Electrochemical behavior of diverse vanadium ions at modified graphite felt electrode in sulphuric solution

Abstract

PAN-based graphite felt (PGF) treated in 98% sulphuric acid for 5 h and then kept at 450 °C for 2 h was evaluated for their electrochemical performance as electrodes of vanadium redox battery (VRB). Structure and characteristic of treated PAN-based graphite felt (TPGF) were determined by means of Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy, Brunauer-Emmett-Teller surface area analysis and VRB test system. The results show that the acid and heat synergistic effect increase the number of —COOH functional groups on the PGF surface, and the PGF is eroded by sulphuric acid oxidation, resulting in the surface area increases from 0.31 m²/g to 0.45 m²/g. The V(II)/V(III) redox reaction is electrochemically reversible on the TPGF electrode, while the V(IV)/V(V) couple is a quasi reversible process. The diffusion coefficients of the oxidation for V(IV)/V(V) obtained from the scope of peak current I_p vs scan rate v^1/2 is 4.4×10⁻⁵ cm²/s. The improvement of electrochemical activity for the electrode is mainly ascribed to the increase of the number of —COOH groups on the TPGF, which behaves as active sites catalyzing the vanadium species reactions and accelerating electron transfer reaction and oxygen transfer.

Keywords

vanadium / redox flow battery / graphite felt / diffusion coefficient