Abstract
Carbon based materials have been found to be one of the most suitable electrode materials for the vanadium (V) reduction reaction at the cathode side of redox flow cell systems. Carbon electrodes modified with oxygen functional groups show a significant improvement in activity and reversibility of the vanadium (V) reduction reaction compared to non-functionalized carbon. The trend in the literature is to use different types of carbon materials modified by different surface functionalisation techniques (1, 2, 3), opening up a number of possibilities for different electrode materials for this application. Since not all these studies are in agreement (4), there appears to be a lack of clear understanding of the surface functionalisation-activity correlation. In order to better understand the role of surface functional groups on the electrochemical properties of vanadium (V) reduction, we present here a systematic study using glassy carbon as a model electrode system. The glassy carbon surface is functionalised by different treatment methods including: i) thermal treatment in oxygen, ii) electrochemical oxidation and iii)acid treatment. The identification and quantification of the different functional groups is evaluated using X-ray photon spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR) techniques. The activity and reversibility of the vanadium (V) reduction reaction is related to the extent of functionalisation i.e. type and amount of functional groups, in order to find the optimum surface termination. Furthermore, the wettability of the carbon surface is investigated. Wettability is inherently related to the presence of surface functional groups, with the surface becoming more hydrophilic in the presence of oxygen containing surface terminations. Finally, the correlation between the relative contributions of surface wettability and surface functional groups towards the overall activity is determined.
Published Version
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