Connected Platinum–Based Catalysts and Carbon-Free Cathode Catalyst Layers for High-Performance PEFCs
Authors: Kuroki Hidenori , Sasaki Kento , Liao Qiancheng , Yamaguchi Takeo 
Published: December 2024

The improvement of the activity and durability of Pt-based electrocatalysts for oxygen reduction reaction (ORR) is essential to realize the widespread uses of polymer electrolyte fuel cells (PEFCs). Our group has developed a carbon-free connected Pt1–Fe1 catalyst with a chemically ordered superlattice structure.1–7 This catalyst consists of a beaded nanonetwork (5–15 nm) by the connection of Pt1–Fe1 nanoparticles with high electrical conductivity, thus eliminating the need for a carbon support. The connected Pt1–Fe1 catalyst exhibits an ORR specific activity about 10 times higher than a commercial Pt/C catalyst. This catalyst with carbon-free and chemically ordered structures improves the durability against start/stop and load cycles.1,4 Furthermore, the carbon-free catalyst layer using the connected Pt1–Fe1 catalyst with a porous, hollow capsule structure has high porosity (> 80%) and thin thickness (~ 1 μm), which would be beneficial for oxygen transport.
To advance connected nanoparticle catalysts, this study addressed structural control of connected Pt-based catalysts and carbon-free catalyst layers using the developed catalysts. Since Fe ions induce the Fenton reaction and accelerate the degradation of electrolyte polymers, carbon-free and iron-free connected Pt3–Co1 catalysts with chemically ordered structures (Figure 1a) were developed using our silica coating method.4 The investigation of the structural effects on ORR performances in 0.1 M HClO4 electrolyte solution indicated that higher ordered degrees of the connected Pt3–Co1 catalysts improved ORR specific activity and load cycle durability. The STEM-EDX line mapping results suggested that a highly ordered structure can greatly suppress metal leaching from the catalyst. Furthermore, as shown in Figure 1b, this study investigated the structural effects on fuel cell performances for the carbon-free cathode catalyst layers. Here, the connected Pt3–Co1 catalyst with a hollow capsule structure was used, and the structural parameters such as ionomer thickness on capsules, capsule size, etc. were controlled. This presentation will discuss the relationship between catalyst layer structures and fuel cell performances through electrochemical and oxygen transport analyses. The developed connected Pt-based catalysts and the findings obtained in this study will contribute greatly to the design of a carbon-free cathode catalyst layer to achieve enhanced PEFC performances.

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

References

Kuroki, T. Yamaguchi et al., [1] Energy Environ. Sci., 8, 3545–3549 (2015). [2] J. Electrochem. Soc., 163, F927–F932 (2016). [3] ACS Appl. Energy Mater., 1, 324–330 (2018). [4] ACS Appl. Nano Mater., 3, 9912–9923 (2020). [5] ACS Appl. Energy Mater., 5, 13176–13188 (2022). [6] J. Chem. Eng. Jpn., 56, 2197946 (2023). [7] Jpn. J. Appl. Phys., 63, 048002 (2024).

Figure 1