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In order to diminish the overpotential required for the electrochemical reduction of CO2, a metal complex-fixed polyaniline (PAn)/prussian blue (PB)-modified electrode has been developed, and the roles of the two laminated films as well as a fixed metal complex are disclosed here. The onset potential for the reduction of CO2 to lactic acid, a major product, is close to the thermodynamic value (E ~ = -0.20 V vs. SCE). The metal complex opr as the catalyst is a large aromatic anion, which is bound to the conducting polymer through w-interaction and not undoped during the cathodic polarization. The existence of R-OH, >CH-OH, R-COOH, and -CO -NH-groups in the coated film was confirmed by Fourier transform infrared reflection spectroscopy, supporting the involvement of the observed products (lactic acid, formic acid, methanol, ethanol, etc.). A cause for the generation of C3 species such as lactic acid may be bifunctional activation of CO2 in which the electrophilic carbon atom links to the amino group of PAn and the basic oxygen atom coordinates to the central metal of the complex.

The SO2 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 0.5A/cm2 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 .