Impact of Accelerated Stress Tests on the Cathodic Catalytic Layer in a Proton Exchange Membrane (PEM) Fuel Cell Studied by Identical Location Scanning Electron Microscopy

Abstract

Platinum is the most used electrocatalyst in proton exchange membrane fuel cells (PEMFCs). Nonetheless, it suffers from various types of degradation. Identical location electron microscopy has previously been used to observe local catalyst changes under accelerated stress tests (ASTs), giving insight into how individual catalyst particles degrade. However, it is important that such studies are carried out under relevant reaction conditions, as these can differ substantially between liquid half-cells and real PEMFC conditions. In this work, a single cell PEMFC was used to study the degradation of a commercial Pt-catalyzed membrane electrode assembly by performing square wave voltage ASTs in a potential range of 0.6 to 1.0 V. Identical location scanning electron microscopy (IL-SEM) was used to follow the degradation of the cathodic catalytic layer (CL) throughout 14,000 AST cycles. From the IL-SEM, we can conclude that the Pt nanoparticles degrade via Ostwald ripening, crystal migration, and coalescence. Small Pt nanoparticles agglomerate to larger particles or dissolve and redeposit to more stable particles, increasing the average particle size during the ASTs. In addition, cross-sectional TEM images show thinning of the ionomer layer during the AST procedure. The IL-SEM technique facilitates observation of local degradation of the CL in real PEMFCs, which will help to understand different degradation mechanisms, allowing for better solutions to be designed.

Beware of cyclic voltammetry! Measurement artefact in accelerated stress test of fuel cell cathode revealed by operando X-ray diffraction

“…Martens et al, 22 reached 10.3 nm from commercial Pt/C MEA in similar conditions after 10,000 triangular wave AST between 0.6 V vs. RHE and 1.0 V vs. RHE at 50 mV s -1 . Similar particle size values were obtained also with different experimental conditions, such as potential cycling to different upper potential limits, different amount of cycles or even after extensive operation at constant current load [14][15][16]20,23 . We now present the WAXS data measured operando over the course of the complete AST protocol.…”

Enhanced Durability of Automotive Fuel Cells via Selectivity Implementation by Hydrogen Spillover on the Electrocatalyst Surface

“…The amount of catalyst loading on the MEA was determined according to the initial MEA performance evaluated through the polarization curve shown in Figure S14. Considering the different experimental conditions, the initial performance of the MEA using commercial Pt/C was similar to the results in benchmark studies. ,,− Current density at 0.6 V was 0.8 or 1.3 A cm –2 in this study but 0.57 A cm –2 in the reference study with the most identical evaluation conditions, in which 0.1 and 0.4 mg Pt cm –2 were loaded on the anode and cathode, respectively, and H 2 /Air of RH 100% was injected without backpressure. In the case of Pt/m-TiO 2 , it was initially evaluated with the loading of 0.4 mg Pt cm –2 on the anode, but contrary to what was expected in the half-cell test, poor performance results were obtained due to its significant Ohmic resistance.…”

Origin of High Activity and Durability of Confined Ordered Intermetallic PtCo Catalysts for the Oxygen Reduction Reaction in Rotating Disk Electrode and Fuel Cell Operating Conditions

“…However, despite the achievements of CN x in benefiting the alloy catalysts, there is still a critical knowledge gap in understanding the specific role of CN x in maintaining the catalyst structure and stability, especially for the real application under MEA operation conditions. Such conditions would accelerate the dissolution of both Pt and Co under elevated temperature and contribute to different degradation behaviors compared to the most studied RDE testing conditions …”