Achieving highly practical capacitance of MnO2 by using chain-like CoB alloy as support

Abstract

The practical performance of MnO₂ as a capacitor material is limited mainly by its poor electronic conductivity. Arranging MnO₂ on the conductive backbone to form a unique hierarchical nanostructure is an efficient way to enhance its capacitor performance. Herein, a hierarchically core–shell structure, in which thin γ-MnO₂ sheets are grown on amorphous CoB alloy nano-chains (CoB@MnO₂), is produced via a simple and scalable solution-phase procedure at room temperature. A specific capacitance of 612.0 F g⁻¹ is obtained for the CoB@MnO₂ capacitor electrode at a discharge current density of 0.5 A g⁻¹, a value higher than those obtained for other conductive materials supported MnO₂ electrodes reported in the literature. A rate retention value of 60.9% of its initial capacitance is obtained when the discharge current density increased by 12-fold. It is found that after 6000 charge–discharge cycles at 2 A g⁻¹, the specific performance of CoB@MnO₂ is 86.5%. The excellent capacitor performance of CoB@MnO₂ is explained to be due to the hierarchical core–shell structure, in which the CoB alloy nano-chain backbone provides a transport pathway for the electron, and the porous MnO₂ outer layers provide the channel for mass transfer, hence allowing further exposure to active sites. The combination of high capacitor performance and low-cost synthesis makes the core–shell CoB@MnO₂ a promising cathode material for alkaline electrolyte supercapacitors.