Design of a highly sensitive and responsive electrode for particulate matter monitoring

In a previous sensor device based on a Pt|Sn0.9In0.1P2O7|Pt electrode system, electrochemical carbon oxidation was realized over the surface of a working electrode, enabling continuous carbon monitoring with self-regeneration of the sensor. Specific reactivity of the active oxygen species for carbon was demonstrated along with a high current efficiency. However, this reaction did not occur over the entire electrode layer, limiting the sensing properties and giving a low sensitivity and response speed. The main reason for carbon oxidation being limited to the surface region was the lack of proton conduction in the working electrode. To overcome this problem, we added proton-conducting Sn0.9In0.1P2O7 particles as an ionomer to the working electrode. The Sn0.9In0.1P2O7 ionomer was successfully distributed over the working electrode at the level of a few micrometers, providing reaction sites for carbon oxidation over the entire electrode layer. The resulting amperometric sensor provided a sensitivity to carbon that was 1.4 times greater than that of the ionomer-free working electrode, as determined by the current at which carbon oxidation had ceased. Moreover, carbon floating in a glass container could be transported to reaction sites present on the external surface of the working electrode, allowing for a large current and a rapid response.