Measuring the true hydroxide conductivity of anion exchange membranes

Authors: Avital Zhegur-Khais, Fabian Kubannek, Ulrike Krewer, Dario R. Dekel In this study, a CO2-in-situ purging technique was used to measure the true OH‾ conductivity of several anion exchange membranes (AEMs). During this process, membranes are in-situ de-carbonated allowing the AEMs to reach their full OH‾ form, and therefore to measure their highest (true) OH‾ conductivity. The de-carbonation process in all the studied AEMs was also investigated. The time constant of the de-carbonation process τ was calculated and related to the membrane properties as well as to the de-carbonation dynamics. The time constant of the de-carbonation process was found to decrease with

Authors: Pietro G. Santori, Abhishek N. Mondal, Dario R. Dekel, Frédéric Jaouen  Anion-exchange membrane fuel cells (AEMFCs) show remarkable and rapid progress in performance, significantly increasing the relevance for research on electrocatalysis of the oxygen reduction reaction (ORR) and hydrogen oxidation reaction (HOR) for this technology. Since much of the recent progress in AEMFC performance can be tied to the improved interface between anion-exchange ionomers (AEIs) and catalysts, this topic deserves specific attention. This work reports the ORR and HOR activity measured in rotating disk electrodes for several ionomer–catalyst combinations, involving five different AEIs and Nafion® and four ORR and HOR catalysts selected

Authors: Israel Zadok, Hai Long, Bryan Pivovar, Aleksandra Roznowska, Artur Michalak, Dario R. Dekel, Simcha Srebnik Understanding the behavior of hydroxide ions in aqueous and non-aqueous media is fundamental to many chemical, biological, and electrochemical processes. Research has primarily focused on a single fully solvated hydroxide ion, either as an isolated cluster or in bulk. This work presents the first computational study to consider hydroxide under low hydration levels in detail, where the anion may not be fully solvated. Under such conditions, we find that the anions are predominantly present as unique water-bridged hydroxide pair complexes, distinct from previously reported structures under

Authors: Nansi Gjineci, Sinai Aharonovich, Sapir Willdorf‐Cohen, Dario R. Dekel, Charles E. Diesendruck The reaction between different N,N ‐diarylcarbazolium salts and hydroxide is investigated to understand the reaction mechanism. The regioselectivity of the reaction and an unexpected H/D exchange indicate that the reaction does not follow the expected SNAr mechanism, but instead proceeds through a radical pathway. The mechanism of the reaction between tetraaryl ammonium salts and hydroxide is studied experimentally for different N,N-diaryl carbazolium salts. The N,N-diarylcarbazolium salts are designed, synthesized, characterized, and reacted with hydroxide under different conditions. The products of the reactions were directly characterized or isolated when possible and, using

Authors: Karam Yassin, Igal G. Rasin, Simon Brandon, Dario R. Dekel During the past decade, one of the main goals of research and development of anion exchange membrane fuel cells (AEMFCs), was to increase the hydroxide conductivity of the anion exchange membranes (AEMs); this goal is based on the obvious and known impact of AEM conductivity on AEMFC performance (including efficiency). We propose a paradigm shift according to which a main AEMFC research goal should be to increase membrane water diffusivity. This is a result of detailed and quantitative computational analyses of AEMFC performance and its stability, presented in this manuscript. Our

Authors: Noam Ralbag, Elena S. Davydova, Meirav Mann-Lahav, Peixi Cong, Jin He, Andrew M. Beale, Gideon S. Grader, David Avnir, Dario R. Dekel A new heterogeneous catalyst for hydrogen oxidation reaction (HOR), metallic palladium within which nanoparticles of ceria are entrapped, CeO2@Pd, is described. Its preparation is based on a new materials methodology of molecular doping of metals. The metallic matrix, which encages the nanoparticles, is prepared in foam architecture, to ensure easy molecular diffusion. Characterization of the structural properties of the CeO2@Pd composite using SEM, STEM, TEM, XRD, EXAFS and nitrogen adsorption reveals its morphological architecture, which leads to improved catalytic activity. In-situ electrochemical and H2 temperature-programmed reduction

Authors: Avital Zhegur, Nansi Gjineci, Sapir Willdorf-Cohen, Abhishek N. Mondal, Charles E. Diesendruck, Nir Gavish, Dario R. Dekel Water content plays a major role in the properties of anionexchange membranes (AEMs) and, therefore, in the AEM fuel cell (AEMFC) performance and performance stability. Characterization of AEMs during membrane degradation is critical in order to understand the membrane behavior during fuel cell operation time. In spite of its importance, the relationship between different membrane properties during chemical degradation has yet to be investigated. In this study, we measure the changes in AEM propertiesin particular, ion exchange capacity (IEC), water uptake (WU) and

Authors : Julian Richard Tolchard, Jørgen Svendby, Maidhily Manikandan, Hamish A Miller, Svein Sunde, Hsiharng Yang, Dario R Dekel, Alejandro Oyarce Barnett The development of active hydrogen oxidation reaction (HOR) and oxygen reduction reaction (ORR) catalysts for use in anion exchange membrane fuel cells (AEMFCs), which are free from platinum group metals (PGMs), is expected to bring this technology one step closer to commercial applications. This paper reports our recent progress developing HOR Pt-free and PGM-free catalysts (Pd/CeO 2 and NiCo/C, respectively), and ORR PGM-free Co 3 O 4 for AEMFCs. The catalysts were prepared by different synthesis techniques and characterized

Authors: Jasmin Muller, Avital Zhegur, Ulrike Krewer, John R Varcoe, Dario R Dekel Anion-exchange membrane (AEM) degradation during fuel cell operation represents the main challenge that hampers the implementation of AEM fuel cells (AEMFCs). Reported degradation values of AEMs are difficult to reproduce as no standard methods are used. The present use of different techniques based on exposure of membranes to aqueous KOH solutions under different conditions and measuring different outputs during time does not allow for a reliable and meaningful comparison of reported degradation data of different AEMs. In this study, we present a practical and reproducible ex-situ technique to

Authors : Tong Huang, Guangwei He, Jiandang Xue, Obed Otoo, Xueyi He, Haifei Jiang, Junfeng Zhang, Yan Yin, Zhongyi Jiang, John C Douglin, Dario R Dekel, Michael D Guiver Combining two facile methods, spinodal blending and self-crosslinking by chloromethyl groups are jointly utilized in fabricating alkaline anion exchange membranes (AEMs). Highly and moderately chloromethylated poly(ether ether ketone)s and sub-equimolar (to chloromethyl) amounts of 1-methylimidazole are mixed and reacted to form blend AEMs. Nanoscale bi-continuous phase separated morphologies are obtained due to spinodal decomposition. Subsequent heat treatment triggers self-crosslinking of the AEMs arising from residual chloromethyl groups in membranes. Compared with unblended