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A number of Pd based materials have been synthesised and evaluated as catalysts for the conversion of carbon dioxide and hydrogen to methanol, a useful platform chemical and hydrogen storage molecule. Monometallic Pd catalysts shows poor methanol selectivity, but this is improved through the formation of Pd alloys, with both PdZn and PdGa alloys showing greatly enhanced methanol productivity compared with monometallic Pd/Al2O3 and Pd/TiO2 catalysts. Catalyst characterisation shows that the 1:1 β-PdZn alloy is present in all Zn containing post-reaction samples, including PdZn/Ga2O3, while the Pd2Ga alloy formed for the Pd/Ga2O3 sample. The heats of mixing were calculated for a variety of alloy compositions with high heats of mixing calculated for both PdZn and Pd2Ga alloys, with values of ca. -0.6 eV/atom and ca. -0.8 eV/atom, respectively. However, ZnO is more readily reduced than Ga2O3, providing a possible explanation for the preferential formation of the PdZn alloy, rather than PdGa. when in the presence of Ga2O3.

The rise in atmospheric CO2 concentration and the concomitant rise in global surface temperature have prompted massive research effort in designing catalytic routes to utilize CO2 as a feedstock. Prime among these is the hydrogenation of CO2 to make methanol, which is a key commodity chemical intermediate, a hydrogen storage molecule, and a possible future fuel for transport sectors that cannot be electrified. Pd/ZnO has been identified as an effective candidate as a catalyst for this reaction, yet there has been no attempt to gain a fundamental understanding of how this catalyst works and more importantly to establish specific design criteria for CO2 hydrogenation catalysts. Here, we show that Pd/ZnO catalysts have the same metal particle composition, irrespective of the different synthesis procedures and types of ZnO used here. We demonstrate that all of these Pd/ZnO catalysts exhibit the same activity trend. In all cases, the β-PdZn 1:1 alloy is produced and dictates the catalysis. This conclusion is further supported by the relationship between conversion and selectivity and their small variation with ZnO surface area in the range 6–80 m2g–1. Without alloying with Zn, Pd is a reverse water-gas shift catalyst and when supported on alumina and silica is much less active for CO2 conversion to methanol than on ZnO. Our approach is applicable to the discovery and design of improved catalysts for CO2 hydrogenation and will aid future catalyst discovery.

The composition of the reducing gas in the activation of Co Fischer-Tropsch synthesis catalysts determines the nature of the catalytically active Co species. This study reports on the effect of H2 versus syngas (H2/CO = 2) on the reducibility of Co3O4 nanoparticles supported on hollow carbon spheres, using ex situ and in situ high-resolution aberration-corrected analytical electron microscopy. High-resolution images revealed twinned fcc Co particles encapsulated in carbon from syngas treatment while H2-treated particles were mostly CoO. Moreover, the electron energy loss of the Co-L3,2 and O-K edge fine structures show improved reducibility in syngas than in H2 at 350 °C. The effect of high temperature on the reducibility of the Co3O4 nanoparticles is also explored. Carbon fiber encapsulation of twinned fcc Co particles observed during the syngas treatment provides sinter resistance at high temperatures. Both ex situ and in situ results indicate that syngas activation is efficient for obtaining highly reduced Co nanoparticles at lower temperatures.

Silica-supported NiO nanoparticles as hosts for isolated PdO catalytic sites. Isolate PdO is confirmed as the species responsible for the chemoselective oxidation of cinnamyl alcohol to cinnamaldehyde by operando X-ray absorption spectroscopy.

The stability of catalysts in dry reforming of methane (DRM) is a known issue. In this paper an encapsulation strategy has been employed to improve the stability compared with conventional impregnation methods. Herein, nickel nanoparticles encapsulated in silicalite-1 were prepared using a range of methods including post treatment, direct hydrothermal and seed-directed methods to investigate the effect of synthesis protocol on the properties of catalysts, such as degree of encapsulation and Ni dispersion, and anti-coking/-sintering performance in DRM. The Ni@SiO2-S1 catalysts obtained by the seed-directed synthesis presented the full encapsulation of Ni NPs by the zeolite framework with small particle sizes (∼2.9 nm) and strong metal-support interaction, which could sterically hinder the migration/aggregation of Ni NPs and carbon deposition. Therefore, Ni@SiO2-S1 showed stable CO2/CH4 conversions of 80% and 73%, respectively, with negligible metal sintering and coking deposition (∼0.5 wt%) over 28 h, which outperformed the other catalysts prepared. In contrast, the catalysts developed by the post-treatment and ethylenediamine-protected hydrothermal methods showed the co-existence of Ni phase on the internal and external surfaces, i.e. incomplete encapsulation, with large Ni particles, contributing to Ni sintering and coking. The correlation of the synthesis-structure-performance in this study sheds light on the design of coking-/sintering-resistant encapsulated catalysts for DRM.

