Hydrated niobium oxides are used as strong solid acids with a wide variety of catalytic applications, yet the correlations between structure and acidity remain unclear. New insights into the structural features giving rise to Lewis and Brønsted acid sites are presently achieved. It appears that Lewis acid sites can arise from lower coordinate NbO and in some cases NbO sites, which are due to the formation of oxygen vacancies in thin and flexible NbO systems. Such structural flexibility of Nb-O systems is particularly pronounced in high surface area nanostructured materials, including few-layer to monolayer or mesoporous NbO·nHO synthesized in the presence of stabilizers. Bulk materials on the other hand only possess a few acid sites due to lower surface areas and structural rigidity: small numbers of Brønsted acid sites on HNbO arise from a protonic structure due to the water content, whereas no acid sites are detected for anhydrous crystalline H-NbO.

Ligand exchange with octylphosphonate enhances PLQY and LED efficiency.

Room-temperature perovskite nanocrystal syntheses have previously lacked the size tunability attainable through high-temperature methods. Herein, we outline a scalable approach whereby the nucleation and growth of CsPbBr 3 nanocrystals (NCs) can be decoupled and controlled at room temperature by utilizing different ligands. We employed octylphosphonic acid (OPA) ligands to regulate the critical radius and the NC growth rate. The subsequent addition of a bulkier didodecyldimethylammonium bromide ligand quenches the NC growth, defining the reaction duration. Management of these three variables enables precise tuning of the NC diameter between 6.8 and 13.6 nm. The photoluminescence quantum yield of the NCs remains above 80% for all sizes even after thorough antisolvent purification. The use of hydrogen-bonding OPA ligands enhances quantum confinement effects, characterized by strong, well-resolved absorption peaks. Solution and solid-state nuclear magnetic resonance spectra confirmed the effective removal of unbound ligands during purification and the presence of a hydrogen-bonded network of OPA ligands on the surface of the purified NCs. Overall, this approach has the potential to facilitate a broad range of future endeavors from studies of hot carrier dynamics to both optically and electrically driven device applications.

It is well established that the inclusion of small atomic species such as boron (B) in powder metal catalysts can subtly modify catalytic properties, and the associated changes in the metal lattice implies that the B atoms are located in the interstitial sites. However, there is no compelling evidence for the occurrence of interstitial B atoms, and there is a concomitant lack of detailed structural information describing the nature of this occupancy and its effects on the metal host. In this work, we use an innovative combination of high-resolution 11 B magic-angle-spinning (MAS) and 105 Pd static solid state NMR nuclear magnetic resonance (NMR), synchrotron X-ray diffraction (SXRD), in-situ X-ray pair distribution function (XPDF), scanning transmission electron microscopy-annular dark field imaging (STEM-ADF), electron ptychography and electron energy loss spectroscopy (EELS) to investigate the B atom positions, properties and structural modifications to the palladium lattice of an industrial type interstitial boron doped palladium nanoparticle catalyst system (Pdint B/C NPs). In this study we report that upon B incorporation into the Pd lattice, the overall face centered cubic (FCC) lattice is maintained, however short range disorder is introduced. The 105 Pd static solid-state NMR illustrates how different types (and levels) of structural strain and disorder are introduced in the nanoparticle history. These structural distortions can lead to the appearance of small amounts of local hexagonal close packed (HCP) structured material in localized regions. The short range lattice tailoring of the Pd framework to accommodate interstitial B dopants in the octahedral sites of the distorted FCC structure can be imaged by electron ptychography. This study describes new toolsets that enables the characterization of industrial metal nanocatalysts across length scales from macro-analysis to micro-analysis, which gives important guidance to structure-activity relationship of the system.

, for use of their electron microscopy/X-ray facilities. We would also like to acknowledge the NTU Center of High Field NMR Spectroscopy and Imaging for the use their NMR facilities.

Halide perovskites are of great interest for lightemitting diodes (PeLEDs) in recent years due to their excellent photo-and electroluminescence properties. However, trap/defects and ion migration of devices under high external driving voltage/current are yet to be overcome. In this work, it is found that upon potassium (K) addition to a CsPbBr3/Cs4PbBr6 (3D:0D = 0.85:0.15) perovskite, a locally-disordered 0D Cs4-xKxPbBr6 phase is formed with nearly 0.35:0.65 admixture of 0D:3D, along with an unreacted KBr phase potentially passivating the surface and grain boundaries. The formation of CsPbBr3 nanocrystals (~10nm) confined within the Cs4-xKxPbBr6 matrix accompanied by larger CsPbBr3 grains (~50nm) is further confirmed by high-resolution transmission electron microscopy. In addition, the kinetics of ion migration were characterized with Auger electron spectroscopy and double-layer polarization using capacitive-frequency measurements, revealing significantly lower hysteresis, halide ion migration and accumulation for the K-incorporated samples during device operation, resulting in substantial improvements in LED performances and stability.

Metal halide perovskites have shown excellent properties for lighting applications, including high photoluminescence quantum yield (PLQY), compositional tunability, and narrow emission line widths. Perovskite light-emitting diodes (LEDs) have achieved external quantum efficiency (EQE) up to 20% in the green, red, and near-infrared (NIR) spectral regions. Recently, nanostructured perovskite NIR-LEDs have displayed 100 h of device stability, making this technology commercially viable and prompting greater awareness of this class of devices, as distinct from visible wavelength perovskite LEDs. Even so, the current generation of high-performance perovskite LEDs are still hampered by slow radiative recombination of charge carriers, unbalanced injection of charge carriers, and light out-coupling efficiency; therefore, more structural and morphological engineering of perovskite LEDs is needed to confine the charge carriers and collect the photons more effectively. It has been observed that 3D bulk perovskites show high performance but have poor stability and offer less control over their optical properties. In contrast, NIR-emitting perovskite nanocrystals offer precise control of their optical properties but exhibit poor optoelectronic properties due to the presence of bulky ligands. Quasi-2D perovskite systems have gained significant attention as they balance high conductivity and stability, while enabling precise color tuning of nanostructures, and the possibility to produce single crystal-LEDs. Here, we assess these and other recent advancements in NIR-emitting perovskite materials. We compare different structural frameworks and how they influence the LED performance in terms of color stability, EQE, and device stability. The practical challenges facing each of these structural classes of perovskite NIR-LED materials and the possible strategies to overcome these obstacles are thoroughly discussed.

Although 105Pd is a very challenging nucleus for solid state NMR, these initial observations demonstrate its potential for characterising catalytically relevant Pd metal systems.