄/C?1:1?possess the best oxygen electrocatalytic activity.Finally,CoMn₂O₄/MnOOH nanocomposites were synthesized by two-step hydrothermal method with MnOOH nanorods are not only as substrate of the composite but the manganese source of CoMn₂O₄.The excellent ORR catalytic performance of CoMn₂O₄/MnOOH composites can be attributed to a high electrochemical active area?ECSA?which improves the active sites of catalysts,and the synergistic effect between CoMn₂O₄ and Mn OOH.CoMn₂O₄/MnOOH also showed pretty good OER catalytic activity,methanol tolerance and stability.In addition,the smaller ?E value compared to other catalysts indicates that CoMn₂O₄/MnOOH is provided with the potential as bifunctional oxygen electrocatalyst for metal-air batteries.