A number of Pd based materials have been synthesised and evaluated as catalysts for the conversion of carbon dioxide and hydrogen to methanol, a useful platform chemical and hydrogen storage molecule. Monometallic Pd catalysts show poor methanol selectivity, but this is improved through the formation of Pd alloys, with both PdZn and PdGa alloys showing greatly enhanced methanol productivity compared with monometallic Pd/Al

Atomically-dispersed metal catalysts (ADMCs) on surfaces have demonstrated high activity and selectivity in many catalytic reactions. However, dispersing and stabilising individual atoms in support materials in an atom/energy-efficient scalable way still presents a significant challenge. Currently, the synthesis of ADMCs involves many steps and further filtration procedures, creating a substantial hurdle to their production at industrial scale. In this work, we develop a new pathway for producing ADMCs in which Pt atoms are stabilised in the nitrogen-interstices of a graphitic carbon nitride (g-C3N4) framework using scalable, solvent-free, one-pot magnetron sputtering deposition. Our approach has the highest reported rate of ADMC production of 4.8 mg h-1 and generates no chemical waste. Deposition of only 0.5 weight percent of Pt onto g-C3N4 led to improved hydrogen production by factor of ca. 3333 ± 450 when compared to bare g-C3N4. PL analysis showed that the deposition of Pt atoms onto g-C3N4 suppressed the charge carrier recombination from the photogenerated electron-hole pairs of Pt/g-C3N4 thereby enhance hydrogen evolution. Scanning transmission electron microscope imaging before and after the hydrogen evolution reaction revealed that the Pt atoms stabilised in g-C3N4 have a high stability, with no agglomeration observed. Herein, it is shown that this scalable and clean approach can produce effective ADMCs with no further synthetic steps required, and that they can be readily used for catalytic reactions.

We present a trainable segmentation method implemented within the python package ParticleSpy. The method takes user labelled pixels, which are used to train a classifier and segment images of inorganic nanoparticles from transmission electron microscope images. This implementation is based on the trainable Waikato Environment for Knowledge Analysis (WEKA) segmentation, but is written in python, allowing a large degree of flexibility and meaning it can be easily expanded using other python packages. We find that trainable segmentation offers better accuracy than global or local thresholding methods and requires as few as 100 user-labelled pixels to produce an accurate segmentation. Trainable segmentation presents a balance of accuracy and training time between global/local thresholding and neural networks, when used on transmission electron microscope images of nanoparticles. We also quantitatively investigate the effectiveness of the components of trainable segmentation, its filter kernels and classifiers, in order to demonstrate the use cases for the different filter kernels in ParticleSpy and the most accurate classifiers for different data types. A set of filter kernels is identified that are effective in distinguishing particles from background but that retain dissimilar features. In terms of classifiers, we find that different classifiers perform optimally for different image contrast; specifically, a random forest classifier performs best for high-contrast ADF images, but that QDA and Gaussian Naïve Bayes classifiers perform better for low-contrast TEM images.Measurement of the size, shape and composition of nanoparticles is routinely performed using transmission electron microscopy and related techniques. Typically, distinguishing particles from the background in an image is performed using the intensity of each pixel, creating two sets of pixels to separate particles from background. However, this separation of intensity can be difficult if the contrast in an image is low, or if the intensity of the background varies significantly. In this study, an approach that takes into account additional image features (such as boundaries and texture) was investigated to study electron microscope images of metallic nanoparticles. In this ‘trainable segmentation’ approach, the user labels examples of particle and background pixels in order to train a machine learning algorithm to distinguish between particles and background. The performance of different machine learning algorithms was investigated, in addition to the effect of using different features to aid the segmentation. Overall, a trainable segmentation approach was found to perform better than use of an intensity threshold to distinguish between particles and background in electron microscope images.

