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Alkaline anion-exchange membranes (AAEM) for alkaline polymer electrolyte fuel cells (APEFC) were successfully prepared using electron beam irradiated poly(ethylene-co-tetrafluoroethylene) precursor films grafted with vinylbenzyl chloride (VBC) monomer. The resulting chloromethyl groups were subsequently reacted with trimethylamine to form quaternary ammonium anion-exchange functional head-groups. The concentration of toxic and expensive VBC, that is required to achieve an optimal level of grafting, was reduced from 100% v/v (undiluted) to 20% v/v by dilution with propan-2-ol and the inclusion of a surfactant. Fuel cell tests using hydrogen and oxygen gave the same peak power densities (164 ± 3 mW cm − 2 ) for the AAEMs prepared with both 100% v/v VBC and 20% v/v VBC. This highlights the (desirable) lack of any detrimental effect on performance of the resulting APEFC with the reduction in grafting monomer concentration used for the synthesis of the component AAEM. [ABSTRACT FROM AUTHOR]

Abstract: Varying thicknesses of ethylene-co-tetrafluoroethylene (ETFE) Alkaline Anion Exchange Membranes (AAEMs) with quaternary ammonium functional groups were prepared using e-beam irradiation. The performances in H2/O2 single cell fuel cells were tested at 50 °C with the thinnest AAEM (S20) achieving the highest peak power density of 230 mW cm−2. The ability to use non-Pt electrocatalysts for the oxygen reduction reaction (ORR) at the cathode was also investigated. [Copyright &y& Elsevier]

Abstract: An in-situ fuel cell reference electrode (RE) consisting of a Pd-coated Pt wire exhibits stable potentials in alkaline polymer electrolyte membrane fuel cells (APEMFC). Results indicate that the overpotential and impedance of the anode are higher than those of the cathode in the cells tested (even at low currents); this is contrary to that found in proton-exchange membrane fuel cells (PEMFC) and it shows that caution is required when translating prior understating of PEMFC to APEMFC. The working hypothesis is that there is flooding-derived mass transport loss at the anode (where water is electro-generated). [Copyright &y& Elsevier]

High performance benzyltrimethylammonium-type alkaline anion-exchange membranes (AEM), for application in electrochemical devices such as anion-exchange membrane fuel cells (AEMFC), were prepared by the radiation grafting (RG) of vinylbenzyl chloride (VBC) onto 25 μm thick poly(ethylene-co-tetrafluoroethylene) (ETFE) films followed by amination with trimethylamine. Reductions in the electron-beam absorbed dose and amount of expensive, potentially hazardous VBC were achieved by using water as a diluent (reduced to 30–40 kGy absorbed dose and 5 vol% VBC) instead of the prior state-of-the-art method that used organic propan-2-ol diluent (required 70 kGy dose and 20 vol% VBC monomer). Furthermore, the water from the aqueous grafting mixture was easily separated from the residual monomer (after cooling) and was reused for a further grafting reaction: the resulting AEM exhibited an ion-exchange capacity of 2.1 mmol g−1 (cf. 2.1 mmol g−1 for the AEM made using a fresh grafting mixture). The lower irradiation doses resulted in mechanically stronger RG-AEMs compared to the reference RG-AEM synthesised using the prior state-of-the-art method. A further positive off-shoot of the optimisation process was the discovery that using water as a diluent resulted in an enhanced (i.e. more uniform) distribution of VBC grafts as proven by Raman microscopy and corroborated using EDX analysis: this led to enhancement in the Cl− anion-conductivities (up to 68 mS cm−1 at 80 °C for the optimised fully hydrated RG-AEMs vs. 48 mS cm−1 for the prior state-of-the-art RG-AEM reference). A down-selected RG-AEM with an ion-exchange capacity = 2.0 mmol g−1, that was synthesised using the new greener protocol with a 30 kGy electron-beam absorbed dose, led to an exceptional beginning-of-life H2/O2 AEMFC peak power density of 1.16 W cm−2 at 60 °C in a benchmark test using industrial standard Pt-based electrocatalysts and unpressurised gas supplies: this was higher than the 0.91 W cm−1 obtained with the reference RG-AEM (IEC = 1.8 mmol g−1) synthesised using the prior state-of-the-art protocol. [ABSTRACT FROM AUTHOR]

