Carbonized wood loading sustainable tannin used as free-standing electrodes for assembling heavy metal-free supercapacitors.

The design of heavy metal-free thick supercapacitor electrodes with excellent energy storage performance through a novel and effective strategy represents an attractive yet challenging area of research. In this study, a sustainable redox-active tannic acid (TA) is loaded on the carbonized wood (CW) collector to construct a low-curvature, high-capacity, heavy metal-free supercapacitor electrode. The uniform loading of TA on the surface of the CW cell wall is achieved through the combined action of mutually stable hydrogen bonding and π-π interactions, which constructs a fast electron transport channel in the collector. The rapid and reversible redox reaction between the phenol and quinone groups of TA allows the CW-TA electrode to exhibit a high specific capacitance of 1321.25 mF cm at 0.5 mA cm and a superior rate capability of 761.90 mF cm at 50 mA cm. The symmetric supercapacitors (SSCs) assembled from CW-TA achieve an areal energy density of 0.12 mWh cmat a power density of 0.30 mW cm, with excellent rate performance and cyclic stability. This simple and environmentally friendly synthesis strategy provides a new avenue for research into the construction of low-cost, heavy metal-free, high energy density, and highly stable electrode materials for energy storage applications.