Carbon nanotubes grown on the inner wall of carbonized wood tracheids for high-performance supercapacitors

Supercapacitors made by wood scraps are low cost, ecofriendly and accessible. However, there are some problems, such as a small specific surface area and low specific capacitance. How to obtain a high-performance supercapacitor by effectively increasing the specific surface area without affecting the conductivity is still a challenge. In this paper, carbon nanotubes (CNTs) were first synthesized on the inner wall of tracheids in wood carbon slices, which have complete structures and do not require any conductive additives and binder. Nanonickel particles as catalysts were uploaded on the inner wall of each tracheid for growing the CNTs, which can increase the specific surface area from 365.5 to 537.9 m2 g−1, while improving the electrochemical performance to 215.3 F g−1 or 76.5 F cm−3. The energy density of the all-solid-state supercapacitor is 39.8 Wh kg−1, and 96.2% of the capacitance could still be retained after 10,000 charging/discharging cycles. This capacitance value is approximately five times as high as that of activated wood carbon and is equal to or higher than that of supercapacitors based on wood carbon slices with pseudocapacitance materials. CNTs will greatly promote the application of wood scraps as valuable commodities.