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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.

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). ...

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.

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...

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.

The surface plasmon response of a cross-sectional segment of a wrinkled gold film is studied using electron energy loss spectroscopy (EELS). EELS data demonstrate that wrinkled gold structures act as a suitable substrate for surface plasmons to propagate. The intense surface variations in these structures facilitate the resonance of a wide range of surface plasmons, leading to the broadband surface plasmon response of these geometries from the near-infrared to visible wavelengths. The metallic nanoparticle boundary element method toolbox is used to simulate plasmon eigenmodes in these structures. Eigenmode simulations show how the diverse morphology of the wrinkled structure leads to its high spectral complexity. Micron-sized structural features that do not provide interactions between segments of the wrinkle have only a small effect on the surface plasmon resonance response, whereas nanofeatures strongly affect the resonant modes of the geometry. According to eigenmode calculations, different eigenenergy shifts around the sharp folds contribute to the broadband response and infrared activity of these structures; these geometrical features also support higher energy (shorter wavelength) symmetric and anti-symmetric plasmon coupling across the two sides of the folds. It is also shown that additional plasmon eigenstates are introduced from hybridization of modes across nanogaps between structural features in close proximity to each other. All of these factors contribute to the broadband response of the wrinkled gold structures.

Pnictogens have multiple allotropic forms resulting from their ns2 np3 valence electronic configuration, making them the only elemental materials to crystallize in layered van der Waals (vdW) and quasi-vdW structures throughout the group. Light group VA elements are found in the layered orthorhombic A17 phase such as black phosphorus, and can transition to the layered rhombohedral A7 phase at high pressure. On the other hand, bulk heavier elements are only stable in the A7 phase. Herein, we demonstrate that these two phases not only co-exist during the vdW growth of antimony on weakly interacting surfaces, but also undertake a spontaneous transformation from the A17 phase to the thermodynamically stable A7 phase. This metastability of the A17 phase is revealed by real-time studies unraveling its thickness-driven transition to the A7 phase and the concomitant evolution of its electronic properties. At a critical thickness of ~4 nm, A17 antimony undergoes a diffusionless shuffle transition from AB to AA stacked alpha-antimonene followed by a gradual relaxation to the A7 bulk-like phase. Furthermore, the electronic structure of this intermediate phase is found to be determined by surface self-passivation and the associated competition between A7- and A17-like bonding in the bulk. These results highlight the critical role of the atomic structure and interfacial interactions in shaping the stability and electronic characteristics of vdW layered materials, thus enabling a new degree of freedom to engineer their properties using scalable processes.

Configuring metal single-atom catalysts (SACs) with high electrocatalytic activity and stability is one efficient strategy in achieving the cost-competitive catalyst for fuel cells' applications. Herein, the atomic layer deposition (ALD) strategy for synthesis of Pt SACs on the metal-organic framework (MOF)-derived N-doped carbon (NC) is proposed. Through adjusting the ALD exposure time of the Pt precursor, the size-controlled Pt catalysts, from Pt single atoms to subclusters and nanoparticles, are prepared on MOF-NC support. X-ray absorption fine structure spectra determine the increased electron vacancy in Pt SACs and indicate the Pt-N coordination in the as-prepared Pt SACs. Benefiting from the low-coordination environment and anchoring interaction between Pt atoms and nitrogen-doping sites from MOF-NC support, the Pt SACs deliver an enhanced activity and stability with 6.5 times higher mass activity than that of Pt nanoparticle catalysts in boosting the oxygen reduction reaction (ORR). Density functional theory calculations indicate that Pt single atoms prefer to be anchored by the pyridinic N-doped carbon sites. Importantly, it is revealed that the electronic structure of Pt SAs can be adjusted by adsorption of hydroxyl and oxygen, which greatly lowers free energy change for the rate-determining step and enhances the activity of Pt SACs toward the ORR.