Abstract: Novel benzimidazolium (BIm) functionalized anion exchange membranes (AEMs) are synthesized and characterized for alkaline fuel cells (AFCs). Poly(phenylene oxide) (PPO) is firstly brominated followed by nucleophilic substitution reaction with methylbenzimidazole to obtain the objective BIm-PPO AEMs. Such solution-casting AEMs show good mechanical and thermal stabilities as well as the favorable fuel cell-related indicators, including high ion exchange capacity, proper water uptake and high ionic conductivity. In addition, a single H2/O2 fuel cell test by employing the optimal BIm-PPO-0.54 AEM yields a peak power density of 13mWcm−2 at 35°C, indicating the potential application of BIm-PPO AEMs in AFCs. Compared with the analogous AEMs based on PPO containing the classical pendant quaternary ammonium and imidazolium cations, BIm-PPO AEMs show the advantages in dimensional, mechanical and thermal stabilities, while simultaneously exhibiting the higher ionic conductivity. Compared with polybenzimidazolium based AEMs, where BIm cations distribute within the polymer backbone, AEMs herein present the higher ionic conductivity and power density (produced from a single cell test) due to the better mobility and aggregation abilities of pendant BIm cations attached to the backbone via a side chain relative to those distribute within the polymer backbone. [Copyright &y& Elsevier]

Abstract: This article describes the preparation of cross-linked anion exchange membranes (AEMs) using a solvent free strategy. A novel casting solution is formed by dissolving cardo polyetherketone (PEK-C) as an essential polymer intensifier in a mixture of vinylbenzyl chloride (VBC) and divinylbenzene (DVB) monomers without any organic solvent. Tetraethylenepentamine (TEPA) is added to act as a cross-linker between VBC and PKE-C. Polymerization and quaternization are successively implemented to obtain the cross-linked AEMs, whose properties are found to compare well to many referenced AEMs. Apart from improving the compatibility of PEK-C with poly(VBC-co-DVB), TEPA also effectively enhances the charge density, ionic conductivity and alkaline stabilities of the resulting AEMs, whilst simultaneously inhibiting the swelling ratio. The optimal membrane shows an ionic conductivity of 76 mS cm−1 at 70 °C and 100% relative humidity and can remain stable after immersing in 2 mol dm−3 KOH solution for 168 h. A power density of 6 mW cm−2 is achieved in a H2/O2 fuel cell test at 50 °C with an optimal AEM but a non-optimized membrane electrode fabrication process. Generally, the novel method herein highlights an environmentally friendly and economically attractive method for the preparation of AEMs used in alkaline fuel cells. [Copyright &y& Elsevier]

Abstract: Novel alkaline anion-exchange membranes (AAEMs) containing pendant guanidinium groups are synthesized from poly(2, 6-dimethyl-1,4-phenylene oxide) (PPO) by benzyl bromination and subsequent reaction with 1,1,2,3,3-pentamethylguanidine (PMG). The performances of the resultant guanidinium-functionalized-PPO (GPPO) AAEMs are controlled by tailoring the amount of guanidinium groups in the membrane matrix. The AAEMs exhibit high ionic conductivities (up to 71 mS cm−1 at room temperature); this stems from the high alkalinity (high pK a) of guanidinium hydroxide, which leads to an augmentation of both the number of dissociated hydroxides and water molecules. Furthermore, the GPPO AAEMs exhibit excellent thermal and alkali stabilities due to the presence of the π electron conjugated systems of the pendant guanidinium head-groups permitting the positive charge to be delocalized over one carbon and three nitrogen atoms. Specifically, the initial decomposition temperatures, from thermogravimmetric analyses of the GPPO AAEMs, are high at 270 °C, while the hydroxide conductivity of the AAEM with the most optimal properties remains stable in aqueous KOH (1 mol dm−3) solution for 192 h at 25 °C. A H2/O2 fuel cell test at 50 °C with a GPPO AAEM yielded a beginning-of-life peak power density of 16 mW cm−2. [Copyright &y& Elsevier]

