MnO₂ Nanowire/Biomass-Derived Carbon from Hemp Stem for High-Performance Supercapacitors

Hierarchical 3D nanostructures based on waste biomass are being offered as promising materials for energy storage due to their processabilities, multifunctionalities, environmental benignities, and low cost. Here we report a facile, inexpensive, and scalable strategy for the fabrication of hierarchical porous 3D structure as electrode materials for supercapacitors based on MnO₂ nanowires and hemp-derived activated carbon (HC). Vertical MnO₂ wires are uniformly deposited onto the surface of HC using a one-step hydrothermal method to produce hierarchical porous structures with conductive interconnected 3D networks. HC acts as a near-ideal 3D current collector and anchors electroactive materials, and this confers a specific capacitance of 340 F g^-1 at 1 A g^-1 with a high rate capability (88% retention) of the 3D MnO₂/HC composite because of its open-pore system, which facilitates ion and electron transports and synergistic contribution of two energy-storage materials. Moreover, asymmetric supercapacitors fabricated using 3D HC as the anode and 3D MnO₂/HC as the cathode are able to store 33.3 Wh kg^-1 of energy and have a power delivery of 14.8 kW kg^-1.