Previous ionomer adsorption (Figure 1) explorations in our group have shown significantly lower adsorption (lower K_eq) of ionomer when platinum (Pt) nanoparticles are present on the carbon support.¹ Such differences can suggest a higher affinity of the polymer chain to carbon, which could suggest that acidic groups on the carbon surface might participate in hydrogen bonding on dipole-dipole interactions with the hydrophilic unit in the polymer.^1,2 This disagrees with many recent suggestions that the interactions with ionomer are driven by specifc adsorption of sulfonic acid or sulfonate on the Pt. Understanding such interactions can be key to further improve the Pt/Carbon/ionomer electrodes structure and, consequently, proton exchange membrane fuel cell (PEMFC) performance.

In this study, the adsorption of ionomer on a series of Pt:C (0:100, 30:70, 50:50 and 70:30) ratios using Vulcan XC-72 Carbon and Ketjenblack (KJB) supports were evaluated to further understand this interaction. The adsorption properties of water-dissolved 3M 825 equivalent-weight (EW) ionomer on both the carbon supports and the series of carbon-supported platinum (Pt/C) catalysts were studied with 400 MHz ¹⁹F Nuclear Magnetic Resonance Spectroscopy (NMR) and Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES).

A detailed structure characterization of the pristine supports and catalyst materials was achieved through Brunauer-Emmet-Teller (BET) nitrogen adsorption-desorption, transmission electron microscopy (TEM) and X-ray diffraction (XRD). The adsorbed ionomer structure was also explored through NMR and Fourier-Transform Infrared (FTIR).

These results will be reported along with context from other studies of ionomer-supported catalyst interactions in the actual catalyst layer.

Acknowledgements

NMC gratefully acknowledges the support from a Fulbright Fellowship as well as the Office of Naval Research. Research was supported at ORNL by the Fuel Cell Technologies Office, Office of Energy Efficiency and Renewable Energy, U.S. Department of Energy.

References

1. N. M. Cantillo, L. Li, J. Peng, G. A. Goenaga, and Thomas A. Zawodzinski ECS Trans., 80, 259–268 (2017) http://ecst.ecsdl.org/content/80/8/259.full.pdf.
2. S. Ma, Q. Chen, F. H. Jøgensen, P. C. Stein, and E. M. Skou, Solid State Ionics, 178, 1568–1575 (2007).