Metal-organic framework-derived carbon as the positive electrode for high-performance vanadium redox flow batteries

Optimizing the properties of carbon electrodes remains a critical challenge in the development of high-efficiency vanadium redox flow batteries. In this work, we correlate the battery performance with microstructures and surface chemistries through the controllable fabrication of perforated carbon platelets derived from metal–organic frameworks. With Raman and X-ray photoelectron spectroscopy analyses, we identify topological carbon defects and nitrogen-dopants as active sites for the oxidation of VO2+, as corroborated by the density functional theory. The optimal PCP electrode rich in these structural features is fabricated at a carbonization temperature of 800 °C to provide high electrical conductivity and a large surface area. It delivers energy efficiencies of 82.0 and 69.7% at current densities of 200 and 400 mA cm−2, respectively in a VRFB, along with high cycling stability. Further dissection of the polarization resistance confirms the catalytic activity as the underlying reason for the outstanding performance.