Carlos López-Gándara

YSZ-Based Oxygen Sensors and the Use of Nanomaterials: A Review from Classical Models to Current Trends

This work reviews physicochemical models on the operation and the response of potentiometric oxygen gas sensors based on ion-conducting electrolytes. The aim for describing the electric response and some properties like response time, ionic conductivity, catalytic activity, or gas selectivity of these devices has led to the development of some models in the last decades. These models have provided information on relations between the response of the sensors, their design and fabrications process, and some morphological properties, like grain size of the electrolyte, diffusion on protective layers, or density of three-phase boundary points in the measuring electrodes. Current trends on improving catalysis, gas selectivity, and activation energy for ion conducting by using nanomaterials are described as well.

Monolithic Ceramic Technology for Sensing Devices

We present a multilayer co-fired ceramic technology for the development of alumina-based gas sensors substrates. These substrates include embedded heater and thermo-resistance as well as electrodes in a 2x2mm dice. Substrate thickness is less than 0.2mm. The substrate technology allows obtaining smooth surface at the nanometer scale. As an example of application, we have studied the growth of nanowires on the presented structure to take advantage of nanoscale phenomena.

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.