Tailoring Cobalt Content in MnO _x Nanowires for Superior Supercapattery Performance

Herein, we report the urea-assisted synthesis of Co-doped MnO _x nanowires with cobalt contents of 5.85, 6.63, and 19.22 wt %. ICP-OES confirmed Co incorporation, while SEM, TEM, and EDS analyses showed that low-to-moderate Co loadings preserve the nanowire morphology with homogeneously dispersed Co species, whereas high Co content induces aggregation. XPS revealed that 6.63 wt % Co optimized the Mn⁴⁺/Mn³⁺ ratio and increased the concentration of defect-related surface oxygen species, while excessive Co doping promoted Mn reduction. EPR/FMR measurements confirmed the formation of metallic Co aggregates at higher loadings. Electrochemical testing in 2 M KOH demonstrated that Co-MnO _x (6.63 wt %) delivered the highest specific capacitance (1468.65 F·g^-1 at 1 A·g^-1) and excellent cycling stability. Moreover, a AC//Co-MnO _x (6.63 wt %) supercapattery achieved an energy density of 393.6 Wh·kg^-1 and a power density of 2928 W·kg^-1 with 61% retention after 2200 cycles. The enhanced electrochemical activity is attributed to an optimized cobalt content that maximizes defect-related oxygen species and promotes favorable Co-Mn electronic interactions without inducing surface saturation, resulting in improved supercapattery performance.