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

PAN-based graphite felt (PGF) treated in 98% sulphuric acid for 5 h and then kept at 450 degrees 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 m(2)/g to 0.45 m(2)/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 nu(1/2) is 4.4x10(-5) cm(2)/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.