Development of Polymer Electrolyte Membranes for Electrochemical Energy Conversion Technology

C. Bae
Rensselaer Polytechnic Institute,
United States

Keywords: polymer, ionomer, materials

Summary:

Anion exchange membranes (AEMs) based on hydroxide-conducting polymers (HCPs) are a key component for anion-based electrochemical energy technology such as fuel cells, electrolyzers, and advanced batteries. Although these alkaline electrochemical applications offer a promising alternative to acidic proton exchange membrane electrochemical devices, access to alkaline-stable and high-performing polymer electrolyte materials has remained elusive until now. Despite vigorous research of AEM polymer design, examples of high-performance polymers with good alkaline stability at an elevated temperature are uncommon. Traditional aromatic polymers used in AEM applications contain a heteroatomic backbone linkage which is prone to degradation via nucleophilic attack by hydroxide ion. To date, one of the main bottlenecks for AEM fuel cells and electrolyzers development has been a lack of standard AEMs that can meet the multiple concurrent requirements of (i) high hydroxide ion conductivity/low area-specific resistance, (ii) good alkaline stability at high temperature, (iii) robust mechanical properties, (iv) convenient synthetic scalability, (v) good solubility in common solvents which is important for device processability in practical applications (Figure 1). In this presentation, we highlight some of the progress our group has made in the development of advanced HCPs for applications in AEMs and electrode ionomers. We propose that a synthetic polymer design with provides an effective solution to the problem of alkaline stability. Because of an all C−C bond backbone and a flexible chain-tethered quaternary ammonium group the critical demand for such a polymer system, we have established new synthetic strategies for polymer functionalization and polycondensation using an acid catalyst. The advantage of good solvent processability and convenient scalability of the reaction process generates considerable interest in these polymers as commercial standard AEM candidates. AEM fuel cell and electrolyzer tests of some of the developed polymer membranes showed excellent performance, suggesting that this new class of HCPs opens a new avenue to electrochemical devices with real-world applications.