Search

Shape-controlled microstructures (triangles and urchin-like) of Ni were synthesized using polyol synthesis in the presence/absence of capping agent (polyvinilpyrrolidone, PVP). Direct visualization of crystal structure and morphology before/after electrochemical tests in KOH were characterized using electron microscopy techniques. Electrochemical characterizations illustrated that urchin-Ni-PVP has highest catalytic activity among all investigated electrocatalysts for glycerol electrooxidation reaction (GEOR). Improved activity was attributed to the surface area and the highly porous structure as identified by electron tomography analysis. All Ni shapes showed similar selectivity. DFT calculations on low-index β-NiOOH and β-Ni(OH) 2 planes were performed as possible surfaces present during electrochemical processes. The (0 0 1) surface is the most thermodynamically stable in both systems and has different possible terminations. For O, Ni and mixed Ni-O atoms terminations the β-NiOOH(0 0 1) present metallic behavior. DFT results show that either Ni or Ni-O exposed β-NiOOH(0 0 1) surfaces are possible scenarios for glycerol adsorption on different catalytic charged surface sites.

Anion exchange membrane water electrolysis (AEMWE) is an attractive technology for hydrogen (H2) production. This process, however, is kinetically hindered by the oxygen evolution half-cell reaction (OER). Nickel (Ni)-based materials in combination with iron (Fe) have been considered a promising option to enhance activity toward OER in alkaline media. Studies have also shown that incorporating ceria (CeO2) into electrocatalysts can help promote the OER. This study investigates the OER activity of bimetallic Ni–Fe spherical nanoparticles, with and without ceria, synthesized by chemical reduction in ethanol using sodium borohydride. First, the iron content is studied for Ni100−xFex / 50 wt% CeO2 (x = 0, 5, 10, 20, 40 at%); then, the ceria content is studied for the best two iron compositions, namely, Ni80Fe20 / y wt% CeO2 and Ni90Fe10 / y wt%CeO2 (y = 0, 5, 7, 10, 20, and 50 wt%). Transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) characterization show spherical particles 4–6 nm in size, where Ni and Fe are co-distributed, and ceria is separately agglomerated. Electrochemical characterization in 1 M KOH shows that at 10 mA cm−2, the Ni80Fe20 catalyst achieved the lowest overpotential for OER of 269 mV, which is better performing than the iridium black benchmark, as well as similar NiFe materials reported in literature. Stability testing indicates that the Ni90Fe10 catalyst is the most stable material with almost no change in overpotential over 12 h at 10 mA cm−2. This study shows that the addition of CeO2 to the catalysts does not significantly improve or impede OER activity.

Nanodiamonds are interesting materials from the point of view of their biocompatibility and their chemical, spectroscopic, and mechanical properties. Current synthetic methods for nanodiamonds involve harsh environments, which are potentially hazardous in addition to being expensive. We report a low-temperature (423 K) hydrothermal approach to form nanodiamonds by using graphene-oxide or nitrated polycyclic aromatic hydrocarbons (naphthalene, anthracene, phenanthrene, or pyrene) as a starting material. The reaction products contain single-crystalline or twinned nanodiamonds with average diameters in the 2-3 nm range. Theoretical calculations prove that, at the nanoscale, sub-4 nm nanodiamonds may adopt a structure that is more stable than graphene-oxide and nitrated polycyclic aromatic hydrocarbons. Our findings show that sp2 carbon in the polycyclic aromatic precursor can be converted to sp3 carbon under unexpectedly moderate temperature conditions by using nanoscale precursors and thus offer a low-temperature approach for the synthesis of sub-4 nm nanodiamonds.

