Highly selective sub–10 ppm H 2 S gas sensors based on Ag-doped CaCu 3 Ti 4 O 12 films

Abstract The detection of the toxic H 2 S gas is of great practical, environmental and industrial interest. This work presents sensing devices fabricated with Ag-doped CaCu 3 Ti 4 O 12 (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 H 2 S gas. The Ag-doped CCTO films were found to be remarkable sensors towards H 2 S in the concentration range of 0.2–10 ppm. In addition, the response of these sensors towards NH 3 , H 2 , NO 2 and ethanol vapor was up to two orders of magnitude lower than that for H 2 S, yielding a highly selective mean of detecting and quantifying H 2 S. 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 H 2 S leading to drastic changes in the electrical resistance via electron injection into CCTO.