Rikukawa Masahiro

This paper presents an overview of the possibility and problems of new proton-conducting polymer electrolyte membranes based on hydrocarbon polymers. Due to their chemical stability, high degree of proton-conductivity, and remarkable mechanical properties, perfluorinated polymer electrolytes such as Nafion^®, Aciplex^®, Flemion^®, and Dow membranes are some of the most promising electrolyte membranes for polymer electrolyte fuel cells. A number of reviews on the synthesis, electrochemical properties, and fuel cell applications of perfluorinated polymer electrolytes have also appeared. While perfluorinated polymer electrolytes have satisfactory properties for a successful fuel cell electrolyte membrane, the major drawbacks to large-scale commercial use involve high cost and low proton-conductivities at high temperatures and low humidities. Presently, one of the most promising ways to obtain high-performance proton-conducting polymer electrolyte membranes is the use of hydrocarbon polymers for the polymer backbone. The present paper attempted to summarize the synthesis, chemical and electrochemical properties, and fuel cell application of new proton conducting polymer electrolytes based on hydrocarbon polymers that have been made during the past decade.

Charge carrier transport in regioregular poly(3-octadecylthiophene) has been studied by the time-of-flight method. The nature of transient photocurrent response is dispersive and holes were found to be the majority photocarriers with no detectable signal for electron transport. The hole mobility at room temperature and at an applied field of $1.3 \times 10^{5}$ V/cm has been measured to be $2.5 \times 10^{-5}$ cm2/V.s. Analysis of the transport mechanism confirms the predictions of the stochastic model of Scher and Montroll as indicated by the universal-scaling behavior of transient photocurrents when they were normalized with respect to transit time. The field and temperature dependence of hole mobility has been analyzed in terms of Poole-Frenkel and Bässler's Gaussian disorder model. The interpretation of the results of hole mobility measurement is made in terms of the concept of hopping among the polymer segments featuring a Gaussian distribution of energies with its variance of 74 meV.