Enhanced electromagnetic fields in nanometer gaps of plasmonic structures increase the optical interaction with matter, including Raman scattering and optical absorption. Quantum electron tunneling across sub-1 nm gaps, however, lowers these effects again. Understanding these phenomena requires controlled variation of gap sizes. Mechanically actuated plasmonic antennas enable repeatable tuning of gap sizes from the weak-coupling over the quantum-electron-tunneling to the direct-electrical-contact regime. Gap sizes are controlled electrically via leads that only weakly disturb plasmonic modes. Conductance signals show a near-continuous transition from electron tunneling to metallic contact. As the antenna's absorption cross-section is reduced, thermal expansion effects are negligible, in contrast to conventional break-junctions. Optical scattering spectra reveal first continuous red shifts for decreasing gap sizes and then blue shifts below gaps of 0.3 nm. The approach provides pathways to study opto- and electromolecular processes at the limit of plasmonic sensing.

In this study, the effect of wrinkled gold wires and films geometries on the surface plasmon response of these systems is studied. This investigation is conducted using electron energy loss spectroscopy (EELS) to map surface plasmon activities with high spatial and energy resolution. Metallic nanoparticle boundary element method (MNPBEM) simulations and polarization modulation infrared (PM-IR) microscopy are utilized as complementary methods. According to experimental results and simulations, wrinkled structures demonstrate a broadband surface plasmon response which is directly resulting from their geometrical complexities.

Electrodeposition is widely used to fabricate tunable nanostructured materials in applications ranging from biosensing to energy conversion. A model based on 3D island growth is widely accepted in the explanation of the initial stages of nucleation and growth in electrodeposition. However, there are regions in the electrodeposition parameter space where this model becomes inapplicable. We use liquid cell transmission electron microscopy along with post situ scanning electron microscopy to investigate electrodeposition in this parameter space, focusing on the effect of the supporting electrolyte, and to shed light on the nucleation and growth of palladium. Using a collection of electron microscopy images and current time transients recorded during electrodeposition, we discover that electrochemical aggregative growth, rather than 3D island growth, best describes the electrodeposition process. We then use this model to explain the change in the morphology of palladium electrodeposits from spherical to open clusters with nonspherical morphology when HCl is added to the electrolyte solution. The enhanced understanding of the early stages of palladium nucleation and growth and the role of electrolyte in this process provides a systematic route toward the electrochemical fabrication of nanostructured materials.

Photoelectrochemical conversion of CO2 with H2O into high-energy fuels and value-added chemicals such as HCOOH provides an appealing strategy for storing solar energy and closing the anthropogenic carbon cycle. However, rational design of catalytic architectures enabling high turnover frequencies (TOFs) for large-scale application has remained a grand challenge. Herein, we report a unique GaN:Sn nanoarchitecture integrated on planar silicon for aqueous photoelectrochemical reduction of CO2 to formic acid. Our density functional theory calculations reveal that the interface of GaN nanowires (NWs) and Sn nanoparticles (NPs), owing to their strong interaction, enables spontaneous CO2 activation, presenting an energetically favorable reaction path for selective HCOOH evolution. Together with the enhanced solar light harvesting, efficient charge carrier extraction, and high catalyst-utilization efficiency, a benchmark TOF of 107 min−1, the highest value ever reported for solar-driven conversion of CO2 to formic acid, is achieved at a high current density of 17.5 mA cm−2, high faradaic efficiency of 76.9%, and low potential of −0.53 V versus reversible hydrogen electrode under one-sun illumination.

In order to gain better control over the functionality of Pd nanostructures used in several CO2-mitigating electrochemical energy conversion systems, it is imperative to underpin different nanoscale phenomena influencing their structural durability. Hitherto, such analyses have been carried out before/after an electrochemical treatment, but not during the entire process. Here, we demonstrate monitoring of morphological evolution in Pd nanostructures over the entire course of electrochemical treatment using a liquid-cell transmission electron microscope (TEM) set-up. Our findings reveal new insights into nanoparticle growth, dissolution, detachment, and aggregation that are relevant for the development of functional Pd nanomaterials.

The optical features and photocatalytic activity of porous undoped and Eu3+-doped zinc oxide (ZnO) sponge-like structures, annealed at various temperatures, were assessed to establish the relations ...

