Effect of the addition of hydrated titanium oxide on proton conductivity for aromatic polymer electrolyte membrane

• Membranes containing hydrated titanium oxide showed higher proton conductivity than the membrane not containing it.
• Micro-phase-separated structures were observed clearly in membranes containing hydrated titanium oxide.
• Well-defined hydrophilic domains functioned as proton paths and enhanced the proton conductivity of the membrane.

To improve the proton conductivities of a polymer electrolyte membrane which is composed of multi-block copolymers, in low humidity conditions, the effect of adding hydrated titanium oxide into a membrane was investigated. Membranes containing hydrated titanium oxide were prepared by using tetraethoxy titanium. Membranes containing hydrated titanium oxide showed higher proton conductivity than the membrane not containing the additives regardless of humidity. This result showed that adding hydrated titanium oxide improved proton conductivity. By contrast, all the polymer electrolyte membranes showed almost the same water content rate. The content rates of hydrated titanium oxide in membranes were lower than 3 wt%. Thus, adding hydrated titanium oxide was not considered to affect the water content rate of membranes. This result showed that proton conductivity was improved by adding hydrated titanium oxide without increasing water content rate. From the scanning transmission electron microscope observation, micro-phase-separated structures were observed clearly in membranes containing hydrated titanium oxide. It seemed that hydrated titanium oxide enhanced the hydrophilic sengments aggregation during the film–forming process. Probably, the well-defined hydrophilic domains functioned as proton paths and enhanced the proton conductivity of the membrane.