Holey three-dimensional wood-based electrode for vanadium flow batteries

The vanadium flow battery (VFB) is widely regarded as one of the most reliable large-scale energy storage technologies due to its flexible design, long cycle life, and high safety. However, novel electrodes for VFBs with a well-suited structure by cost-effective manufacturing processes are still highly sought after to penetrate the growing energy storage market. Here, we demonstrate a holey three-dimensional (3D) wood-based electrode for VFBs, which was engineered by the facile perforation and carbonization of earth-abundant, low-cost, and sustainable wood. The 3D-wood electrode inherits the intrinsic, vertically-aligned channels (i.e. low tortuosity structure) of the original crude wood material, which provides fluent electrolyte transport paths in the flow battery system. Furthermore, small holes (approximately 1.3 ​mm) are drilled across the 3D-wood electrode in the perpendicular direction to connect the parallel channels, thereby enabling ion exchange and reducing flow resistance. The concentration polarization is significantly reduced during the charge and discharge process in VFB, due to these electrode modifications. The porous structure of the 3D-wood electrode, with a high specific surface area of 216.77 ​m2 ​g−1 and oxygen functional groups, provides sufficient reaction sites for vanadium cations to enhance the electrochemical reactivity of VFBs. The superior structure of the 3D-wood electrode ensures the feasibility in VFBs and offers a promising direction for developing flow battery electrodes through pore engineering of earth-abundant biomaterials.