Impact of Pre-Exchanging Anion-Exchange Polymer for Water Electrolysis and Fuel Cell Applications

Pretreatment of anion-exchange membranes (AEMs) prior to their use in AEM fuel cells (AEMFCs) and AEM water electrolyzers (AEMWEs) is typically required to replace the anions with hydroxide (OH–). Herein, hexamethyl-p-terphenyl poly(benzimidazolium) iodide (HMT-PMBI) (I–) was used as a model AEM to investigate the exchange process. The exchanging solution (containing I–, released from AEMs) was first examined by silver ions, where we found that no more precipitates can be visually observed after 3 exchanges. Moreover, we developed a quantitative method based on UV–vis spectroscopy, which is able to show that ∼61, 84, and 87% of the original I– was removed after 1, 2, and 3 exchanges in 3 M KOH. In operando electrochemical studies revealed that current–voltage characteristics of AEMFCs are sensitive to residual iodide within the membrane, requiring at least three exchange cycles (>90% removal of iodide) to reach maximum performance. In contrast, AEMWEs are less sensitive to the exchange process, with trace iodide being effectively flushed during electrolysis.