Nobutaka Endo

Cross-Linked Sulfonated Polyimide Membranes for Polymer Electrolyte Fuel Cells

The SO 2 cross-linked membranes of sulfonated polyimides (SPIs) bearing sulfophenoxy side groups were prepared and evaluated as polymer electrolyte membranes for polymer electrolyte fuel cells (PEFCs). They maintained a high mechanical strength and proton conductivity after aging in water at 130°C for 500 h, indicating their high water stability. PEFCs with the SPI membranes showed high performances at 90°C under a high feed-gas humidity of 84% relative humidity (RH), and also fairly high performances even at a low feed-gas humidity of 30% RH due to the back-diffusion of water formed at the cathode. The PEFCs were operated under a constant current density of 0.5 A/cm 2 at 90°C and 84% RH for 1600 h without any reduction in cell performance. There was no change in the Fourier transform infrared spectra for the SPI membranes before and after the durability test. These results indicate that they have a high durability in PEFC operation. The cross-linked SPI membranes have a high potential for PEFCs at higher temperatures above 80°C.

Poly(phenylene) block copolymers bearing tri-sulfonated aromatic pendant groups for polymer electrolyte fuel cell applications

Novel poly(tri-sulfonated phenylene)-block-poly(arylene ether sulfone) copolymers (PTSP-b-PAESs) were synthesized by Ni(0)-catalyzed copolymerization of 2,5-dichloro-3′-sulfo-4′-((2,4-disulfo)phenoxy)-benzophenone and chlorobenzophenone-endcapped oligo(arylene ether sulfone). Their physical properties, morphology and polymer electrolyte fuel cell (PEFC) performance were investigated compared to those of poly(mono-sulfonated phenylene)-block-poly(arylene ether sulfone) and the corresponding random copolymers. They had a low ion exchange capacity (IEC) of 1.1–1.2 meq. g−1 and showed very low water uptake and in-plane dimensional change in water. They exhibited a more well-defined microphase-separated structure composed of hydrophilic and hydrophobic domains, where the hydrophilic domains were well-connected to each other to form the channels for proton conduction, than the mono-sulfonated one. This led to the relatively high proton conductivity under low relative humidities. The corresponding random copolymers exhibited a homogeneous morphology and much lower proton conductivity in spite of a high IEC of 2.0–2.1 meq. g−1. Even under the low humidification of 30% RH at 90 °C and 0.2 MPa, they exhibited high PEFC performance and durability; for example, a cell voltage of 0.69 V at a load current density of 0.5 A cm−2 and a maximum output of 0.73 W cm−2, which was comparable to that of the mono-sulfonated one with a much higher IEC of 1.8 meq. g−1 and much higher than those of the corresponding random copolymers. PTSP-b-PAESs have high potential as polymer electrolyte membranes for fuel cell applications.

Electrochemical reduction of CO{sub 2} with a functional gas-diffusion electrode in aqueous solutions with and without propylene carbonate

A functional gas‐diffusion electrode consisting of a modified platinum mesh electrode and a glass filter has been developed in order to convert to a useful substance at an overpotential as low as possible. The modification was made by laminating Prussian blue (inner) and polyaniline (outer) on a Pt mesh substrate, and a metal complex was further immobilized onto polyaniline. The improvement of the usefulness of the product and the required overpotential was brought about by using such functional gas‐diffusion electrode in a KCl aqueous solution containing 10% propylene carbonate. This is attributed to the maintenance of a high concentration of at the electrode surface owing to the direct supply of through the gas phase, the high solubility of to the solution, and the stabilization of reaction intermediates. The maximum total current efficiency for the reduction of was 74.9% at −0.6 V vs. Ag/AgCl, and the main products were ethanol and lactic acid.