Molybdenum Dichalcogenide Nanotube Arrays for Hydrogen-Evolution-Reaction Catalysis: Synergistic Effects of Sulfur and Selenium in a Core-Shell Tube Wall

The present work shows the growth and conversion of self-organized anodic Mo-oxide nanotube arrays to core-shell structures consisting of a conducting molybdenum sub-oxide core and a shell of Mo-Se/S – this structure is then investigated for electrochemical hydrogen evolution catalysis. To form the core-shell tubes, we first anneal MoO3 nanotube arrays under vacuum conditions, to induce reduction to MoO2. Subsequently these oxide tubes are thermally sulfurized and selenized resulting in dichalcogenide@sub-oxide structures. Under optimized conditions, the mixed dichalcogenide (selenized and sulfurized) tube walls on the conductive oxide core lead to a synergistic beneficial effect for the electrocatalytic H2 generation from H2SO4 solution

TiO2 ALD Coating of Amorphous TiO2 Nanotube Layers: Inhibition of the Structural and Morphological Changes Due to Water Annealing

The present work presents a strategy to stabilize amorphous anodic self-organized TiO2 nanotube layers against morphological changes and crystallization upon extensive water soaking. The growth of needle-like nanoparticles was observed on the outer and inner walls of amorphous nanotube layers after extensive water soakings, in line with the literature on water annealing. In contrary, when TiO2 nanotube layers uniformly coated by thin TiO2 using atomic layer deposition (ALD) were soaked in water, the growth rates of needle-like nanoparticles were substantially reduced. We investigated the soaking effects of ALD TiO2 coatings with different thicknesses and deposition temperatures. Sufficiently thick TiO2 coatings (≈8.4 nm) deposited at different ALD process temperatures efficiently hamper the reactions between water and F− ions, maintain the amorphous state, and preserve the original tubular morphology. This work demonstrates the possibility of having robust amorphous 1D TiO2 nanotube layers that are very stable in water. This is very practical for diverse biomedical applications that are accompanied by extensive contact with an aqueous environment

Nanocrystalline diamond protects Zr cladding surface against oxygen and hydrogen uptake : Nuclear fuel durability enhancement

In this work, we demonstrate and describe an effective method of protecting zirconium fuel cladding against oxygen and hydrogen uptake at both accident and working temperatures in water-cooled nuclear reactor environments. Zr alloy samples were coated with nanocrystalline diamond (NCD) layers of different thicknesses, grown in a microwave plasma chemical vapor deposition apparatus. In addition to showing that such an NCD layer prevents the Zr alloy from directly interacting with water, we show that carbon released from the NCD film enters the underlying Zr material and changes its properties, such that uptake of oxygen and hydrogen is significantly decreased. After 100–170 days of exposure to hot water at 360 °C, the oxidation of the NCD-coated Zr plates was typically decreased by 40%. Protective NCD layers may prolong the lifetime of nuclear cladding and consequently enhance nuclear fuel burnup. NCD may also serve as a passive element for nuclear safety. NCD-coated ZIRLO claddings have been selected as a candidate for Accident Tolerant Fuel in commercially operated reactors in 2020

Preparation of porcupine-like Bi2O3 needle bundles by anodic oxidation of bismuth

A new Bi2O3 structure resembling bundles of needles was prepared by anodic oxidation of a bismuth substrate in H2SO4 electrolyte followed by annealing in air. Needle growth occurred on the timescale of minutes. The resulting porcupine-like needle bundles were characterized using SEM and XRD before and after annealing. The as-grown needles consisted of bismuth aqua sulfate hydroxide; however, upon annealing at 250°C in air, tetragonal β-Bi2O3 was produced without any morphological change. Keywords: Anodization, Bismuth, Bismuth oxide, Breakdown, Needle

Self-organized Anodic TiO2 Nanotube Layers: Influence of the Ti substrate on Nanotube Growth and Dimensions

In this contribution, various Ti thin substrates were explored and compared for the anodic growth of self-organized TiO2 nanotube layers for the first time. In order to evaluate differences in the electrochemical anodization characteristics and the tube dimensions, five different Ti substrates from four established suppliers were anodized in the widely used ethylene glycol electrolytes containing 88 mM NH4F and 1,5 vol.% water. Two anodizations were carried out to elucidate an influence of the pre-anodized substrates used for the second anodization. By thorough evaluation of the nanotube dimensions, large variations between the dimensions of the nanotubes were found for the different substrates, ranging from ∼32 μm to ∼50 μm for the nanotube length and from ∼109 nm to ∼127 nm for the nanotube diameter after the second anodization. Upon AFM measurements, Goodfellow Ti substrates (99.99% purity), yielded the smoothest surface and the highest degree of ordering from all substrates. Moreover, considerably different consumption of Ti substrates via anodization was revealed by profilometric measurements between the original non-anodized part of the Ti substrates, and the anodized part after the removal of the nanotube layer. Orientation imaging microscopy revealed considerable differences in the size and orientation of the substrate grains