Proton conductivity of acid-functionalised periodic mesoporous organosilicas

A study on the physico-chemical and electrical properties of acid-functionalised benzene-bridged periodic mesoporous organosilicas (PMO) is presented. Materials obtained by the co-condensation of both acid and benzene-silica precursors, using a liquid-crystal template mechanism, are intended to be used as additives in polymeric membranes for application in proton exchange membranes fuel cells (PEMFC). Proton conductivity data recovered from electrochemical impedance spectroscopy measurements, under different temperatures and relative humidity conditions, are reported in order to assess the combined effects of the protogenic group (SO₃H or P(O)(OH) ₂), and microstructural features such as pore size, specific surface area and meso- and molecular-scale order. The conductivity is found to increase significantly with increasing surface area, acid concentration and relative humidity. A proton conductivity of 1×10^-2 Scm^-1 at 100°C and 100% relative humidity is reported for a sulfonic acid functionalised PMO, which is three orders of magnitude higher than the value reported for a similar material obtained by post-synthetic grafting of the acid counterpart on the silanol group.