From wood to thin porous carbon membrane: Ancient materials for modern ultrafast electrochemical capacitors in alternating current line filtering

Ultrafast electrochemical capacitors with alternating current line filtering function have attracted growing attention owing to their potential to replace the state-of-the-art bulky aluminum electrolyte capacitors. In spite of rapid advance recently involving nanomaterials as electrode building units, it remains largely unexplored how to structurally and chemically engineer electrodes out of renewable resource with competitive or better rate performance. Herein, wood as a renewable resource was used to fabricate highly conductive, robust, porous thin carbon membranes as free-standing electrodes for ultrafast electrochemical capacitors. Transformation of wood slice to carbon membrane proceeds via wet-chemical treatment of wood slices and subsequent morphology-maintaining carbonization by spark plasma sintering. Judiciously combining high conductivity, characteristic porous architecture with low tortuosity and high continuity, and the ultrathin thickness down to 20 μm, the carbon membrane-based electrochemical capacitor exhibits excellent frequency response with efficient 120 Hz filtering (phase angle = −83.5^o). Compared to the latest electrodes for line filtering application that are fabricated from carbon nanotubes, graphene, and MXene, the wood-derived carbon membranes possess a competitive specific areal capacitance of up to 509.7 µF cm⁻², and extremely low resistance-capacitance constant of 164.7 µs, plus the inexpensive scalable fabrication strategy.