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The long-term durability of the catalyst layers of a lowworking temperature fuel cell such as a polymer electrolyte membrane fuel cell (PEMFC) is of significant scientific interest because of their operation criteria and high initial cost. Identification of degradation mechanisms quantitatively during an accelerated stress test (AST) is essential for assessing and improving the durability of such catalyst layers. In this study, we present a quantitative analysis of the degradation mechanisms such as (i) electronic connectivity loss due to carbon support corrosion, (ii) proton connectivity loss due to ionomer/catalyst interface loss, (iii) catalyst loss due to dissolution or detachment, and (iv) physical surface area loss due to particle growth that is responsible for the electrochemical surface area (ECSA) loss in Pt-based catalyst layers for PEMFCs during an AST performed through potential cycling (linear sweep cyclic voltammetry) between 0.4 and 1.6 V for 7000 cycles in Ar-saturated 1 M H 2 SO 4 . Using a half-membrane electrode assembly (half-MEA), where a gas diffusion electrode with genuine three-phase boundaries is used as a working electrode through a solid electrolyte, we have observed the ECSA loss due to ionomer/catalyst interface loss and identified a catalyst heterogeneous degradation pattern during an AST. Results suggest a significant ECSA loss due to catalyst isolation (∼64% of ECSA loss) from loss of electron and proton connectivities by catalyst support corrosion (∼45%) and ionomer/catalyst interface loss (∼19%), followed by particle growth (∼30%) and dissolution/detachment (6%). Such knowledge and methodology can effectively contribute to catalyst material screening and electrode structure development to advance the PEMFC technology.

A robust catalyst support is pivotal to Proton Exchange Membrane Fuel Cells (PEMFCs) to overcome challenges such as catalyst support corrosion, low catalyst utilization and overall capital cost. SiC is a promising candidate material which could be applied as a catalyst support in PEMFCs. SiC nanocrystals are here synthesized using nano-porous carbon black (Vulcan Ò XC-72) as a template using two different reactions, which result in particle sizes in the ranges of 50-150 nm (SiC-SPR) and 25-35 nm (SiC-NS). Pt nano-catalysts of size 5-8 nm and 4-5 nm have successfully been uniformly deposited on the nanocrystals of SiC-SPR and SiC-NS by the polyol method. The SiC substrates are subjected to an acid treatment to introduce the surface groups, which help to anchor the Pt nano-catalysts. These SiC based catalysts have been found to have a higher electrochemical activity than commercially available Vulcan based catalysts (BASF & HISPEC). These promising results signal a new era of SiC based catalysts for fuel cell applications.

Large-scale applications of polymer electrolyte membrane fuel cells (PEMFCs), are throttled primarily by high initial cost and durability issues of the electrodes, which essentially consist of the nanoparticulate catalysts (e. g. Pt) having accessibility to electrons (e-), protons (H +) and fuel/oxidant through catalyst support, polymer electrolyte ionomer and porous gas diffusion layer, respectively. Hence, to achieve high electrode performance in terms of activity and/or durability, understanding and optimization of the catalyst/support and catalyst/ionomer interfaces is of significant importance. Present study demonstrates an alternative route to inspect the catalyst/ionomer interface through accelerated stress test (AST) combined with electrochemical impedance spectroscopy (EIS). Various interface is created through catalyst inks prepared using commercial Pt/C catalyst powder dispersed in different solvents. Electrode degradation pattern turns out to be a very useful tool to interpret catalyst/ionomer interface structure. Variations of interfacial impedance, electrochemical surface area (ECSA) and double layer capacitance (DLC) with the number of potential cycles suggested significant impact of catalyst/ionomer interface on the catalyst performance. A quantification of the degradation mechanisms responsible for ECSA loss during AST was employed to further understand the correlations between the electrochemical

Thin film-rotating disc electrode (TF-RDE) experiment provides a fast research platform for screening of newly developed electrocatalysts for oxygen reduction reaction (ORR) activity, however, precise estimation of their performance parameters is necessary to avoid wastage of resources in the testing of otherwise unpromising electrocatalyst in actual fuel cells. Here we show the importance of the accurate amount of catalyst (e.g. Pt) on glassy carbon (GC) disk of RDE in TF-RDE experiment by characterizing the commercial catalysts for their electrocatalysis performance (electrochemical surface area and ORR activity) values. The Pt loadings used to calculate these performance values were obtained using two schemes, namely, using the literature based (conventional) scheme and an X-ray fluorescence (XRF) based scheme. A parameter called 'catalyst-density-ofthe-ink' is used to correlate the variations observed in performance values and the amount of Pt on GC disk of RDE obtained using both the schemes. The investigation suggests that the actual Pt loading on GC disk of RDE varies with the ink-conditions, which is considered constant in the conventional scheme and might be one of the reasons of irreproducibility of the data obtained by TF-RDE experiments. The XRF based scheme, which is simple and direct, can have the potential to replace conventional scheme for accurate catalyst loading estimation, improve experimental reproducibility and open many other possibilities (e.g. postmortem analysis of catalyst) in electrocatalysis studies.

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Accelerated stress test (AST) protocol meant to study the durability of catalyst support in a polymer electrolyte membrane fuel cell (PEMFC) electrode has been critically evaluated. For nanoparticulate catalysts supported on high surface area conductive materials (e.g. Pt/C), potential cycling meant to study the support durability causes significant impact on the catalyst particles presumed to be passivated due to formation of oxide layer. X-ray diffraction (XRD) patterns of pre-AST and post-AST samples suggest significant change in crystallite size during potential cycling between 1.0 and 1.6 V (vs. RHE), which may be considered to growth induced by dissolution/redeposition rather than particle growth through agglomeration due to support corrosion. Significant (~50%) electrochemical surface area loss due to catalyst particle growth during support corrosion AST should be taken into account while development/screening of durable catalyst supports. To reduce such contribution, frequent observation cycle should be minimized.

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