Cost-Effective Asymmetric Supercapacitors Based on Nickel Cobalt Oxide Nanoarrays and Biowaste-Derived Porous Carbon Electrodes

Two nanostructured electrode materials are fabricated and used to construct cost-effective asymmetric supercapacitors (ASCs). Hierarchical nickel cobalt oxide nanoarrays (NCO-NA) consisting of nanosheets (NCO-NS) or nanowires (NCO-NW) are uniformly grown on Ni foam by a simple, effective, and generally applicable method, while biowaste-derived hierarchical porous carbon (Bio-HPC) with an interconnected microstructure is fabricated by pretreatment with potassium hydroxide and followed by direct pyrolysis. Considering the mass of NiCo₂O₄, the maximum specific capacitance of the hierarchical NCO-NS and NCO-NW electrodes are 2300 and 2333 F g^–1, respectively, and the specific capacitance of the Bio-HPC electrode is 253.9 F g^–1 at a scan rate of 5 mV s^–1. NCO-NA, Bio-HPC, a piece of polypropylene membrane, and 30 wt % KOH solution are assembled into a high-performance, low-cost ASC with the capability of rapidly storing electrical energy. The NCO-NW//Bio-HPC ASC exhibits a higher energy density compared with NCO-NS//Bio-HPC ASC, while the latter shows better cycling performance (the capacitance still remains 91.12% after 2000 cycles)