Durability enhancement of Pd-based plasmonic hydrogen sensors by tunable mesoporous metal oxide layers

Hydrogen Economy is a model envisaging a zero-carbon emmission future, encompassing subtopics such as hydrogen production, utilization, storage and detection, where hydrogen serves as a energy carrier. This model holds significant potential as an alternative energy source to fossil fuels, owning to features such as the ability to produce hydrogen without carbon emission using renewable energy sources, the release of only water molecules as byproducts when used in hydrogen fuel cells, and its threefold higher energy density compared to fossil fuels. However, hydrogen is an explosive gas when its concentration exceeds 4% in the air. Therefore, fast and reliable detection of potential hydrogen leaks plays a crucial role in the hydrogen economy. In recent years, palladium-based plasmonic hydrogen sensors have attracted attention due to their excellent response time even at low hydrogen concentrations. Although palladium dissociate hydrogen molecules under atmospheric conditions and undergo a reversible phase transformation from metal to metal hydride phase, and even though this transformation can be tracked with measurable optic signals, they have some drawbacks. Challanges such as hysteresis formation during hydrogen absorbtion/desorption, sensor deactivation due to strong chemical interactions with CO, and the necessity for selectivity against molecules such as CO2 and CH4 pose obstacles for plasmonic hydrogen sensors. In the literature, studies have attempted to address these challanges by alloying palladium with metals like gold and copper and applying various polymeric (PMMA,PTFE) thin film coatings. Althoug both methods can improve the properties of plasmonic hydrogen sensors, degradation of polymeric coatings over time will prevent the long-term use of the sensors. In the scope of this thesis, inspired by polymeric coatings, efforts made to enhance the durability of plasmonic hydrogen sensors by creating a protective layer that would not degrade over time under different environmental conditions. Towards this goal, Pd70Au30 nanodisks, which have been demonstrated in the literature to suppress hysteresis formation, were fabricated using the hole-mask colloidal litography. Subsequently, the synthesis of ordered mesoporous SiO2 which has high resistant to hars conditions and have controllable structure with controllable parameters such as precursor/surfactant ratio, calcination temperature/time and coating time/speed was carried out using sol-gel method, and thin films were fabricated onto the alloy nanodisks via spin-coating. Finally, a test reactor and two software programs for gas flow control and signal analysis were developed through collaborative efforts with fellow students from different disciplines. Performance tests were then conducted for the fabricated sensors. The test results demonstrated that the prepared ordered mesoporous SiO2 thin film made the sensor resistant to CO molecules, reduced the response time and have selectivity over CO2 and CH4 molecules.