Single-particle reconstruction can be used to perform three-dimensional (3D) imaging of homogeneous populations of nano-sized objects, in particular viruses and proteins. Here, it is demonstrated that it can also be used to obtain 3D reconstructions of heterogeneous populations of inorganic nanoparticles. An automated acquisition scheme in a scanning transmission electron microscope is used to collect images of thousands of nanoparticles. Particle images are subsequently semi-automatically clustered in terms of their properties and separate 3D reconstructions are performed from selected particle image clusters. The result is a 3D dataset that is representative of the full population. The study demonstrates a methodology that allows 3D imaging and analysis of inorganic nanoparticles in a fully automated manner that is truly representative of large particle populations.

Supported bimetallic nanoparticles (BNPs) are promising catalysts, but study on their compositional and structural changes under reaction conditions remains a challenge. In this work, the structure of PtNi BNPs supported on UiO-67 metal–organic framework (MOF) catalyst (i.e., PtNi@UiO-67) was investigated by in situ by near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS). The results showed differences in the reduction behaviour of Ni species in PtNi BNPs and monometallic Ni supported on UiO-67 catalysts (i.e., PtNi@UiO-67 and Ni@UiO-67), suggesting charge transfer between metallic Pt and Ni oxides in PtNi@UiO-67. Under CO oxidation conditions, Ni oxides segregated to the outer surface of the BNPs forming a thin layer of NiOx on top of the metallic Pt (i.e., a NiOx-on-Pt structure). This resulted in a core-shell structure which was confirmed by high-resolution scanning transmission electron microscopy (HR-STEM). Accordingly, the layer of NiOx on PtNi BNPs, which is stabilised by charge transfer from metallic Pt, was proposed as the possible active phase for CO oxidation, being responsible for the enhanced catalytic activity observed in the bimetallic PtNi@UiO-67 catalyst.

The general and cost-effective synthesis of single atom electrocatalysts (SAECs) still remains a great challenge. Herein, we report a general synthetic protocol for the synthesis of SAECs via a simple condensation–carbonization process, in which furfural and cyanamide were condensation polymerized in the presence of polystyrene nanospheres and metal ions, followed by a pyrolysis to N-doped carbon nanosheet (NCNS) supported SAECs. Six types of SAECs containing platinum, palladium, gold, nickel, cobalt and iron were synthesized to demonstrate the generality of the synthesis protocol. This methodology affords a facile solution to the trade-off between support conductivity and metal loading of SAECs by optimizing the ratio of carbon/nitrogen precursors, i.e., furfural and cyanamide. The presence of single metal atoms was confirmed by high-angle annular dark field scanning transmission electron microscopy and X-ray absorption fine structure measurements. The three-dimensional distribution of single platinum atoms was vividly revealed by depth profile analysis using a scanning transmission electron microscope. The resulting SAECs showed excellent performance for glycerol electro-oxidation and water splitting in alkaline solutions. Notably, Pt/NCNSs possessed an unprecedent mass-normalized current density of 5.3 A per milligram of platinum, which is 32 times that of the commercial Pt/C catalyst. Density functional theory calculations were conducted to reveal the adsorption behavior of glycerol over the SAECs. Using Ni/NCNSs and Co/NCNSs as anodic and cathodic electrocatalysts, we constructed a solar panel powered electrolytic cell for overall water splitting, leading to an overall energy efficiency of 8.8%, which is among the largest solar-to-hydrogen conversion efficiencies reported in the literature.

Solar H

Precisely tuning an organic semiconductor’s crystalline order allows exciton transport to proceed 2-3 orders of magnitude faster., Efficient energy transport is desirable in organic semiconductor (OSC) devices. However, photogenerated excitons in OSC films mostly occupy highly localized states, limiting exciton diffusion coefficients to below ~10−2 cm2/s and diffusion lengths below ~50 nm. We use ultrafast optical microscopy and nonadiabatic molecular dynamics simulations to study well-ordered poly(3-hexylthiophene) nanofiber films prepared using living crystallization-driven self-assembly, and reveal a highly efficient energy transport regime: transient exciton delocalization, where energy exchange with vibrational modes allows excitons to temporarily re-access spatially extended states under equilibrium conditions. We show that this enables exciton diffusion constants up to 1.1 ± 0.1 cm2/s and diffusion lengths of 300 ± 50 nm. Our results reveal the dynamic interplay between localized and delocalized exciton configurations at equilibrium conditions, calling for a re-evaluation of exciton dynamics and suggesting design rules to engineer efficient energy transport in OSC device architectures not based on restrictive bulk heterojunctions.

