(Invited) Electrocatalysts Dissolution Assessment in Fuel Cell and Water Electrolysis Research
Authors: Cherevko Serhiy , Ehelebe Konrad , Escalera López Daniel , Knöppel Julius , Ku YuPing , Milosevic Maja 
Published: July 2022

Durability and degradation are in the focus of modern electrocatalysis research. Before moving to real applications, e.g. fuel cells in transportation or water electrolyzers for production of green hydrogen, novel electrocatalytic materials must prove acceptable stability, but “how to test the stability of electrocatalysts”?

In the relatively mature proton exchange membrane fuel cell (PEMFC) research, stability is evaluated using various accelerated stress tests (ASTs). Unfortunately, even for the most studied Pt/C electrocatalysts, degradation processes like carbon corrosion and Pt dissolution that occur during common ASTs are not easily distinguishable [1]. Moreover, advanced electrocatalysts such as different shape-controlled Pt alloy nanostructures, showing promising stability in ASTs performed in model aqueous systems, are often rendered useless when moved to real applications [2]. Catalysts free of platinum-group-metals, e.g. FeNC, demonstrate different degradation extents if tested in oxygen or argon [3]. Iridium oxides, the state of the art oxygen evolution reaction (OER) electrocatalysts, are prone to dissolution in aqueous media but much more stable in solid electrolyte based electrolyzers [4]. These examples demonstrate the need for rethinking current approaches to test electrocatalyst stability.

This work highlights our recent results on using coupled electrochemical techniques and tuned gas diffusion electrode (GDE) and membrane electrode assembly (MEA) cells in fuel cell and water electrolysis research. It shows that by hyphenating GDE with inductively coupled plasma mass spectrometry (ICP-MS) it is possible to investigate dissolution of electrocatalysts, such as Pt/C for PEMFC and Fe-N-C for anion exchange membrane fuel cells (AEMFC), in-operando at conditions closely resembling those in real devices [5, 6]. As another representative example, the use of model MEAs to address the discrepancy of Ir dissolution in aqueous and solid polymer electrolytes is given [7]. Based on these examples, new strategies to test and understand electrocatalysts’ degradation are discussed.

References:

[1] E. Pizzutilo et al., On the need of improved accelerated degradation protocols (ADPs): Examination of platinum dissolution and carbon corrosion in half-cell tests, J. Electrochem. Soc., 163 (2016) F1510-F1514.

[2] K. Kodama et al., Challenges in applying highly active Pt-based nanostructured catalysts for oxygen reduction reactions to fuel cell vehicles, Nature Nanotechnology, 16 (2021) 140-147.

[3] K. Kumar et al., On the influence of oxygen on the degradation of Fe-N-C catalysts, Angew. Chem. Int. Ed., 59 (2020) 3235-3243.

[4] S. Geiger et al., The stability number as a metric for electrocatalyst stability benchmarking, Nature Catalysis, 1 (2018) 508-515.

[5] K. Ehelebe et al., Platinum dissolution in realistic fuel cell catalyst layers, Angew. Chem. Int. Ed., 60 (2021) 8882-8888.

[6] Y.-P. Ku et al., Oxygen reduction reaction causes iron leaching from Fe-N-C electrocatalysts, (2021) Submitted, DOI: 10.21203/rs.3.rs-1171081/v1.

[7] J. Knöppel et al., On the limitations in assessing stability of oxygen evolution catalysts using aqueous model electrochemical cells, Nature Communications 12 (2021) 2231.