A high-performance aqueous asymmetric supercapacitor based on dual redox-electrolyte enhanced systems

Abstract

Aqueous supercapacitors (SCs) have attracted extensive attention owing to the low cost, high safety, easy handling, environment friendliness and high ionic conductivity of aqueous electrolytes. However, their energy density is constrained by the voltage threshold of water decomposition. To overcome this limitation, asymmetric SCs (ASCs) have been designed to expand the cell voltage. Moreover, the development of novel electrode materials and suitable redox-active electrolytes holds promise for achieving enhanced capacitance and increased energy density. In the present study, Ni(OH)₂/Mn (hydr)oxide was loaded on activated carbon cloth via an electrochemical deposition method. It was then paired with a redox electrolyte of KOH + [Fe(CN)₆]^3-/4- to serve as the positive compartment for the construction of a redox electrolyte enhanced aqueous ASC. Meanwhile, electrochemically activated carbon cloth coupled with a KOH + p-phenylenediamine redox electrolyte was utilized as the negative compartment. The resulting aqueous ASC exhibited a broad cell voltage of 1.7 V and a high capacitance of 410.8 mF cm^-2 at a current density of 40 mA cm^-2. Its energy density reached 3.7 Wh L^-1 at a power density of 396.2 W L^-1, which remained 2.2 Wh L^-1 even at a higher power density of 776.9 W L^-1. This work provides an efficient strategy for fabricating high-performance aqueous SCs.