Tailoring the Durability of Carbon-Coated Pd Catalysts Towards Hydrogen Oxidation Reaction (HOR) in Alkaline Media

Abstract

For the hydrogen oxidation reaction (HOR), platinum group metal (PGM)-based carbon-supported are still the norm, and their large initial catalytic activity is counterbalanced by their uncertain durability in alkaline environments: harsh degradations proceed, like detachment and agglomeration of metallic nanoparticles from the carbon support, as witnessed from dedicated accelerated stress tests (AST). Herein, a strategy to increase such catalysts' durability is provided, using carbon layers surrounding the Pd-based carbon-supported nanoparticles. The robustness of such catalysts, baring 0.5 or 0.7 nm thick carbon cap over the Pd nanoparticles, is evaluated from AST combined with several pre/post-test characterization techniques: identical-location 2 transmission electron microscopy (IL-TEM), ex situ X-ray photoelectron spectroscopy (XPS) and ex situ inductively coupled plasma-mass spectrometry (ICP-MS). The carbon layer protection limits the Pd-based nanoparticles' agglomeration, detachment and metal leaching, improving longterm catalyst durability in HOR-like operation. Thicker carbon layers surrounding the Pd nanoparticles lead to higher materials durability and lower degradation rate (larger performance stability) upon AST, compared to thinner carbon layers. In addition, the carbon-capped catalysts enable to maintain better the required Pd/PdO state of surface that is essential for fast HOR, resulting in superior intrinsic HOR activity versus unprotected Pd/C. Overall, this work demonstrates that the activity-durability relationship can be tuned for carbon-capped catalysts.

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“…HOR catalysts have received less attention in the context of AEMFCs compared to ORR catalysts owing to their higher activities. It is worth noting that Pt/C catalysts exhibit fast HOR kinetics in alkaline environments and that other precious-metal catalysts such as Ir, Pd, 127 Ru, and their alloys are not superior to the Pt-based catalysts, as demonstrated in the comparison of HOR activities among Pt/C, Ni/C, and other precious-metal catalysts (Fig. 7 and Table 7).…”

“…Fig.7HOR activities measured using the half cell with state-of-the-art catalysts. Mass-and area-specific exchange current densities of various HOR catalysts evaluated for 0.1 or 1.0 M aqueous alkali solution in a RDE system (Table7) 123,127,[131][132][133][134][135][136][137][138][139][140]. …”