Electrochemical Characteristics of Polymer Electrolyte Fuel Cells Using Pt-Ta-Co Electrocatalysts
Authors: Miyamoto Ryo , Sanami Kojiro , Suzuki Takashi , Kubo Kakeru , Yasutake Masahiro , Noda Zhiyun , Nishihara Masamichi , Matsuda Junko , Lyth Stephen Matthew , Sasaki Kazunari 
Published: December 2024

Introduction

Polymer electrolyte fuel cells need highly active and durable electrocatalysts. Our research group has developed Pt-Ta-Co-based electrocatalysts, achieving higher electrochemical performance (1,2). To evaluate and further improve cell performance using these new catalysts, this study aims to evaluate the current-voltage characteristics, various overvoltages, and potential cycle durability by varying preparation conditions of MEAs using the Pt-Ta-Co catalysts, and to clarify the materials design principles for higher power density, higher performance, and higher durability of polymer electrolyte fuel cells.

Experimental

A novel electrocatalyst (Pt7Ta2Co1/KB) was prepared by loading Pt-Ta-Co catalyst on Ketjenblack as a carbon support framework by using such as cobalt nitrate as precursors. MEAs with a standard Pt/C electrocatalyst (TEC10E50E, Tanaka Kikinzoku Kogyo, Japan) for the anode, and the alternative catalyst for the cathode, were prepared by spray printing (Nordson, USA). The cathode electrocatalyst layer was deposited with various ionomer and solid contents, while the other cells were prepared along with the previous conditions (1,2). The MEAs prepared were subjected to performance tests, start-stop cycle durability tests, and load cycle durability tests. Their cell performance was analyzed by overvoltage separation and subsequent microstructural observation using field-emission scanning electron microscopy (FE-SEM).

Results and discussion

Figure 1 shows IR-free cell voltage of MEAs with the new Pt-Ta-Co electrocatalyst under operating conditions of 80°C, 100% relative humidity, and 1.5 bar. In the preparation of the cathode electrocatalyst layer using the new electrocatalyst, it was found that high current-voltage characteristics were obtained at the solid content of 3.5 wt.% and the ionomer-to-carbon ratio (I/C) of 1.2. As shown in Figure 1, in the low current density region, IR-free cell voltage is about 0.83 V at 0.2 A cm-2, and in the low current density region, about 0.51 V at 3 A cm-2. These electrocatalysts were highly active on the half-cell level and its single cell performance was also superior to that using the standard Pt/C (TEC10E50E) for both electrodes.

As shown in Figures 2 and 3, the ECSA retention in the load cycle tests and the start-stop cycle test was higher than that of the Pt/C (TEC10E50E), suggesting that the addition of Ta contributes to suppressing the degradation of the electrocatalyst layer.

In the future, we will optimize various fabrication conditions such as the ratio of water to ethanol solvent during MEA fabrication to further improve the cell performance. We will also evaluate the cell performance of new electrocatalysts with different catalyst compositions.

Acknowledgments

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

References

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Figure 1