A Rheo-Impedance investigation on the interparticle interactions in the catalyst ink and its impact on electrode network formation in a proton exchange membrane fuel cell

The performance of a proton exchange membrane fuel cell is highly dependent on the microstructure of the catalyst layer. The catalyst layer consists of a network of platinum supported by carbon particles mixed with an ion-conductive ionomer. Optimum coverage of ionomer on catalyst is essential in providing proton conductive pathways while maintaining minimal oxygen transport resistance. Considering that most of the catalyst and ionomer interactions occur as a result of ink formulation and evolution during the high-shear coating process, a new methodology involving a combination of ink flow properties and electrochemical impedance spectroscopy is introduced to study interparticle interactions in catalyst ink. Five ink samples with ionomer-to-carbon ratios ranging from 0 to 1 are used to investigate the interplay between ionomer and catalyst. The flow and impedance properties of the ink are measured simultaneously to investigate the agglomerate characteristics and the percolation of conductive catalyst in the catalyst ink, while fixing the carbon to solvent ratio. This study successfully demonstrate the effectiveness of the newly developed characterization tools, which can be used for evaluating new materials and processing parameters. The insights gained from this study can be applied to optimize the triple-phase-boundaries and form efficient electrode structure with low Pt loading to enhance overall fuel cell performance.