Oxygen-deficient and nitrogen-doped MnO2 nanowire-reduced graphene oxide–cellulose nanofibril aerogel electrodes for high-performance asymmetric supercapacitors†
A simple and effective strategy was developed to prepare a three-dimensional manganese oxynitride nanowire (MnOxNy)–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 MnOxNy, a highly open and continuous porous aerogel structure, and the superior hydrophilicity of CNFs, the novel MnOxNy/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 (MoOxNy)/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.