High Proton Conductivity from Titanium Oxide Nanosheets and Their Variation Based on Crystal Phase

Abstract

Abstract The specific structural arrangement of atoms in the different crystalline phases of a polymorph material has a significant influence on their electrochemical behavior. Herein, we have demonstrated the proton conductivity of titanium dioxide (TiO2) nanosheets based on their different crystalline phases. The successful preparation of three different crystalline phases including rutile (r-TiO2), anatase (a-TiO2) and brookite (b-TiO2) with the sheet size within nanometer range was confirmed using powder X-ray diffraction (PXRD) and transmission electron microscope (TEM) analysis. The corresponding TiO2 membrane films were prepared through a reduced pressure-driven route followed by humidity and temperature-dependent proton conductivities measurement. At room temperature and 90% relative humidity, b-TiO2 shows a high proton conductivity of 3.04 × 10−3 S cm−1 which is almost one order higher than a-TiO2 (4.41 × 10−4 S cm−1) and two orders higher than that of the corresponding r-TiO2 (8.04 × 10−6 S cm−1). The activation energies below 0.35 eV for all samples suggest that the proton conduction occurred through the Grotthuss mechanism. The differences in the structural arrangement in each crystal phase of TiO2, which is responsible for the water adsorption ability, can be attributed to the current findings of different proton conductivity.