Functionalized Well-Aligned Channels Derived from Wood as a Convection-Enhanced Electrode for Aqueous Flow Batteries
Yang Yang, Xiao Sun, Zheng Cheng, Alolika Mukhopadhyay, Avi Natan, Chao Liu, Daxian Cao, Hongli Zhu
Abstract
Nature has provided scientists and engineers with tremendous inspirations and resources to design new materials, architectures, and devices. Inspired by the transportation of water and ions in trees, a natural freestanding wood carbon (WC) electrode with vertically well-aligned channels and pit pores on the channel walls was adopted as a convection-enhanced electrode for aqueous vanadium redox flow batteries (VRFBs). In addition, carboxylic groups were introduced on WC via nitric acid treatment (A-WC) to improve its wettability and electrochemical catalytic activity. The large specific surface area (542.28 m2 g–1) after functionalization afforded sufficient electrochemical reaction sites. Negatively charged A-WC with a zeta potential of −50.6 mV provides an extra driving force for the adsorption of vanadium cations toward the electrode surface. The discharge capacity retention for the A-WC electrode full cell is 83.58% after 100 cycles at 100 mA cm–2, whereas the WC electrode full cell only has a capacity retention of 57.21% after 100 cycles at 100 mA cm–2. Moreover, the A-WC electrode has a predominant effect on the positive side of the VRFB, and it has a voltage efficiency of 92.10% and an energy efficiency of 88.23% at a current density of 40 mA cm–2. Notably, the positive half-cell has a discharge capacity retention of 90.19% after 100 cycles at 100 mA cm–2. This work opens a new strategy to apply nature-derived structures and materials in the flow battery field.