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Morphological shape in chemistry and biology owes its existence to anisotropic growth and is closely coupled to distinct functionality. Although much is known about the principal growth mechanisms of monometallic shaped nanocrystals, the anisotropic growth of shaped alloy nanocrystals is still poorly understood. Using aberration-corrected scanning transmission electron microscopy, we reveal an element-specific anisotropic growth mechanism of platinum (Pt) bimetallic nano-octahedra where compositional anisotropy couples to geometric anisotropy. A Pt-rich phase evolves into precursor nanohexapods, followed by a slower step-induced deposition of an M-rich (M = Ni, Co, etc.) phase at the concave hexapod surface forming the octahedral facets. Our finding explains earlier reports on unusual compositional segregations and chemical degradation pathways of bimetallic polyhedral catalysts and may aid rational synthesis of shaped alloy catalysts with desired compositional patterns and properties.

Core–shell particles with earth-abundant cores represent an effective design strategy for improving the performance of noble metal catalysts, while simultaneously reducing the content of expensive noble metals 1 – 4 . However, the structural and catalytic stabilities of these materials often suffer during the harsh conditions encountered in important reactions, such as the oxygen reduction reaction (ORR) 3 – 5 . Here, we demonstrate that atomically thin Pt shells stabilize titanium tungsten carbide cores, even at highly oxidizing potentials. In situ, time-resolved experiments showed how the Pt coating protects the normally labile core against oxidation and dissolution, and detailed microscopy studies revealed the dynamics of partially and fully coated core–shell nanoparticles during potential cycling. Particles with complete Pt coverage precisely maintained their core–shell structure and atomic composition during accelerated electrochemical ageing studies consisting of over 10,000 potential cycles. The exceptional durability of fully coated materials highlights the potential of core–shell architectures using earth-abundant transition metal carbide (TMC) and nitride (TMN) cores for future catalytic applications. Using core–shell particles represents an effective design strategy for improving the performance of noble metal catalysts, but their stabilities can suffer during reactions. Atomically thin Pt shells are shown to stabilize titanium tungsten carbide cores, even at highly oxidizing potentials.

Although Cu/ZnO-based catalysts have been long used for the hydrogenation of CO 2 to methanol, open questions still remain regarding the role and the dynamic nature of the active sites formed at the metal-oxide interface. Here, we apply high-pressure operando spectroscopy methods to well-defined Cu and Cu 0.7 Zn 0.3 nanoparticles supported on ZnO/Al 2 O 3 , γ-Al 2 O 3 and SiO 2 to correlate their structure, composition and catalytic performance. We obtain similar activity and methanol selectivity for Cu/ZnO/Al 2 O 3 and CuZn/SiO 2 , but the methanol yield decreases with time on stream for the latter sample. Operando X-ray absorption spectroscopy data reveal the formation of reduced Zn species coexisting with ZnO on CuZn/SiO 2 . Near-ambient pressure X-ray photoelectron spectroscopy shows Zn surface segregation and the formation of a ZnO-rich shell on CuZn/SiO 2 . In this work we demonstrate the beneficial effect of Zn, even in diluted form, and highlight the influence of the oxide support and the Cu-Zn interface in the reactivity. The nature of the active species over Cu/ZnO catalysts for methanol synthesis remains elusive. Here, the authors shed light on the evolution of the nanoparticle/support interface and correlate its structural and chemical transformations with changes in the catalytic performance.

