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

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.