Cathode catalysts of polymer electrolyte fuel cells (PEFCs) are subjected to a severe environment of strong acidity and high potential, leading to catalyst degradation^[1]. In particular, catalyst degradation in fuel cell vehicles is often caused by oxidative corrosion of their carbon support during start-stop cycles, and by dissolution and re-deposition of platinum particles during load cycles^[2]. Our research group has been studying nanocomposite catalysts (Pt-oxide) combining Pt with metal oxides (TiO₂, SnO₂) of a few nm in size, suppressing the aggregation and degradation of Pt catalysts during load cycles and also during start-stop cycles^[3]. Here in this study, we prepare nanocomposite catalysts using SnO₂ as a metal oxide, evaluate their electrochemical performance, and control support framework and heat treatment conditions to consider design guidelines for higher performance and durability of PEFC electrocatalysts.

Experimental

Pt-SnO₂ nanocomposite electrocatalysts were prepared by the acetylacetonate (acac) method^[4], in which Pt and Sn are loaded simultaneously to form nanocomposite of Pt and SnO₂. This study used mesoporous carbon (MC) with 10 nm diameter mesopores as a support framework to impregnate the nanocomposite within the mesopores. The loading of Pt-SnO₂ was 42 wt.%, and the volume ratio of Pt:SnO₂ was 1:2. Loadings of Pt and SnO₂ in the prepared Pt-SnO₂/MC were confirmed by Inductively coupled plasma atomic emission spectroscopy (ICP-AES) and TG analysis. Microstructure was observed by STEM. The initial activity and durability of the electrocatalysts were evaluated by half-cell measurements.

Results and discussion

ICP-AES and TG analysis of the prepared Pt-SnO₂/MC confirmed that Pt-SnO₂ nanocomposite was loaded at a volume ratio of Pt:SnO₂=1:2, which was close to the designated ratio. EDS elemental analysis confirmed the presence of Sn between the Pt particles, suggesting the formation of a nanocomposite structure. STEM microstructural observation confirmed that catalyst particles were loaded inside the mesopores besides on MC (agglomerate) surfaces. The ratio of internal particles was 55 %. The obtained catalyst was subjected to load cycle tests (100,000 cycles), and was found to be more durable in catalytic activity. In this presentation, electrochemical properties using related materials will be presented.

Acknowledgment

This research was partly supported by the New Energy and Industrial Technology Development Organization (NEDO).

References

[1] T. Takahashi, T. Ikeda, K. Murata, O. Hotaka, S. Hasegawa, Y. Tachikawa, M. Nishihara, J. Matsuda, T. Kitahara, S. M. Lyth, A. Hayashi, and K. Sasaki, J. Electrochem. Soc., 169, 044523 (2022).

[2] A. Ohma, K. Shinohara, A. Iiyama, T. Yoshida, and A. Daimaru, ECS Trans., 41, 775 (2011).

[3] T. Tonosako, D. Kawachino, Z. Noda, J. Matsuda, A. Hayashi, and K. Sasaki, ECS Trans., 92 (8), 493 (2019).

[4] A. Hayashi, H. Notsu, K. Kimijima, J. Miyamoto, and I. Yagi, Electrochim. Acta, 53, 6117 (2008).