Highly Stable, Anion Conductive, Comb-Shaped Copolymers for Alkaline Fuel Cells

Abstract

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 ...

Characterization and Chemical Stability of Anion Exchange Membranes Cross-Linked with Polar Electron-Donating Linkers

“…However, it is known that SAXS measurements are not always able to detect phase separation, especially when relatively short side chains are present (weak separation between the two components) 66,67 with low phase contrast.…”

CO-sensing Properties of Potentiometric Gas Sensors Using an Anion-conducting Polymer Electrolyte and Au-loaded Metal Oxide Electrodes

“…The reduction of Au(OH) 3 to Au metal by the heat-treatment was clearly confirmed by the change in the color from yellow (Au(OH) 3 ) to violet (Au nanoparticles), which was derived from the surface plasmon resonance [32].…”

“…The pH of the solution was adjusted to 7 by the further addition of the NH 3 aqueous solution and the solution was stirred at 70°C for 1 h, to deposit Au-based precipitates (Au(OH) 3 ) on the surface of the MO powders, and then they were centrifuged and washed with pure water, repeatedly. They were dried at 100°C and then heat-treated at 100, 250 or 400°C for 1 h in air or H 2 to obtain Au-loaded MO powders (nAu/MO(Tm), n: the loading amount of Au, 0.5~2 wt%, T: heat-treatment temperature, 100, 250 or 400, m: heat-treatment atmosphere, air or H 2 ).…”

“…14(a)(ii)). It is highly possible that they may be Au clusters highly-dispersed on the In 2 O 3 , because the 2.0Au/In 2 O 3 (100air) powder was merely heat-treated at low temperature (100ºC) in air after the deposition of Au(OH) 3 . On the other hand, some Au nanoparticles were clearly observed on the surface of the 2.0Au/In 2 O 3 (250H 2 ) powder, and the particle size was slightly larger than that of 2.0Au/In 2 O 3 (400air) powder (see Fig.…”

“…Highly conductive anion-conducting polymers (ACP) have recently been developed by some researchers and companies, and their large OH -conductivities and improved long-term stabilities were quite attractive for an electrolyte of polymer-electrolyte fuel cells (PEFCs) [1][2][3][4][5]. For example, Matsumoto et al have reported that the PEFCs using an ACP electrolyte showed high current density as well as high power density with relatively low overpotential [6], and their properties except for the long-term stability have been already comparable to those of PEFCs using proton-conducting polymers such as Nafion ® , which has been put into practical use.…”