Pt-Ta-Co Electrocatalysts for Polymer Electrolyte Fuel Cells

Abstract

Introduction Electrocatalysts with both high catalytic activity and high potential cycling durability are required for polymer electrolyte fuel cells. It is of technological interest to develop electrocatalysts using mesoporous carbon as a support framework and Pt-Ta-Co as a catalyst. Fuel cells using this novel electrocatalyst have to be prepared to evaluate their electrochemical performance. Here in this study, we aim to examine polymer electrolyte fuel cells using these new electrocatalysts by evaluating the current-voltage characteristics and various overvoltages under different electrocatalyst layer preparation conditions such as ionomer and solid contents. Experimental A novel electrocatalyst (Pt0.7Ta0.2Co0.1/MC) was prepared by loading Pt-Ta-Co catalyst onto mesoporous carbon as a support framework by the acac method [1]. MEAs with Pt/C (TEC10E50E, Tanaka Kikinzoku Kogyo, Japan) as the anode electrocatalyst layer and a new electrocatalyst as the cathode electrocatalyst layer were prepared by spray printing. The cathode electrocatalyst layer was deposited with various ionomer and solid contents, and fabrication conditions of other cells were based on previous conditions [2]. The MEAs prepared were subjected to performance tests and overvoltage separation. Their cell performance was analyzed by subsequent microstructural observation using field emission scanning electron microscopy (FE-SEM). Results and discussion Figure 1 shows cell voltage of MEAs with the new electrocatalyst with various ionomer contents under operating conditions of 80°C and 100% relative humidity. In the preparation of the cathode electrocatalyst layer using the new electrocatalyst, it was found that relatively high performance was obtained at the solid content of 3.5 wt.% and ionomer content of 35 wt.%. The solid content of 3.5 wt.% was found to exhibit higher performance than that of 5 wt.%. Although the new electrocatalyst was highly active on the half-cell level, its electrochemical performance in a single cell has still lower than that of the cell fabricated using the standard Pt/C (TEC10E50E) for both electrodes. The concentration overvoltage was particularly high, as shown in Fig. 2, and microstructural observations revealed issues related to the microstructure of the electrocatalyst layer. Further improvement of cell performance has to be made through detailed analysis and optimization of the microstructure of the electrocatalyst layers such as their porosity. Acknowledgments This paper is based on results obtained from a project, JPNP20003, commissioned by the New Energy and Industrial Technology Development Organization (NEDO). References A. Hayashi, H. Notsu, K. Kimijima, J. Miyamoto, and I. Yagi, Electrochim. Acta, 53, 6117–6125 (2008).T. Ogawa, Y. Inoue, K. Yamamoto, M. Yasutake, Z. Noda, S. M. Lyth, J. Matsuda, M. Nishihara,Hayashi, and K. Sasaki, ECS Trans., 109 (9), 241 (2022). Figure 1