Electrolyte-engineered in-situ formation of Mn-based cathode composite with cotton fiber derived hierarchical porous carbon for high-performance zinc-ion hybrid supercapacitors

This study introduces an advanced zinc-ion hybrid supercapacitor (ZIHS) with optimized electrolyte composition and cathode material modifications to enhance electrochemical performance. Hierarchically porous activated carbon derived from the Red Cotton Tree was utilized as the cathode, offering improved ion diffusion and charge storage capability. Remarkably, a systematic investigation of MnSO₄ concentrations in a 2 M ZnSO₄ electrolyte identified 0.5 M MnSO₄ as the optimal concentration, significantly boosting capacitance retention by 172 % after 2000 cycles and achieving a maximum specific capacitance of 281 F g⁻¹. Electrochemical tests confirmed the synergistic effect of redox reactions and electric double-layer capacitance, resulting in a high energy density of 288.6 Wh kg⁻¹ and a power density of 497.8 W kg⁻¹ at 0.5 A g⁻¹. The in-situ formation of manganese-based active species during cycling is a primary reason for the significant contribution of redox reactions in the electrochemical mechanism, as well as the elevated specific capacitance observed during cycling. Post-cycling XRD, FTIR, SEM, and EDS analyses revealed the in-situ formation of battery-type Mn-based active sites—specifically MnCO₃, Mn₂O₃, and MnO₂, on the electrochemical double layer capacitor-type porous activated carbon cathode, contributing to enhanced performance and stability. This study demonstrates a sustainable and scalable approach to high-performance ZIHSs, paving the way for future energy storage applications.