Extraordinary Supercapacitor Performance of a Multicomponent and Mixed-Valence Oxyhydroxide

We report a novel multicomponent mixed-valence oxyhydroxide-based electrode synthesized by electrochemical polarization of a de-alloyed nanoporous NiCuMn alloy. The multicomponent oxyhydroxide has a high specific capacitance larger than 627 Fcm^-3 (1097±95 Fg^-1) at a current density of 0.25 Acm^-3, originating from multiple redox reactions. More importantly, the oxyhydroxide electrode possesses an extraordinarily wide working-potential window of 1.8 V in an aqueous electrolyte, which far exceeds the theoretically stable window of water. The realization of both high specific capacitance and high working-potential windows gives rise to a high energy density, 51 mWhcm^-3, of the multicomponent oxyhydroxide-based supercapacitor for high-energy and high-power applications.