Impact of the pore structure on non-wetting phase distribution and gas phase mass transport within cathode-side catalyst layers of PEM fuel cells

Much of the efficiency of PEMFCs is determined by the water handling properties of the cathode-side catalyst layer (CCL), which depend upon its particular pore structure and distribution of the various phases therein. A new (to this application) gas adsorption-based method has been used to assess the global spatial variation in coverage of the catalyst support with ionomer for differing ionomer contents. The rarely-used nitrogen over-condensation method was proven essential for the comprehensive characterisation of CCLs with pores that span a much wider size range than can be seen with conventional adsorption, and is also more statistically-representative than imaging methods. Percolation theory-based models have been used to predict the impact of different saturation levels of the invasion percolating phase (using mercury, as a model for condensed water) on gas phase mass transport rates. A novel scaling analysis has shown that the saturation level and disposition of the invading phase impacts void space accessibility via modifying the apparent diffusional penetration depth for mass transfer. This showed the key importance of surface clusters of larger pores to both water handling and gas phase mass transport. • Method to assess spatial variation in coverage of the catalyst with ionomer. • Gas overcondensation detected macroporous voids. • Percolation model predicted impact of non-wetting fluid saturation on gas transfer.