Efficient energy transport is highly desirable for organic semiconductor (OSC) devices such as photovoltaics, photodetectors, and photocatalytic systems. However, photo-generated excitons in OSC films mostly occupy highly localized states over their lifetime. Energy transport is hence thought to be mainly mediated by the site-to-site hopping of localized excitons, limiting exciton diffusion coefficients to below ~10-2 cm2/s with corresponding diffusion lengths below ~50 nm. Here, using ultrafast optical microscopy combined with non-adiabatic molecular dynamics simulations, we present evidence for a new highly-efficient energy transport regime: transient exciton delocalization, where energy exchange with vibrational modes allows excitons to temporarily re-access spatially extended states under equilibrium conditions. In films of highlyordered poly(3-hexylthiophene) nanofibers, prepared using living crystallization-driven self-assembly, we show that this enables exciton diffusion constants up to 1.1 ± 0.1 cm2/s and diffusion lengths of 300 ± 50 nm. Our results reveal the dynamic interplay between localized and delocalized exciton configurations at equilibrium conditions, calling for a re-evaluation of the basic picture of exciton dynamics. This establishes new design rules to engineer efficient energy transport in OSC films, which will enable new devices architectures not based on restrictive bulk heterojunctions.

A rapidly-growing 3D printing technology is innovatively employed for the manufacture of a new class of heterogenous catalysts for the conversion of CO2 into industrially relevant chemicals such as cyclic carbonates. For the first time, directly printed graphene-based 3D structured nanocatalysts have been developed combining the exceptional properties of graphene and active CeZrLa mixed-oxide nanoparticles. It constitutes a significant advance on previous attempts at 3D printing graphene inks in that it does not merely explore the printability itself, but enhances the efficiency of industrially relevant reactions, such as CO2 utilisation for direct propylene carbonate (PC) production in the absence of organic solvents. In comparison to the starting powder, 3D printed GO-supported CeZeLa catalysts showed improved activity with higher conversion and no noticeable change in selectivity. This can be attributed to the spatially uniform distribution of nanoparticles over the 2D and 3D surfaces, and the larger surface area and pore volume of the printed structures. 3D printed GO-supported CeZeLa catalysts compared to unsupported 3D printed samples exhibited higher selectivity and yield owing to the great number of new weak acid sites appearing in the supported sample, as observed by NH3-TPD analysis. In addition, the catalyst's facile separation from the product has the capacity to massively reduce materials and operating costs resulting in increased sustainability. It convincingly shows the potential of these printing technologies in revolutionising the way catalysts and catalytic reactors are designed in the general quest for clean technologies and greener chemistry.

We report a rapid solution-phase strategy to synthesize alloyed PtNi nanoparticles which demonstrate outstanding functionality for the oxygen reduction reaction (ORR). This one-pot co-reduction colloidal synthesis results in a monodisperse population of single-crystal nanoparticles of rhombic dodecahedral morphology, with Pt enriched edges and compositions close to Pt1Ni2. We use nanoscale 3D compositional analysis to reveal for the first time that oleylamine (OAm)-aging of the rhombic dodecahedral Pt1Ni2 particles results in Ni leaching from surface facets, producing aged particles with concave faceting, an exceptionally high surface area and a composition of Pt2Ni1. We show that the modified atomic nanostructures catalytically outperform the original PtNi rhombic dodecahedral particles by more than 2-fold and also yield improved cycling durability. Their functionality for the ORR far exceeds commercially available Pt/C nanoparticle electrocatalysts, both in terms of mass-specific activities (up to a 25-fold increase) and intrinsic area-specific activities (up to a 27-fold increase)., Comment: 14 pages, 4 figures, supplementary information

The oxidation of cyclohexane via the in-situ production of H2O2 from molecular H2 and O2 offers an attractive route to the current industrial means of producing cyclohexanone and cyclohexanol (KA oil), key materials in the production of Nylon. The in-situ route has the potential to overcome the significant economic and environmental concerns associated with the use of commercial H2O2, while also allowing for the use of far lower reaction temperatures than those typical of the purely aerobic route to KA oil. Herein we demonstrate the efficacy of a series of bi-functional Pd-based catalysts, which offer appreciable concentrations of KA oil, under conditions where limited activity is observed using O2 alone. In particular the introduction of V into a supported Pd catalyst is seen to improve KA oil concentration by an order of magnitude, compared to the Pd-only analogue. In particular we ascribe this improvement in catalytic performance to the development of Pd domains of mixed oxidation state upon V incorporation as evidenced through X-ray photoelectron spectroscopy. Graphic Abstract

