In-situ construction of binder-free MnO₂/MnSe heterostructure membrane for high-performance energy storage in pseudocapacitors

Manganese (Mn)-based oxides are considered suitable positive electrode materials for supercapacitors (SCs). However, their cycle stability and specific capacitance are significantly hindered by key restrictions such as structural instability and low conductivity. Herein, we demonstrated a novel nanorod (NR)-shaped heterostructured manganese dioxide/manganese selenide membrane (MnO₂/MnSe) on carbon cloth (CC) (denoted as MnO₂/MnSe-NR@CC) with a high aspect ratio by a straightforward and facile hydrothermal process. Experiments have demonstrated that doping selenium atoms to oxygen sites reduce electronegativity, increasing the intrinsic electronic conductivity of MnO₂, decreasing electrostatic interactions with electrolyte ions, and thus boosting the reaction kinetics. Further, the selenium doping results in an amorphous surface with extensive oxygen defects, which contributed to the emergence of additional charge storage sites with pseudocapacitive characteristics. As expected, novel heterostructured MnO₂/MnSe-NR@CC as an electrode for SC exhibits a high capacitance of 740.63 F/g at a current density of 1.5 A/g, with excellent cycling performance (93% capacitance retention after 5000 cycles). The MnO₂/MnSe-NR@CC exhibited outstanding charge storage capability, dominating capacitive charge storage (84.6% capacitive at 6 mV/s). To examine the practical applications of MnO₂/MnSe-NR@CC-ASC as a positive electrode, MnO₂/MnSe-NR@CC//AC device was fabricated. The MnO₂/MnSe-NR@CC//AC-ASC device performed exceptionally well, with a maximum capacitance of 166.66 F/g at 2 A/g, with a capacitance retention of 94%, after 500 GCD cycles. Additionally, it delivers an energy density of 75.06 Wh/kg at a power density of 1805.1 W/kg and maintains 55.044 Wh/kg at a maximum power density of 18,159 W/kg. This research sheds fresh information on the anionic doping method and has the potential to be applied to the synthesis of positive electrode materials for energy storage applications.