Effect of dispersing solvents for ionomers on the performance and durability of catalyst layers in proton exchange membrane fuel cells

Abstract

The microstructure of catalyst layers (CLs) plays a crucial role in determining the performance and durability of membrane electrode assemblies (MEAs) in proton exchange membrane fuel cells (PEMFCs). The microstructure substantially influences electrochemical reactions occurring at CLs due to the effect of triple-phase boundary formed by the physicochemical interaction of electrocatalyst, ionomer binder, and dispersing solvent. In catalyst inks comprising of the aforementioned three main components, dispersing solvents could be a key parameter for the formation of the optimal microstructure. In this study, the effect of the solvents in ionomer dispersions on the performance and durability of CLs for PEMFCs is investigated. Commercially available (water based) and laboratory-made (glycol based) ionomer dispersions are used. As a result, the physicochemical and electrochemical evaluation of the MEAs using glycol solvent based ionomer dispersions shows the thinner ionomer layer surrounding electrocatalyst and the crack-free surface of CLs, compared with that of the MEA using water based ionomer dispersion as expected. Among the MEAs using various glycol solvent based ionomer dispersions, ethylene glycol based ionomer dispersion results in the highest mobility of the main chain of ionomer in the corresponding solvent and the highest performance and durability for PEMFCs due to the lowest viscosity. This study provides useful knowledge in the selection of dispersing solvents for CLs with enhanced performance and durability in PEMFCs.