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Carbonized wood (CW) electrodes with low-tortuosity and high conductivity have received extensive attention in the fields of energy storage and electrocatalysis. Directly carbonized wood electrodes have low specific surface area and high electrochemical impedance, and require secondary physical or chemical activation to achieve acceptable performance. Herein, we reported a facile method to prepare the CW electrode with superior surface area through self-activation using CO 2 and water vapor generated during the pyrolysis which was conducted with a low inert gas flow rate. The specific surface area and electrical conductivity of the self-activated carbonized wood (SCW, ~ 0.46 g cm−3) were as high as 1145 m2 g−1 and 20.3 S cm−1, respectively. The SCW applied as a freestanding electrode demonstrated an impressive specific capacitance of 6.63 F cm−2 (143.6 F g−1) at 1 mA cm−2. After 10,000 cycles, the capacitance of the SCW electrode was retained as high as 101.7%. The symmetrical supercapacitor (SSC) assembled with two SCW electrodes showed an energy density of 0.27 mWh cm−2 (8.60 Wh L−1) at a power density of 0.5 mW cm−2 (11.8 W L−1). This work provides a simple, low-cost and green procedure for fabricating high-performance CW electrodes, which has great promotional significance and practical value on valorization of biomass. • Pre-oxidation of wood at 220 °C produced substantial amount of CO 2. • Low inert gas rate retains the concentration of CO 2 allowing self-activation. • Self-activated carbonized wood electrode exhibited superior specific surface area. • The freestanding SCW electrode exhibited high energy density at the device level. [ABSTRACT FROM AUTHOR]

• Copper nanoparticles (Cu NPs) were grown in nitrogen-doped carbonized wood (NCW). • Cu 1.0 NPs@NCW-1000 exhibited high specific capacitance of 10.39 F cm−2. • SSC delivered 0.59 mWh cm−2 with a retention of 92.02 % after 5000 cycles. • Cu 1.0 NPs@NCW-1000 showed a overpotential of 100.43 mV at 10 mA cm−2. • Cu 1.0 NPs@NCW-1000 exhibited a Tafel slope of 95 mV dec−1. The development of self-supporting electrodes using natural wood is promising for energy storage and conversion but still challenging. Here, the nitrogen-doped carbonized wood electrode decorated with copper nanoparticles is synthesized to escalate its capacitive performance and HER. Cu 1.0 NPs@NCW-1000 exhibits a high specific capacitance of 10.39 F cm−2 at 1 mA cm−2. The symmetric supercapacitor achieves an energy density of 0.59 mWh cm−2 at 3.5 mW cm−2 while achieving a capacitance retention of 89.51 % after 8,000 cycles. Cu 1.0 NPs@NCW-1000 also displays good HER activity, comprising an overpotential of 100.43 mV at 10 mA cm−2 and a Tafel slope of 95 mV dec−1. Its outstanding properties were attributed to doping-nitrogen, high specific surface area, hierarchical porous structure, and the interaction between Cu NPs and NCW, which increased active sites and accelerated charge transfer. This work provides a new strategy for the preparation of self-supported carbon electrodes for the energy storage and electrocatalysis applications. [ABSTRACT FROM AUTHOR]