Abstract
Introduction One of the key components of polymer electrolyte fuel cells (PEFCs) is the polymer electrolyte membrane (PEM). The PEM facilitates the transport of protons from the anode to the cathode, acts as an electronic insulator to prevent short circuits, and plays a role in preventing the direct reaction of hydrogen gas and oxygen in air. One of the major technical issues with PEMs is their chemical degradation, causing decomposition of their molecular structure. This leads to reduced protonic conductivity, increased hydrogen and oxygen crossover, and reduced mechanical strength, all of which significantly affect the power generation performance and durability of PEFCs (1). In addition, in our laboratory, the use of SnO2 and mesoporous carbon (MC) as cathode catalyst supports has been suggested to suppress membrane degradation (2). However, the relationship between the cathode catalyst materials and the chemical degradation of PEM has not yet been fully understood. Here in this study, we conduct durability tests such as accelerated chemical degradation of PEM in cells using cathode electrocatalysts with different carbon support materials, aiming to clarify the effects of carbon support materials properties (structure, contaminants, and graphitization) on the chemical degradation of electrolyte membranes. Experimental A commercial Pt/KB catalyst (TEC10E50E, Tanaka Kikinzoku Kogyo, Japan) was used as the anode catalyst. Several types of cathode catalysts were applied and compared: the commercial Pt/KB; Pt/MC where Pt was directly deposited on the MC; and various electrocatalysts where Pt was directly deposited on carbon supports such as graphitized AB (acetylene black). The durability test at open circuit voltage (OCV) was performed for 100 h. Before and after the durability test, cell performance, hydrogen crossover current density, and electrochemical surface area (ECSA) were characterized. The degree of membrane degradation was evaluated by measuring fluoride-ion emission rate (FER) by ion chromatography, and membrane thickness by cross-sectional observation with a focused-ion-beam scanning electron microscope (FIB-SEM), as illustrated in Fig.1. Moreover, contaminants and graphitization of the carbon support materials were also analyzed, and their relationship to membrane degradation was considered. Results and discussion The results of OCV holding tests up to 100 h for four different MEAs are shown in Fig. 2. The voltage drop in using Pt/MC as cathode catalysts was smaller than that in using Pt/KB. The FER of Pt/MC as cathode catalysts was lower than that of Pt/KB as shown in Fig. 3, suggesting that the use of MC as carbon supports may suppress PEM degradation. In this presentation, we will show the effects of carbon support materials properties (structure, contaminants, and graphitization) in cathode catalysts on PEM degradation, and discuss possible mechanisms based on the characteristics of various carbon supports. Acknowledgements 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) through the program “Adopting Sustainable Partnerships for Innovative Research Ecosystem” (ASPIRE), Grant Number JPMJAP2307. The presenting author (S. Nakamura) is supported by the Miyamoto Jun-ichi Hydrogen Research Award, and the Kyushu University Q-PIT Support Program for Young Researchers and Doctoral Students. References M. Zatoń, J. Rozière, and D. J. Jones, Sustain. Energy Fuels, 1, 409 (2017).S. Nakamura, T. Ogawa, Z. Gautama, Z. Noda, M. Yasutake, S. M. Lyth, J. Matsuda, A. Hayashi, M. Nishihara, and K. Sasaki, ECS Trans., 112 (4), 315 (2023). Figure 1
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