Polarization Effects of a Rayon and Polyacrylonitrile Based Graphite Felt for Iron‐Chromium Redox Flow Batteries

Abstract In this paper, a rayon based graphite felt (R‐GF) and a polyacrylonitrile based graphite felt (PAN‐GF) are studied to clarify the influence of the precursor on the polarization effect from three aspects: concentration polarization, ohmic polarization, and electrochemical polarization. The essential difference in chemical structure between R‐GF and PAN‐GF is that the precursor material makes PAN‐GF easier to be graphitized. The higher degree of graphitization leads to a higher conductivity of PAN‐GF. At the same thickness and porosity, the conductivity of PAN‐GF is higher and the loss of ohmic polarization is smaller. These factors make PAN‐GF have better electrocatalytic properties and kinetic reversibility in the Fe/Cr electrolyte environment. While the surface roughness of R‐GF is larger, which is contributing to the diffusion and surface mass transfer of the electrolyte on the surface. The effect of precursor on the concentration polarization of R‐GF and PAN‐GF is related to the surface mass transfer, which ultimately affects the performance of ICRFB.