Abstract
Manganese oxides (MnO2) with nanowire morphology materials are promising candidates for improving oxygen evolution and oxygen reduction reaction (OER/ORR) performance. In this work, we developed transition metal cation doping strategy into the alpha-MnO2 tunnel structure to tune the Mn oxidation states and control the uniform nanowire morphology, crystalline structure to investigate the effect of doping over bifunctional activity. The single Ni2+ cation doping in alpha-MnO2 with various loading concentrations resulted in 8Ni-MnO2 exhibiting remarkable OER and ORR activity owing to their excessive concentration of Mn3+ and Mn4+ octahedral sites respectively. Further, Co2+ cation doping in 8Ni-MnO2 leads to an enhanced synergistic effect that significantly improves the fraction of Mn3+ quantity which is confirmed by average oxidation state. For electrochemical OER performance, 8Co-8Ni-MnO2 exhibits a potential of 1.77 V, Tafel slope value of 68 mV dec(-1) and lower charge transfer resistance and it is active in ORR with more positive onset potential of 0.90 V, half-wave potential of 0.80 V, better current density (4.7 mA cm(-2)) and a four-electron pathway. Moreover, bifunctional activity (Delta E=E-OER@10 mA cm(-2) - ORR@E-1/2) of 8Co-8Ni-MnO2 demonstrated 0.97 V, indicates an excellent activity in alkaline electrolyte solution.