Control of Cluster Structures in Catalyst Inks by a Dispersion Medium

Area of Science:

• Electrochemistry
• Materials Science
• Chemical Engineering

Background:

• Proton exchange membrane fuel cell (PEMFC) performance is critically dependent on catalyst ink cluster structure.
• Ink composition, including solvent, ionomer, and catalyst, dictates cluster formation and subsequent catalyst layer properties.
• Optimizing catalyst layer microstructure and morphology is key to enhancing conductivity for protons, electrons, and water.

Purpose of the Study:

• To investigate the impact of solvent composition on ionomer cluster structure in PEMFC catalyst ink.
• To understand how different alcohols affect ionomer dissolution, ink rheology, and cluster formation.
• To correlate ink properties with potential improvements in catalyst layer performance.

Main Methods:

• Characterization of ionomer dissolution using relative viscosity, ζ-potential, effective proton fraction, and NMR spectroscopy.
• Rheological testing (viscosity, amplitude scanning) of catalyst inks with varying solvent compositions and solid content.
• Analysis of cluster size and network structure evolution under different conditions.

Main Results:

• Alcohol-water solutions promote ionomer chain stretching, resulting in smaller ionomer clusters compared to pure water.
• Pure water inks exhibit larger clusters and stronger network structures, which can rapidly reform after shear.
• Alcohols create smaller, more brittle clusters that slowly recombine post-disruption; ethanol yields the smallest clusters and weakest network.

Conclusions:

• Reducing solid content significantly weakens the ink's network structure, promoting cluster dispersion.
• Smaller alcohol molecules and more dispersed ionomers are beneficial for achieving a well-dispersed cluster structure in the ink.
• Optimized ink formulation is crucial for enhancing PEMFC catalyst layer conductivity and overall performance.