Water electrolysis is a promising approach to hydrogen production from renewable energy sources. Even though it is not necessarily environmentally friendly and a large number of possible feedstocks for hydrogen production include fossil resources such as coal, natural gas, and mineral oil, but also biomass, water, and components such as ethanol, methane, or ammonia can be used for hydrogen production. Also, a large variety of different energy sources can be used for hydrogen production. The combination of hydrogen production with renewable energy systems, such as photovoltaics, hydropower, or wind energy is very suitable though. Many innovative processes have been subject to intense research and some have already reached high efficiencies. Alkaline water electrolyzers with anion-conducting membranes hold many advantages in comparison to other systems. As cheaper, non-noble metals are stable in alkaline media, the relatively low cost of the electrode materials is one of the main advantages of alkaline systems over electrolyzers using proton-conducting electrolytes. Therefore, the main part of published literature on alkaline electrolysis describes electrodes based on low cost materials such as nickel for both anode and cathode. Yet still alkaline water electrolyzers have to compete against other forms of hydrogen production, such as steam reforming of natural gas. Even though many studies expect water electrolysis to become economically viable on a long-term basis, conventional hydrogen production is still hard to under-price.

A series of novel cross-linked highly quaternized chitosan and quaternized poly (vinyl alcohol) membranes were successfully synthesized to be applied in alkaline direct ethanol fuel cells. Cross-linking was accomplished using two different cross-linking agents and an additional thermal process to improve both chemical and thermal properties. Equivalent blends of chitosan and poly (vinyl alcohol) membranes with various degrees of cross-linking were prepared by using different amounts of glutaraldehyde and ethylene glycol diglycidyl ether as cross-linkers. To investigate their applicability in direct ethanol fuel cells, the membranes were characterized in terms of their structural properties, chemical, thermal and alkaline stability, ion transport and ionic properties using following methods: Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy, scanning electron microscopy, thermogravimetric analysis, water uptake by mass change, ethanol permeability in the diffusion cell, back titration method (ion exchange capacity) and electrochemical impedance spectroscopy (anion conductivity). Despite the high degree of quaternization of the applied materials and regardless of the thin film thickness of the blend membranes, the novel cross-linked products displayed outstanding mechanical stability. The lower crosslinked membranes exhibited the best transport and ionic properties with a high anion conductivity of 0.016 S cm-1 and a high ion exchange capacity of 1.75 meq g-1 , whereas membranes with a higher degree of cross-linking performed superior in terms of reduced ethanol permeability of 3.30•10-7 cm 2 s-1 at 60°C. The blend membranes-chemically and thermally cross-linked-provide excellent thermal stability with an onset degradation temperature above 280°C and superb alkaline stability in 1.0 M KOH at 60°C for 650 h. Therefore, these composite membranes exhibit high potential for application as alkaline electrolytes in fuel cells.

Anion exchange membrane fuel cells have unique advantages and are thus gaining increasing attention. Poly(vinyl alcohol) (PVA) is one of the potential polymers for the development of anion exchange membranes. This review provides recent studies on PVA-based membranes as alternative anion exchange membranes for alkaline fuel cells. The development of anion exchange membranes in general, including the types, materials, and preparation of anion exchange membranes in the last years, are discussed. The performances and characteristics of recently reported PVA-based membranes are highlighted, including hydroxide conductivity, water uptake, swelling degree, tensile strength, and fuel permeabilities. Finally, some challenging issues and perspectives for the future study of anion exchange membranes are discussed.

Membrane degradation is a severe factor limiting the lifetime of polymer electrolyte fuel cells. Therefore, obtaining a deeper knowledge is fundamental in order to establish fuel cells as competitive product. A segmented single cell was operated under open circuit voltage with alternating relative humidity. The influence of the catalyst layer on membrane degradation was evaluated by measuring a membrane without electrodes and a membrane-electrode-assembly under identical conditions. After 100 h of accelerated stress testing the proton conductivity of membrane samples near the anode and cathode was investigated by means of ex situ electrochemical impedance spectroscopy. The membrane sample near the cathode inlet exhibited twofold lower membrane resistance and a resulting twofold higher proton conductivity than the membrane sample near the anode inlet. The results from the fluoride ion analysis have shown that the presence of platinum reduces the fluoride emission rate; which supports conclusions drawn from the literature.

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