Porosity Engineering of Pt-Loaded Nb-SnO2 Catalyst Layers in Polymer Electrolyte Fuel Cells

Recently, the emphasis on hydrogen-fuel utilization technologies─particularly polymer–electrolyte fuel cells (PEFCs)─has recently shifted from light-duty to heavy-duty vehicles. There is consequently an urgent need to develop a catalyst with excellent durability. In this study, we have endeavored to improve the power-generating performance of PEFCs by using high-durability Nb–SnO2 (NTO) nanoparticles and by controlling the porosity of the catalyst layer. We tuned the fused-aggregate network structure of the NTO nanoparticles by annealing them at 1000 or 1200 °C. This treatment promoted the development of aggregated structures of the NTO nanoparticles, which resulted in an increase in the porosity of the catalyst layer. In these catalysts, the maximum current density increased with increasing porosity. The gas-diffusion resistance calculated from the current–voltage (I–V) characteristics decreased from 148 m/s for NTO nanoparticles before annealing, to 113 m/s after annealing at 1000 °C, and to 102 m/s after annealing at 1200 °C. This study thus demonstrates that high-performance catalysts with high durability for PEFCs can be achieved by precisely engineering the porosity of the catalyst layer.