No abstract

Sulfonic acid-functionalized graphene (S-graphene) is employed as a promising inorganic filler as well as a solid acid proton conducting medium to realize a composite membrane with Nafion for polymer electrolyte fuel cell (PEFC) applications under reduced relative humidity (RH). The functionalization of graphene is performed by sulfonic acid-containing aryl radicals to increase the number of sulfonate groups per unit volume of a domain. A Nafion−S-graphene composite membrane is obtained by embedding S-graphene in Nafion, which provides high absorption of water and fast proton-transport across the electrolyte membrane under low RH values. The proton conductivity of the Nafion−S-graphene (1%) composite membrane at 20% RH is 17 mS cm −1 , which is five times higher than that of a pristine recast Nafion membrane. PEFCs incorporating the Nafion−S-graphene composite membrane deliver a peak power density of 300 mW cm −2 at a load current density of 760 mA cm −2 while operating at optimum temperature of 70 °C under 20% RH and ambient pressure. By contrast, operating under identical conditions, a peak power density of 220 mW cm −2 is achieved with the pristine recast Nafion membrane. The Nafion−S-graphene composite membrane could be used to address many critical problems associated with commercial Nafion membranes in fuel cell applications.

No abstract

Proton exchange membranes (Nafion) have been studied using current sensing atomic force microscopy to examine the correlation between the surface morphology and the ionic domains, and to probe the local ionic conduction distribution in the membranes. It is found that the local ionic conduction generated from the current sensing images follows a Gaussian-like distribution, with the peak value and the width of the distribution increasing with the relative humidity in the sample chamber and, thus, the water content in the membranes. Two types of Nafion membranes, Nafion 112 and Nafion 117, were studied using the method. The implications of the distribution in relation to the ionic conducting channels in the membranes are discussed.