Metal-organic framework-derived carbon as a 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.