Designing a highly efficient and stable photoelectrochemical (PEC) tandem cell for unassisted solar water splitting is considered a promising approach for large-scale solar energy storage. To date, various tandem device configurations have been reported. However, the achievement of a solar-to-hydrogen conversion efficiency (ηSTH) of 10% is still full of challenges, due to the incompatibility between the two photoelectrode materials. Here, we report a highly efficient and stable photovoltaic (PV)–PEC tandem device composed of a dual Si photoelectrode and two series-connected ordinary Si PV cells. The dual-photoelectrode device consists of an n+np+-Si photocathode and p+pn+-Si photoanode, which allow back illumination from the Si substrate, spatially and functionally decoupling the optical absorption and the catalytic activity. By further employing a Ni protective layer together with a bifunctional Ni–Mo catalyst for both the Si photocathode and photoanode, the PV–PEC tandem cell can perform spontaneous water splitting without any applied bias. A high ηSTH of 9.8% with a stability of over 100 h was achieved in alkaline solution under parallel AM 1.5G 1 sun illumination. This work essentially allows a modular independent optimization of each component which can enhance the efficiency and stability of the PV–PEC cells.

A wide range of reconstruction methods exist nowadays to retrieve data from their undersampled acquisition schemes. In the context of Scanning Transmission Electron Microscopy (STEM), compressed sensing methods successfully demonstrated the ability to retrieve crystalline lattice images from undersampled electron micrographs. In this manuscript, an alternative method is proposed based on the principles of Moire sampling by intentionally generating aliasing artifacts and correcting them afterwards. The interference between the scanning grid of the electron beam raster and the crystalline lattice results in the formation of predictable sets of Moire fringes (STEM Moire hologram). Since the aliasing artifacts are simple spatial frequency shifts applied on each crystalline reflection, the crystal lattices can be recovered from the STEM Moire hologram by reverting the aliasing frequency shifts from the Moire reflections. Two methods are presented to determine the aliasing shifts for all the resolved crystalline reflections. The first approach is a prior knowledge-based method using information on the spatial frequency distribution of the crystal lattices (a common case in practice). The other option is a multiple sampling approach using different sampling parameters and does not require any prior knowledge. As an example, the Moire sampling recovery method detailed in this manuscript is applied to retrieve the crystalline lattices from a STEM Moire hologram recorded on a silicon sample. The great interest of STEM Moire interferometry is to increase the field of view (FOV) of the electron micrograph (up to several microns). The Moire sampling recovery method extends the application of the STEM imaging of crystalline materials towards low magnifications.

Electrochemical templating through porous membranes is applied to form arrays of micrometer long Ni nanowires (NWs). Detailed structural and electrochemical characterization, including electrochemi...

The wet oxidation performance of a high-Si (5.9 wt.%) Type 310 stainless steel exposed in flowing ambient pressure (0.1 MPa) air-10% H2O mixture at 800 °C was investigated. A lower parabolic rate constant, relative to that exhibited by conventional low-Si (0.6 wt.%) Type 310S stainless steel, in the observed paralinear kinetics is linked to the formation of a continuous SiO2 layer at the oxide scale/metal interface. Accelerated formation of non-protective Fe-rich oxides is significantly delayed due to Cr-rich silicide intermetallic phase, present in the starting microstructure, serving as reservoir to sufficiently supply Cr to replace oxidized Cr lost to volatilization.

The effect of Pt on the structural evolution of nanoporous gold (NPG) is complex and is controlled by processes including secondary dealloying of Ag, surface diffusion of Au, and Pt segregation. High-resolution studies are carried out to investigate the interplay of the inherent processes. Observations such as Pt segregation at nanoligament surfaces, core-shell structures of nanoligaments, and Ag retention inside individual nanoligaments are seen at unprecedented detail using high resolution characterization techniques, including Atom Probe Tomography (APT) and Electron Energy Loss Spectroscopy (EELS). Quantitative estimates of the surface area-to-volume ratios of nanoporous layers with different Pt content indicate their relative functionalities for surface area driven applications.

The dissolution of transition metal ions from positive electrodes and loss of (both electroactive and transport) Li+ ions seriously impair the durability of lithium ion batteries. We show herein that the improvement in the cycle life of lithium manganate spinel-graphite cells effected by multifunctional separators results from smaller interfacial resistances at both positive and negative electrodes, that can in turn be traced back to thinner, more uniform, and chemically different surface films, due to lessened parasitic reactions and a decreased accumulation of parasitic reaction products at electrode surfaces, as evidenced by HR-SEM, FIB-SEM, EDX, 19F MAS NMR, and ICP-OES data.

