A Tantalum-Rich Pt-Ta-Co Electrocatalyst for Polymer Electrolyte Fuel Cells
Authors: Sanami Kojiro , Kubo Kakeru , Miyamoto Ryo , Yasutake Masahiro , Noda Zhiyun , Lyth Stephen Matthew , Matsuda Junko , Sasaki Kazunari 
Published: December 2024

Abstract

Wide-spread use of fuel cell vehicles (FCVs) requires both high activity and high durability of catalysts for PEFCs. Especially, significant performance and durability improvement is required for application to heavy duty vehicles (HDVs) [1]. A variety of catalysts, such as Pt-Co alloy catalysts, have been studied and developed to increase catalytic activity, but further improvement is desirable for HDV applications [2]. Here in this study, we aim to improve performance and durability of Pt-Co catalysts by adding tantalum, which is stable under strongly-acidic PEFC conditions. Compared to catalysts on Ta-based catalyst support with a similar composition [3], Pt-Ta-Co catalysts are advantageous if these three elements (Pt, Ta, and Co) are loaded at the same time to prepare both catalyst support and alloy catalyst. Various Pt-Ta-Co catalysts (such as Pt:Ta:Co = 7:2:1)[4] were found to be superior to Pt catalyst with respect to degradation caused by load fluctuation. However, in PEFCs for FCVs, the degradation of the carbon support due to start-stop cycles has also to be suppressed [5]. In this study, Ta-rich catalysts (Pt:Ta:Co = 3:4:1, 3:2:1) were prepared by increasing the amount of Ta to Pt-Co to improve the durability against start-stop cycles. These Ta-rich compositions may minimize direct contact between Pt and carbon support by the separation to the Pt-Co and Ta-rich phases in the catalyst particles, forming a nanocomposite during the preparation process.
Platinum acetylacetonate, tantalum ethoxide, and cobalt nitrate hydrate were used as precursors for catalyst preparation. These precursors were mixed with a dispersion in which mesoporous carbon (MC) support (MH-18, Toyo Tanso, Japan) was dispersed, dried, and heat-treated. The catalysts prepared were characterized by microstructural observation by STEM, and their electrochemical performance was evaluated.
In Pt3Ta4Co1/MC, STEM images with EDS mapping in Figure 1 confirmed the presence of a Ta-rich phase around Pt-based catalysts, indicating the formation of nanocomposites. The initial performance of prepared catalysts (ECSA≈100 m2/g, MA≈600 A/g) measured by half-cell electrochemical measurements was better than the standard Pt/C catalyst (TEC10E50E, Tanaka Kikinzoku Kogyo, ECSA≈80 m2/g, MA≈250 A/g). In this presentation, load cycle durability measured by half-cell electrochemical measurements and start-stop cycle durability measured by MEA tests will also be presented and discussed.

Acknowledgment

This paper is based on results obtained from a project, JPNP20003, commissioned by the New Energy and Industrial Technology Development Organization (NEDO). An educational part for young scientists was supported by the Japan Science and Technology Agency (JST) as a part of Adopting Sustainable Partnerships for Innovative Research Ecosystem (ASPIRE), Grant Number JPMJAP2307.

Reference

A. Cullen, K. C. Neyerlin, R. K. Ahluwalia, R. Mukundan, K. L. More, R. L. Borup, A. Z. Weber, D. J. Myers, and A. Kusoglu, Nat. Energy, 6, 462 (2021).

Janssen, P. Weber, and M. Oezalan, Current Opinion in Electrochem., 40, 101337 (2023).

Sanami, R. Nishiizumi, M. Masahiro, Z. Noda, S. M. Lyth, J. Matsuda, A. Hayashi, and K. Sasaki, ECS Trans., 112 (4), 369 (2023).

Miyamoto, T. Ogawa, R. Nishiizumi, M. Masahiro, Z. Noda, M. Nishihara, A. Hayashi, J. Matsuda, and K. Sasaki, ECS Trans., 112 (4), 353 (2023).

M. Roen, C. H. Paik, and T. D. Jarvi, Electrochem. Solid-State Lett., 7, A19 (2004).

Figure 1