Recent Advances in Catalyst Accelerated Stress Tests for Polymer Electrolyte Membrane Fuel Cells

Abstract

The U.S. Department of Energy (DOE) set the 2020 durability target for polymer electrolyte membrane fuel cell transportation applications at 5000 hours. Since it is impractical to test every fuel cell for this length of time, there is ever increasing interest in developing accelerated stress tests (ASTs) that can accurately simulate the material component degradation in the membrane electrode assembly (MEA) observed under automotive operating conditions, but over a much shorter time frame. In this work, a square-wave catalyst AST was examined that shows a 5X time acceleration factor over the triangle-wave catalyst AST and a 25X time acceleration factor over the modified wet drive-cycle catalyst durability protocol, significantly decreasing the testing time. These acceleration factors were correlated to the platinum (Pt) particle size increase and associated decrease in electrochemical surface area (ECSA). This square-wave AST has been adopted by the DOE as a standard protocol to evaluate catalyst durability. We also compare three catalyst-durability protocols using state-of-the-art platinum-cobalt catalysts supported on high surface area carbon (SOA Pt-Co/HSAC) in the cathode catalyst layer. The results for each of the three tests showed both catalyst particle size increase and transition metal leaching. Moreover the acceleration factors for the alloy catalysts were smaller due to Co leaching being the predominant mechanism of voltage decay in ∼5 nm PtCo/C catalysts. Finally, an extremely harsh carbon corrosion AST was run using the same SOA Pt-Co/HSAC catalyst. This showed minimal change in particle size and a low percentage Co loss from the cathode catalyst particles, despite a significant loss in catalyst layer thickness and cell performance. The carbon corrosion rates during these various ASTs were directly measured by monitoring the CO 2 emission from the cathode, further confirming the ability of the square-wave AST to evaluate the electro-catalyst independently of the support.

Experimental Analysis of the Performance and Load Cycling of a Polymer Electrolyte Membrane Fuel Cell

“…As introduced previously, degradation is a major research field in PEMFCs [1] and several accelerated stress test (ASTs) have been derived [2]. ASTs for automotive applications can be found in the literature, as in the work of Mukundan et al [22] or Stariha et al [23], using the U.S. DRIVE-FCTT drive cycle. In Mukundan et al, a combination of chemical/mechanical ASTs was developed, where the relative humidity was also applied to the cycles at OCV [22].…”

Evolution of the degradation mechanisms with the number of stress cycles during an accelerated stress test of carbon supported platinum nanoparticles

“…For example, degradation of carbon-based catalyst support may be studied by electrochemical cycling of the electrode potential ranging between ~1.0 and ~1.7 V in acidic baths [12][13][14][15][16][17][18]. In this range of potentials, the carbon support corrosion becomes a significant degradation mechanism besides the degradation of Pt and Pt-alloy nanoparticulate catalysts which starts at potentials below 1.1 V [19]. Recently, we also observed Pt nanoparticle growth based on dissolution-redeposition mechanism at high potentials (>1V) despite surface passivation [20].…”

Single-Atom Catalysts: A Perspective toward Application in Electrochemical Energy Conversion

“…, respectively, 109 but various protocols are applied. 110 Recently, a more fundamental understanding of the degradation mechanisms in play led to improvements for a combined covering the transition from load to start/stop conditions (0.6–1.5 V RHE ). 109 , 111 , 112 A major question remains whether this is appropriate for MNC based ORR catalyst systems.…”