Ex situ and in operando characterization of Pt and Pt3Co catalyst degradation for proton-exchange membrane fuel cells

With the aim of reducing greenhouse gases emissions, it is become essential developing efficient and cost-effective systems able to either produce and use green hydrogen as energy vector. In fact, fuel cell technology has seen remarkable improvements over the last decades, and Proton Exchange Membrane Fuel Cells (PEMFCs) in particular, started to be used in the automotive and transportation sectors. However, the complex architecture characterizing the Membrane Electrode Assemblies (MEAs) slows down the research and development aiming to enhance catalyst efficiency and lifespan while reducing production costs (Y. Wang et al., 2020). Concerning the catalyst layer, notable progress has been made by alloying transition metals to form Pt bimetallic alloys, and Pt3Co was found having superior performance compared to pure Pt catalysts in catalysing the Oxygen Reduction Reaction (ORR). Nevertheless, dissolution and leaching of the less noble metal from the alloy was reported, leading to catalyst degradation and the formation of a Pt-rich shell structure with Co remaining inside the catalyst nanoparticles (Wang & Spendelow, 2021). Significant advancements in optimizing fuel cell architecture and catalyst loading have been achieved by means of in operando analyses, which allowed to deepen the understanding of catalyst degradation phenomena (Shan et al., 2016). Furthermore, in operando analyses conducted at synchrotron facilities or using neutron probes have revealed critical insights into fuel cell operation and degradation. In example, Small Angle X-ray Scattering (SAXS) revealed an excellent solution in monitoring catalyst morphological evolution (Martens et al., 2022; Povia et al., 2018) supported by earlier studies on catalyst model systems (Bogar et al., 2021; Ruge et al., 2017). X-Ray Absorption Spectroscopy (XAS) has provided detailed information on reaction kinetics and local changes of the chemical environment surrounding (Ishiguro & Tada, 2018). In this context, we developed an electrochemical cell capable of functioning as a reversible unified electrochemical cell, specifically optimized for investigating the chemical and morphological evolution of catalyst materials designed for PEM fuel cells and water electrolysers. In this study we compare the degradation of bare Pt and Pt3Co catalysts using two different degradation protocols, examined under both ex situ and in operando conditions, using Small Angle X-ray Scattering (SAXS), X-ray Absorption Spectroscopy (XAS), and the most common electrochemical techniques (such as impedance spectroscopy and cyclic voltammetry). As a result, we highlight how differently degradation evolves according to the catalyst composition and by using two different types of Accelerated Stress Tests (AST), a milder one targeting the catalyst layer only, and a harsher one supposed to induce catalyst degradation over the whole MEA.