The role of Mn in widening the potential window of solid solution derived electrodes for aqueous supercapacitors

Abstract

The interaction mechanism of the multi-element oxide electrodes remains a challenge, despite the fact that their synergy can not only improve the electronic structure, but also broaden the working potential window to some extent. Herein, the simple NiMn alloy system was taken up as a model to investigate the origin of the wide voltage window. Compared with conventional electrodes, this sandwich-type nanoporous-NiO(MnO_x)@Ni electrode derived from a NiMn alloy could exhibit a wide working potential window of 1.5 V in aqueous electrolyte. The facilitated successive redox reactions between NiO and MnO_x throughout the entire potential window strongly promote the capacitance extension without water decomposition, despite the fact that the cycling lifespan was limited by chemical dissolution of MnO_x. The assembled quasi-solid-state supercapacitor can overcome the irreversible conversion and exhibit a remarkable lifespan of 5000 cycles at 10 A cm⁻³ (91% retention) and high energy density (37.67 mW h cm⁻³ at 0.2 A cm⁻³). This work provides new perceptions for the design of multi-element collaborative energy storage electrodes.