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The electrochemical corrosion of the carbon-based catalyst support materials used in proton exchange membrane fuel cells (PEMFCs), especially at the cathode, has a significant impact on PEMFC lifetime. Thus, an effective and reliable method for the evaluation of the corrosion resistance of new carbon supports, as they are developed, is required. In the present work, a novel approach that allows for the ranking of carbon supports for their corrosion susceptibility has been developed, based on the testing of a conventional microporous carbon material (Vulcan carbon, VC) and two ordered mesoporous carbons (OMCs), synthesized using sucrose and anthracene as the carbon precursors. While cyclic voltammetry does reveal important information about surface area and surface oxidation changes, the charge passed during potential stepping between 0.8 and 1.4 V vs. RHE was found to be still more informative, with the cathodic charge used to continuously correct for the changing surface area of the carbon during its oxidation. Based on this approach, it was found that VC, which is the more crystalline material, is more stable to oxidation than the OMCs, as expected, while the anthracene precursor leads to a more stable OMC than when sucrose is used. [ABSTRACT FROM AUTHOR]

As an example of nanoporous carbon materials, colloid-imprinted carbons (CICs) have been reported to have promising properties for use in a variety of applications. However, the wettability of these carbons has not been investigated as yet. In this work, CICs with different pore sizes (20–50 nm) were synthesized and heat treated at 1500 °C under a N 2 atmosphere. Heat treatment was found to not alter the nanoporous structure of these carbons, but did significantly decrease their oxygen content. Contact angle kinetics (CAK) and water vapor sorption (WVS) experiments were carried out to determine the wettability of the CICs, before and after heat treatment, showing that the as-synthesized CICs surfaces are much more hydrophilic when compared to commercial carbon black (Vulcan carbon, VC). The high hydrophilicity of the CICs is likely due to their high surface-specific oxygen atomic density (∼10 μmol m −2 ). Further heat treatment significantly decreases the hydrophilicity of CICs because of the removal of oxygen atoms from their surfaces, as also reflected by their cyclic voltammetric response in acidic solutions. [ABSTRACT FROM AUTHOR]

Abstract: Two mesoporous carbons (with 15 (CIC-15) and 26nm (CIC-26) diameter pores) were synthesized using a silica colloid imprinting method, loaded with 10wt.% Pt, and then evaluated (against Vulcan™ carbon (VC)) as oxygen reduction (ORR) catalysts for use in proton exchange membrane fuel cells. Both Pt/CICs reproducibly out-performed Pt/VC, with Pt/CIC-15 demonstrating higher ORR activity than Pt/CIC-26, despite its smaller pore size and lower surface area. Transmission electron tomography showed that the Pt nanoparticles (4–5nm diameter) are fully deposited throughout the pores of the CICs and that the pore distribution in CIC-26 is partially ordered, while CIC-15 shows no ordering of its pores. Importantly, using the powerful imaging capabilities of transmission electron tomography, a first-time correlation is demonstrated between the ORR activity and the wall thickness of the carbon support materials. Pt/CIC-15 has significantly thicker walls, giving a lower measured electronic resistance, a lower ORR Tafel slope, and thus better performance overall compared to Pt/CIC-26. [ABSTRACT FROM AUTHOR]

In this study, the effect of surface functionalization on the electrochemical corrosion resistance of a high surface area, mesoporous colloid imprinted carbon powder (CIC), as well as microporous Vulcan carbon (VC, serving as the benchmark), was demonstrated, primarily for PEM fuel cell applications. CIC-22, which is highly hydrophilic and was synthesized with 22 nm silica colloid templates, and as-received, mildly hydrophobic, VC powders, were functionalized with 2,3,4,5,6-pentafluorophenyl (-PhF 5 ) surface groups using a straightforward diazonium reduction reaction. These carbons were then subjected to corrosion testing, involving a potential cycling-step sequence in room temperature 0.5 M H 2 SO 4 . Using cyclic voltammetry and charge/time analysis, the double layer and pseudo-capacitive gravimetric charges of the carbons, prior to and after the application of these potential steps, were tracked in order to obtain information about surface area changes and the extent of carbon oxidation, respectively. It is shown that the corrosion resistance was improved by ca. 50–80% by surface functionalization, likely due to a combination of surface passivation (loss of carbon active sites) and increased surface hydrophobicity. [ABSTRACT FROM AUTHOR]