Herein we synthesized bi-metallic Pd@Ni and Au@Ni core-shell-like nanoparticles (NPs) for glycerol electrooxidation reaction (GEOR) in alkaline media. The morphological, structural and surface properties of the NPs were evaluated using a range of physicochemical techniques. The catalytic activity and stability were studied using the three-electrode electrochemical cell and 25 cm2- continuous electrolysis cell. Among different atomic ratios, Ni80Pd20 and Ni90Au10 nanoparticles showed the highest current densities which are ~4.5 and 4.2 times higher than spherical Ni, respectively. The addition of Pd and Au (

To pave the way for InGaN-on-Si integrated photovoltaics, uniform and close-packed n-GaN/(Al)InGaN/p-GaN nanowire (NW) arrays with a ∼0.29 μm thick absorption segment of ∼2.35 eV energy bandgap were fabricated on a Si substrate using Ti-mask selective area growth (SAG) in a molecular beam epitaxy (MBE) chamber. Instead of using thick and insulting buffer layers, this SAG process was realized by employing a 3 nm AlN/GaN: Ge buffer layer to facilitate electrical and thermal conduction between NWs and Si. Scanning transmission electron microscopy and high-resolution electron energy loss spectroscopy mapping revealed the discontinuities of AlN and the embedments of GaN:Ge which contribute to a negligible resistance of the NWs-on-Si interface. AlInGaN active segment exhibits core-shell structures, which suppress nonradiative surface recombination at NW surfaces. Working of AlInGaN core-shell NW solar cells was demonstrated with improved open-circuit voltage (Voc) and higher energy conversion efficiency (η) than those reported for InGaN NW solar cells. Stable output characteristics including the Voc of 1.41 V and η of 2.46% were obtained under 30-Sun illuminations. Such NWs-on-Si devices use Si substrate as the bottom electrode. With a low series resistance of ∼1 Ω, this work paves the way to monolithically integrate MBE-SAG III-nitride devices and Si-based electronics, such as Si solar cells and CMOS devices.

Nanoporous gold made by dealloying AgAuPt (NPG-Pt) has been shown to exhibit several interesting catalytic properties, tied to its exceptionally high surface area; however, structural degradation may occur owing to thermal coarsening. To understand the effect of atmosphere chemistry on thermal coarsening and degradation, and means of limiting it, this study focuses on the high-resolution characterization of NPG-Pt layers coarsened in reductive Ar-H2 atmosphere, and in oxidative air. Atom probe tomography (APT) analysis is performed on NPG-Pt, coarsened separately in either Ar-H2 or air, to characterize the atomic-scale chemical changes in the nanoligaments and to develop a mechanistic view of the inherent processes. A tendency of Ag to segregate to the surface during coarsening is found to lead to complete elimination of the nanoligament core-shell structures in both cases. Large Pt segregates form during coarsening in Ar-H2, but under the surface of the ligaments, having relatively little effect on the coarsening rate. The oxygen-induced segregation of Pt was observed to cause the inhibition of thermal coarsening after minor loss in surface area-to-volume ratio. Findings in this paper help in understanding further the thermal coarsening of heterogeneous nanomaterials made by dealloying, and the pertinent factors that come into play in different chemical environments.

Amorphous Ni79.2–xCoxNb12.5Y8.3 (x = 0 and 5 at %) nanoparticles were produced through a two-stage ball milling process for use as electrocatalysts in the alkaline oxygen evolution reaction (OER). ...

The selective hydrogenation of cinnamaldehyde (CAL) is an extremely important transformation. Herein, oxygen functionalized carbon nanotubes (oCNTs) supported a series of PtxCoy bimetallic nanoparticles (NPs) with varied Pt to Co ratios were synthesized. The introduction of Co significantly affects the electronic structure of Pt NPs, which clearly promotes the selectivity to cinnamyl alcohol (COL). Among all PtxCoy-oCNTs catalysts, PtCo3-oCNTs exhibited the best catalytic performance and a selectivity of over 76% towards COL at a CAL conversion of 99% was obtained. Further characterization of the fresh, used and cycled catalysts revealed that the NP structures were stable and did no change. The structural evolutions during the catalytic reaction were also investigated by identical location transmission electron microscopy (IL-TEM) method in detail, which found that the deactivation of PtCo3-oCNTs catalyst during the cycle experiment results from the agglomeration and detachment of PtCo3 NPs.

We report results on the synthesis of unsupported and carbon-supported nickel hydroxide nanoparticles (β-Ni(OH)2 NPs). Their characterization using X-ray diffraction (XRD) and trans-mission electro...

