High-temperature polymer electrolyte membrane (HT-PEM) electrochemical hydrogen pumps (EHPs) are an enticing platform for hydrogen recovery, compression, and separation from gas mixtures(1). The electrodes used in HT-PEM EHPs often use poly(tetrafluoroethylene) (PTFE) as an electrode binder. PTFE is not conductive; and thus, it results in poor platinum electrocatalyst utilization in HT-PEM EHPs. This leads to excessive platinum group metal (PGM) loadings in the electrodes to facilitate high current density values (e.g., &gt; 1 A cm-2) and to compensate for the poor PGM utilization. Inspired by recent work by Los Alamos National Laboratory showing that poly(pentafluorostyrene-co-tetrafluorostyrene phosphonic acid) (PTFSPA) blended with Nafion® (a perfluorosulfonic acid (PFSA) ionomer) yields exceptional HT-PEM fuel cell performance(2), we have examined the thin film electrochemical properties of various phosphonic acid and PTFSPA blends on interdigitated electrode arrays decorated with a thin film of nanoscale PGM electrocatalyst(3, 4). Our current results have revealed the following: 1.) Aquivion®, a short-side chain PFSA blended with PTFSPA, yields higher ionic conductivity and great thin film EHP current density on IDEs when compared to Nafion® blended with PTFSPA. 2.) PFSA prevents anhydride formation and promotes ionic conductivity in a variety of phosphonic acid ionomers including poly(vinyl phosphonic acid) (PVPA) and poly(vinyl benzyl phosphonic acid) (PVBPA) in addition to PTFSPA. Fabricating a membrane electrode assembly (MEA) using our ion-pair HT-PEM, we demonstrate a EHP that can operate at 4 A cm-2 at 1 V.

High-temperature electrode ionomer binders for electrochemical hydrogen pumps

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