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

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In this work, as-received pristine GDLs were degraded (aged) through an accelerated ageing process by immersion into a 35% wt. solution of H 2 O 2 at 90 • C for 12 hours. Pristine and degraded GDLs were assembled in custom-built fuel cells for in operando synchrotron X-ray visualization. Electrochemical impedance spectroscopy (EIS) measurements were obtained, while synchrotron X-ray radiography was performed to investigate the effect of ageing on liquid water transport behavior. In both pristine and aged GDLs, the liquid water profile converged to an upper (terminal) threshold in the saturation pattern as the current density increased. The terminal steady state liquid water profile was established at a lower current density for the aged GDLs compared to that of the pristine GDLs. Higher water quantities of liquid water accumulated at the GDL/flow field channel and MPL/carbon fiber substrate interfaces of the fuel cell with an aged GDL compared to the fuel cell with a pristine GDL. The aged GDLs exhibited more liquid water accumulation at lower current densities. Increases in liquid water accumulation and reduced performance were attributed to the reduction in hydrophobicity of the GDL.

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