Strategies for improving sensitivity to nitrogen oxides in electrochemical gas sensors for lean combustion engines

Sensitivity to nitrogen monoxide (NO) was studied in conventional planar exhaust gas sensors after implementing layers made of microstructured or nanostructured tungsten trioxide (WO₃) over one of their electrodes. The sensors were made of an YSZ solid electrolyte and covered by two catalytic Pt-based electrodes. They showed different sensitivities to NO depending on the WO₃ layer configuration: nanostructured WO₃, microstructured WO₃, YSZ mixed with WO₃, etcetera. Sensitivity in terms of each layer configuration has been attributed to a competition between diffusion and catalytic activity in each layer. Maximum sensitivity to NO in multi-component gas mixtures was found in sensors with 20μm-thin layers of nanostructured WO₃.