The Control and Effect of Pore Size Distribution in AEMFC Catalyst Layers

Abstract

Catalyst ink for anion-exchange catalyst coated membranes based on FuMA-Tech FAA-3 membranes and ionomer typically requires high-boiling solvents. Here, we investigate the disproportionate effect of even small quantities of high-boiling solvent in the catalyst ink on the catalyst layer microstructure. High porosity in the mesoporous regime, 20–100 nm, is found to be an essential characteristic of effective anion-exchange catalyst layers for increasing membrane hydroxide ion conductivity and reducing mass-transport losses. High porosity in the nanoporous regime (<20 nm pore diameter) facilitates improvements in the kinetic region of polarization curves at the expense of mass-transport losses. New strategies are introduced to improve the control of distribution of pore sizes in the catalyst layer and to increase the mesoporosity. Beginning-of-life power densities for O2/H2 anion exchange membrane fuel cells (AEMFCs), under zero backpressure, were accordingly increased from 276 to 428 mW·cm−2, placing it among the highest AEMFC power densities reported in the literature under the conditions studied, representing a significant improvement over previously reported performances for FAA-3. The study highlights a need to develop anion-exchange solid polymer ionomers soluble in low-boiling solvents for preparing catalyst inks, and a more rigorous evaluation of porosimetry data and catalyst layer preparation methods for AEMFCs.