Simultaneously improving energy efficiency (EE) and material stability in electrochemical CO2 conversion remains an unsolved challenge. Among a series of ternary Sn-Ti-O electrocatalysts, 3D ordered mesoporous (3DOM) Sn0.3 Ti0.7 O2 achieves a trade-off between active-site exposure and structural stability, demonstrating up to 71.5 % half-cell EE over 200 hours, and a 94.5 % Faradaic efficiency for CO at an overpotential as low as 430 mV. DFT and X-ray absorption fine structure analyses reveal an electron density reconfiguration in the Sn-Ti-O system. A downshift of the orbital band center of Sn and a charge depletion of Ti collectively facilitate the dissociative adsorption of the desired intermediate COOH* for CO formation. It is also beneficial in maintaining a local alkaline environment to suppress H2 and formate formation, and in stabilizing oxygen atoms to prolong durability. These findings provide a new strategy in materials design for efficient CO2 conversion and beyond.

The possibility of surrogating high-pressure supercritical water (SCW) with an ambient pressure air-10% H2O (wet air) mixture for studying wet oxidation of Type 310S stainless steel (UNS S31008) at high temperatures was examined using gravimetric measurements coupled with electron microscopy techniques. A distinctly different wet oxidation kinetic rate law was observed in the two environments at 550°C: parabolic for the wet air mixture and para-linear (“breakaway”) for SCW. The differing rate law is attributed to differences in the mass transport kinetics parameters, which are not well defined for SCW, that likely control Cr volatilization from the oxide scale, starting with the presumed MnCr2O4 spinel outer layer. Although the wet air mixture is not considered to be a suitable surrogate environment for SCW at the temperature of interest, it may prove useful to help determine microstructure instability effects on wet oxidation at elevated temperatures.

An equilateral triangular prism is used as the fundamental building block to con- struct additive Sierpinski fractals, enabling new surface plasmon resonances (SPR) in the first three generations of Sierpinski triangles, as well as topological intermediaries between generations. The modes are characterized using electron energy loss spectroscopy accompanied by eigenmode calculations and optical finite-difference time domain simulations. The complex fractal geometries present a predictable hierarchy of new resonances, each arising from the previous generational building blocks used to construct the fractal. Intermediate structures break the polarization degeneracy of the equilateral fractals while maintaining a rich multiband spectral response. Engineering defects in the narrow conductive channels of the fractal allows further manipulation of the SPR response, emphasizing higher order SPR modes over the lowest energy peak. The knowledge gained is used to develop guidelines for engineering the response of more complex fractal-based structures, including the spectral response and hotspot distribution.

Plasmonic polymeric nanoassemblies offer valuable opportunities in photoconversion applications. Localized surface plasmon mechanisms behind such nanoassemblies govern their functionalities under light illumination. However, an in-depth investigation at the single nanoparticle (NP) level is still challenging, especially when the buried interface is involved, due to the availability of suitable techniques. Here, we synthesized an anisotropic heterodimer composed of a self-assembled polymer vesicle (THPG) capped with a single gold NP, enabling an 8-fold enhancement in hydrogen generation compared to the nonplasmonic THPG vesicle. We explored the anisotropic heterodimer at the single particle level by employing advanced transmission electron microscopes, including one equipped with a femtosecond pulsed laser, which allows us to visualize the polarization- and frequency-dependent distribution of the enhanced electric near fields at the vicinity of Au cap and Au–polymer interface. These elaborated fundamental findings may guide designing new hybrid nanostructures tailored for plasmon-related applications.

A detailed study aimed at understanding and confirming the reported highly promising performance of a La

Nowadays, sub-50 meV atom-wide electron probes are routinely produced for electron energy loss spectroscopy in transmission electron microscopes due to monochromator technology advances. We review how gradual improvements in energy resolution enabled the study of very low-energy excitations such as lattice phonons, molecular vibrations, infrared plasmons and strongly coupled hybrid modes in nanomaterials. Starting with the theoretical framework needed to treat inelastic electron scattering from phonons in solids, we illustrate contributions in detecting optical surface phonons in photonic structures. We discuss phonon mapping capabilities in real and reciprocal space, and the localized phonon response near nano-/atomic-scale structural features. We also survey the progress of aloof spectroscopy in studying vibrations in organic materials and applications in measuring local temperature and photonic density of states in single nanostructures using phonon scattering. We then turn towards studies on infrared plasmons in metals and semiconductors. Spectroscopy analyses now extend towards probing extremely complex broadband platforms, the effects of defects and nanogaps, and some far-reaching investigations towards uncovering plasmon lifetime and 3D photonic density of states. In doped semiconductors, we review research on the use of the electron probe to correlate local doping concentration and atomic-scale defects with the plasmonic response. Finally, we discuss advances in studying strong coupling phenomena in plasmon–exciton and plasmon–phonon systems. Overall, the wealth of information gained extends our knowledge about nanomaterial properties and elementary excitations, illustrating the powerful capabilities of high-energy resolution scanning transmission electron microscopy–electron energy loss spectrometry.

