(Invited) Highly Durable and Active Electrocatalysts Using SnO2 Supports for Polymer Electrolyte Fuel Cells
Authors: Kakinuma Katsuyoshi , Uchida Makoto , Iiyama Akihiro 
Published: December 2020

Toward the widespread use of polymer electrolyte fuel cells (PEFCs) in electric vehicles, highly durable and active catalysts are required. Pt catalysts loaded on high surface area carbon blacks are promising candidate catalysts with high oxygen reduction reaction (ORR) activity [1]. In the future, the improvement of the catalyst durability is also desired for PEFCs for heavy use applications. Alternative candidate catalysts with high activity and high durability, during both startup/shutdown and load cycling, are Pt catalysts supported on non-carbon ceramic supports [2,3]. Our group confirmed that Pt catalysts supported on SnO2 (Pt/M-SnO2, M = Nb, Ta) without carbon additive were superior in ORR activity and durability (startup/shutdown, load cycling) to those of commercial Pt catalysts, e.g., supported on either graphitized carbon black (Pt/GCB, TEC10EA30E, TKK) or carbon black (Pt/CB, TEC10E30E, TKK), by evaluation of membrane-electrode assemblies [4-8]. The non-carbon support of SnO2 nanoparticles has a unique carbon-like microstructure consisting of a fused-aggregate network structure, which enhances the electronically conducting pathways via the aggregated microstructure and gas diffusion pathways via the open pores in the microstructure. In addition, the interface control between Pt and SnO2 support also affects the decrease of both the overpotential for the ORR and the resistance of the cathode catalyst layer (CL). We have also proposed ways to design the three-phase boundary within the CL to diminish the gas diffusion resistance (Fig. 2). The cell performance using the Pt/SnO2 cathode CL at operating temperatures from 80oC to 120oC is quite promising for the development of high power density with simultaneous high durability.

Acknowledgments

This work was partially supported by funds for the “Superlative, Stable, and Scalable Performance Fuel Cell” (SPer-FC) project and the “Advanced Research Program for Energy and Environmental Technologies” from the New Energy and Industrial Technology Development Organization (NEDO) of Japan, and JSPS KAKENHI Grant Number (B24350093, B17H03410) from the Ministry of Education, Culture, Sports, Science and Technology.

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Figure 1