Modification of Nafion (R) Using 3-mercaptopropyl Trimethoxysilane

Abstract

The modification of a Nafion (R) membrane by incorporation of 3-mercaptopropyltrimethoxysilane (MPTS) is investigated through a simple sol-gel process to reduce the methanol crossover without sacrificing the proton conductivity. The MPTS monomers incorporated in the Nation (R) matrix are hydrolyzed, forming a silicate phase by polymerization. The thiols of MPTS are finally oxidized into a sulfonic acid form. Compared to Nation (R), the obtained modified membranes show significantly reduced solvent uptake with an accompanying low volume expansion ratio. A maximum 42% methanol crossover reduction is observed with improved proton conductivity. The proton conductivities of the obtained membranes increase from 8.0 x 10(-3) Scm(-1) to 1.9 x 10(-2) Scm(-1) at 70 degrees C with increasing MPTS amount from 0 to 1.96 wt%. The low methanol crossover and the high proton conductivity of the modified membranes are attributable to the MPTS-derived silicate phase blocking the ionic cluster pathway and to the simultaneous supply of a high sulfonic acid concentration to the Nation (R) matrix.