Highly selective sub–10 ppm H2S gas sensors based on Ag-doped CaCu3Ti4O12 films

Abstract

The detection of the toxic H2S gas is of great practical, environmental and industrial interest. This work presents sensing devices fabricated with Ag-doped CaCu3Ti4O12 (CCTO) thin films using a cost effective sol-gel deposition method. When compared with undoped CCTO sensors, very low doping levels of Ag cause a dramatic improvement of the response towards H2S gas. The Ag-doped CCTO films were found to be remarkable sensors towards H2S in the concentration range of 0.2–10 ppm. In addition, the response of these sensors towards NH3, H2, NO2 and ethanol vapor was up to two orders of magnitude lower than that for H2S, yielding a highly selective mean of detecting and quantifying H2S. Gas sensing experiments were conducted at operating temperatures ranging from 150 to 350 °C with an optimum response found at 250 °C. In the studied temperature range, Ag-doped CCTO film sensors also showed much shorter response times than that of undoped one. It is found that Ag plays a role promoting the adsorption and catalytic oxidation of H2S leading to drastic changes in the electrical resistance via electron injection into CCTO.