Mn ₃ O ₄ Supported on MgO Nanosheet for Long‐Duration Supercapacitor

Manganese oxide is a commonly used electrode material for supercapacitor (SC) energy storage; however, it suffers from a limited cycling life due to its unstable microstructure. In this study, we have successfully prepared manganese tetroxide (Mn 3 O 4 ) supported on MgO nanosheet using a sacrificial template ion exchange method. The resulting Mn 3 O 4 particles have an average size of approximately 40 nm and are evenly distributed on the MgO support. The uniform size of the Mn 3 O 4 particles allows for more redox‐active sites to be exposed, while the stabilization effect of the MgO support further enhances the energy storage capability of the composites compared to unsupported Mn 3 O 4 . Specifically, the composites with an optimal ratio (Mg/Mn = 2:1) exhibit a specific capacitance of 282 F/g at 1.0 A/g, as opposed to 262 F/g for unsupported Mn 3 O 4 , and a higher energy density of 33.2 Wh/kg at 760 W/kg, than that of unsupported Mn 3 O 4 (24.4 Wh/kg at 760 W/kg) and some reported Mn‐based SCs. Moreover, the developed Mg 2 Mn 1 ‐O‐based asymmetric SC demonstrates an unprecedented cycling performance, with nearly 98% capacitance retention after 30,000 continuous charge/discharge cycles. This study provides a valuable strategy for synthesizing supported metal oxide composites with enhanced properties for various applications in the field of energy storage.