Ultra-thick wood biochar monoliths with hierarchically porous structure from cotton rose for electrochemical capacitor electrodes

The inspiration from biomass resources allows an efficient route to produce novel carbon materials for sustainable development of energy storage. The carbon monoliths are prepared by directly pyrolyzing cotton rose wood in an inert atmosphere. Their physicochemical properties and pore structure are controlled by altering the pyrolysis temperature. The obtained wood biochar monoliths (WBMs) inherit the hierarchically porous morphology of pristine wood, with unidirectional honeycomb channels with thin channel wall (0.7 μm) and unique interconnected macro-mesoporous pathway on the channel wall, as well as meso-micropores on the carbon sheets. The ultra-thick 1 mm WBM electrode that is pyrolyzed at 800°C with a specific surface area of 486 m2 g−1 shows the optimal electrochemical performance of 133 F g−1 (27 F cm−3) at 10 mA cm−2, which is higher than other reported wood biochar monoliths. Even the 10 mm thickness electrode retains 86% of the capacitance above. What’s more, the electrode in a symmetric electrochemical capacitor delivers a competitive energy density of 9.4 W h kg−1 and an outstanding stability of 111% after 10,000 cycles. It is demonstrated that cotton rose wood is a promising carbon precursor for the production of ultra-thick electrodes.