(Industrial Electrochemistry and Electrochemical Engineering Division H. H. Dow Memorial Student Achievement Award Address) Anion Exchange and Bipolar Membranes for Electrochemical Energy Conversion and Storage

Abstract

Ion-conducting membranes play a central role in electrochemical devices. The rise in anion exchange membrane fuel cell (AEMFC) research is attributed to the viability of using platinum-group-metal free electrocatalysts for hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR).1 However, there are two major obstacles to apply anion exchange membranes (AEMs) as separators in alkaline electrochemical energy conversion devices. The first challenge is to develop the AEM with hydroxide ion conductivities above 100 mS/cm at 70 °C. The second challenge is to synthesize stable AEM (especially stable cationic head-groups) that exhibit high durability in strongly alkaline environments (e.g. in the presence of nucleophilic OH- ions). To solve the first problem, a triblock copolymer-based polymer backbone has been developed to synthesize AEMs with high ion conductivities by engineering a phase-separated morphology. To address the second problem, cycloaliphatic quaternary ammonium based AEM have been prepared that demonstrate excellent alkaline stability.Except for the performance of the separator, there are other factors including the design of electrocatalysts for HOR and ORR, and the structure of catalyst layer contributes to overall fuel cell performance. Herein, significant amount of effort has been made to better design the ionomer/electrocatalysts interface and to better understand the transport of the ionomer in confined regime. The use of a pH-gradient-enabled microscale bipolar interface (PMBI) to effectively separate the anolyte and catholyte of a direct borohydride/ hydrogen peroxide liquid fuel cell (DBFC) has been engineered and demonstrated, which enables record high DBFC performance. 2 The PMBI-type electrodes provide a new and fascinating design to engineer fuel-cell membrane electrode assemblies. Interdigitated electrode arrays (IDEs) have been developed as a platform for highly sensitive electrochemical measurements of polymer thin film with thickness of less than 100 nm.3 The IDEs coupled with electrochemical impedance spectroscopy (EIS) has been demonstrated as an effective platform to probe ion transport of polymer thin film, which provide direct translation to the design of the ionomer in fuel cell. References (1) Arges, C. G.; Zhang, L. Anion Exchange Membranes’ Evolution toward High Hydroxide Ion Conductivity and Alkaline Resiliency. ACS Applied Energy Materials 2018, 1 (7), 2991-3012, DOI: 10.1021/acsaem.8b00387.(2) Wang, Z.; Parrondo, J.; He, C.; Sankarasubramanian, S.; Ramani, V. Efficient pH-gradient-enabled microscale bipolar interfaces in direct borohydride fuel cells. Nature Energy 2019, DOI: 10.1038/s41560-019-0330-5.(3) Sharon, D.; Bennington, P.; Liu, C.; Kambe, Y.; Dong, B. X.; Burnett, V. F.; Dolejsi, M.; Grocke, G.; Patel, S. N.; Nealey, P. F. Interrogation of Electrochemical Properties of Polymer Electrolyte Thin Films with Interdigitated Electrodes. J Electrochem Soc 2018, 165 (16), H1028-H1039, DOI: 10.1149/2.0291816jes.