Porous Flexible Wood Scaffolds Designed for High-Performance Electrochemical Energy Storage

Abstract

Natural wood has been physically or chemically modified to create new hierarchical structures for vast applications. We report herein the facile methods to synthesize porous flexible conductive wood for high-performance energy storage. Our delignification and densification increase micro–mesopores for higher surface area but decrease macropores to improve the scaffold’s density, thus leading to ultra-high flexibility and excellent mechanical strength. Such hydroxyl-enriched flexible wood scaffolds (FW-RC) are readily chemically deposited with carbon nanotubes (CNTs) to promote fast electron/ion transport and a lower internal resistance (ca. 2.1 Ω). Interestingly, the as-prepared CNT@FW-RC electrode exhibited organic redox reactions originating from oxygen-containing groups on the wood surface. The electrode showed an areal specific capacitance of 640 mF cm–2 at a 0.1 mA cm–2 scan rate and over 93% capacitance retention for 10,000 galvanostatic charge/discharge cycles, outperforming most reported carbonized wood electrodes. Asymmetric supercapacitors demonstrated a maximum energy density of 108 mW h L–1 at the power density of 2.06 W L–1, which retains a value of 36 mW h L–1 at the highest volumetric power density of 20.5 W L–1. Further in situ electrodeposition of conducting polymers on the CNTs@wood electrodes was explored for scalable energy storage devices. The design strategies surely provide guidance on constructing porous flexible wood-based hierarchical nanostructures for emerging applications, utilizing surface functional groups of the wood surface for organic redox reactions.