In-situ synthesis of synergistic ZnMn2O4/MnOOH nanocomposite as a cutting-edge pseudocapacitive electrode material for all-solid-state asymmetric supercapacitors

Currently, there has been a growing interest in constructing metal oxide composite structures through the in-situ synthesis method, especially for fabricating electrode materials for supercapacitors. This approach offers several advantages, such as improved contact between different materials, enhanced conductivity, efficient ion diffusion, and better overall electrochemical performance. This work investigates the synthesis of zinc manganese oxide and manganese oxyhydroxide (ZnMn₂O₄/MnOOH) composite using a solvothermal method. The structure, surface morphology, and composition of the ZnMn₂O₄/MnOOH composite were elucidated using standard physicochemical characterization techniques where the presence of ZnMn₂O₄ and MnOOH phases was confirmed and the ZnMn₂O₄/MnOOH nanocomposite behaved as a pseudocapacitive electrode with a notable specific capacitance of 1039.2 F g⁻¹ at a current density of 1 A g⁻¹. When subjected to a 10-fold increase in current density, the ZnMn₂O₄/MnOOH electrode maintained 50 % of its initial capacity, registering 513.4 F g⁻¹. Additionally, the electrode showcased excellent cyclic stability, preserving 95 % of its initial capacity after 5000 cycles at 10 A g⁻¹. Moreover, the constructed ZnMn₂O₄/MnOOH//activated carbon (AC) asymmetric supercapacitor (ASC) device attained a high energy density of 29.45 Wh kg⁻¹ at a power density of 1384.5 W kg⁻¹. The results confirm that the ZnMn₂O₄/MnOOH composite, prepared in a single synthesis step, shows great potential as a phenomenal pseudocapacitive electrode for energy storage applications.