Photocatalytic hydrogen production from biomass is a promising alternative to water splitting thanks to the oxidation half-reaction being more facile and its ability to simultaneously produce solar fuels and value-added chemicals. Here, we demonstrate the coproduction of H 2 and diesel fuel precursors from lignocellulose-derived methylfurans via acceptorless dehydrogenative C−C coupling, using a Ru-doped ZnIn 2 S 4 catalyst and driven by visible light. With this chemistry, up to 1.04 g g catalyst −1  h −1 of diesel fuel precursors (~41% of which are precursors of branched-chain alkanes) are produced with selectivity higher than 96%, together with 6.0 mmol g catalyst −1  h −1 of H 2 . Subsequent hydrodeoxygenation reactions yield the desired diesel fuels comprising straight- and branched-chain alkanes. We suggest that Ru dopants, substituted in the position of indium ions in the ZnIn 2 S 4 matrix, improve charge separation efficiency, thereby accelerating C−H activation for the coproduction of H 2 and diesel fuel precursors. Biomass can be used to scavenge photogenerated holes in photocatalytic hydrogen production, but the oxidized molecules that form are not always useful products. Here, the authors use Ru-ZnIn 2 S 4 to photocatalyse the dehydrogenative C−C coupling of lignocellulose-derived methylfurans, forming both hydrogen and diesel fuel precursors.

Exsolution-active catalysts allow for the formation of highly active metallic nanoparticles, yet recent work has shown that their long-term thermal stability remains a challenge. In this work, the dynamics of exsolved Ni nanoparticles are probed in-situ with atomically resolved secondary electron imaging with environmental scanning transmission electron microscopy. Pre-characterization shows embedded NiO x nanostructures within the parent oxide. Subsequent in-situ exsolution demonstrates that two populations of exsolved particles form with distinct metal-support interactions and coarsening behaviors. Nanoparticles which precipitate above embedded nanostructures are observed to be more stable, and are prevented from migrating on the surface of the support. Nanoparticle migration which fits random-walk kinetics is observed, and particle behavior is shown to be analogous to a classical wetting model. Additionally, DFT calculations indicate that particle motion is facilitated by the support oxide. Ostwald ripening processes are visualized simultaneously to migration, including particle redissolution and particle ripening. Exsolution enables the formation of active catalytic nanoparticles, but their thermal stability remains limited. Here, the authors use secondary-electron imaging at atomic resolution to directly visualize the coarsening of exsolved nanoparticles.

Atomically dispersed supported catalysts can maximize atom efficiency and minimize cost. In spite of much progress in gas-phase catalysis, applying such catalysts in the field of renewable energy coupled with electrochemistry remains a challenge due to their limited durability in electrolyte. Here, we report a robust and atomically dispersed hybrid catalyst formed in situ on a hematite semiconductor support during photoelectrochemical oxygen evolution by electrostatic adsorption of soluble monomeric [Ir(OH) 6 ] 2− coupled to positively charged NiO x sites. The alkali-stable [Ir(OH) 6 ] 2− features synergistically enhanced activity toward water oxidation through NiO x that acts as a “movable bridge” of charge transfer from the hematite surface to the single iridium center. This hybrid catalyst sustains high performance and stability in alkaline electrolyte for >80 h of operation. Our findings provide a promising path for soluble catalysts that are weakly and reversibly bound to semiconductor-supported hole-accumulation inorganic materials under catalytic reaction conditions as hybrid active sites for photoelectrocatalysis. Atomically disperse catalysts can offer promising activity due to the high exposure of active sites. Here, iridium complexes in solution undergo a binding equilibrium with a nickel oxide surface resulting in atomically disperse iridium and high turnover frequencies for oxygen evolution.

Two ways to deliver ultrasmall gold nanoparticles and gold-bovine serum albumin (BSA) nanoclusters to the colon were developed. First, oral administration is possible by incorporation into gelatin capsules that were coated with an enteric polymer. These permit the transfer across the stomach whose acidic environment damages many drugs. The enteric coating dissolves due to the neutral pH of the colon and releases the capsule’s cargo. Second, rectal administration is possible by incorporation into hard-fat suppositories that melt in the colon and then release the nanocarriers. The feasibility of the two concepts was demonstrated by in-vitro release studies and cell culture studies that showed the easy redispersibility after dissolution of the respective transport system. This clears a pathway for therapeutic applications of drug-loaded nanoparticles to address colon diseases, such as chronic inflammation and cancer.

