Large-scale synthesis of hybrid metal oxides through metal redox mechanism for high-performance pseudocapacitors

Electrochemical performance and production cost are the main concerns for the practical application of supercapacitors. Here we report a simple and universally applicable method to prepare hybrid metal oxides by metal redox reaction utilizing the inherent reducibility of metals and oxidbility of for the first time. As an example, Ni(OH)₂/MnO₂ hybrid nanosheets (NMNSs) are grown for supercapacitor application by self-reaction of Ni foam substrates in KMnO 4 solution at room temperature. The obtained hybrid nanosheets exhibit high specific capacitance (2,937 F g^-1). The assembled solid-state asymmetric pseudocapacitors possess ultrahigh energy density of 91.13 Wh kg^-1 (at the power density of 750 W kg^-1) and extraordinary cycling stability with 92.28% capacitance retention after 25,000 cycles. Co(OH)₂/MnO₂ and Fe₂O₃/MnO₂ hybrid oxides are also synthesized through this metal redox mechanism. This green and low-cost method is capable of large-scale production and one-step preparation of the electrodes, holding promise for practical application of high-performance pseudocapacitors.