Maximilian Pfeiffer receives the award from the Association of Friends of TU Darmstadt for his outstanding master's thesis
The Association of Friends of the Technical University of Darmstadt e.V. awarded the prize of 1,000 euros for the best master's thesis in the Department of Chemistry at TU Darmstadt last year on July 19, 2022. This year's recipient is Mr. Maximilian Pfeiffer, who conducted his master's thesis in the field of Physical Chemistry in the research group of Prof. Dr. Christian Hess. The award was presented during the graduation ceremony of the Department of Chemistry at TU Darmstadt.
In his master's thesis titled Investigation of Au-Doped SnO2 Gas Sensors Using Transient IR Spectroscopy, Mr. Pfeiffer focused on the mechanistic elucidation of surface reactions occurring during ethanol gas sensing on gold-loaded and unloaded tin oxides.
Chemoresistive gas sensors, as investigated by Mr. Pfeiffer in his master's thesis, are widely used in safety technology for the early detection of toxic and explosive gases. Additionally, they are applied in medical diagnostics and quality control of food. Their operation is based on a change in electrical conductivity in the presence of the target molecules to be detected, which adsorb on the surface and react with the surface of the sensor material or other adsorbed surface species.
In the application areas mentioned at the beginning, ethanol is one of the most important analytes to be detected in ambient and breath air. The semiconducting metal oxide tin oxide, on the other hand, is among the first sensor materials used in gas sensors and is still one of the most commonly used sensor materials today due to its high sensitivity and easy manufacturability. Its sensor properties can be further improved by doping with small amounts of noble metals such as gold, for example, to increase sensitivity to the target analyte or to enhance selective sensor response in the presence of other potential analytes in the ambient air.
For a rational design of improved sensor materials, a profound understanding of the processes occurring at the sensor surface is crucial. This understanding can be obtained through suitable in situ spectroscopic methods that interrogate the surface species present during the reaction. In his master's thesis, Mr. Pfeiffer utilized in situ infrared spectroscopy, combining it with resistance measurements and other ex situ characterization methods. Typically, the mechanistic investigation of surface reactions is disturbed by so-called observer species that are not directly involved in the actual reaction. Therefore, the application of a transient method of infrared spectroscopy is particularly noteworthy. This method involves the periodic variation of the gas phase composition and subsequent phase-sensitive detection to selectively query the surface species actively involved in the reaction. Furthermore, this method allows the investigation of the dynamics of active surface species, i.e., the temporal sequence of adsorption/desorption or reaction steps. While this approach has found occasional application in the field of heterogeneous catalysis, it has not been applied in this form to the study of gas sensors. Thus, Mr. Pfeiffer succeeded in developing a spectroscopy-based internally consistent mechanism for the sensor response of ethanol on gold-loaded tin oxide and elucidating the influence of gold on surface reaction and sensor properties (see figure below). Additionally, he identified surface species not observed before, accessible only through time-resolved (transient) spectra, and expanded existing models for describing gas sensing on metal oxides.
The results of the master's thesis were published in the prestigious scientific journal Journal of Physical Chemistry C.