State of the art electrocatalysts for the hydrogen evolution reaction (HER) are based on metal nanoparticles (NPs). It has been shown that the localized surface plasmon resonance (LSPR) excitation in plasmonic NPs can be harvested to accelerate a variety of molecular transformations. This enables the utilization of visible light as an energy input to enhance HER performances. However, most metals that are active toward the HER do not support LSPR excitation in the visible or near-IR ranges. We describe herein the synthesis of gold-rhodium core-shell nanoflowers (Au@Rh NFs) that are composed of a core made up of spherical Au NPs and shells containing Rh branches. The Au@Rh NFs were employed as a model system to probe how the LSPR excitation from Au NPs can lead to an enhancement in the HER performance for Rh. Our data demonstrate that the LSPR excitation at 533 nm (and 405 nm) leads to an improvement in the HER performance of Rh, which depends on the morphological features of the Au Rh NFs, offering opportunities for optimization of the catalytic performance. Control experiments indicate that this improvement originates from the stronger interaction of Au@Rh NFs with H2O molecules at the surface, leading to an icelike configuration, which facilitated the HER under LSPR excitation.

Herein, we report a facile route to synthesize isolated single iron atoms on nitrogen-sulfur-codoped carbon matrix via a direct pyrolysis process in which hemoglobin, a by-product of the meat industry, was utilized as a precursor for iron, nitrogen and sulfur while bamboo-shaped carbon nanotubes served as a support owing to their excellent conductivity and numerous defects. The resulting metal-nitrogen complexed carbon showed outstanding catalytic performance for the oxygen evolution reaction (OER) in alkaline solutions. At an overpotential of 380 mV, the optimal sample yielded a current density of 83.6 mA cm−2, which is 2.5 times that of benchmark IrO2 (32.8 mA cm−2), rendering it as one of the best OER catalysts reported so far. It also showed negligible activity decay in alkaline solutions during long-term durability tests. Control experiments and X-ray absorption fine structure analyses revealed that Fe-Nx species in the samples are the active sites for OER. Further density functional theory calculations indicated that the presence of sulfur in the carbon matrix modified the electronic structures of active species, thereby leading to the superior activity of the sample.

Activity of catalysts increase linearly with increasing ratio of Pd/Pt bimetallic to oxide species as observed in XRD. Bimetallic catalysts consisting of Pd and Pt on TiO 2 -zeolite (mordenite, beta, ZSM-5) supports were prepared and tested for the combustion of methane. The activity of the catalysts was found to be dependent on the zeolite topology and SiO 2 : Al 2 O 3 ratio and was linearly dependent on the proportion of Pd and Pt present in a bimetallic phase observed in XRD diffractograms of the catalysts. This linear dependence was valid for a range of zeolites used. STEM-EDS and electron tomography showed the Pd and Pt to be largely co-located and XAS and XPS indicated that the metals are mostly present in the form of oxide nanoparticles with a minor contribution from the metals at high SiO 2 : Al 2 O 3 ratios. Catalyst characterization showed there to be little difference overall in the metal loading and physical characteristics of the samples and NH 3 -TPD suggested that the activation of methane over acid sites is not important. Adding water to the feed, slightly reduced the conversion but did not affect the deactivation profile of the catalysts tested.

We develop herein plasmonic-catalytic Au-IrO2 nanostructures with a morphology optimized for efficient light harvesting and catalytic surface area; the nanoparticles have a nanoflower morphology, with closely spaced Au branches all partially covered by an ultrathin (1 nm) IrO2 shell. This nanoparticle architecture optimizes optical features due to the interactions of closely spaced plasmonic branches forming electromagnetic hot spots, and the ultra-thin IrO2 layer maximizes efficient use of this expensive catalyst. This concept was evaluated towards the enhancement of the electrocatalytic performances towards the oxygen evolution reaction (OER) as a model transformation. The OER can play a central role in meeting future energy demands but the performance of conventional electrocatalysts in this reaction is limited by the sluggish OER kinetics. We demonstrate an improvement of the OER performance for one of the most active OER catalysts, IrO2, by harvesting plasmonic effects from visible light illumination in multimetallic nanoparticles. We find that the OER activity for the Au-IrO2 nanoflowers can be improved under LSPR excitation, matching best properties reported in the literature. Our simulations and electrocatalytic data demonstrate that the enhancement in OER activities can be attributed to an electronic interaction between Au and IrO2 and to the activation of Ir-O bonds by LSPR excited hot holes, leading to a change in the reaction mechanism (rate-determinant step) under visible light illumination.

