Nanotubular Cr-doped TiO2 for use as high-temperature NO2 gas sensor

Realization of highly selective and sensitive sensors for various emission gases at higher temperatures is a demanding task of combustion related applications. One of the challenges in meeting these requirements is to develop nano-structured and smart functional materials to detect and monitor emission gases selectively. This work describes the functionalization of TiO2-nanotubular layers for NO2-sensing through homogeneously distribution of Cr3+-doping. Fully incorporation of Cr into the TiO2 lattice has been demonstrated by TEM, XPS and XRD analysis. No other oxide phase separation occurred even after annealing at temperatures up to 700 °C. By Cr-incorporation into the lattice, TiO2-NTs display p-type semiconducting sensing behaviour. As small as 2.5% Cr-doping of TiO2-NTs results in improvement of the high-temperature NO2-sensing capability in the temperature range of 300-500 °C and in concentrations between 25 and 100 ppm. Furthermore, the cross-sensitivity to CO has been reduced by doping as demonstrated during the mixed gas detection of NO2.