Nafion/TiO 2 composite membranes with different TiO 2 contents were studied in an H 2 /O 2 proton exchange membrane fuel cell ͑PEMFC͒ over a wide range of relative humidity ͑RH͒ values from 26 to 100% at temperatures of 80 and 120°C. The composite membranes, which were prepared using a recast procedure, showed a pronounced improvement over unmodified Nafion membranes when operated at 120°C and reduced RH. For instance, at 50% RH, the Nafion/20% TiO 2 membrane demonstrated a performance identical to that of an unmodified Nafion membrane operated at 100% RH. This performance level was comparable to that of a bare Nafion membrane at 80°C. The high performance of the Nafion/TiO 2 composite membranes at low RH was attributed to improved water retention due to the presence of absorbed water species in the electrical double layer on the TiO 2 surface. The zeta potential and thickness of the hydrodynamically immobile water layer at the TiO 2 /water interface were discussed as parameters influencing the water balance in the membranes. The obtained experimental PEMFC performance data were fitted using an analytical equation, and calculated parameters were analyzed as functions of RH and TiO 2 content in the composite membranes.

The Cu-Cl thermochemical cycle is among the most attractive technologies proposed for hydrogen production due to moderate temperature requirements and high efficiency. In this study, the key step of the cycle, H 2 gas evolution via oxidation of CuCl͑s͒ dissolved in high concentrated HCl͑aq͒, was experimentally investigated. The electrolysis parameters and system performance were studied by linear sweep voltammetry and electrochemical impedance spectroscopy at ambient temperature. Promising performance of the electrolyzer was obtained when pure water was used as catholyte. A thermodynamic model previously developed for speciation of the CuCl-CuCl 2 -HCl aqueous solutions was used to speculate on the effects of reagent concentration, flow rate, and temperature on electrolysis kinetics. The experimental decomposition potential necessary to initiate the hydrogen evolution reaction was more than 3 times lower than the potential necessary for water electrolysis at the same conditions. Close correspondence of the hydrogen production rate to Faraday's law of electrolysis indicated the current efficiency of about 98%, while the voltage efficiency was estimated at 80% at 0.5 V and 0.1 A/cm 2 .

This paper discusses a new class of high performance polyethylene-based anion exchange membranes (PE–AEMs) that contain a wide concentration range of pendant (flexible) ammonium chloride (NR3 +Cl–) groups and with or without a cross-linked PE matrix structure. The chemistry involves a metallocene-mediated polymerization of ethylene, silane-protected α,ω-amino-olefin [C x N(SiMe3)2], with or without styrenic diene (cross-linker), to form ethylene/C x N(SiMe3)2 copolymers and ethylene/C x N(SiMe3)2/diene terpolymers, respectively. The resulting co- and ter-polymers were completely soluble in common organic solvents and were solution-casted into uniform films (thickness, 50–70 μm; without backing material) and then thermal cross-linked in ethylene/C x N(SiMe3)2/diene case, further interconverting the silane-protected amino groups into the desired −NR3 +Cl– groups (R: H, CH3, and C3H7) under solid state conditions. The resulting PE–NR3 +Cl– and cross-linked x-PE–N(CH3)3 +Cl– membranes were systematically studied to understand how the PE structure (−NR3 +Cl– concentration, R group, cross-linking density, etc.) affects ionic conductivity, water uptake, film stability, and ion selectivity. For comparison, several commercially available AEMs were also examined. Evidently, an x-PE–N(CH3)3 +Cl– membrane, with 28.1 mol % −N(CH3)3 +Cl– groups and 0.2 mol % cross-linkers, shows moderate water swelling and outperforms all commercial membranes with exceptionally high ionic conductivities of 119.6 mS/cm in 2 N HCl solution and 78.8 mS/cm in 2 N HCl–0.2N CuCl solution at room temperature.

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Nafion/10% ͑mass % is used in this paper͒ TiO 2 composite membranes were studied in a H 2 /O 2 proton exchange membrane ͑PEM͒ fuel cell over a range of relative humidity ͑RH͒ from 26 to 50% at temperatures of 80 and 120°C. According to the scanning electron microscopy-energy dispersive spectroscopy ͑SEM-EDS͒ structural analysis, the composite Nafion/TiO 2 membranes had a two-layer structure, one layer enriched with TiO 2 particles, and the other dominated by the Nafion polymer. Although the TiO 2 particles were mainly concentrated on one side of the composite membrane, sufficient hydration was apparently achieved for the whole membrane. Two TiO 2 ͑rutile͒ powders used for the preparation of the composite membranes differed in specific surface area ͑SSA͒, surface zeta potential, and particle morphology. A TiO 2 powder with five times higher SSA, 22 mV higher zeta potential ͑at the low-pH limit͒, and distinctly different individual particle and particle aggregate morphologies resulted in a four-times increase of current density ͑at 0.6 V͒ when the composite membranes were made and tested in PEM fuel cell at temperature of 120°C and relative humidity of 26%. We speculate that a greater number of protonated sites per unit mass of powder in the membrane and a higher density of the protonated sites contribute to the enhanced fuel cell performance.