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

The influence of grit blasting and UV/Ozone treatments on Ti-Ti adhesive bonds and their durability after sol-gel and primer application

In this study, different surface pretreatments were applied to clean and activate titanium alloy surfaces. The samples were subjected to grit blasting treatments using two different pressures and afterwards, a UV/Ozone treatment was applied at different times to study the wettability and surface oxidation of the titanium samples. Scanning electron microscopy and laser confocal microscopy showed the surface morphology and the increased roughness with grit blasting pressure. X-ray Photoelectron Spectroscopy revealed that titanium was increasingly oxidized with increasing UV/Ozone treatment time, which leads to a reduced contact angle and a better adhesive performance in a butt tension test proving the effectivity of this surface treatment for titanium. Furthermore, the addition of sol-gel AC-120 and corrosion inhibition primer BR 6747 showed to be an additional improvement in the initial adhesion and after different degrees of aging by exposure to salt-spray, making the surface treatment techniques used in this research, a promising environmental friendly alternative to improve adhesive bonding performance.Structural Integrity & CompositesChemE/O&O groepAdhesion Institut

How Deep Hole Traps Affect the Charge Dynamics and Collection in Bare and Bilayers of Methylammonium Lead Bromide

Wide-band-gap perovskites such as methylammonium lead bromide (MAPB) are promising materials for tandem solar cells because of their potentially high open-circuit voltage, which is yet still far below the maximum limit. The relatively short charge-carrier lifetimes deduced from time-resolved photoluminescence (TRPL) measurements seem in strong contrast with the long lifetimes observed with time-resolved photoconductance measurements. This is explained by a large amount of hole defect states, NT > 1016 cm-3, in spin-coated layers of MAPB residing at or near the grain boundaries. The introduction of hypophosphorous acid (HPA) increases the average grain size by a factor of 3 and reduces the total concentration of the trap states by a factor of 10. The introduction of HPA also increases the fraction of initially generated holes that undergo charge transfer to the selective contact, Spiro-OMeTAD (SO), by an order of magnitude. In contrast to methylammonium lead iodide (MAPI)/SO bilayers, a reduction of the carrier lifetime is observed in MAPB/SO bilayers, which is attributed to the fact that injected holes undergo interfacial recombination via these trap states. Our findings provide valuable insight into the optoelectronic properties of bromide-containing lead halide perovskites essential for designing efficient tandem solar cells.ChemE/Opto-electronic MaterialsChemE/O&O groe

Hydrogenation Kinetics of Metal Hydride Catalytic Layers

Catalyzing capping layers on metal hydrides are employed to enhance the hydrogenation kinetics of metal hydride-based systems such as hydrogen sensors. Here, we use a novel experimental method to study the hydrogenation kinetics of catalyzing capping layers composed of several alloys of Pd and Au as well as Pt, Ni, and Ru, all with and without an additional PTFE polymer protection layer and under the same set of experimental conditions. In particular, we employ a thin Ta film as an optical indicator to study the kinetics of the catalytic layers deposited on top of it and which allows one to determine the absolute hydrogenation rates. Our results demonstrate that doping Pd with Au results in significantly faster hydrogenation kinetics, with response times up to five times shorter than Pd through enhanced diffusion and a reduction in the activation energy. On the other hand, the kinetics of non-Pd-based materials turn out to be significantly slower and mainly limited by the diffusion through the capping layer itself. Surprisingly, the additional PTFE layer was only found to improve the kinetics of Pd-based capping materials and has no significant effect on the kinetics of Pt, Ni, and Ru. Taken together, the experimental results aid in rationally choosing a suitable capping material for the application of metal hydrides and other materials in a hydrogen economy. In addition, the used method can be applied to simultaneously study the hydrogenation kinetics in thin-film materials for a wide set of experimental conditions.Instrumenten groepChemE/O&O groe

Wafer-scale transfer-free process of multi-layered graphene grown by chemical vapor deposition

Chemical vapour deposition (CVD) has emerged as the dominant technique to combine high quality with large scale production of graphene. The key challenge for CVD graphene remains the transfer of the film from the growth substrate to the target substrate while preserving the quality of the material. Avoiding the transfer process of single or multi-layered graphene (SLG-MLG) has recently garnered much more interest. Here we report an original method to obtain a 4-inch wafer fully covered by MLG without any transfer step from the growth substrate. We prove that the MLG is completely released on the oxidized silicon wafer. A hydrogen peroxide solution is used to etch the molybdenum layer, used as a catalyst for the MLG growth via CVD. X-ray photoelectron spectroscopy proves that the layer of Mo is etched away and no residues of Mo are trapped beneath MLG. Terahertz transmission near-field imaging as well as Raman spectroscopy and atomic force microscopy show the homogeneity of the MLG film on the entire wafer after the Mo layer etch. These results mark a significant step forward for numerous applications of SLG-MLG on wafer scale, ranging from micro/nano-fabrication to solar cells technology.Electronic Components, Technology and MaterialsChemE/O&O groe

