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To produce an anion-conductive and durable polymer electrolyte for alkaline fuel cell applications, a series of quaternized poly(2,6-dimethyl phenylene oxide)s containing long alkyl side chains pendant to the nitrogen-centered cation were synthesized using a Menshutkin reaction to form combshaped structures. The pendant alkyl chains were responsible for the development of highly conductive ionic domains, as confirmed by small-angle X-ray scattering (SAXS). The combshaped polymers having one alkyl side chain showed higher hydroxide conductivities than those with benzyltrimethyl ammonium moieties or structures with more than one alkyl side chain per cationic site. The highest conductivity was observed for comb-shaped polymers with benzyldimethylhexadecyl ammonium cations. The chemical stabilities of the comb-shaped membranes were evaluated under severe, accelerated-aging conditions, and degradation was observed by measuring IEC and ion conductivity changes during aging. The comb-shaped membranes retained their high ion conductivity in 1 M NaOH at 80°C for 2000 h. These cationic polymers were employed as ionomers in catalyst layers for alkaline fuel cells. The results indicated that the C-16 alkyl side chain ionomer had a slightly better initial performance, despite its low IEC value, but very poor durability in the fuel cell. In contrast, 90% of the initial performance was retained for the alkaline fuel cell with electrodes containing the C-6 side chain after 60 h of fuel cell operation. ■ INTRODUCTIONFuel cells are efficient energy conversion devices that generate electric power from energy-dense chemical fuels and have been attracting attention as a clean energy technology. 1−3 The most widespread low-temperature fuel cell technologies are based on sulfonated polymer membranes to separate the oxidant and fuel chambers and conduct protons between the anode and cathode of the cell. 4−6 These proton exchange membrane fuel cells (PEMFC) principally employ Nafion, a product from DuPont, as the sulfonated polymeric proton conductor. PEMFCs require platinum or other precious metal-based catalysts because these are the only types of metal catalysts stable under the low pH and electrochemical conditions of an operating cell. The expensive Pt-based catalysts, combined with perfluorinated membranes and corrosion-resistant cell hardware increase the cost of PEMFC devices beyond what is currently commercially viable. 7,8 Alkaline fuel cells (AFCs) have received significant interest in recent years relative to acidic fuel cells, 9−14 because of advantages when operating under alkaline conditions, which include enhancement of the electrode reaction kinetics, especially at the cathode, and the catalysts are not subjected to corrosion at high pH. 9,12,13 Consequently, non-noble metals or inexpensive metal oxides can be used as catalysts to greatly reduce the cost of the device. 13−16 In addition, high energy density liquids and gases such as ethanol, hydrazine, and ammonia can be adopted as fuels. 17,18 Alkaline fuel ...

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We report high-performance, durable alkaline membrane water electrolysis in a solid-state cell. An anion exchange membrane (AEM) and catalyst layer ionomer for hydroxide ion conduction were used without the addition of liquid electrolyte. At 50 °C, an AEM electrolysis cell using iridium oxide as the anode catalyst and Pt black as the cathode catalyst exhibited a current density of 399 mA/cm(2) at 1.80 V. We found that the durability of the AEM-based electrolysis cell could be improved by incorporating a highly durable ionomer in the catalyst layer and optimizing the water feed configuration. We demonstrated an AEM-based electrolysis cell with a lifetime of >535 h. These first-time results of water electrolysis in a solid-state membrane cell are promising for low-cost, scalable hydrogen production.