The Effect of Pt Catalysts with Controlled Hydrophilicity on the Surface on the Dispersibility of Ionomers and Durability in Polymer Electrolyte Fuel Cells
Authors: Nagamori Kiyotaka , Aoki Satoshi , Ikegawa Mayumi , Seki Yasuhiro , Igarashi Hiroshi , Tamoto Kayoko , Uchida Makoto 
Published: December 2024

Polymer electrolyte fuel cells (PEFCs) are attracting attention as a promising system that can generate electricity without emitting greenhouse gases such as CO2. In recent years, there has been growing interest in the use of FCVs for Heavy duty commercial vehicles(HDV) due to the relationship between cruising range, vehicle size, and fuel costs, and many manufacturers are actively pursuing development. HDV require high power density and a cruising range of over 1 million km on a single charge, and achieving this requires a large amount of platinum catalyst, so striking a balance between performance and durability is important1. The distribution of ionomers on the surface of the catalyst and within the catalyst layer is an important topic for improving performance, and has been clarified through extensive research, including the mechanism of activity reduction due to adsorption poisoning of Pt by sulfonic acid functional groups2,3 and the adsorption and occupation of Pt by ionomers deposited in the pores or on the outer surface of the support4,5. In order to discuss the dispersion of the ionomer on the catalyst surface, it is necessary to consider the balance of the surface conditions of the platinum and carbon support surface. We evaluated the effect of differences in hydrophilicity on the dispersion of ionomers by chemical treatment of the catalyst surface to give differences in hydrophilicity derived from the balance of functional groups and Pt oxides. Furthermore, assuming use under actual operating conditions, the impact of the hydrophilicity of the catalyst on durability was evaluated using water-generating load cycle durability test6.
We prepared a reference catalyst of 50% Pt/Ketjen EC300J (K-1), and then prepared K-2 and K-3 with different hydrophilicities using two different surface treatment methods.
K-2 was found to have excessive hydrophilicity, while K-3 had moderate hydrophilicity. Through surface treatment, we found that there were differences in the amount of hydrophilic functional groups and the amount of Pt oxide. In addition, we observed the dispersibility of the ionomers using a low-accelerate-voltage TEM, and found differences in the dispersibility of the ionomer layer on the catalyst surface and the pore blockage within the catalyst layer depending on the hydrophilicity. We achieved high dispersibility of the ionomers by appropriately controlling the hydrophilicity, as in K-3. In addition, the Pt utilization ratio (U
Pt) was measured using electrochemical measurements. K-3showed a high U
Pt with moderate hydrophilicity. In addition, in water-generating load cycle durability test, K-3 with moderate hydrophilicity showed high durability.
Based on this, it is expected that the surface condition of the catalyst can be appropriately controlled to promote improvements in the MEA structure, its performance, and durability. s durability.

Acknowledgement

This work was partially based on results obtained from a project, JPNP20003,
commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

References

1)D. A. Cullen, et al., Nat. Energy, 6, 462−474(2021).
2)K. Kodama, et al., ECS Trans., 58, 363−368(2013).
3)K. Kodama, et al., ACS Catal.,
8
, 694−700(2018).
4)Y. C. Park, et al., J. Power Sources, 315, 179−191(2016).
5)A. Kobayashi, et al., ACS Appl. Energy Mater., 4, 2307−2317(2021).
6)C. Takei, et al., J. Power Sources,
324, 729−737(2016).

Figure 1