(Invited) Effect of Water Management in Membrane and Cathode Catalyst Layers on Suppressing the Performance Hysteresis Phenomenon in Anion-Exchange Membrane Fuel Cells

Abstract

Anion exchange membrane fuel cells (AEMFCs) are vulnerable to water management problems, since water is produced at the anode and consumed at the cathode. Previously we found severe voltage losses when increasing the current density in an AEMFC with a commercial Fe–N–Cp cathode catalyst and an in-house-developed anion exchange ionomer (quaternized poly(arylene perfluoroalkylene), i.e., QPAF-4, developed in this laboratory (Figure 1)1,2. In the present work,3 we have clearly identified the problem as being related to water management and developed two approaches to alleviating the problem: i) by use of a thin hydrophilized membrane, the diffusivity of water at the surface was improved, and the severe I–V hysteresis was suppressed, despite the cell using an Fe–N–Cp cathode catalyst with high-water absorption (Figs. 2a and 3a); ii) the voltage loss was also alleviated by the use of a recently developed Fe–N–Cc catalyst with higher hydrophobicity, which decreased the absorption of back-diffusing water into the catalyst layer and increased the amount of water supplied to the reaction sites. These improvements have demonstrated that water transport is the main limitation for the previously reported hysteresis and provide strategies to achieve higher performance AEMFCs through proper water management and formation of water transport pathways (Figs. 2b and 3b). Acknowledgements This project was partly supported by the New Energy and Industrial Technology Development Organization (NEDO) Japan through funds for the “Advanced Research Program for Energy and Environmental Technologies,” by the Japan Society for the Promotion of Science (JSPS) and the the Swiss National Science Foundation (SNSF) under the Joint Research Projects (JRPs) program, and by the Japan Science and Technology (JST) through the Strategic International Collaborative Research Program (SICORP). We are grateful to Pajarito Powder supplying the Fe–N-Cp catalyst. Also, we are deeply grateful to Dr. Weilin Xu and Dr. Ping Song of Changchun Institute of Applied Chemistry and Dr. Shuanjin Wang of Sun Yat-sen University for supplying the Fe–N-Cc catalyst, and to Takahata Precision Co. Ltd. for kindly providing the QPAF-4 membrane and ionomer. References H. Ono, T. Kimura, A. Takano, K. Asazawa, J. Miyake, J. Inukai, K. Miyatake, Robust anion conductive polymers containing perfluoroalkylene and pendant ammonium groups for high performance fuel cells, J. Mater. Chem. A 5 (2017) 24804–24812, https://doi.org/10.1039/c7ta09409d.K. Otsuji, N. Yokota, D. A. Tryk, K. Kakinuma, K. Miyatake, M. Uchida, Performance hysteresis phenomena of anion exchange membrane fuel cells using an Fe–N–C cathode catalyst and an in-house developed polymer electrolyte, J. Power Sources, 487 (2021) 229407, https://doi.org/10.1016/j.jpowsour.2020.229407K. Otsuji, Y. Shirase, T. Asakawa, N. Yokota, K. Nagase, W. Xu, P. Song, S. Wang, D. A. Tryk, K. Kakinuma, J. Inukai, K. Miyatake, M. Uchida, J. Power Sources, 522 (2022) 230997, https://doi.org/10.1016/j.jpowsour.2022.230997 Figure 1