M. Rikukawa

Properties of selected sulfonated polymers as proton-conducting electrolytes for polymer electrolyte fuel cells

Abstract Two kinds of polymers were fabricated and tested as candidates of proton-conducting membranes for polymer electrolyte fuel cell (PEFC) applications. Poly benzimidazole (PBI) and poly(4-phenoxybenzoyl-1,4-phenylene, Poly-X 2000) (PPBP) were sulfonated and characterized as proton-conducting membranes. PBI was sulfonated as PBI-PS (propanesultone) and PBI-BS (butanesultone). PPBP was prepared at various sulfonation levels. Proton conductivities were measured at 60–160 °C. Power output characteristics of both polymers were measured by using commercial Pt/C electrodes.

Synthesis and evaluation of phosphonated poly(4-phenoxybenzoyl-1,4-phenylene)

Poly(4-phenoxybenzoyl-1,4-phenylene) (PPBP), which has high thermal stability and mechanical properties, was phosphonated by the three-step reaction. The phosphonated PPBP (P-PPBP) was characterized by FT-IR, 1 H-NMR, elemental analysis, and ICP emission spectroscopy. The thermal and electrical properties of P-PPBP were also investigated. The P-PPBP film containing 40 mol % phosphonic acid groups showed a proton conductivity of about 10 -4 S cm -1 at 90 %R.H.

Effects of regioregularity on carrier transport in poly(alkylthiophene) films with various alkyl chain lengths

Abstract Transport properties in regioregular poly(3-alkylthiophene) (PAT) films (alkyl=butyl, hexyl, decyl, dodecyl and octadecyl) have been studied by the time-of-flight (TOF) method for the sandwich cell of indium tin oxide (ITO)/film (spin-coated)/Al. It is found that the photocarriers are the holes, and their mobilities decrease and activation energies increase with increasing alkyl chain length. Poly(3-butylthiophene) exhibits the largest mobility of 1.8×10 −2 cm 2 / V s at a field ( E ) of around 10 kV/cm. The mobility of poly(3-octadecylthiophene) with a value of 1.0×10 −6 cm 2 / V s at E =0.2 mV/cm shows slightly different behavior in field dependence. The TOF mobilities at low field regions show negative field dependence apparently. The negative field dependence of mobilities is explained by proposing a model of heterogeneous field distribution for the Schottky-type cell. The field dependences of the mobilities in regioregular PAT are discussed, comparing them with the results of regiorandom PAT films.

Photovoltaic Effect in Schottky Junction of Poly(3-alkylthiophene)/Al with Various Alkyl Chain Lengths and Regioregularities

Photovoltaic effects of the Schottky junction cell consisting of indium tin oxide/poly(3-alkylthiophene) (PAT) films/Al have been studied as a function of alkyl chain length, regioregularity and film thickness. The photocurrents of the cell based on the excitation spectra with respect to their illumination sides were measured in order to elucidate the carrier generation mechanisms. It was found that the enhanced photocurrent is observed upon illumination of the Al side for shorter alkyl side chain lengths and highly regioregular PAT. The results have been discussed through a model in which the carrier generation occurs predominantly at the depletion layer of the Schottky junction with a typical thickness of approximately 60 nm.

Regiocontrolled synthesis of poly(thiophene) derivatives: EL devices utilizing chiral poly(thiophene) derivatives

We synthesized an optically active and regioregular poly(3-substituted thiophene), head-to-tail poly(3-[2-((S)-2-methylbutoxy)ethyl]thiophene (HT-P(S)MBET), according to a modified Rieke method. The HT-P(S)MBET was an optically active polymer with the head-to-tail linkage of 94 %. HT-P(S)MBET films showed longer maximum absorption wavelengths and lower bandgap than those of regiorandom poly(3-hexylthiophene). Organic light-emitting diodes (OLED) devices of HT-P(S)MBET showed red electroluminescence with a maximum wavelength of 697 nm.

Fabrication of two-dimensional layered perovskite [NH3(CH2)12NH3]PbX4 thin films using a self-assembly method

Ultra-thin films of the two-dimensional layered perovskites [NH3(CH2)12NH3]PbX4 (X = Br, I) with the quantum confinement effect have been fabricated by a convenient self-assembly method.

Synthesis of novel proton conducting polymer electrolytes containing phosphoric acid

Copolymers of acid phosphoxyethyl methacrylate (PHM) and 2,2,2-trifluoroethylacrylate (TFEA) were synthesized in order to construct hydrophilic and hydrophobic domains as well as Nafion membrane. Thermal decomposition temperatures of PHM-TFEA copolymers were about 250 °C, which showed sufficient thermal stability for polymer electrolyte fuel cells (PEFC). Water uptake of these copolymers was higher than that of Nafion 115 under low relative humidity, and proton conductivity of these polymers exhibited about 10 -3 S cm -1 under 90 % relative humidity at 80 °C.

Incorporation of conjugated polydiacetylene systems into organic–inorganic quantum-well structures

A new type of organic–inorganic semiconductor heterostructure has been successfully fabricated by incorporating a polydiacetylene backbone into layered perovskite compounds by solid-state polymerization.

Regiocontrolled synthesis of poly(thiophene) derivatives with fluoroalkyl side chains

Poly(3-(perfluorohexyl)thiophene) (PFHT) was synthesized from 2, 5-dibromo-3-(perfluorohexyl)thiophene via Grignard metathesis method. Obtained polymer was dissolved in a wide variety of organic solvents such as chloroform, tetrahydrofuran, and o-dichlorobenzene. Transition temperatures of PFHT were observed at 54 °C due to melting of perfluorohexyl groups. Electron-withdrawing effect of C-F bonds and weak interaction among the side chains were observed as shorter maximum absorption wavelengths. Stable monolayers of PFHT were formed on a water subphase due to strong hydrophobicity and the weak interactions of the perfluorohexyl groups.

Photoluminescence from the Even-Parity State in Polythiophene Derivative

The time-resolved photoluminescence spectrum of a polythiophene derivative has been analyzed from the viewpoint of the vibronic structure and its dynamics. We found that the photoluminescence (PL) originates from two vibronic coupled states which consist of the odd-parity 1 B u component and the even-parity 2 A g component. Since the fluorescences from the two states have different time constants and different vibronic structures, the PL shows a biexponential decay and a spectral change.