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Concept of an impedance-based ammonia sensor for SCR applications

Title data

Wöhrl, Thomas ; Hagen, Gunter ; Moos, Ralf:
Concept of an impedance-based ammonia sensor for SCR applications.
Event: Eurosensors XXXIV , 19.-23. Sept. 2022 , Leuven, Belgium.
(Conference item: Conference , Speech )

Abstract in another language

In the next few years, the importance of renewable energies will continue to increase in order to comply with the increasingly stricter climate targets for the reduction of greenhouse gases. In this context, the energetic use of biogenic residual and waste materials represents an alternative to the combustion of fossil fuels. However, the high content of nitrogen in biomass favors the formation of harmful nitrogen oxides (NOX). Therefore, systems for selective catalytic reduction (SCR) of NOX using ammonia (NH3) will be necessary in the future. For this purpose, a specific ammonia gas sensor is needed to ensure optimal dosing of the reducing agent. Therefore, in the following an impedimetric sensor principle will be described, which offers a cost-efficient fabrication in thick film technology. The basis for the NH3 sensor is an aluminum oxide substrate to which different layers are applied. In the first step, a meander-shaped platinum heat conductor structure is applied to the back of the substrate. It heats the sensor to an optimum temperature during operation. To prevent oxidation of ammonia on the heat conductor structure an additional insulating covers the heater. On the front side, a solid gold surface is applied using a screen-printing process. The gold layer is then transferred to an interdigital electrode (IDE) structure using a laser. The electrodes have each a width and distance of 20 µm. The final step involves the deposition of a H-ZSM5-zeolite layer with a module of 55, whose electrical properties depend on the ammonia concentration in the exhaust gas. The entire sensor setup is shown in Figure 1. These properties are investigated in more detail by using an impedance measurement system. For that, a sinusoidal voltage with a fixed frequency (here: Ueff = 250 mV and f = 1 MHz) is applied to the electrodes and the resulting current is measured. The magnitude of the complex impedance |Z | is determined for the evaluation. The functional tests of the sensors were carried out in the laboratory using synthetic gas (10 % O2, 7.5 % CO2, 2 % H2O in N2, V ̇= 6 l/min) while varying the ammonia concentration from 0 - 240 ppm. An example measurement at a sensor temperature of 440 °C is shown in Figure 2. It can be seen that the sensor shows significant signal change to each different ammonia level and returns to its base value after dosing. The highest sensitivity to ammonia can be found at low concentrations. The sensor shows almost no cross-sensitivity to other exhaust components. The sensor temperature also plays an important role in the further development of the sensor, which was investigated in more detail in Figure 3. With increasing temperature, the sensitivity to ammonia decreases, but the response time of the sensor improves. In the further course, other influencing parameters, e.g., zeolite composition, electrode structure, etc., are to be investigated with respect to the sensor behavior in order to find an optimum sensor configuration.

Further data

Item Type: Conference item (Speech)
Refereed: Yes
Institutions of the University: Faculties > Faculty of Engineering Science
Faculties > Faculty of Engineering Science > Chair Functional Materials > Chair Functional Materials - Univ.-Prof. Dr.-Ing. Ralf Moos
Profile Fields > Advanced Fields > Advanced Materials
Research Institutions > Research Centres > Bayreuth Center for Material Science and Engineering - BayMAT
Faculties > Faculty of Engineering Science > Chair Functional Materials
Profile Fields
Profile Fields > Advanced Fields
Research Institutions
Research Institutions > Research Centres
Result of work at the UBT: Yes
DDC Subjects: 600 Technology, medicine, applied sciences > 620 Engineering
Date Deposited: 27 Sep 2022 07:18
Last Modified: 27 Sep 2022 07:18