Oxygen-deficient and nitrogen-doped MnO2 nanowire-reduced graphene oxide–cellulose nanofibril aerogel electrodes for high-performance asymmetric supercapacitors

Abstract

A simple and effective strategy was developed to prepare a three-dimensional manganese oxynitride nanowire (MnO_xN_y)–reduced graphene oxide (RGO)–cellulose nanofibril (CNF) aerogel electrode with high areal mass loading (∼6.02 mg cm⁻²). The electrical conductivity and electrochemical performance of MnO₂ nanowires were intrinsically improved by inducing oxygen vacancies and nitrogen doping during hydrazine vapor treatment. Due to the synergistic effects of highly conductive RGO, highly pseudocapacitive MnO_xN_y, a highly open and continuous porous aerogel structure, and the superior hydrophilicity of CNFs, the novel MnO_xN_y/RGO/CNF aerogel electrode we developed demonstrated a high capacitance of 455.8 F g⁻¹ (2743.7 mF cm⁻²) and excellent rate capability. Pairing it with the similarly developed molybdenum oxynitride (MoO_xN_y)/RGO/CNF negative electrode, the asymmetric supercapacitors (ASCs) can achieve a high voltage window of 1.8 V, revealing a high energy density of 49.0 W h kg⁻¹ at a power density of 953.7 W kg⁻¹ in an aqueous electrolyte (i.e., 1.0 M Na₂SO₄ solution) and 43.7 W h kg⁻¹ at a power density of 948.3 W kg⁻¹ in a solid-state polymer gel electrolyte (i.e., poly(vinyl alcohol)/Na₂SO₄). This strategy for engineering high-performance electrodes with high mass loading will open up new opportunities for developing highly efficient energy storage devices for practical applications.