Influence of nickel doping on MnO2 nanoflowers as electrocatalyst for oxygen reduction reaction

Doping is promising strategy for the alteration of nanomaterials to enhance their optical, electrical, and catalytic activities. The development of electrocatalysts for oxygen reduction reactions (ORR) with excellent activity, low cost and durability is essential for the large-scale utilization of energy storage devices such as batteries. In this study, MnO2 and Ni-doped MnO2 nanowires were prepared through a simple co-perception technique. The influence of nickel concentration on electrochemical performance was studied using linear sweep voltammetry and cyclic voltammetry. The morphological, thermal, structural, and optical properties of MnO2 and Ni-doped MnO2 nanowires were examined by SEM, ICP-OES, FT-IR, XRD, UV-Vis, BET and TGA/DTA. Morphological analyses showed that pure MnO2 and Ni-doped MnO2 had flower-like and nanowire structures, respectively. The XRD study confirmed the phase transformation from epsilon to alpha and beta phases of MnO2 due to the dopant. It was also noted from the XRD studies that the crystallite sizes of pure MnO2 and Ni-doped MnO2 were in the range of 2.25-6.6 nm. The band gaps of MnO2 and 0.125 M Ni-doped MnO2 nanoparticles were estimated to be 2.78 and 1.74 eV, correspondingly, which can be seen from UV-Vis. FTIR spectroscopy was used to determine the presence of functional groups and M-O bonds (M = Mn, Ni). The TGA/TDA examination showed that Ni-doping in MnO2 led to an improvement in its thermal properties. The cyclic voltammetry results exhibited that Ni-doped MnO2 nanowires have remarkable catalytic performance for ORR in 0.1 M KOH alkaline conditions. This work contributes to the facile preparation of highly active and durable catalysts with improved catalytic performance mainly due to the predominance of nickel.