Robust, selective NOx species sensor for tailpipe emissions

Diagnostic characterization of tailpipe emission of nitrogen oxides (NOx) is becoming increasingly important as environmental concern and government regulations are requiring the use of complex NOx monitoring and destruction schemes, especially in diesel-fueled engines. As these systems become more efficient, tailpipe emissions can retreat to the parts per million (ppm) level, which requires an equally precise NOx sensor to provide feedback for the active destruction system in the presence of the many components of post catalyzer exhaust gas. Equally important to maintaining the NOx destruction efficiency is the ability to provide diagnostic information on an ever-shorter timescale to tighten the engine control loop about its most efficient operating point. Finally, reliability, cost and manufacturability are crucial to helping these systems achieve widespread implementation and acceptance. New robust transducer structures that have high sensitivity, quick responses selective molecular determination and high concentration precision determination are needed to go along with cost effective manufacturability and robustness in the face of the extreme environmental conditions present in the exhaust of internal combustion engines. Over the course of Phase II program, Nanohmics has been developing a novel detection system that involves custom electroactive materials with electrolyte layers to significantly improve structural integrity and catalytic conversion efficiency at the tri-phase interface. The geometry provides a means for increased electroactive surface area and higher sensitivity when read-out in mixed potential mode. In this regard, the geometry provides a large increase in the catalytic exchange surface sites for electrical carriers during reactive coupling of the target species, namely NOx and NH3. The matrix of the electroactive material provides a means for gas target entrainment and diffusion which impacts the kinetics of the target species and ultimately presents as differences in the mixed potential measurement during real time read-out. In addition to the high sensitivity of the electroactive materials, co-processing with the oxide diffusion electrolyte materials leads to much stronger interfacial bonding that provides device longevity through prevention of material layer delamination over the lifetime of the vehicle. As a final measure, the team created structures for a read-out system that provides several enhancements compared to commercial amperometric devices or state-of-the art sensors. During the Phase II program, Nanohmics and team demonstrated the basic principles of the compact gas detection system and has been developing methods to integrate the novel materials with electrode readout arrays supported on electrolyte materials. For the Phase IIA program, Nanohmics proposes to continue development of the high-temperature and environmentally-stable sensor array device based on this core detection technology.