High dielectric filler for all-solid-state lithium metal battery

Lithium metal with its high theoretical capacity and low negative potential is considered one of the most important candidates to raise the energy density of all-solid-state batteries. However, lithium filament growth and its induced solid electrolyte decomposition pose severe challenges to realize a long cycle life. Here, dendrite growth in solid-state Li metal batteries is alleviated by introducing a high dielectric material, barium titanate, as a filler that removes the electric field gradients that catalyze dendrite formation. In symmetrical Li-metal cells, this results in a very small over-potential of only 48 mV at a relatively high current density of 1 mA cm−2, when cycling a capacity of 2 mA h cm−2 during 1700 h. The high dielectric filler improves the Coulombic efficiency and cycle life of full cells and suppresses electrolyte decomposition as indicated by solid-state nuclear magnetic resonance (NMR) and X-ray photoelectron spectroscopy (XPS) measurements. This indicates that the high dielectric filler can suppress dendrite formation, thereby reducing solid electrolyte decomposition reactions, resulting in the observed low overpotentials and improved cycling efficiency.RST/Storage of Electrochemical EnergyRID/TS/Instrumenten groepRID/TS/Technici PoolChemE/O&O groe

Combinatorial Screening of Bimetallic Electrocatalysts for Nitrogen Reduction to Ammonia Using a High-Throughput Gas Diffusion Electrode Cell Design

The electrochemical nitrogen reduction reaction (NRR) is a promising alternative to the current greenhouse gas emission intensive process to produce ammonia (NH3) from nitrogen (N2). However, finding an electrocatalyst that promotes NRR over the competing hydrogen evolution reaction (HER) has proven to be difficult. This difficulty could potentially be addressed by accelerating the electrocatalyst development for NRR by orders of magnitude using high-throughput (HTP) workflows. In this work, we developed a HTP gas diffusion electrode (GDE) cell to screen up to 16 electrocatalysts in parallel. The key innovation of the cell is the use of expanded Polytetrafluoroethylene (ePTFE) gas diffusion layers (GDL) which simplifies the handling of catalyst arrays compared to carbon fabrics and enables sufficient N2 mass transport. We demonstrate the robustness of the HTP workflow by screening 528 bimetallic catalysts of composition AB (A,B = Ag, Al, Au, Co, Cu, Fe, Mn, Mo, Ni, Pd, Re, Ru, W) for NRR activity. None of the materials produced ammonia significantly over background level which emphasizes the difficulty of finding active electrocatalysts for NRR and narrows down the search space for future studies.ChemE/Materials for Energy Conversion and StorageChemE/O&O groe

Metal-insulator multilayer precursors for enhanced Sm²⁺ absorption and Tm²⁺ luminescence in SiAlO thin films prepared by magnetron sputtering

Silicon-aluminum-oxigen (SiAlO) coatings doped with Sm2+ and prepared by reactive magnetron co-sputtering of Si, Al, and Sm targets, are attractive for luminescence solar concentrator applications but suffer from the low absorption between 300 and 600 nm. This article reports that the main cause of low absorption is a high concentration of undesired Sm3+. This finding is supported by optical transmittance, photoluminescence emission and excitation characterization, and X-ray photoelectron spectroscopy data of the Sm's 3d5/2 edge. We present an alternative deposition process for obtaining Sm doped SiAlO layers with enhanced Sm2+ absorption by incorporating Sm through the use of multilayer thin-film precursors composed of metallic Sm and SiAlO layers. After thermal post-deposition treatments, diffusion and reaction of the metallic Sm layers with the SiAlO host results in coatings showing the characteristic 5d → 4f transitions of Sm2+ in the region between 250 and 600 nm which were not detectable in Sm-doped single layers. This same deposition strategy produces Tm doped SiAlO coatings with Tm2+‘s characteristic luminescence at 1132 nm when the SiAlO host is in the mullite composition region. The photoluminescence excitation spectrum of Tm2+ is compared to phosphor with similar composition and covers the range between 300 and 700 nm.RST/Luminescence MaterialsQN/AfdelingsbureauChemE/O&O groe