Assessment of transport-limited catalyst utilization for engineering of ultra-low Pt loading polymer electrolyte fuel cell anode

In this study, transport-limited catalyst utilization in polymer electrolyte fuel cell (PEFC) anodes is assessed via an agglomerate model with a broader view of designing ultra-low Pt loading, high performance anode. The model accounts for electrical and chemical potential-driven transport of electrons/protons and dissolved hydrogen, respectively and multi-component gas-phase transport in the catalyst layer. The model employs the kinetics of hydrogen oxidation reaction based on dual-pathway reversible reaction mechanism reported recently [J.X. Wang, T.E. springer, R.R. Adzic, J. Electrochem. Soc. 153 (2006) A1732]. The model predictions show that for conventional, randomly-structured catalyst transport limitations exist at two levels. At single-agglomerate level, the catalyst utilization is restricted by dissolved hydrogen diffusivity limiting the reaction to occur primarily in the outer shell of the agglomerate. At the catalyst layer level, the catalyst utilization is limited primarily by poor protonic conductivity. However, significant electronic potential gradients can exist in the catalyst layer thereby effectively reducing the available overpotential. Simulation results also show that by engineering the catalyst layer to overcome the transport limitations and, thereby, improving the effective catalyst utilization, high performance can be achieved in a PEFC anode at ultra-low Pt loading of 0.0225 mg/cm2.