We have explored the synthesis of Au@HgxCd1-xTe core@shell nanorods by sequential aqueous cation exchange (ACE) for near-infrared photodetector application. A number of related Au@telluride core/shell nanorod structures were put forwarded, taking advantage of multi-step transformations through a binary and then a ternary phase for the telluride shells. The latter have a high degree of crystallinity thanks to the step-wise ACE method. The use of only trace amounts of Cd2+ coordinated with tri-n-butylphosphine, assisted the phase transformation from an amorphous Ag2Te shell to a highly crystalline Ag3AuTe2 shell in the first stage; this was followed by a further cation exchange (CE) step with far higher Cd2+ levels to fabricate a highly crystalline CdTe shell, and with an additional CE with Hg2+ to convert it to a HgxCd1-xTe shell. The composition of the shell components and the well-controlled thickness of the shells enabled tunable surface plasmon resonance properties of the Au@telluride nanorods in the NIR region. Utilizing the enhanced NIR absorption, a hybrid photodetector structure of Au@HgxCd1-xTe nanorods on graphene was fabricated, showing visible to NIR (vis-NIR) broadband detection with high photoresponsivity (~106 A/W).

The new generation of analytical electron microscopes with aberration correction and new EDX detectors provide improved possibilities for microanalysis. Here, we apply a new approach to quantitative EDX based on using partial cross sections. Our quantification method is applied to alloy PtCo nanoparticles, which have been acid leached to provide Pt enrichment or rather Co depletion at the particle surface. Such surface Co depletion is absent at the vertices of the more facetted nanoparticles. The leaching process demonstrates very little change in Co composition when investigating the whole particle but produces a localised surface depletion, which can only be determined by the high-resolution EDX elemental maps.

It is shown that approximately 2 wt% of graphene in the matrix of a unidirectionally-reinforced carbon fiber epoxy composite leads to a significant enhancement in mechanical properties. Particularly, it is found that the axial stiffness of the composites is increased by ∼10 GPa accompanied by an increase in axial strength of 200 MPa. X-ray computed tomography and polarized Raman spectroscopy have demonstrated that the graphene is predominately aligned parallel to the carbon fibers axes. Stress-induced Raman band shifts showed that the confined and self-aligned graphene is subjected to high levels of stress during axial deformation of the composite, with an effective Young's modulus of ∼825 GPa, approaching its theoretical value of 1050 GPa. This behavior has been modeled using the rule of mixtures and shear-lag analysis and it is demonstrated that highly-aligned graphene in a constrained environment between fibers gives significantly better mechanical reinforcement than graphene in conventional polymer-based nanocomposites.

The permeation characteristics of palladium pore filled (PF) membranes have been investigated with gas permeation and structural characterization of the membranes. PF membranes have been prepared by filling with Pd the nanoporous γ-Al2O3/YSZ (or pure YSZ) layer supported onto porous α-Al2O3 and ZrO2. The number of nanoporous layers and the applied vacuum level during the electroless plating process have been studied. Gas permeation properties of the PF membranes have been determined in a temperature range of 300-550 °C. The measured hydrogen permeances have been found to be lower than previously reported for similar membranes. It has been found that the hydrogen fluxes do not depend on the thickness of the nanoporous layers (γ-Al2O3/YSZ or pure YSZ) or on the vacuum pump employed for filling with Pd. The physicochemical characterization performed showed that the palladium deposited does not form a percolated network across the mesoporous layer(s), leading to low hydrogen permeances and thus low H2/N2 perm-selectivities. The presented work is funded within FERRET project as part of European Union’s Seventh Framework Programme (FP7/2007-2013) for the Fuel Cells and Hydrogen Joint Technology Initiative under grant agreement n° 621181. The Talos TEM was funded as part of HEFCE funding in the UK Research Partnership Investment Funding (UKRPIF) Manchester RPIF Round 2.

