Role of Carbon Support Structure on PEMFC Durability
Authors: Perrin Eugénie , Heitzmann Marie , Celle Caroline 
Published: December 2024

Proton exchange membrane fuel cells (PEMFCs) are the electrochemical generators increasingly being studied as part of the energy transition. Among the key components of these systems, catalysts based on carbon-supported platinum nanoparticles (Pt/C) for PEMFC applications in the transport sector are the focus of numerous research efforts aimed at improving their durability1,2. Indeed, catalyst durability depends on the nature of carbon support used : in real systems, these materials undergo significant degradation phenomena, such as corrosion of the carbon support or deterioration of the Pt active sites (nanoparticle migration, dissolution, coalescence, Ostwald ripening)3, particularly at the cathode where water (a degradation factor) is present and the limiting ORR reaction occurs. Faced with the challenges of performance and durability, mesoporous carbon supports could meet the needs for PEMFC catalyst applications. These carbons offer a number of advantages for improving performance (high specific surface area) and durability (Pt nanoparticles anchored inside pores that are less exposed to degradation and ionomer poisoning)4,5. Thus, the properties of the carbon used as a catalyst support and in particular its structure, can play a crucial role in mitigating degradation processes, and consequently in improving the stability of PEMFC electrodes.
The aim of this study is to analyze the influence of mesoporous carbon structures on the durability of PEMFC catalysts. To this end, two major parameters are explored: mesoporosity tuning and carbon hydrophilicity, since it has been reported that wettability has repercussion on catalyst layer performance and durability6. The structural and physico-chemical properties of different types of mesoporous carbon supports are analyzed before and after electrochemical tests assessed by AST ("Accelerated Stress Tests", protocol inspired by the US DOE7).
To this end, three carbon supports with variable grain size, graphitization, hydrophilicity, BET surface area and mesoporous volumes were chosen to synthesize 40 wt% Pt/C catalysts by a polyol route. Synthesized carbons and catalysts are characterized using various physico-chemical analysis tools in order to evaluate and compare their structural and chemical properties. As water plays a major role in the MEA (membrane electrode assemblies) operation, we also chose to carry out dynamic vapour sorption (DVS) measurements, which are rarely used for PEMFC applications, to analyze the hydrophilicity of the materials (carbons, catalysts and active layers) and their sorption behavior. Catalysts are then integrated into similar cathodic catalyst layers (ink formulation, coating and transfer onto PEM membranes) and electrochemically degraded in a 1.8cm² differential cell (small active surface area) using the AST protocol simulating carbon support degradation in particular (corrosion during system start-up/shut-down phases). Accelerated degradation is monitored using various advanced electrochemical characterization techniques at different cycles at the cathode. Post-mortem analyses are also carried out from time to time to complement the electrochemical observations made. Taken together, the results provide first promising trends and new insights into the impact of mesoporous structures on the durability of catalytically active layers. They suggest that the choice of critical structural and physico-chemical properties is favorable to electrode longevity.

References

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Figure 1