Nano-catalytic layer engraved carbon felt via copper oxide etching for vanadium redox flow batteries

Electrode architecture design is vitally important for achieving high-power and long-life vanadium redox flow batteries. This work starts with a rationale for the polarization losses of current flow battery electrodes on a basis of the well-developed design of a proton exchange membrane fuel cell. With a gained understanding from the electrode design of a fuel cell, an attempt is made to engineer the architecture of carbon felt by creating a nano-catalytic layer on carbon fiber surfaces via a facile and powerful copper oxide etching method. By engraving nano-holes on fiber surfaces, the carbon felt can deliver attributes of expanded reaction surface area, abundant defective sites and excellent structural stability under swift-flowing electrolyte without sacrificing mass transport properties. With the nano-holed and defective carbon felt, the battery demonstrates a remarkably improved performance with 85.1% energy efficiency at 320 mA cm−2, 21.8% larger than that of the pristine carbon felt. In addition, the flow battery with this new electrode shows excellent long-term stability up to 2000 cycles. It is envisioned that such an electrode design strategy would inspire the future development of advanced fibrous electrodes for flow cell applications.