Two novel automated methods for the determination of surface roughness and chemical distribution in individual nanoparticles are presented and applied to nanoparticles synthesised by the galvanic replacement reaction. The two methodologies apply the determination of circumferential and radial line profiles to determine surface roughness and elemental distribution respectively. The surface roughness analysis provides details on localised changes in roughness in comparison to single measures of circularity. The X-ray spectroscopic concentric ring scan outperforms conventional line scans when elemental distribution approximately possesses a spherical symmetry.

There are a huge array of characterization techniques available today and increasingly powerful computing resources allowing for the effective analysis and modelling of large datasets. However, each experimental and modelling tool only spans limited time and length scales. Correlative tomography can be thought of as the extension of correlative microscopy into three dimensions connecting different techniques, each providing different types of information, or covering different time or length scales. Here the focus is on the linking of time lapse X-ray computed tomography (CT) and serial section electron tomography using the focussed ion beam (FIB)-scanning electron microscope to study the degradation of metals. Correlative tomography can provide new levels of detail by delivering a multiscale 3D picture of key regions of interest. Specifically, the Xe+ Plasma FIB is used as an enabling tool for large-volume high-resolution serial sectioning of materials, and also as a tool for preparation of microscale test samples and samples for nanoscale X-ray CT imaging. The exemplars presented illustrate general aspects relating to correlative workflows, as well as to the time-lapse characterisation of metal microstructures during various failure mechanisms, including ductile fracture of steel and the corrosion of aluminium and magnesium alloys. Correlative tomography is already providing significant insights into materials behaviour, linking together information from different instruments across different scales. Multiscale and multifaceted work flows will become increasingly routine, providing a feed into multiscale materials models as well as illuminating other areas, particularly where hierarchical structures are of interest.

Coccolithophores create an intricate exoskeleton from nanoscale calcite platelets. Shape, size, and crystal orientation are controlled to a remarkable degree. In this study, the structure of Rhabdosphaera clavigera is described in detail for the first time through a combination of electron microscopy techniques, including three-dimensional electron tomography. The coccolithophore exhibits several micrometer long 5-fold symmetric spines with diameters of approximately 0.5 μm. The nanorystals constituting the spine are arranged radially along the longitudinal axis, protruding from the almost flat disks that form the coccosphere. The stem of the spine is shown to consist of {104} calcite rhombohedra single crystalline platelets, arranged in five separate spiral “staircases”. The spine tip shows 15 structural elements: five large “panels” protruding outward along the lateral plane and five leaf-shaped smaller units which form the topmost steps of the staircases. The outer tip consists of five long thin platel...

A new design of in situ liquid cells is demonstrated, providing the first nanometer resolution elemental mapping of nanostructures in solution. The technique has been applied to investigate dynamic liquid-phase synthesis of core-shell nanostructures and to simultaneously image the compositional distribution for multiple elements within the resulting materials.

A new method to perform X-ray absorption correction for spherical particles in quantitative energy-dispersive X-ray spectroscopy in the scanning transmission electron microscope is presented. An absorption correction factor is derived and simulated data is presented encompassing a range of X-ray absorption conditions. Theoretical calculations are compared with experimental data of X-ray counts from Au nanoparticles to verify the derived methodology. The effect of detector elevation angle is considered and a comparison with thin-film absorption correction is included.

The polarizable organic/water interface is used to construct MoS

The new generation of energy-dispersive X-ray (EDX) detectors with higher count rates than ever before, paves the way for a new approach to quantitative elemental analysis in the scanning transmission electron microscope. Here we demonstrate a method of calculating partial cross sections for use in quantifying EDX data, beneficial especially because of the simplicity of its implementation. Applying this approach to acid-leached PtCo catalyst nanoparticles leads to quantitative determination of the Pt surface enrichment.

This chapter summarises recent applications of scanning transmission electron microscope (STEM) based imaging and analysis to characterise nanomaterials. We focus on two areas of nanoscience that have developed rapidly in recent years: two dimensional (2D) crystals and inorganic nanoparticles. The discovery of graphene has led to an explosion of interest in exploring the structure and properties of other 2D crystals. The STEM provides a powerful tool for obtaining local structural data for this new class of materials, aiding the transition from scientific curiosity to engineering applications. In contrast, inorganic nanoparticles are already widely applied in a range of applications, including catalysis, medical imaging and in solar cells. Here the principle challenge for the STEM is to elucidate structure–property relationships in established systems, in order to aid the development of more controllable, lower cost, synthesis routes and improve performance for each application.

