Public Abstract: Carbon-supported platinum–rare earth nanoalloys are promising electrocatalysts for the oxygen reduction reaction. However, their structure–activity–stability trends are poorly understood. Herein, we followed the evolution of Pt–Nd/C nanoalloys during the electrochemical surface conditioning, i.e., prior to the initial evaluation of electrocatalytic activity, and observed that their compositional, morphological, and structural ex situ properties are considerably modified by the electrochemical activation step. It is these stabilized properties, therefore, that should be considered when discussing the electrocatalyst beginning-of-life state for the structure–activity–stability relationships rather than those determined ex situ on the as-synthesized electrocatalyst.

DOI: https://doi.org/10.1021/acscatal.3c03641
HAL repository: https://hal.science/hal-04240566/document

Public Abstract:  In fuel cell applications with long lifetime requirements, the management of stressing operating conditions—such as hydrogen starvation events—plays a pivotal role. Among other remedies, the incorporation of an OER-enhancing co-catalyst, is widely employed to improve the intrinsic stability of Pt/C-based anode catalyst layers in PEM fuel cells. The present study investigates several supported and unsupported Ir-based co-catalysts comprising different oxidation states of iridium: from metallic to oxidic character, both anhydrous rutile-type IrO₂ and hydrated amorphous form. Utilizing a single-cell setup, cell reversal experiments were conducted initially after break-in of the MEA and after seven days of continuous operation under reductive H₂ atmosphere at application-relevant conditions. The initial cell reversal tolerance was found to increase in the order metallic Ir < crystalline Ir oxide < amorphous Ir oxyhydroxide. By contrast, after continuous operation under H₂ the order changes drastically to amorphous Ir oxyhydroxide ∼ metallic Ir < crystalline Ir oxide. This led us to conclude that the amorphous Ir oxyhydroxide is likely reduced to metallic Ir during continuous H₂ operation, while IrO₂ provides a reasonable trade-off between initial OER activity, high structural and chemical stability at high anode potentials during H₂ starvation and low reducibility under prolonged H₂ operation. 

DOI: https://doi.org/10.1149/1945-7111/aceb8d