In Situ characterization of the proton enhanced conductivity of 20nm TiO2 thin-films obtained on the surface of optical fiber

TL;DR

This study demonstrates that 20nm TiO2 thin-films on optical fibers exhibit significantly enhanced proton conductivity in hydrogen at high temperatures, with potential applications in energy and sensing technologies.

Contribution

First in situ characterization of proton-enhanced conductivity in TiO2 thin-films on optical fibers, revealing high conductivity and insights into proton incorporation mechanisms.

Findings

Conductivity of 700 S/cm achieved in hydrogen at 800-900°C.

Retention of conductivity after cooling confirmed by Hall measurements.

Films are in rutile phase with potential for high-temperature energy applications.

Abstract

We report in situ characterized TiO2 thin-films deposited on optical fiber, having thicknesses in the 20-100nm range, and having enhanced conductivity values of 700S/cm upon interacting with hydrogen. This conductivity was achieved in pure hydrogen at 800-900C, having a measured activation energy of 0.26eV of the hopping type. Given the variability in the observed results, it is postulated that the highest conductivity achievable may be much greater than what is currently demonstrated. The conductivity is retained after cooling to ambient temperatures as confirmed by Hall measurements, and subsequent grazing-incidence x-ray diffraction and TEM measurements show the films to be in the rutile phase. The exceptional conductivity in these films is hypothesized to result from direct proton incorporation into the lattice populating the conduction band with excess electrons, or from altering the Titania lattice to form conductive Magneli phases. The films did not display any evidence of transformations, however formation of Magneli phases was confirmed for powders. These interesting results, observed by examining 20nm films on the surface of optical fiber in combination with the first impedance spectroscopy performed on films on optical fiber in high temperature Fuel Cell type environments, confirm hypotheses arrived at in prior publications where thin-films of Titania had optical properties which could only be explained by the current claim. Titania thin-films on optical-fiber are being explored for high temperature hydrogen derived energy generation, thermo-photonic energy conversion, and associated sensors due to their unique interactions with hydrogen.