Investigating the influence of varying cobalt doping on the cross-sectional widths and surface composition of MnO_x nanowires in the context of battery–supercapacitor systems

Nanomaterials based on manganese oxides (MnO_x) show considerable potential for large-scale electrochemical energy storage devices, driving significant research to explore their capabilities. One intriguing approach to enhance their performance involves the incorporation of other metals within their structure. Thus, we analyzed hierarchically obtained Cobalt (Co)-doped MnO_x nanowires with different Co content, examining their storage properties. Notably, the initial impact of Co was observed in the structural characteristics of MnO_x-based nanowires. As the Co content increased, there was a noticeable decrease in the cross-sectional widths of these nanowires. Also, we observed by XRD analysis that Co could effectively substitute manganese (Mn) within the crystal lattice. By XPS, the impact of Co doping on the Mn(IV)/Mn(III) ratio was of particular significance, as this ratio exhibited a direct correlation with the Co content (more Co, higher Mn(IV)/Mn(III) ratio), emphasizing the pivotal role of Co in modulating the oxidation states within these materials. Electrochemical studies revealed a remarkable dual behavior in the nanowires, combining pseudocapacitance and battery-like energy storage characteristics. Notably, our investigation uncovered a distinctive storage performance trend resembling a volcano, with the optimal energy storage material achieved using 1.4 wt.% Co-doped MnO_x–Co nanowires. Applying the optimum material for a hybrid supercapacitor application, the energy and power density values were calculated as 48.08 Wh kg⁻¹ and 2339.02 W kg⁻¹, respectively. Thus, we believe that our comprehensive exploration of Co-doped MnO_x nanowires provides valuable insights into understanding these materials’ optimization for energy storage applications. Graphical abstract: (Figure presented.)