Development of α‐MnO2 Nanowire with Ni‐ and (Ni, Co)‐Cation Doping as an Efficient Bifunctional Oxygen Evolution and Oxygen Reduction Reaction Catalyst. Issue 2 (18th January 2022) - Selvakumar, Karuppiah
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 α‐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 Ni 2+ cation doping in α‐MnO2 with various loading concentrations resulted in 8Ni−MnO2 exhibiting remarkable OER and ORR activity owing to their excessive concentration of Mn 3+ and Mn 4+ octahedral sites respectively. Further, Co 2+ cation doping in 8Ni−MnO2 leads to an enhanced synergistic effect that significantly improves the fraction of Mn 3+ 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 (ΔE=EOER @10 mA cm −2 – ORR@E1/2 ) of 8Co−8Ni−MnO2 demonstrated 0.97 V, indicates an excellent activity in alkaline electrolyte solution. Abstract : Various loading concentrations of Ni 2+ ‐ and Co 2+ ‐doped α‐MnO2 nanowire for tuning the Mn oxidation state and control the nanowire morphology were developed. The simultaneous doping of both Co 2+ and Ni 2+ cations in α‐MnO2 leads to an enhanced synergistic effect without affecting crystallography and morphology. The 8Co−8Ni−MnO2 catalyst demonstrates superior bifunctional OER/ORR activity owing to their high density of Mn 3+ and Mn 4+ sites.