A New Approach to Probe the Degradation of Fuel 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. In contrast to standard rotating disk electrode measurements or identical location microscopy, typical metal loadings for proton exchange membrane fuel cells (PEMFCs), i.e. 0.2 mgPt cm-2geo, 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. <br>

Elucidating Pt-Based Nanocomposite Catalysts for the Oxygen Reduction Reaction in Rotating Disk Electrode and Gas Diffusion Electrode Measurements

“…The recipe of the catalyst ink for the GDE measurements was reported previously [24].The catalyst ink was formed by dispersing the catalysts in a mixture of Milli-Q water and IPA (Vwater: VIPA= 3:1) to obtain the concentration of Pt is 0.50 g L -1 . Nafion (D1021, 10 wt.…”

“…Copenhagen with a SAXSLab instrument as previously detailed [24,29,31]. The instrument is equipped with a 100XL + micro-focus sealed X-ray tube from Rigaku, producing a photon beam with a wavelength of 1.54 Å.…”

“…In Pt-based alloy catalysts, both the addition of Ir and Au is reported to improve the ORR performance [15,16]. The performance of the nanocomposite catalysts is investigated in conventional rotating disk electrode (RDE) measurements [13,17,18] as well as in recently introduced gas diffusion electrode (GDE) measurements [19][20][21][22][23][24][25] that in contrast to the RDE measurements provide realistic catalyst loadings as well as realistic mass transport conditions.…”

Elucidating Pt-Based Nanocomposite Catalysts for the Oxygen Reduction Reaction in Rotating Disk Electrode and Gas Diffusion Electrode Measurements

“…In addition to more realistic reaction conditions, the GDE investigations also allow an ex situ analysis of the used (degraded) catalyst layers with SAXS [24,29]. Comparing the particle size distributions derived from SAXS at BOT and EOT indicates that the improved stability and ORR activity of the Pt-Au/C nanocomposite can be assigned to a reduced Pt particle growth, see Figure 4 and Table S2.…”