Within the scope of the project, a long-term stable combustible catalytic micro gas sensor will be developed for detecting hydrogen of very low concentration. Metalic nanoparticles linked by organic ligands will be used as catalysts. Long-term stability will be earned by creating a homogeneous temperature field on a catalytic layer by optimizing the design of the microfabricated sensor. Along with long-term stability, the sensor will have low power consumption, high sensitivity, low response time and low cross sensitivity.
The main objective of the project is to improve the stability, performance and selectivity of the catalytic micro gas sensor by optimizing the design of the sensor and ligand-linked nanoparticles network. For achieving long-term stability of ligand linked nanoparticles network, an IR transparent adiabatic reactor will also be developed for in-situ investigation.
Precise detection of hydrogen is always necessary due to the safety issue associated with the handling of this highly explosive gas. Therefore, hydrogen gas sensors should have high sensitivity, selectivity, fast response, low power consumption for portable application and stability for long-term operation. The main working principle of the combustible catalytic gas sensor is to measure the temperature increment during exothermic reaction of hydrogen oxidation. The Classical sensor of this type has high power consumption, low sensitivity and slow response due to their robust structure. Power consumption and response time can be reduced by micro technologically designed sensors with low heat conductive membrane. The sensitivity of the sensor can be increased by expanding the active surface area of the catalyst. This can be done with the help of ligand linked nanoparticles of the catalyst material. IMSAS, in collaboration with IPAC, developed a catalytic micro gas sensor with this concept under the project ‘KatSense- Katalytische Gassensoren’. Within the scope of the project ‘Ligand’, improvement of the performance of the concept will be achieved by the optimization of stability and sensitivity of ligand-linked nanoparticles.
The basic element of the sensor is high temperature stable, low-stress silicon rich LPCVD silicon nitride membrane created by DRIE process, where the ligand-linked nanoparticles (catalytic layer) are to be deposited. The power consumption of the sensor is reduced by optimizing membrane and sensing element geometry. Ligand-linked nanoparticles are catalytically very active due to their large surface area. However, poisoning and sintering during operation create deactivation of the catalytic layer and prevent long-term stability of the sensor. The microsensor with IR transparent membrane and housing with IR transparent windows is to be fabricated with microtechnology. It will facilitate in-situ investigation of sintering and poisoning effect during catalysis by IR spectroscopy. That will eventually help to find the reason for deactivation of the catalytic layer and thus improving stability.
One of the main reasons for deactivation of the catalyst is an inhomogeneous temperature field over the ligand-linked nanoparticles layer on the membrane. It creates the autocatalytic effect. The main challenge is to change the design of the membrane and the heater in such a way that results in homogeneity in the temperature distribution without hampering IR transparency for IR spectroscopy. Considering all requirements, a homogeneous temperature field over the membrane is achieved by round shape membrane with round heater with small loops in the corner.
The effect of operating conditions such as temperature, humidity in the reaction chamber will be analysed to improve the stability of the sensor. Moreover, the other factors for stability such as ligand-linked nanoparticles network, type of ligand will be optimized by the investigation.
Although the selectivity of hydrogen gas is higher at lower operating temperature, the increasing humidity at a lower temperature can cause deactivation of the catalyst. Optimizing sensor operation at a lower temperature without causing deactivation is a great challenge and an objective of the work.
Finally, the design of an optimal micro technological sensor that improves the stability of the catalytic layer has lower power consumption, high sensitivity and selectivity will be developed.
Institute for Applied and Physical Chemistry, University of Bremen, iapc.
M.Sc Anmona Shabnam Pranti
IMSAS, NW1, Raum O1050
Tel. +49 421 218 62 613
E-mail: aprantiprotect me ?!imsas.uni-bremenprotect me ?!.de
Prof. Dr.-Ing. Walter Lang
IMSAS, NW1, Raum O2120
Tel: +49 421 218 62 602
E-mail: wlangprotect me ?!imsas.uni-bremenprotect me ?!.de
The Project LIGAND is funded by the DFG - Deutsche Forschungsgemeinschaft from 2017 to 2019.