New AgAu tadpole nanocrystals were synthesized in a one-step reaction involving simultaneous galvanic replacement between Ag nanospheres and AuCl4(-)(aq.) and AuCl4(-)(aq.) reduction to Au in the presence of citrate. The AgAu tadpoles display nodular polycrystalline hollow heads, while their undulating tails are single crystals. The unusual morphology suggests an oriented attachment growth mechanism. Remarkably, a 1 nm thick Ag layer was found to segregate so as to cover the entire surface of the tadpoles. By varying the nature of the seeds (Au NPs), double-headed Au tadpoles could also be obtained. The effect of a number of reaction parameters on product morphology were explored, leading to new insights into the growth mechanisms and surface segregation behavior involved in the synthesis of bimetallic and anisotropic nanomaterials.

This paper presents an investigation of the limitations and optimisation of energy dispersive X-ray (EDX) tomography within the scanning transmission electron microscope, focussing on application of the technique to characterising the 3D elemental distribution of bimetallic AgAu nanoparticles. The detector collection efficiency when using a standard tomography holder is characterised using a tomographic data set from a single nanoparticle and compared to a standard low background double tilt holder. Optical depth profiling is used to investigate the angles and origin of detector shadowing as a function of specimen field of view. A novel time-varied acquisition scheme is described to compensate for variations in the intensity of spectrum images at each sample tilt. Finally, the ability of EDX spectrum images to satisfy the projection requirement for nanoparticle samples is discussed, with consideration of the effect of absorption and shadowing variations.

In this work, a simple but powerful method for controlling the size and surface morphology of AgAu nanodendrites is presented. Control of the number of Ag nanoparticle seeds is found to provide a fast and effective route by which to manipulate the size and morphology of nanoparticles produced via a combined galvanic replacement and reduction reaction. A lower number of Ag nanoparticle seeds leads to larger nanodendrites with the particles' outer diameter being tunable in the range of 45-148 nm. The size and surface morphology of the nanodendrites was found to directly affect their catalytic activity. Specifically, we report on the activity of these AgAu nanodendrites in catalyzing the gas-phase oxidation of benzene, toluene and o-xylene, which is an important reaction for the removal of these toxic compounds from fuels and for environmental remediation. All produced nanodendrite particles were found to be catalytically active, even at low temperatures and low metal loadings. Surprisingly, the largest nanodendrites provided the greatest percent conversion efficiencies.

We demonstrate the control of perpendicular magnetic anisotropy (PMA) in multilayer films without modification of either the microstructure or saturation magnetization by tuning the Ar+ ion energy using remote plasma sputtering. We show that for [Co/Pd]8 multilayer films, increasing the Ar+ ion energy results in a strong decrease in PMA through an increase in interfacial roughness determined by X-ray reflectivity measurements. X-ray diffraction and transmission electron microscope image data show that the microstructure is independent of Ar+ energy. This opens a different approach to the in-situ deposition of graded exchange springs and for control of the polarizing layer in hybrid spin transfer torque devices.

The passage of an electric current through graphite or few-layer graphene can result in a striking structural transformation, but there is disagreement about the precise nature of this process. Some workers have interpreted the phenomenon in terms of the sublimation and edge reconstruction of essentially flat graphitic structures. An alternative explanation is that the transformation actually involves a change from a flat to a three-dimensional structure. Here we describe detailed studies of carbon produced by the passage of a current through graphite which provide strong evidence that the transformed carbon is indeed three-dimensional. The evidence comes primarily from images obtained in the scanning transmission electron microscope using the technique of high-angle annular dark-field imaging, and from a detailed analysis of electron energy loss spectra. We discuss the possible mechanism of the transformation, and consider potential applications of 'three-dimensional bilayer graphene'.

Significant elemental segregation is shown to exist within individual hollow silver-gold (Ag-Au) bimetallic nanoparticles obtained from the galvanic reaction between Ag particles and AuCl4(-). Three-dimensional compositional mapping using energy dispersive X-ray (EDX) tomography within the scanning transmission electron microscope (STEM) reveals that nanoparticle surface segregation inverts from Au-rich to Ag-rich as Au content increases. Maximum Au surface coverage was observed for nanoparticles with approximately 25 atom % Au, which correlates to the optimal catalytic performance in a three-component coupling reaction among cyclohexane carboxyaldehyde, piperidine, and phenylacetylene.