A solid-state particulate matter sensor based on electrochemical oxidation of carbon by active oxygen

The carbon oxidation activity and sensing performance of an electrochemical sensor incorporating a robust SnP2O7–SnO2 composite ceramic as a solid electrolyte were investigated at an operating temperature of 200 °C. Specific reactivity of the electrochemically formed active oxygen toward carbon was accomplished with a high current efficiency estimated from the four-electron reaction (C + 2H2O → CO2 + 4H+ + 4e−). However, this reaction did not occur over the entire electrode layer, which resulted in low sensitivity and a slow response speed. This problem could be overcome by distributing a SnP2O7 ionomer over the working electrode at a level of several micrometers. Moreover, an additional benefit of the present sensor for practical applications is that little interference was encountered when sensing carbon at levels of 1000 ppm CO and 1000 ppm C3H8 in the sample gas. The resulting amperometric mode sensor could successfully produce a current signal that corresponded to the quantity of particulate matter (PM) in the bench test apparatus. These results demonstrate that the present sensor is able to continuously monitor the PM concentration while self-regenerating.