State-of-the-art polymer electrolyte fuel cells rely on platinum (Pt) or Pt-alloy on carbon supports mixed with ionomer for high power density. The high Pt loading in the cathode is still a barrier for commercialization of PEFCs. Conventional electrodes are fabricated in an uncontrolled ink deposition process that produces random aggregates of catalyst, ionomer, and pore volume (1). The high tortuosity and poor percolation of ionomer in these random aggregates cause low effective conductivity, requiring the use of high ionomer content to minimize Ohmic losses due to proton conduction. This causes severe mass transport limitations during high current density operation and requires a higher loading of Pt to meet the performance targets. The diffusion of reactants through the thick ionomer film adds an additional transport resistance and becomes significant at lower Pt loadings (2). The ionomer also poisons the surface of the catalyst, reducing the activity of the catalyst. Decreasing the negative effects of ionomer films would enable a significant increase in performance.

In our previous work, we have shown that aligned Nafion pillars in the cathode catalyst layer can improve ionic conductivity enabling reduction of ionomer in the catalyst layer (3). In this work, we present a novel electrode architecture where the three functional domains (catalyst, ionomer, and pore) are separated and aligned vertically as shown in Figure 1a. Pt nanofilm is coated surrounding the Nafion nanowire to fabricate a coaxial nanowire electrode. Figure 1b. shows the High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image of the coaxial nanowire electrode. The pore domain provides an additional modifiable parameter to control the wettability of the electrode.

Acknowledgments

This research is supported by DOE Fuel Cell Technologies Office, through the Fuel Cell Performance and Durability (FC-PAD) Consortium; Technology manager: Greg Kleen.

References

1. S. Litster and G. McLean, Journal of Power Sources, 130, 61 (2004).
2. N. Nonoyama, S. Okazaki, A. Z. Weber, Y. Ikogi and T. Yoshida, Journal of The Electrochemical Society, 158, B416 (2011).
3. S. K. Babu, J. S. Spendelow and R. L. Borup, in Meeting Abstracts, p. 1385 (2017).