Enhancing the capacitance of carbonized wood by regulating the morphology and valence state of guest electrochemically active materials

•Integrating carbonization, activation, and in-situ growth of CuxOy in one step.•Regulating the morphology and valence state of CuxOy by constant potential method.•The specific capacitance of electrode is boosted by 98.6% after regulating CuxOy. Using bottom-top methodology to load metal oxides with high pseudocapacitive activity onto carbonized wood (CW) is an efficient strategy to fabricate electrodes with large capacitance, while the morphology and metal valence in metal oxides are as important as their content but have received little attention. Herein, a heating treatment integrating carbonization and activation processes is used on Cu2+ loaded natural wood to prepare CW/CuxOy electrodes in which CuxOy with pseudocapacitive activity and CW with a high specific surface area (SSA) of 832 m2/g and good electric conductivity of 1.25 S cm−1 are collaboratively achieving a capacitance of 430.5F/g at 150 mA g−1. Then, a constant potential method is utilized not only to regulate the valence state of Cu and Cu2+ in CuxOy to Cu+ with much higher pseudocapacitive activity, but also to convert the morphology of CuxOy from sphericity to urchin-like and cluster structure with more available active sites. Therefore, the optimized electrode achieves a greatly improved capacitance of 855F/g, and the fabricated supercapacitor delivers an energy density of 75.93 Wh kg−1 at 138 W kg−1. This work provides an approach to enhance the specific capacitance of metal oxides-based electrodes from a fresh perspective.