Abstract: This study reports the development of imidazolium-type alkaline anion exchange membranes (Im-AAEMs) based on the functionalization of bromomethylated poly(2,6-dimethyl-1,4-phenylene oxide) (BPPO) using 1-methylimdazole. Aromatic polymers bearing bromomethyl, instead of chloromethyl, functional groups were employed as base materials to avoid complicated chloromethylation which require toxic reagents. 1H NMR and FT-IR spectroscopic data indicated the synthesis of a series of membranes with controlled IECs (achieved by varying the amount of 1-methylimdazole). Due to the conjugated structures of imidazolium cations, the novel Im-AAEMs display enhanced short-term thermal and chemical stabilities compared with classical quaternary ammonium-type AAEMs. In addition, the imidazolium salts exhibit excellent solubility in polar solvents, such as NMP and DMSO, which allowed the exploitation of a pre-functionalized strategy for the synthesis of the AAEMs. Accordingly, the Im-AAEMs displayed conductivities up to >100mScm−1 at 80°C, which derived from the establishment of a nano-scale phase-separated morphology as directed by the solvent casting process. A H2/O2 fuel cell test yielded a peak power density of 30mWcm−2 at a current density of 76mAcm−2; this will be improved on development of a chemical compatible imidazolium-based alkaline ionomer for use as ionic polymer binder in the electrodes'' catalyst layers. [Copyright &y& Elsevier]

Abstract: Poly(2,6-dimethyl-1,4-phenylene oxide) (PPO)-based organic–inorganic hybrid alkaline membranes with enhanced hydroxyl (OH−) conductivity are prepared in response to the relatively low conductivity of previously reported PPO-based systems. The membranes also exhibit higher swelling-resistant properties and the hydroxyl (OH−) conductivity values are comparable to previously reported fluoropolymer-containing membranes: 0.012–0.035Scm−1 in the temperature range 30–90°C. Other favorable properties for fuel cell application include high tensile strengths up to 25MPa and large ion-exchange capacities in the range 2.01–2.27mmolg−1. Beginning-of-life fuel cell testing of a membrane with a thickness of 140μm yielded an acceptable H2/O2 peak power density of 32mWcm−2 when incorporated into an alkaline membrane electrode assembly. Therefore, this class of hybrid membrane is suitable for application in alkaline membrane fuel cells. [Copyright &y& Elsevier]

Abstract: Alkaline anion-exchange membranes (AAEMs) are being developed for metal-cation-free solid alkaline fuel cells. Reduced solvent uptakes were observed after immersion in methanol, ethanol and ethylene glycol relative to a Nafion®-115 proton-exchange membrane (PEM); this translated directly into lower alcohol permeabilities. Alkaline polymer electrolytes showed lowered degrees of swelling (membrane thickness), when immersed in methanol and ethanol, relative to Nafion-115. The open circuit voltages, V OCV, of the corresponding direct alcohol fuel cells were superior to acid equivalents with membranes of identical fully hydrated thicknessess; this is indicative of a combination of reduced alcohol permeabilities and changed electrokinetics on PtRu anode catalysts at high pH. V OCV values for the AAEM-DAFCs were higher with ethanol than with methanol (consequent on lower permeability to ethanol), but were lower with ethylene glycol. Promisingly, and contrary to Nafion equivalents, peak power densities were not reduced when C2 alcohols (Cntaining) replaced methanol. [Copyright &y& Elsevier]