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

Abstract

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-pterphenyl 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.