Modification Of Carbon Paper Electrode For Vanadium Redox Battery

To improve the electrochemical activity of electrodes in the vanadium redox battery, carbon paper was treated according to the hydrothermal acid oxidation and hydrothermal ammoniated method in this paper. The relationship between wetting property and electrochemical activity of V(IV)/(V) redox couples is discussed. The main points can be summarized as following.Hydrothermal acid oxidation of carbon paper for vanadium redox battery was first employed in this paper, the sulfuric acid was diluted to3mol/L for treatment. Compared with traditional acid oxidation and heat treatment method, the electrochemical activity of carbon paper after hydrothermal oxidation is better. The treated conditions were systematic screened, the best treatment temperature is180℃, to use the mixture of sulfuric acid and hydrogen peroxide to treat carbon paper is better than use them alone, and the most suitable volume ratio is2:1(VH2SO4/VH2O2). A single-cell employing carbon papers treated under these conditions as electrodes at a current density of20mA/cm2have obtained an energy efficiency of83.5%, the corresponding coulombic and voltage efficiencies were96.6%and86.4%, respectively.Then the carbon paper was hydrothermal acid oxidated under different time at180℃, Fourier transformation infrared spectroscopy (FTIR), Scanning electron microscopy (SEM) and the water contact angle test were employed to characterize the surface topography and structure. The FTIR results showed that oxygen-containing groups, such as the carbonyl and carboxyl groups, had been successfully introduced to the carbon papers. And the water contact angle test showed that a treatment time of12h resulted the contact angle is100.8°which is the lowest observed. The corresponding cyclic voltammetry, electrochemical impedance spectroscopy, and charge-discharge tests showed that the electrochemical performance of this sample is the best, thus illustrated that the enhancement of wetting property can improve the electrochemical activity of electrode. A single-cell employing carbon paper treated for12h as an electrode has exhibited excellent performance. The energy efficiency reached80%at a current density of30mA/cm2. The corresponding coulombic and voltage efficiencies were96%and84%, respectively.To hydrothermal ammoniate carbon papers under different temperature was developed, the hydrophilic and electrochemical activity of carbon paper electrode also enhanced markedly after the treatment, the optimal treatment temperature is220℃. The battery with hydrothermal ammoniated modified carbon paper electrode exhibits an energy efficiency of87.4%under10mA/cm2. Indicating that the introduce of nitrogen-containing functional groups can enhance the surface properties of carbon papers, at the same time, the electrochemical catalytic activity of them were improved, then the performance of cell became better.