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A highly active state‐of‐the‐art catalyst was synthesized by cobalt–nitrogen co‐doping of multi‐walled carbon nanotubes (Co/N/MWCNT) as non‐precious metal catalyst using cobalt chloride and dicyandiamide by high‐temperature treatment. A range of physicochemical characterization methods were used to observe the surface structure and composition of the synthesized electrocatalyst material. The kinetics of the oxygen reduction reaction (ORR) on this catalyst material was studied in 0.1 m KOH solution by using the rotating‐disk electrode method. The Co/N/MWCNT catalyst showed excellent electrocatalytic activity for ORR in alkaline media. In addition, the performance of the catalyst in a fuel cell was evaluated by fabricating membrane electrode assemblies employing a Tokuyama® anion exchange membrane (AEM), with hydrogen and oxygen gases at various temperatures. AEM fuel cell with Co/N/MWCNT cathode catalyst exhibited a power density of 115 mW cm−2 with H2/O2 gases (100 % RH) at ambient pressure at 50 °C.

Perfluorosulfonic acid ionomer membranes are subjected to simultaneous chemical and mechanical degradation under fuel cell operation. Despite the importance of membrane durability, the understanding of its structural degradation and failure modes has been considerably restricted by conventional 2D imaging. In this work, non-invasive micro X-ray computed tomography (XCT) is adopted to visualize the 3D membrane decay at different life stages during combined chemical and mechanical degradation. A detailed survey exhibits damage density of 6 and 10 cracks per mm 2 observed at the near-final and final end of life stages respectively. Through-thickness membrane cracks with unbranched I-shaped cracks and Y-and X-shaped cracks with one and two branches respectively are observed. The observed damage development at each life stage is correlated to supplementary diagnostic data including hydrogen leak rate, open circuit voltage, and tensile strength. In particular, large X-shaped cracks formed due to embrittlement from underlying chemical degradation are deemed to have a critical impact on the eventual failure development by facilitating large hydrogen leaks. Overall, the comprehensive 3D perspective enabled by XCT imparts new knowledge pertaining to the degradation process, and could also be extended to other fuel cell failure modes and degradation mechanisms.

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Effective catalyst layer design is vital for high-performing polymer electrolyte fuel cells. However, the desired catalyst layer structure may be compromised by operational degradation, causing performance decay. The present work investigates the multi-scale catalyst layer structure and properties across different stages of degradation, including liquid water distribution in an operating fuel cell. A correlative, multi-scale imaging workflow with a combined analysis by operando lab-based micro-X-ray computed tomography (XCT) and nano-XCT is developed for this purpose. From operando XCT results, the catalyst layer solid area fraction was found to gradually decrease by 25% with crack formation and severe localized corrosion accompanied by up to 50% thinning and significantly altered liquid water distribution. Localized degradation features such as nano-scale cracks and internal pore-size distribution changes were resolved using nano-XCT and tracked by 3+1D imaging at different stages of degradation. Porosity changes quantified by nano-XCT on the order of 40% from beginning-of-life to end-of-life with reduction in connected pore fraction were observed as well as increase in average pore size by 50%. The effect of changes at the nano-scale on diffusion properties were calculated and an empirical model is proposed for degraded catalyst layer structures where Knudsen effects are dominant.