Impact of Pre-Exchanging\nAnion-Exchange Polymer for\nWater Electrolysis and Fuel Cell Applications

Pretreatment of anion-exchange membranes\n(AEMs) prior to their\nuse in AEM fuel cells (AEMFCs) and AEM water electrolyzers (AEMWEs)\nis typically required to replace the anions with hydroxide (OH<sup>–</sup>). Herein, hexamethyl-<i>p</i>-terphenyl\npoly(benzimidazolium) iodide (HMT-PMBI) (I<sup>–</sup>) was\nused as a model AEM to investigate the exchange process. The exchanging\nsolution (containing I<sup>–</sup>, released from AEMs) was\nfirst examined by silver ions, where we found that no more precipitates\ncan be visually observed after 3 exchanges. Moreover, we developed\na quantitative method based on UV–vis spectroscopy, which is\nable to show that ∼61, 84, and 87% of the original I<sup>–</sup> was removed after 1, 2, and 3 exchanges in 3 M KOH. In operando\nelectrochemical studies revealed that current–voltage characteristics\nof AEMFCs are sensitive to residual iodide within the membrane, requiring\nat least three exchange cycles (>90% removal of iodide) to reach\nmaximum\nperformance. In contrast, AEMWEs are less sensitive to the exchange\nprocess, with trace iodide being effectively flushed during electrolysis.