Self-Assembled 1-Octadecanethiol Membrane on Pd/ZnO for a Selective Room Temperature Flexible Hydrogen Sensor

A layer of self-assembled 1-octadecanethiol was used to fabricate a palladium (Pd)/zinc oxide (ZnO) nanoparticle-based flexible hydrogen sensor with enhanced response and high selectivity at room temperature. A palladium film was first deposited using DC sputtering technique and later annealed to form palladium nanoparticles. The formation of uniform, surfactant-free palladium nanoparticles contributed to improved sensor response towards hydrogen gas at room temperature. The obtained sensor response was higher than for previously reported room temperature Pd/ZnO sensors. Furthermore, the use of the polymer membrane suppressed the sensor’s response to methane, moisture, ethanol, and acetone, resulting in the selective detection of hydrogen in the presence of the common interfering species. This study shows a viable low-cost fabrication pathway for highly selective room temperature flexible hydrogen sensors for hydrogen-powered vehicles and other clean energy applications.

Membrane Covered Probes for O2 and H2 Determination - Diffusion through Liquid Films and Solid Membrane in Practice

In the era of the expansion of hydrogen use, its concentration measurement becomes more important. We further focus on one of the H2 concentration measurement purposes, where the hydrogen diffusion in a solid membrane and in a liquid electrolyte play the key role. To keep optimal process conditions in the primary cooling circuit of nuclear power plants, various chemical species are dosed in. Among the species the concentration of which is monitored in primary coolant, belong oxygen and hydrogen. While plenty of companies offer oxygen sensors suitable for the measurement in the primary coolant, the hydrogen sensor, really selective to H2 concentration, is offered by only one company. It is worth, therefore, accomplishing the development of a hydrogen sensor, which began at UCT Prague in the 1990's and, after several successful measurements in nuclear power plant, interrupted due to fateful events in the research team. We introduce here the results of the first part of contemporary work of the Mass Transfer Laboratory based on new technologies but using the experience from 1990's. Having at disposal modern functional samples to measure both oxygen and hydrogen concentrations, we verified a fair long-term stability of the sensors and, further, we would like to cooperate with an industrial partner to finalize the development of prototypes and start the production of monitoring units.

Development of a fiber optic sensor for hydrogen monitoring in transformers

<p>Electric vehicles and photovoltaic power generation are two of factors that are increasing the demands on the electrical grid. To cope with these challenges and to improve grid stability, the development of a transformer monitoring system as a fundamental part of the smart grid is necessary. Dissolved hydrogen in the transformer oil can serve as a primary indicator of the transformer health. Depending on the hydrogen concentration and rate of increase the transformer can be diagnosed. The goal of this thesis was to develop a highly sensitive hydrogen sensor for online health monitoring of transformers. The developed sensors are based on palladium and fiber Bragg gratings (FBG). Palladium expands with hydrogen absorption and this expansion is measured with an FBG. Detailed guidance for optimizing the sensor design is given. First, the selection of the working temperature is discussed. Second, the influence of the palladium geometry on the sensitivity is elaborated: by varying the cross-sectional area ratio of palladium to fiber the sensitivity can be tuned. Two different options to attach palladium are discussed: vapour deposition of palladium and adhesive bonding of palladium foils. The sensitivity of the palladium foil sensors was improved by improved manufacturing processes. The foil sensor have a sensitivity of up to 295 pm/% hydrogen and a resolution of 0.006% hydrogen in gas atmosphere at 90◦C and 1060 mbar. To further increase the hydrogen sensitivity two concepts for amplification of the signal are presented. One relies on palladium silver foils, which have an increased hydrogen solubility and therefore expansion compared to pure palladium, which achieved an increase in sensitivity of a factor of 17. This leads to sensitivity of over 4500 pm/% hydrogen, which is the most sensitive hydrogen sensor reported so far. The other concept relies on a novel concept for strain concentration using a pre-strained palladium foil and FBG, which achieved an amplification of a factor of 2.5. The sensors were characterised in gas and oil environment in a newly developed setup which is stable in pressure, temperature and gas concentration. In gas the sensors were tested at 60, 75, 90, 105, and 120◦C and for a hydrogen concentration range of 0.01 (100 ppm) to 5%. In oil the sensor was tested at 90◦C and for a hydrogen concentration range of 5- 4000 ppm dissolved hydrogen. Furthermore, the influence of carbon monoxide (CO) on the hydrogen sensitivity was examined. A slowed response could be observed, but CO had no impact on the precision of the sensor. Finally, the hydrogen calibration of the sensor is discussed by investigating the strain transfer between expanding palladium and fiber. Three different methods are elaborated to determine the coefficient of strain transfer: (a) via hydrogen measurement, (b) via temperature measurement, and (c) via strain measurement. Methods (a) and (b) were applied directly on the hydrogen sensor, and gave similar results. Method (c) was applied on a reference structure and used to verify method (b). A hydrogen sensor suitable for transformer health monitoring has been developed and characterised, and is currently being implemented in a transformer in the New Zealand network.</p>