Investigations On Manganese Dioxide Composite Catalysts Used For Oxygen Reduction

Aluminum-air battery is a new energy with great potential for development,oxygen reduction catalyst of air electrode in aluminum-air battery has research hot in recent years.In this paper,based on energy and state density,elements zirconium and molybdenum doped?-MnO₂ nanowires were determined by quantum chemistry calculation to prepare high performance oxygen reduction catalysts.The hydrothermal synthesis of Zr?Mo?-doped?-MnO₂ nanowires catalyst in solution with different Zr/Mn,Mo/Mn ionic ratios.Based on this,?-MnO₂/graphene and?-MnO₂/CNT composite catalysts were prepared by hydrothermal method.The structures and morphologies of the catalysts were characterized by XRD,SEM,TEM and XPS.The electrochemica l properties of the catalyst were characterized by LSV,CV and EIS electrochemical tests.Zr-doped?-MnO₂ nanowires were prepared by hydrothermal method in different Zr/Mn ionic ratios.The Zr-doped?-MnO₂ nanowires,acetylene black,PTFE and ethanol in a certain proportion were pressed to prepare air electrode.It is found that the Zr-doped?-MnO₂ nanowires catalyst prepared with Zr/Mn ionic ratio of 1/110 has the best electrocatalytic performance.I n 3mol/L KOH solution,anodic current density of the air electrode composed of this catalyst can reach 60.33mA·cm^-2 compared with that of?-MnO₂(49 mA·cm^-2)showed 23%higher for oxygen reduction reaction?O RR?at potential-0.2V.The result of EIS analysis showed that the oxygen reduction electrochemical process on the air electrode prepared with Zr-doped?-MnO₂ nanowires were carried out in one step,and the adsorption step of oxygen is the control step in oxygen reduction reaction on the air electrode.The DFT calculations showed that the doping of element zirconium increase the d orbital state density of the element manganese in?-MnO₂ and the center of d band is shifted,which favor the adsorption O₂ capacity of the Zr-doped?-MnO₂ nanowires.The morphology of the Mo-doped?-MnO₂ catalysts synthesized by hydrothermal method in solution with different Mo/Mn ionic ratio were changed from nanowires to particleswith the increase of Mo/Mn ionic ratio,gradually.The electrochemical performance of Mo-doped?-MnO₂ nanowires synthesized in a solution with ionic ratio of 1/49 was the best.In 0.1 mol/L KOH solution,the current density of this catalyst was 23.8%higher than pure?-MnO₂ nanowires at potential-0.2V.The EIS analysis showed that the electrochemical process of oxygen reduction on the Mo-doped?-MnO₂ nanowires catalysts were carried out in two steps,and the speed control step of the electrode process was the reaction of O₂^-reduce to OH^-.The?-MnO₂/graphene and?-MnO₂/CNT composite catalysts were successfully prepared by hydrothermal synthesis and the?-MnO₂ among them have a rod-like structure with a diameter more than 100nm,which was not conducive to oxygen reduction.