Properties of mesoporous carbon modified carbon felt for anode of all-vanadium redox flow battery

A novel anode material for all-vanadium redox flow battery was synthesized by dispersion coating of sol-gel processed (resorcinol-furaldehyde) mesoporous carbon (MPC) onto the surface of polyacrylonitrile carbon felt (CF). The coated samples were then annealed at 900 degrees C and 1100 degrees C and the subsequent morphology, surface chemistry, and electrochemical properties of the MPC coated CF were characterized and compared with an uncoated CF. Addition of the MPC coating is shown to dramatically increase surface area while also increasing the number of active surface oxygen groups particularly for samples annealed at 1100 degrees C. MPC coating shows a mixed effect on electrochemical properties. Characterization with cyclic voltammetry reveals the introduction of MPC coating provides roughly 30% increase in peak current density for the oxidation and reduction reactions of the V(IV)/V(V) redox couple, which is attributed to the significantly increased number of active reaction sites. However, MPC coating seems to be accompanied by a reduction in conductivity as demonstrated by increased redox peak separation and charge transfer resistance. This negative effect on conductivity can be mitigated by heat treatment (at or above 1100 degrees C) which improves surface graphitization reducing redox peak separation and charge transfer resistance such that it is comparable with uncoated samples.