Sulfonation of porous materials and their proton conductivity

Micro - and mesoporous materials have gained increased interest over the last decades, due to their variety of tuneable properties. This review presents ordered mesoporous silica (OMS), periodic mesoporous organosilicas (PMOs), zeolites, metal organic frameworks (MOFs) and covalent organic frameworks (COFs) as the most relevant and investigated groups of porous and solid materials as solid state proton conductors. Their high specific surface area is the ideal playground for introducing very acidic sulfonic acid groups, in order to form solid state acids. The sulfonic acid functionalization of these type of materials leads to their applicability in catalysis and proton conduction applications, e.g. in proton-conducting membranes of fuel cells or electrolysers. Herein, current sulfonation methods for porous materials are summarized and the resulting enhancement effect on proton conductivity is presented.