Ryo Akiyama

Proton conductive aromatic block copolymers from a new bistriazole monomer

We have designed and synthesized a new bistriazole compound, 3,3′-(1,3-phenylene)bis[4-phenyl-5-(4-fluorophenyl)-4H-1,2,4-triazole], as a comonomer for a series of sulfonated block poly(arylene ether) copolymers. The bistriazole was successfully synthesized from isophthalic dihydrazide and 4-fluorobenzoyl chloride via bisoxadiazole. The bistriazole monomer was polymerized with 4,4′-biphenol or 4,4′-dihydroxydiphenyl ether to obtain hydroxyl-terminated hydrophobic oligomers, which were copolymerized with sulfonated oligomers to obtain the title block copolymers. The block copolymers were high-molecular-weight (Mw = 91–500 kDa) and provided tough and bendable membranes by solution casting. Because of the sequenced block copolymer structures, the membranes exhibited hydrophilic/hydrophobic phase-separated morphology as confirmed by scanning transmission electron microscopic (STEM) images. The membranes showed proton conductivity under humidified conditions; the highest proton conductivity was 6 × 10−2 S cm−1 at 95% relative humidity (RH) and 80 °C. The membranes were mechanically stable with high storage moduli (ca. 109 Pa) and loss moduli (ca. 108 Pa). These mechanical properties were independent on the ion exchange capacity (IEC) of the membranes. The triazole groups were effective in improving the mechanical and oxidative stability of the sulfonated poly(arylene ether) block copolymer membranes.

Design of flexible polyphenylene proton-conducting membrane for next-generation fuel cells

A novel design has enabled development of polyphenylene ionomer membranes that address major issues for fuel cell applications. Proton exchange membrane fuel cells (PEMFCs) are promising devices for clean power generation in automotive, stationary, and portable applications. Perfluorosulfonic acid (PFSA) ionomers (for example, Nafion) have been the benchmark PEMs; however, several problems, including high gas permeability, low thermal stability, high production cost, and environmental incompatibility, limit the widespread dissemination of PEMFCs. It is believed that fluorine-free PEMs can potentially address all of these issues; however, none of these membranes have simultaneously met the criteria for both high performance (for example, proton conductivity) and durability (for example, mechanical and chemical stability). We present a polyphenylene-based PEM (SPP-QP) that fulfills the required properties for fuel cell applications. The newly designed PEM exhibits very high proton conductivity, excellent membrane flexibility, low gas permeability, and extremely high stability, with negligible degradation even under accelerated degradation conditions, which has never been achieved with existing fluorine-free PEMs. The polyphenylene PEM also exhibits reasonably high fuel cell performance, with excellent durability under practical conditions. This new PEM extends the limits of existing fluorine-free proton-conductive materials and will help to realize the next generation of PEMFCs via cost reduction as well as the performance improvement compared to the present PFSA-based PEMFC systems.