INDIUM OXIDE-BASED GAS SENSOR FOR SELECTIVE DETECTION OF CO

Among various single-metal oxides, In2O3, SnO2 and ZnO were found to e xhibit rather high sensitivities to CO at 300 degrees C and above. Esp ecially In2O3 appeared to be most attractive in view of the selectivit y to CO over H-2. It was further found that modifications of In2O3 wit h the addition of alkali metal carbonates, especially Rb2CO3, were ver y effective for enhancing the sensitivity and the selectivity to CO. T he sensor element using Rb-In2O3 could detect 500-4000 ppm CO in wet a ir at 300 degrees C satisfactorily, while its cross-sensitivities to o ther gases such as H-2, CH4, C3H6, and NO were comparatively small. Ca talytic activity test and TPD measurements showed that, as a reason fo r the promoting effects, the addition of Rb2CO3 to In2O3 enhances the catalytic activity of CO oxidation. In addition, XPS data indicated th at, as another reason, Rb2CO3 forms the strongest p-n junctions with I n2O3 among alkali metal carbonates.