Effects of Mesoporosity on Catalyst Layer Degradation Mechanisms in PEM Fuel Cells

Electrochemically-accelerated corrosion of support materials and dissolution of active materials in proton exchange membrane fuel cell (PEMFC) catalyst layers are two degradation modes that represent key challenges to the long-term performance and cost effectiveness of fuel cell systems. Comparisons between microporous and mesoporous carbon materials as high surface area (HSA) supports for precious metal catalysts (e.g., Pt) has conventionally focused on their respective effects on the electrochemical performance or I-V curves of membrane electrode assemblies (MEAs). Specifically, different carbon materials have been extensively studied for their roles in dispersing nanoparticles and ionomer molecules, electron conductivity, gas transport, and water management—properties largely relevant to PEMFC performance. Here, we examine carbon support materials of varying mesoporosities, and instead compare their effects on PEMFC durability, in the context of the two aforementioned degradation modes. Using accelerated stress tests (ASTs) of single-cell MEAs, we find that, while Pt dissolution resistance in highly-microporous HSA carbon blacks can be moderately enhanced via surface functionalization/doping, highly-mesoporous carbon support materials can be tailored to strongly modulate Pt dissolution resistance whilst offering comparable MEA performance. Similarly, by performing graphitization treatments to modulate carbon corrosion AST durability, we show that mesoporous carbons are able to offer significantly different performance-durability tradeoffs than their microporous counterparts. <i>Ex situ</i> characterization of both microporous and mesoporous carbon-containing catalyst layers, before and after undergoing ASTs, gives us mechanistic insights into the relationship between mesoporosity and the generally-accepted physical models underlying the two degradation modes.