Morphology Evolution and Adsorption Behavior of Ionomers from Solution to Pt/C Substrates

Coarse-grained molecular dynamics simulations were performed to understand the morphological evolution and adsorption mechanism of Nafion ionomers from the aqueous solutions to the Pt/C substrate surface under various solution compositions and substrate properties. We found that the ionomer coverage did not increase with the increasing ionomer-to-carbon ratio but was related to the size and concentration of the ionomer aggregates, following the Langmuir adsorption model that shows a wettability switching behavior due to their changed morphology from solution to the surface. Ionomer aggregates in the solution tended to unfold and spread on the carbon substrate rather than Pt particles, although the cylindrical ionomer aggregates were easily attracted by Pt particles initially due to their hydrophilic ionic shells. The smaller Pt particles had a greater effect on ionomer adsorption. With the increasing number of Pt particles, ionomer coverage increased first and then decreased, depending on whether there was enough carbon surface to anchor the ionomer backbone. A balanced Pt/C ratio and the appropriate distribution of the Pt particles were required for tuning the ionomer coverage and distribution toward the design of the catalyst ink structure to improve the power performance.

Automated summary

Morphological evolution and adsorption mechanism of Nafion ionomers from aqueous solutions to Pt/C substrate surface were studied through coarse-grained molecular dynamics simulations. The coverage and distribution of ionomers were found to be influenced by the size and concentration of ionomer aggregates, requiring a balanced Pt/C ratio and appropriate distribution of Pt particles for optimal catalyst ink structure design and power performance improvement.