Intergranular oxidation in Alloy 600 exposed to 480 °C hydrogenated steam was examined at the nano-scale level with analytical electron microscopy and atom probe tomography. The fundamental processes of minor element oxidation and diffusion-induced grain boundary migration (DIGM) were explored. Intergranular oxidation was observed, with Ti and Al oxidation preceding Cr oxidation. Extensive DIGM is observed, with concentrations of minor elements far exceeding bulk values. Calculations are performed which support that the mechanism of DIGM causes large-scale segregation of minor elements. Also, discrete oxide particles ahead of the oxide front provide evidence for classical intergranular internal oxidation at temperatures below 500 °C.

Lithium-rich layered oxides are promising cathode candidates because of their exceptional high capacity. The commercial application of these high-energy cathodes, however, is thwarted by the undesired rapid performance decay during cycling. Surface degradation has been widely considered to correlate with the performance decay of the cathodes, whereas, in this work, we demonstrate that the degradation of Li-rich high-energy Li1.2Ni0.13Mn0.54Co0.13O2 (HENMC) cathode material not only takes place at surfaces but also proceeds from its internal structure. In addition to demonstrating the surface reconstruction and the formation of a cathode–electrolyte interphase (CEI) layer of cycled HENMC cathode, this study uncovers the irreversible bulk phase transition from a Li-excess monoclinic (C2/m) solid solution into a conventional “layered” (R3m) phase, accompanied by complete loss of Li+ from the TM layers during cycling. Furthermore, the internal grains of HENMC bear lattice distortions, leading to the formatio...

High-resolution electron energy loss spectroscopy (EELS) in a transmission electron microscope is performed on titanium oxide coatings obtained by plasma electrolytic oxidation (PEO) with application of different electrical parameters. Core loss spectra were used to evaluate the structural evolution occurring at the two main regions characterizing a PEO coating, i.e. barrier and porous layers. Local crystalline information, extracted from EELS, was correlated to macroscopic technological parameters such as duty cycle and frequency, based on advanced data analysis. Using the spectral differences, structural maps are, for the first time, provided for titanium oxide grown anodically. Cathodic current was found to favour the growth of a mainly crystalline barrier layer, responsible for abundant O2 evolution during the treatment. A detailed mechanism regarding the stimulation of type-B discharges, when using cathodic polarization at high frequency, is given comparing outcomes from optical emission spectroscopy and structural information. As the result of the intense plasma interaction with the growing layer, the structure evolved towards the formation of 18 nm of titanium oxide characterized by a strong Ti+3 fingerprint, followed by 85 nm of Ti3O5 formed according to high temperatures and the de-oxidative condition encountered.

Ni-rich cathode materials suffer from poor capacity retention due to micro-cracking and interfacial reactivity with electrolyte. Addition of tungsten (W) to some Ni-rich materials can improve capacity retention. Here, a WO3 surface coating is applied on Ni-rich hydroxide precursors before heating with lithium hydroxide. After heating in oxygen, Ni-rich materials with any of the commonly used dopants (magnesium, aluminum, manganese, etc.) show a “universal” improvement in capacity retention. Experimental characterization and theoretical modelling showed W was concentrated in the grain boundaries between the primary grains of secondary particles of the layered oxides, and W is incorporated in amorphous LixWyOz phases rather than as a substituent in the LiNiO2 lattice. This self-infusion of W in the grain boundaries during synthesis also significantly restricts primary crystallite grain growth. Along with smaller primary grain size, the LixWyOz phases in the grain boundaries lead to improved resistance to microcracking and reduced surface or interfacial reactivity. Improving the intrinsic properties of primary grains through doping of Mg, Al, or Mn and reinforcing the secondary particle structure mechanically and chemically using W or a similar element, M, that forms LixMOy phases and does not substitute into LiNiO2 is a universal strategy to improve polycrystalline Ni-rich materials.