Understanding the mechanism for capacity delivery in conversion/alloying materials (CAM) electrodes, such as ZnO, in lithium-ion batteries (LIBs) requires careful investigation of the electrochemical reactions. Here, we used magic angle spinning (MAS at 60 kHz) 7Li nuclear magnetic resonance (NMR) as a sensitive analytical means to probe the reactions occurring between electrode materials and Li+ ions. The ZnO nanolayer generated on carbon substrate by atomic layer deposition (ALD) enhanced the cyclic capacity of half cell LIB up to 40%. 7Li NMR revealed LixZn alloy formation through an irreversible conversion reaction during discharge. MAS results revealed the dealloying of LixZn at the full charge step which left atomic zinc nanograins that do not undergo the re-oxidation of zinc atoms according to the cyclic voltammetry. An in situ formation of elemental zinc at the initial cycles facilitates uniform lithium deposition on subsequent cycles due to the reduced energy barrier for lithium nucleation on pure zinc as compared to ZnO. X-ray diffraction analysis indicated the crystalline formation of the LixZn alloy while scanning electron microscope showed the uniform morphology for the lithiated discharge products. Cyclic voltammetry and differential capacity functions initially predicted the conversion and alloying reactions.

Employing photo-energy to drive the desired chemical transformation has been a long pursued subject. The development of homogeneous photoredox catalysts in radical coupling reactions has been truly phenomenal, however, with apparent disadvantages such as the difficulty in separating the catalyst and the frequent requirement of scarce noble metals. We therefore envisioned the use of a hyper-stable III–V photosensitizing semiconductor with a tunable Fermi level and energy band as a readily isolable and recyclable heterogeneous photoredox catalyst for radical coupling reactions. Using the carbonyl coupling reaction as a proof-of-concept, herein, we report a photo-pinacol coupling reaction catalyzed by GaN nanowires under ambient light at room temperature with methanol as a solvent and sacrificial reagent. By simply tuning the dopant, the GaN nanowire shows significantly enhanced electronic properties. The catalyst showed excellent stability, reusability and functional tolerance. All reactions could be accomplished with a single piece of nanowire on Si-wafer., A highly efficient re-usable semiconductor as a radical coupling catalyst in MeOH.

Core–shell or concentration-gradient structures have been reported to improve the structural and chemical stability of Ni-rich electrode materials; however, a core–shell or concentration-gradient s...

Single atom catalysts exhibit particularly high catalytic activities in contrast to regular nanomaterial-based catalysts. Until recently, research has been mostly focused on single atom catalysts, and it remains a great challenge to synthesize bimetallic dimer structures. Herein, we successfully prepare high-quality one-to-one A-B bimetallic dimer structures (Pt-Ru dimers) through an atomic layer deposition (ALD) process. The Pt-Ru dimers show much higher hydrogen evolution activity (more than 50 times) and excellent stability compared to commercial Pt/C catalysts. X-ray absorption spectroscopy indicates that the Pt-Ru dimers structure model contains one Pt-Ru bonding configuration. First principle calculations reveal that the Pt-Ru dimer generates a synergy effect by modulating the electronic structure, which results in the enhanced hydrogen evolution activity. This work paves the way for the rational design of bimetallic dimers with good activity and stability, which have a great potential to be applied in various catalytic reactions., Atomically precise control over elemental distributions presents a challenge in the preparation of catalytic nanomaterials. Here the authors report Pt-Ru bimetallic dimer structures through atomic layer deposition process and identify the roles of Pt and Ru in hydrogen evolution reaction.

Pt single-atom catalysts are receiving more and more attention due to their different properties compared with nanostructures. As one typical kind of single-atom catalysts, Pt-based single-atom all...

