Improvement of In2O3-Based CO Sensor by Using Surface Modifiers

Aiming at developing a semiconductor CO sensor applicable to the safety control of gas appliances, we carried out an extensive material search for promoters to In2O3-based elements. Among the elements added (0.5 wt%) with each of 12 transition metal oxides, the Co3O4-added one was outstanding in sensitivity and selectivity to CO at 200°C. Remarkably the sensing properties of this element could be improved further by the addition of Au (0.04 wt%). The doubly promoted element, Au (0.04 wt%)-Co(0.5 wt%)-In2O3, gave excellent characteristics in sensitivity to CO, selectivity to CO over H2 and other selected gases, and response rates at 250°C. The promoting effects of the additives were shown to originate from the proper enhancement of catalytic activity for CO oxidation.