Hydrogen production from anion exchange membrane water electrolysis (AEMWE) is an efficient cost-effective solution to renewable energy storage. Contrary to proton exchange membrane (PEM) electrolysis, AEMWE requires further optimization of its cell design, particularly for the kinetically unfavourable oxygen evolution anode half-cell reaction (OER). In this work we optimize the commercial Fumatech fumion ionomer content in AEMWE anodes using nickel (Ni) nanoparticles (NP) synthesized by chemical reduction. The optimal ionomer content is then applied to Ni-iron (Fe)-based NPs with and without ceria (CeO2), all prepared using the same method. Scanning Electron Microscopy (SEM) of the resulting electrode surfaces, Particle-size Distribution (PSD) of the catalyst inks, and in-situ testing of the monometallic Ni NPs show that the best and most active catalytic layer is obtained using 15 wt% ionomer. AEMWE performance and short-term durability are evaluated in different concentrations of potassium hydroxide (KOH), where the Ni90Fe10 is the best performing Ni-based electrode showing 1.72 V at 0.8 A cm−2 in 1 M KOH after IR-correction, and a degradation rate of 3.3 mV h−1. The addition of ceria to the Ni-based catalysts shows more consistent mass transfer over time likely due to more efficient water transport and bubble release.

Colloidal quantum dots are emerging solution-processed materials for large-scale and low-cost photovoltaics. The recent advent of quantum dot inks has overcome the prior need for solid-state exchanges that previously added cost, complexity, and morphological disruption to the quantum dot solid. Unfortunately, these inks remain limited by the photocarrier diffusion length. Here we devise a strategy based on n- and p-type ligands that judiciously shifts the quantum dot band alignment. It leads to ink-based materials that retain the independent surface functionalization of quantum dots, and it creates distinguishable donor and acceptor domains for bulk heterojunctions. Interdot carrier transfer and exciton dissociation studies confirm efficient charge separation at the nanoscale interfaces between the two classes of quantum dots. We fabricate the first mixed-quantum-dot solar cells and achieve a power conversion of 10.4%, which surpasses the performance of previously reported bulk heterojunction quantum dot devices fully two-fold, indicating the potential of the mixed-quantum-dot approach., Solution processed colloidal quantum dots are emerging photovoltaic materials with tuneable infrared bandgaps. Here, Yang et al. create a class of quantum dot bulk heterojunction solar cell via ligand design, enabling longer photocarrier diffusion lengths for greater photocurrent and performance.

We have physicochemically characterized the formation of PtRu nanoparticles, deposited by evaporation onto highly oriented pyrolytic graphite, using in situ X-ray photoelectron spectroscopy, ex situ high-angle annular dark-field/scanning transmission electron microscopy, electron energy loss spectroscopy, and time-of-flight secondary ion mass spectrometry. We used three different orders of metal deposition: Pt evaporated onto Ru, Ru evaporated onto Pt and both metals evaporated simultaneously, and then followed the evolutions of the alloys as a function of annealing temperature. The C 1s, O 1s, Ru 3d, and Pt 4f core level spectra were employed to describe the alloying interactions between the metals. For all deposition methods, Ru diffuses to the NP surface through the Pt, and not the reverse. Each of the preparation methods produces surface and volume structures that differ from those of the others, even after prolonged annealing at temperatures over 700 °C, indicating the source of confusion in the lite...

In this study, we demonstrate that bipolar electrochemistry is a viable strategy for “wireless” electrochemical intercalation of graphite flakes and further large-scale production of high-quality graphene suspensions. Expansion of the graphite layers leads to a dramatic 20-fold increase in the yield of high-shear exfoliation. Large graphite flakes, which do not produce graphene upon high shear if left untreated, are exfoliated in a yield of 16.0 ± 0.2%. Successful graphene production was confirmed by Raman spectroscopy and scanning transmission electron microscopy, showing that the graphene flakes are 0.4–1.5 μm in size with the majority of flakes consisting of 4–6 graphene layers. Moreover, a low intensity of the D peak relative to the G peak as expressed by the ID/IG ratio in Raman spectroscopy along with high-resolution transmission electron microscopy images reveals that the graphene sheets are essentially undamaged by the electrochemical intercalation. Some impurities reside on the graphene after the electrochemical treatment, presumably because of oxidative polymerization of the solvent, as suggested by electron energy loss spectroscopy and X-ray photoelectron spectroscopy. In general, the bipolar electrochemical exfoliation method provides a pathway for intercalation on a wider range of graphite substrates and enhances the efficiency of the exfoliation. This method could potentially be combined with simultaneous electrochemical functionalization to provide graphene specifically designed for a given composite on a larger scale.

