Analyzing Platinum Catalyst Degradation in Fuel Cells Using Accelerated Stress Tests and X-Ray Absorption Spectroscopy
Authors: Ferreira Gomes Lobo Bruna , Jalan Rameshwori , Lobo Carlos M.S. , Schuster Michael , Nguyen Bui Duc Long , Roth Christina 
Published: December 2024

The exploration of sophisticated characterization techniques in the study of electrochemical processes is pivotal for progressing our understanding of energy conversion mechanisms. Among such , particularly the coupling with X-Ray Absorption Spectroscopy (XAS), have shown significant promise. To follow dynamic changes of the electrocatalysts during operation, such as activation, conditioning and degradation, advanced measurement routines are required to capture these changes, but in a much reduced analysis time. Accelerated stress test (AST) protocols are the method of choice here and have been published and agreed upon by various sources, e.g. the DOE. This work details our recent investigation using XAS to study the structural and oxidation state changes in supported platinum catalyst under accelerated stress (for oxygen reduction reaction).

Our experiment was conducted at the P64 Beamline (DESY, Hamburg) with three distinct accelerated stress test (AST) protocols applied to carbon-supported platinum catalysts (Pt/C) to probe their durability and degradation patterns. These tests are crucial for understanding the longevity and efficiency of catalysts in practical applications. Pt/C material, commonly used in fuel cells, was spray-coated onto a gas diffusion layer with 1 mgPt cm-2 loading and tested in a 1 mol L-1 HClO4 electrolyte. After 5000 cycles, we collected the Pt L2,3-edges XAS spectra at open circuit potential. This was done ten times for each test protocol. All measurements were done in a nitrogen atmosphere using a special half-cell designed for fluorescence measurements. Three electrochemical protocols were being tested and compared for their applicability: Loading Cycling, Startup/Shut Down, and a Mixed Protocol [1-3]. Each of these protocols simulates different stress conditions that the catalyst might experience in real-world applications. Through these tests, we could observe and analyze the agglomeration and dissolution phenomena in the Pt nanoparticles.

A key observation across all three protocols was that the degradation manifested itself through the dissolution of the PtO layer, evidenced by a reduction in the Pt-O coordination number. Additionally, we noted an increase in the Pt-Pt coordination number, indicative of nanoparticle agglomeration. These phenomena are critical as they directly impact the efficiency and lifespan of the catalyst. We hypothesize that the carbonaceous support material undergoes oxidation under extreme conditions set by the AST protocols. This oxidation potentially facilitates nanoparticle agglomeration. Concurrently, the oxide layer formed on the nanoparticle surface dissolves into the electrolyte, further contributing to the degradation process.

Understanding these degradation mechanisms is vital for improving catalyst design and optimizing their performance in realistic conditions. This work demonstrates the efficacy of XAS coupled with electrochemical testing in providing insightful data on catalyst behavior under stress. These findings are instrumental in guiding the development of more durable and efficient electrochemical systems, particularly in the field of energy conversion.

References

Alinejad, S. et al 2020
Phys. Energy 2 024003.

Ohma, A. et al 2011
ECS Trans. 41 775.

Loukrakpam, R. et al 2023
Power Sources 569 232905.