Tantalum-Palladium: Hysteresis-Free Optical Hydrogen Sensor Over 7 Orders of Magnitude in Pressure with Sub-Second Response

Hydrogen detection in a reliable, fast, and cost-effective manner is a prerequisite for the large-scale implementation of hydrogen in a green economy. Thin film Ta1−yPdy is presented as an effective optical sensing material with extremely wide sensing ranges covering at least 7 orders of magnitude in hydrogen pressure. Nanoconfinement of the Ta1−yPdy layer suppresses the first-order phase transitions present in bulk and ensures a sensing response free of any hysteresis. Unlike other sensing materials, Ta1−yPdy features the special property that the sensing range can be easily tuned by varying the Pd concentration without a reduction of the sensitivity of the sensing material. Combined with a suitable capping layer, sub-second response times can be achieved even at room temperature, faster than any other known thin-film hydrogen sensor.Instrumenten groepChemE/AfdelingsbureauChemE/Materials for Energy Conversion & Storag

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Photochromism of rare-earth metal-oxy-hydrides

Recently, thin films of yttrium oxy-hydride (YOxHy) were reported to show an unusual color-neutral photochromic effect promising for application in smart windows. Our present work demonstrates that also oxy-hydrides based on Gd, Dy, and Er have photochromic properties and crystal structures similar to YOxHy. Compared to YOxHy, the optical bandgaps of the lanthanide based oxy-hydrides are smaller while photochromic contrast and kinetics show large variation among different cations. Based on these findings, we propose that cation alloying is a viable pathway to tailor the photochromic properties of oxy-hydride materials. Furthermore, we predict that the oxy-hydrides of the other lanthanides are also potentially photochromic.ChemE/Materials for Energy Conversion & StorageChemE/Afdelingsburea

Ammonia Synthesis at Ambient Conditions via Electrochemical Atomic Hydrogen Permeation

Direct electrochemical nitrogen reduction holds the promise of enabling the production of carbon emission-free ammonia, which is an important intermediate in the fertilizer industry and a potential green energy carrier. Here we show a strategy for ambient condition ammonia synthesis using a hydrogen permeable nickel membrane/electrode that spatially separates the electrolyte and hydrogen reduction side from the dinitrogen activation and hydrogenation sites. Gaseous ammonia is produced catalytically in the absence of electrolyte via hydrogenation of adsorbed nitrogen by electrochemically permeating atomic hydrogen from water reduction. Dinitrogen activation at the polycrystalline nickel surface is confirmed with 15N2 isotope labeling experiments, and it is attributed to a Mars-van Krevelen mechanism enabled by the formation of N-vacancies upon hydrogenation of surface nitrides. We further show that gaseous hydrogen does not hydrogenate the adsorbed nitrogen, strengthening the benefit of having an atomic hydrogen permeable electrode. The proposed approach opens new directions toward green ammonia. ChemE/Materials for Energy Conversion & StorageChemE/O&O groe

Metal Hydride Based Optical Hydrogen Sensors

Hydrogen is playing a key role in the transition to a sustainable economy and in a variety of industrial processes. For its safe handling, the detection of hydrogen in a fast, reliable and accurate manner is crucial. Thin film metal hydride based optical hydrogen sensors provide an attractive option to sense hydrogen in a variety of conditions and have an attractive safety benefit over other methods of detection: They do not require the presence of electrical leads near the sensing area. These sensors rely on a change of the optical properties arising from a change in the hydrogenation of the metal hydride sensing layer in response to a different partial hydrogen pressure in the environment of the sensor. In this paper, we review how the performance and characteristics of an optical hydrogen sensor are related to the material properties of the metal hydride sensing layer and we discuss previously considered materials and challenges and opportunities left for the future.Accepted Author ManuscriptInstrumenten groepChemE/Materials for Energy Conversion & StorageChemE/Afdelingsburea