Ni-based alloys, which are used in nuclear applications with a high thermal flux, are shown to contain a high density of helium bubbles within the matrix and aligned along grain boundaries, resulting in lost strength and ductility. In the current investigation, material with and without helium is irradiated with protons up to approximately 60 dpa and 18 000 appm helium. With the use of advanced microscopy and nano-indentation, the microstructural evolution and mechanical hardening has been characterized. The addition of helium decreases the rate of disordering of the gamma prime phase, and suppresses void swelling by forming a region with a high density of helium bubbles, and thereby inhibiting the mobility of freely-migrating point defects. Mechanical hardening from proton-irradiation is consistent with neutron-irradiated Inconel X-750 and Alloy 718.

We characterize the structural and chemical changes that take place in an electrochemically tested proton-exchange fuel cell cathode material composed of platinum nanoparticles on a niobium oxide-carbon black hybrid support. Two hybrid catalysts with different niobium oxide content (5 wt% and 12 wt%) are compared at the beginning and end of potential cycling. We observe an overall increase in the particle size of the hybrid catalysts after potential cycling, mediated by Ostwald ripening process. The general nanostructure of the catalysts was composed of small Pt-rich particles that were linked to niobium oxide particles. Nanoscale and microscale spectroscopy of the pristine materials reveals several co-existing oxidized forms of niobium (5 + , 4 + , 2 + ) in the systems; the most predominant being Nb(V). The study of the energy loss near-edge structure of the Niobium L 2,3 edge of catalysts after being subjected to accelerated stress test (AST) potential cycles provides clues on the evolution of niobium oxides (NbO x ), in which the relative distribution of Nb(V) decreases, while the number of Nb particles in lower oxidation states slightly increases. Furthermore, energy-dispersive spectroscopy reveals that the content of Nb decreased after cycling, implying that the loss of NbO x eventually altered the fraction of linked Pt-NbO x sites. The observed nanoscale catalyst changes and the presence of the NbO x may have important implications for developing an alternative design for improved hybrid catalyst materials.

To evaluate the beneficial effects of intergranular carbides on inhibiting stress corrosion cracking (SCC), Alloy 600 samples in the thermally-treated (TT) and solution-annealed (SA) conditions were analyzed after exposure to 480 °C hydrogenated steam. Intergranular oxidation was observed in both samples, along with diffusion-induced grain boundary migration (DIGM). Compositional mapping revealed DIGM to be more severe in 600SA, while conventional intergranular solute diffusion involving static boundaries appeared dominant in 600TT. 3D serial sectioning of the boundaries revealed strong variations in the intergranular oxide for 600TT, particularly in the depth of oxide penetration. This was attributed to Cr carbide precipitates, present due to the thermal treatment, pinning against DIGM. Immobilizing the boundary via carbide pinning reduces oxide growth by effectively starving it of the ready solute supply otherwise available to a migrating boundary. Because of this interaction between boundary migration, carbide pinning, and oxide growth, the intergranular oxidation in 600TT is highly variable and discontinuous compared to 600SA, where DIGM is unchecked and easier oxide growth produces near-uniform coverage of the boundary. This marked decrease in boundary oxide coverage likely contributes to the improved SCC resistance of 600TT. These results demonstrate the necessity of investigating such phenomena using 3D analysis methods.

Aluminum-rich AlGaN is the ideal material system for emerging solid-state deep-ultraviolet (DUV) light sources. Devices operating in the near-UV spectral range have been realized; to date, however, the achievement of high-efficiency light-emitting diodes (LEDs) operating in the UV-C band (200–280 nm specifically) has been hindered by the extremely inefficient p-type conduction in AlGaN and the lack of DUV-transparent conductive electrodes. Here, we show that these critical challenges can be addressed by Mg dopant-free Al(Ga)N/h-BN nanowire heterostructures. By exploiting the acceptor-like boron vacancy formation, we have demonstrated that h-BN can function as a highly conductive, DUV-transparent electrode; the hole concentration is ∼1020 cm–3 at room temperature, which is 10 orders of magnitude higher than that previously measured for Mg-doped AlN epilayers. We have further demonstrated the first Al(Ga)N/h-BN LED, which exhibits strong emission at ∼210 nm. This work also reports the first achievement of M...