A New Approach to Probe the Degradation of Fuel Cell Catalysts under Realistic Conditions: Combining Tests in a Gas Diffusion Electrode Setup with Small Angle X-ray Scattering

Abstract

A new approach for efficiently investigating the degradation of fuel cell catalysts under realistic conditions is presented combining accelerated stress tests (ASTs) in a gas diffusion electrode (GDE) setup with small angle X-ray scattering (SAXS). GDE setups were recently introduced as a novel testing tool combining the advantages of classical electrochemical cells with a three-electrode setup and membrane electrode assemblies (MEAs). SAXS characterization of the catalyst layer enables an evaluation of the particle size distribution of the catalyst and its changes upon applying an AST. The straight-forward approach not only enables stability testing of fuel cell catalysts in a comparative and reproducible manner, it also allows mechanistic insights into the degradation mechanism. Typical metal loadings for proton exchange membrane fuel cells (PEMFCs), i.e. 0.2 mgPt cm−2 geo, are applied in the GDE and the degradation of the overall (whole) catalyst layer is probed. For the first time, realistic degradation tests can be performed comparing a set of catalysts with several repeats within reasonable time. It is demonstrated that independent of the initial particle size in the pristine catalyst, for ASTs simulating load cycle conditions in a PEMFC, all catalysts degrade to a similar particle size distribution.

Platinum Dissolution in Realistic Fuel Cell Catalyst Layers

“…In general, it has to be stated that GDE half‐cell experiments offer unique opportunities to study catalyst layers and their degradation by combining them with different analytical methods such as identical location transmission electron microscopy (IL‐TEM), [33] operando X‐ray and neutron imaging, [34] small‐angle X‐ray scattering (SAXS), [35] mass spectrometry for gaseous and volatile products, [36] and with the present work also ICP‐MS.…”

“…However, to further approach realistic fuel cell conditions,t he elevated temperature in fuel cell applications needs to be considered as this leads to significant increase of catalyst degradation. [32] In general, it has to be stated that GDE half-cell experiments offer unique opportunities to study catalyst layers and their degradation by combining them with different analytical methods such as identical location transmission electron microscopy (IL-TEM), [33] operando X-ray and neutron imaging, [34] small-angle X-ray scattering (SAXS), [35] mass spectrometry for gaseous and volatile products, [36] and with the present work also ICP-MS.…”

Operando SAXS study of a Pt/C fuel cell catalyst with an X-ray laboratory source

“…The size change of NPs supported on carbon was assessed by SAXS measurements as previously reported. [11,12] SAXS measurements were performed at the Niels Bohr Institute, University of Copenhagen, Denmark, on a Ganesha instrument (SAXSLab). The Ganesha is equipped with a 100XL+ microfocus sealed X-ray tube (Rigaku), producing a photon beam with a wavelength of 1.54 Å, and a 2D 300 K Pilatus detector (Dectris).…”

“…[2,7] The stability of catalysts is often investigated by performing accelerated stress tests (ASTs) to decrease the testing time. [8,9] Such ASTs were recently performed on commercial Pt catalysts in gas diffusion electrode (GDE) setups [10][11][12] simulating load cy-cles and start-stop conditions as recommended by the Fuel Cell Commercialization Conference of Japan (FCCJ) [13,14] under realistic mass transport conditions. To determine changes in particle size as result of the AST protocol the measurements in the GDE setup were coupled to ex situ small-angle X-ray scattering (SAXS).…”

“…To determine changes in particle size as result of the AST protocol the measurements in the GDE setup were coupled to ex situ small-angle X-ray scattering (SAXS). [11,12] However, ex situ measurements provide only the possibility to determine the particle size at few points in time (i.e., at the beginning and the end of treatment). To establish a timeresolved picture of catalyst degradation the number of samples would need to be enormously increased.…”