Biochar prepared from the pyrolysis of maple wood was studied as supercapacitor electrode materials. Three kinds of electrodes were fabricated: mini-chunk electrodes, thin-film electrodes, and large-disk-chunk electrodes. Their capacitive behaviors were studied using cyclic voltammetry, galvanostatic charge–discharge, and electrochemical impedance spectroscopy. The mini-chunk supercapacitor shows an electrochemical behavior similar to the supercapacitor using the thin-film electrodes. It exhibits outstanding performance characteristic of a high specific capacitance of approximately 32 F g−1 and a high stability without obvious capacitance decays upon 2,600 potential cycles. This indicates that the mini-chunk supercapacitor can be used as an mF-scale power source for electronic device applications. Moreover, the mini-chunk electrode provides a simple and fast technique to evaluate biochar materials used as potentially high-performance, low-cost, and environmental friendly supercapacitor electrodes without the need of binder and complicated fabrication procedures. However, the supercapacitor using large-disk-chunk biochar electrodes shows lower specific capacitive performance due to the high ohmic resistance stemming from long tubular structures within biochar.