The invention of silicon drift detectors has resulted in an unprecedented improvement in detection efficiency for energy-dispersive X-ray (EDX) spectroscopy in the scanning transmission electron microscope. The result is numerous beautiful atomic-scale maps, which provide insights into the internal structure of a variety of materials. However, the task still remains to understand exactly where the X-ray signal comes from and how accurately it can be quantified. Unfortunately, when crystals are aligned with a low-order zone axis parallel to the incident beam direction, as is necessary for atomic-resolution imaging, the electron beam channels. When the beam becomes localized in this way, the relationship between the concentration of a particular element and its spectroscopic X-ray signal is generally nonlinear. Here, we discuss the combined effect of both spatial integration and sample tilt for ameliorating the effects of channeling and improving the accuracy of EDX quantification. Both simulations and experimental results will be presented for a perovskite-based oxide interface. We examine how the scattering and spreading of the electron beam can lead to erroneous interpretation of interface compositions, and what approaches can be made to improve our understanding of the underlying atomic structure.

Proton exchange membrane fuel cells (PEMFCs) provide efficient, green power solutions. However, the sluggish kinetics of the oxygen reduction reaction (ORR) at the cathode, with its need for elevated Pt loadings, lowers efficiency and raises cost, which hinders their wider implementation. Pt‐based designer alloy electrocatalysts, more specifically ternary PtNiX nanocatalysts, hold great potential for improving ORR activity and thus overall cell performance. This study explores synthesis and performance evaluations of novel ternary PtNiIr ORR catalysts prepared using seed‐mediation at different catalyst loadings and deposited on various carbon support materials. Membrane electrode assembly (MEA) performance evaluations are carried out to assess catalyst activity and stability under operating conditions, revealing better performance and durability for seed‐mediated catalysts compared to the non‐seed‐mediated catalyst used as a reference. The results showed further improved performance and durability of the seed‐mediated catalysts on porous carbon than solid carbon, due to the deposition of catalyst nanoparticles inside the carbon pores. Degradation analysis using online inductively coupled plasma – mass spectrometry (ICP‐MS) indicated the dissolution of metals during contact with the electrolyte and under operating conditions, confirming the observed catalyst stability trends in MEA. The experiments highlighted the impact of catalyst composition and supports on the stability of the materials. The seed‐mediation synthesis approach offers increased activity and stability for the PtNiIr nanocatalysts. It is designed as an oxygen reduction reaction catalyst in proton exchange membrane fuel cells (PEMFC), further enhanced by deposing the particles inside the porous carbon support material. The improved stability of the particles is confirmed by online inductively coupled plasma mass spectrometry (ICP‐MS) measurements.

Fluorescent peptides were covalently attached to the surface of ultrasmall gold nanoparticles (2 nm), that is, FITC‐AlaCys, FITC‐Ala‐Ala‐Ala‐Cys, and Trp‐Ala‐Cys (WAC). For comparison, the fluorescent dye AlexaFluor‐647 was attached to glutathione‐coated gold nanoparticles via click chemistry. Each particle carried between 10 and 20 fluorescent ligands, except for WAC where about 60 peptides were attached to each nanoparticle. The photophysical properties of dissolved and nanoparticle‐conjugated dyes were assessed by UV‐Vis and fluorescence spectroscopy, including measurements of the absolute photoluminescence quantum yields at the same dye concentration. After conjugation to the nanoparticles, the quantum yield decreased by a factor of 10 to 20 in the FITC systems but only by a factor of 1.5 in the AlexaFluor‐647 system. The intrinsic fluorescence was almost completely lost for WAC after conjugation to the nanoparticles. The fluorescence intensity at temperatures up to 85°C showed a decrease with temperature in all cases which was stronger for dissolved dyes than for nanoparticle‐conjugated dyes. The fluorescence was fully recovered after cooling back to ambient temperature, that is, there was no permanent change of the particles caused by heating. The covalent attachment of fluorescent ligands to the surface of ultrasmall gold nanoparticles leads to fluorescent probes that can be used for imaging. The degree of quenching due to the vicinity of the metal core is much less than for larger plasmonic nanoparticles. Together with the fluorescent shell, the ultrasmall nanoparticle has a hydrodynamic diameter of 3 to 4 nm.