Cu/Zn co-doped manganese dioxide cathode for zinc-ion hybrid capacitors

Zinc-ion hybrid supercapacitors (ZIHSCs) are emerging as a promising energy storage device, combining the benefits of traditional batteries and capacitors, including high energy density, incredible power density, a wide voltage window, and excellent capacity retention. In this study, a Cu²⁺ and Zn²⁺ co-doped needle-like tunnel-structured α-MnO₂ material is proposed as the cathode (Cu-Zn-MnO₂@CC), which is grown on an acid-treated flexible carbon cloth substrate using a simple hydrothermal synthesis method. Along with an anode made of super-mesoporous activated carbon derived from waste rice husks (ACrh@CC). The synergistic effect of the co-doping stabilizes the nanowire tunnel structure and provides more active sites. As a result, the Cu-Zn-MnO₂@CC//2 M ZnSO₄//ACrh@CC ZIHSC achieves an ultrahigh specific capacitance of 1241.85 mF cm⁻² at 1 mA cm⁻², representing an improvement of more than 50 % in performance compared to with conventional MnO₂@CC ZIHSC. And a maximum areal energy density of 689.9 μWh cm⁻² at a power density of 1 mW cm⁻². After 20,000 cycles, it retains 86.35 % of its initial capacitance. Furthermore, the assembled flexible device achieves a specific capacitance of 1070.21 mF cm⁻² at 1 mA cm⁻². This device can provide long-term power for electronic devices such as digital watches and timers. The study offers crucial understanding regarding structure of ZIHSC electrode materials and opens up possibilities for their potential applications.