In this study, we investigated the influence of thermal treatment, soaking in H 2 SO 4 and electrochemical ageing on commercially available carbon felt materials from SGL carbon. We compared both the influence of the pre-treatment (carbonization or graphitization) and the influence of the precursor (Rayon or PAN). By thermogravimetric analysis coupled with mass spectrometry (TGA-MS) we showed, that after thermal treatment, the thermal stability was lower for carbonized felts compared to graphitized felts and the Rayon based felts were more stable than PAN based ones. Soaking had a stronger impact on the thermal stability of PAN based felts, whereas it was similar to the electrochemical ageing for Rayon based felts. X-ray photoelectron spectroscopy and Raman spectroscopy revealed that thermal treatment reduces the overall surface oxygen content for all felt types and the degree of graphitization doesn't change, but the content of single bonded oxygen was increased for graphitized carbon felts, only. For carbonized felts, thermal treatment highly reduced the electrochemical activity characterized by cyclic voltammetry due to a reduced overall oxygen content and increased C=O and C=C contents. In this work, we provide a comprehensive overview of commercially available carbon felts and characterize the effects of several treatment methods.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 141.52.96.103 Downloaded on 2018-09-04 to IP A2578 Journal of The Electrochemical Society, 165 (11) A2577-A2586 (2018) ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 141.52.96.103 Downloaded on 2018-09-04 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 141.52.96.103 Downloaded on 2018-09-04 to IP

The wetting behavior and affinity to side reactions of carbon‐based electrodes in vanadium redox flow batteries (VRFBs) are highly dependent on the physical and chemical surface structures of the material, as well as on the cell design itself. To investigate these properties, a new cell design was proposed to facilitate synchrotron X‐ray imaging. Three different flow geometries were studied to understand the impact on the flow dynamics, and the formation of hydrogen bubbles. By electrolyte injection experiments, it was shown that the maximum saturation of carbon felt was achieved by a flat flow field after the first injection and by a serpentine flow field after continuous flow. Furthermore, the average saturation of the carbon felt was correlated to the cyclic voltammetry current response, and the hydrogen gas evolution was visualized in 3D by X‐ray tomography. The capabilities of this cell design and experiments were outlined, which are essential for the evaluation and optimization of cell components of VRFBs.

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We successfully conducted electrochemical and online mass spectrometric measurements on commercial carbon felt electrodes with a differential electrochemical spectrometry setup. Its capability is demonstrated by simultaneous mass spectrometric and electrochemical measurements. Half-cell tests, such as cyclic voltammetry, and coulometry of the redox couples can be performed under stopped flow of the electrolyte. We use different potential windows, and two types of electrolytes while monitoring potential dependent H 2 , O 2 and CO 2 formation. At oxidizing potentials, we did not observe oxygen evolution, only carbon corrosion. An increase in CO 2 and H 2 formation at high and low potentials in the presence of vanadium is observed.

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