Mo-doped MnO2@CC electrode for high-performance 2.4 V aqueous asymmetric supercapacitors.

[Display omitted] • Understand the key factors for broadening the operating voltage of supercapacitors. • The overpotential of MnO 2 can be modulated by tailoring its Fermi energy level. • The ASC exhibits a wide voltage of 2.4 V and a high energy density of 0.89 mWh cm−2. Despite many advantages of supercapacitors based on aqueous electrolytes, the inherently low operating voltage severely limits their energy density and practical applicability to many applications. Thus, it is a key scientific challenge to broaden the potential window of electrode materials for supercapacitors. Here we report our findings in tailoring the Fermi level of MnO 2 -based electrode by doping with a high-valence Mo6+ ion, thus modulating its overpotential in aqueous electrolytes and potential window. For example, the redox potential of Mo-doped MnO 2 is effectively increased, resulting in a wider potential window. When grown on a carbon support, the specific capacitance of Mo-doped MnO 2 @CC with a mass loading of 15.1 mg cm−2 reaches 3.22 F cm−2 in a wide potential window of 1.2 V. The enhanced performance is attributed to the additional redox behavior induced by the Mo dopant, as confirmed by in situ Raman and ex-situ XPS analyses. When coupled with a C-Ti 3 C 2 T x /WO 3 @CC negative electrode to construct an ASC with a total mass loading of 35.8 mg cm−2, the ASC exhibits a wide voltage window of 2.4 V, demonstrating a remarkable energy density of 0.89 mWh cm−2 at a power density of 2.56 mW cm−2. In addition, the device is operational in a wide operating temperature range of −10 to 50 °C, and a voltage of ∼ 58% is retained after self-discharge for 48 h. This work provides some new insights into the development of aqueous ASC devices of commercial-grade mass loadings with high output voltage, high energy density, and slow self-discharge rates. [ABSTRACT FROM AUTHOR]