Alumina substrate-supported electrochemical device for potential application as a diesel particulate matter sensor

The carbon oxidation activity and sensing performance of an alumina substrate-supported sensor comprised of Sn0.9In0.1P2O7 as a proton conductor and Pt as an electrocatalyst were investigated. Electrochemically formed active oxygen species exhibited high activity for carbon oxidation, where the current efficiency was estimated from the four-electron reaction (C + 2H2O → CO2 + 4H+ + 4e−) and reached approximately 90%. An operating temperature of 225 °C was found to be the most effective to achieve the highest possible electrochemical carbon oxidation and the lowest possible non-electrochemical carbon oxidation. When carbon introduced to the Sn0.9In0.1P2O7–Pt interface was oxidized by active oxygen, a large potential jump was observed due to a significant increase in the polarization resistance, which was strongly dependent on the carbon content in the working electrode. Two types of carbon sensors, amperometric and potentiometric, were tested in a feed mixture of 3 vol% water vapor and 10 vol% O2. In the case of the amperometric sensor, the current increased linearly with increasing carbon content, which enabled the determination of a wide range of carbon content from the current signal. In the case of the potentiometric sensor, a threshold quantity of carbon could be recognized by selection of the current and subsequent monitoring of the sudden potential increase.