The Electrochemical Properties of the Porous Nafion Membrane for Proton Exchange Membrane Fuel Cells (PEMFCs)

摘要

Proton exchange membrane fuel cells (PEMFCs) have been paid a great attention as a clean power generator to convert the chemical energy of hydrogen to electric energy and they have major advantages, such as the high power density and energy efficiency, rapid start-up, etc., for the portable electronic devices and transportation/stationary power systems. In order to achieve the high fuel cell performance, a polymer electrolyte membrane in the PEMFCs must satisfy some requirements, for examples, high proton conductivity, zero electronic conductivity, adequate mechanical strength, chemical, and electrochemical stability. Among these properties, the proton conductivity is the most important factor because it directly affects the cell performance. Hence, the relationships between the proton conductivity and other factors have been extensively studied, and it has been reported that the proton conductivity of the membrane is closely related to its microscopic structure. Early studies proposed a cluster-network structure of ionic clusters (～50 A) interconnected with narrow ionic channels (～10 A) in the presence of water. Moreover, recent studies have reported that the vapor pressure of water in the small size of pores is significantly reduced and therefore the retention of water in the membrane is improved at the elevated temperature.9'10 In this study, the proton conductivity and the fuel cell performance are investigated as a function of pore size in the porous Nafion membrane.