Abstract
Polymer electrode fuel cells are fabricated by drying a ‘catalyst ink’, that is, a mixture of carbon, ionomers, Pt and water, and it is of particular importance to elucidate the structural evolution of the catalyst ink during its drying process. The structural evolution of catalyst ink was investigated by contrast-variation small-angle neutron scattering. The scattering functions of the catalyst ink at various concentrations were successfully decomposed to the corresponding partial structure factors SCC(q), SPP(q) and SCP(q) for all ink concentrations, where the subscripts C and P denote the carbon and polymer, respectively, and q is the magnitude of the scattering vector. The cross term SCP(q) indicates that the microscopic structure of the catalyst ink retains the carbon agglomerates surrounded by an ionomer shell during the drying process. SCC(q) and SPP(q) indicate that a catalyst ink is formed with carbon agglomerates of core radius of ~42 nm and an ionomer shell of thickness >8 nm. Both the size of the carbon agglomerates and the thickness of the ionomer shells decrease with increasing ink concentration, which is attributed to the exclusion of solvent molecules from the carbon and ionomer agglomerates during the drying process.
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Acknowledgements
The SANS experiment was performed by using a 40 m SANS instrument at the High-flux Advanced Neutron Application Reactor (HANARO), Korea Atomic Energy Research Institute (KAERI), Daejeon, South Korea, which was transferred from SANS-U at JRR-3 with the approval of the Institute for Solid State Physics, The University of Tokyo (proposal no. 13596), Japan Atomic Energy Agency, Tokai, Japan. We are grateful to T. W. Kim and Y. S. Han for helpful assistance in the SANS experiments.
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Kusano, T., Hiroi, T., Amemiya, K. et al. Structural evolution of a catalyst ink for fuel cells during the drying process investigated by CV-SANS. Polym J 47, 546–555 (2015). https://doi.org/10.1038/pj.2015.36
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DOI: https://doi.org/10.1038/pj.2015.36
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