Summary Ammonia is one of the most important bulk chemicals in modern society. However, the highly energy-extensive contemporary industrial production of ammonia was developed in the early 20th century and requires extensive heating of highly pressurized flammable hydrogen gas, whose global production still relies heavily on non-sustainable petroleum. The development of “sustainable” nitrogen fixation process represents a grand aspirational chemical pursuit concerning our future human well-being. Herein, we report an ultra-stable nitride-based photosensitizing semiconductor that enables efficient, sustainable, and mild photochemical nitrogen fixation. The catalyst exhibits strong chemisorption of nitrogen and enables immediate electron donation from its surface vacancy to nitrogen. In addition, it was also demonstrated that the nitride-based semiconductor possesses the potential to minimize electron-hole recombination., Graphical Abstract, Highlights • Efficient photo-N2 fixation • Strong chemisorption of N2 • Uses water as H source, Chemical Reaction; Catalysis; Density Functional Theory (DFT); Nanostructure

Glycerol partial electrooxidation was studied on NixPd1–x (x = 100, 95, 90, and 80 atom %) nanoparticles synthesized using a polyol method. The shape-controlled urchin-like monometallic Ni and sphe...

Electrochemical promotion of Ni9Pd nanoparticles (NPs) with low Pd content (Ni:Pd = 9:1 atomic ratio) supported on yttria-stabilized zirconia (YSZ) solid-electrolyte was evaluated for the first time for complete methane oxidation. Electron Energy Loss Spectroscopy (EELS) showed a Pd core with a Ni first shell surrounded by 3–4 nm layer of Pd outer shell. This core double-shell structure of Ni9Pd NPs enhanced the catalytic activity and stability compared to mono-metallic Pd and Ni NPs under open-circuit. The reversible electrochemical promotion of Ni9Pd was obtained upon positive polarization between 425 and 500 °C. At 425 °C, the reaction rate increase reached 240% corresponding to apparent Faradaic efficiency of 25. On Ni9Pd NPs the reaction exhibited electrophobic behavior, i.e., the rate increased with anodic polarization, under all experimental conditions of this study. The results demonstrate the advantage of using Ni9Pd bi-metallic nanoparticles with core double-shell structure for methane complete oxidation due to the synergetic effect between Pd and Ni and very low amount of expensive Pd phase. EPOC with this type of highly dispersed and low noble metal content catalysts may find a way in the real world catalytic converters for gas exhaust treatment.

Decreasing Pt loading in the anode layer below ∼0.025 mg·cm–2 is found to reduce the hydrogen oxidation reaction rate during polymer electrolyte membrane fuel cells (PEMFCs) normal operation, when using conventional Pt/C catalysts and electrode coating methods. To achieve extremely low Pt loading in the anode catalyst layer while maintaining high PEMFC performance and durability, a series of membrane electrode assemblies (MEAs) with low Pt loading in the anode layer are successfully prepared using an atomic layer deposition (ALD) technique. When the ALD cycle number is controlled, the Pt nanoparticles (NPs) with different sizes and loadings are directly deposited on the carbon layer to form the anode catalyst layer. The ALDPt NPs with uniform particle sizes are highly distributed on the carbon surface, which promotes the ALDPt with high electrochemical active surface area and enables enhanced performance of ALDPt-MEAs. Particularly, the 50ALDPt-MEA with the anode Pt prepared by 50ALD cycles shows excellen...

We have used X-ray photoelectron spectroscopy, time-of-flight secondary ion mass spectrometry, transmission electron microscopy and reconstructed electron diffraction patterns, to study the contamination of the Cu nanoparticle surface on atmospheric exposure, as would occur on using such nanoparticles as antimicrobials deposited onto bandages intended for use as wound dressings. Our study suggests that the surface contaminant initially formed by residual gases in vacuum is Cu2CO3. On atmospheric exposure, this is oxidized to CuCO3, combined with Cu(OH)2, as found in azurite and malachite; pure CuO is not found in nature. On subsequent exposure to high energy irradiation, which might occur in the bandage packaging process, the azurite/malachite contaminant breaks down, forming CuO, which is reduced by reaction with carbon, forming Cu0, before ultimately re-oxidizing to reform the surface contaminants. We discuss the implications of these results on possible mechanisms of the antimicrobial action of such nanoparticles when deposited onto bandages.