In recent years, exhaust sensors have become increasingly attractive for use in energy and environmental technologies. Important issues regarding practical applications of these sensors, especially for soot measurements, include the further development of ion-conductive electrolytes and active electrode catalysts for meeting performance and durability requirements. Herein, we design a proton conductor with a high breakdown voltage and a sensing electrode with high sensitivity to electrochemical carbon oxidation, enabling continuous soot monitoring with self-regeneration of the sensor. A Si0.97Al0.03HxP2O7-δ layer with an excellent balance between proton conductivity and voltage endurance was grown on the surface of a Si0.97Al0.03O2-δ substrate by reacting it with liquid H3PO4 at 600 °C. Specific reactivity of the electrochemically formed active oxygen toward soot was accomplished by adding a Pt-impregnated Sn0.9In0.1HxP2O7-δ catalyst into a Pt sensing electrode. To make the best use of these optimized materials, a unipolar electrochemical device was fabricated by configuring the sensing and counter electrodes on the same surface of the electrolyte layer. The resulting amperometric mode sensor successfully produced a current signal that corresponded to the quantity of soot.

There have been many attempts to develop solid-state sensor devices for detecting particulate matter (PM) in diesel exhaust; however, in most of these, the accumulated PM must be burned intermittently to allow subsequent sensing cycles. Here, we report a selfregenerable PM sensor using a proton conductive solid electrolyte and an active working electrode for PM oxidation. The withstanding voltage capability of BaZr 0.8 Y 0.2 O 3-δ was greatly improved by the growth of a dense Zr 1-x Y x P 2 O 7 film on the electrolyte surface. The reaction of PM with active oxygen under anodic polarization was further enhanced by the addition of IrO 2 to the working electrode. As a result of these combined modifications, when the working electrode was anodically polarized, PM was oxidized to CO 2 according to a four-electron reaction (C + 2H 2 O → CO 2 + 4H + + 4e -) while remaining below the self-ignition temperature. This amperometric sensor successfully produced a current signal corresponding to the quantity of PM in a gas stream at an operating temperature of 300 • C. These results demonstrate that the sensor can carry out continuous monitoring of PM concentrations while self-regenerating.