This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Researchers from Kanazawa University, the University of Tokyo and HORIBA, Ltd. have shown that the initial state of platinum-on-carbon (Pt/C) catalyst particles before they are mixed with an ionomer strongly influences how a polymer electrolyte fuel cell (PEFC) catalyst ink subsequently develops. The paper is published in the Chemical Engineering Journal.
Catalyst layers are among the most important components of PEFCs because the electrochemical reactions responsible for power generation occur there. They are commonly fabricated from catalyst inks containing Pt/C catalyst, ionomer and solvents. In Pt/C catalysts, platinum nanoparticles are supported—that is, finely dispersed and immobilized—on the surface of carbon particles.
Previous studies of catalyst-ink preparation have mainly focused on factors such as solvent composition, ionomer content, dispersion method and mixing time. However, much less attention has been paid to the state of the Pt/C catalyst before the ionomer is added. The research team therefore introduced a controlled pre-mixing step in which Pt/C catalyst was mixed with deionized water for different periods before ionomer addition.
This produced different initial Pt/C aggregate states. After adding the ionomer and ethanol, the researchers prepared catalyst inks using different main-mixing times and evaluated their particle-size distributions, rheological properties, elemental composition by SEM-EDX and electrochemical surface area (ECSA). Without pre-mixing, the Pt/C catalyst initially contained relatively large agglomerates.
These structures were gradually broken down during subsequent main mixing, and the ECSA increased as mixing continued. In contrast, short-time pre-mixing produced smaller and relatively uniform Pt/C aggregates before ionomer addition. This initial state facilitated subsequent dispersion, and the highest ECSA in the study, 64.42 m² gPt−1, was obtained after 1 hour of main mixing.
Long-time pre-mixing produced a broader particle-size distribution consistent with re-agglomeration. Even after prolonged main mixing, a fraction of the larger Pt/C structures remained resistant to further breakup. The combined particle-size, rheological, SEM-EDX and electrochemical results indicate that these persistent structures limited the electrochemical accessibility of Pt surfaces and resulted in lower ECSA.
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