Variable temperature proton conductivity of mesoporous titanium oxides doped with naphthalene sulfonate formaldehyde resin

In this report we attempt to synthesize materials resistant to dehydration by exploiting the interaction of sulfonate groups with the hydrophilic surfaces of the inner pore walls of mesoporous titanium oxides to form channels for proton conduction. Thus, six mesoporous titanium oxide composites of naphthalene sulfonate formaldehyde (NSF) were synthesised, fully characterised and formed into pellets for potentiostatic impedance measurements. The most promising sample, a NSF composite of mesoporous TiO₂ (mTiO₂), displays a proton conductivity of 1.837 mS cm^-1 at 100 C surpassing that of a pellet of Nafion 117 constructed as a reference under the same conditions (1.143 mS cm^-1). This material also has greater conductivity than pure hydrated NSF (0.122 mS cm^-1), confirming a synergistic interaction between the NSF and the oxide mesostructure in the proton conductivity mechanism. Both ¹H and ¹³C solid state NMR studies of the NSF material and the mTiO₂-NSF composites demonstrate that the oligomeric nature of the NSF is preserved while in contact with the mTiO₂ surface, thus facilitating conductivity.