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Abstract: The nature and evolution of FeNxCy moieties in Fe/C/N catalysts has been studied by analysing Fe and N environments. TEM and Fe-XAS reveal the presence of FeNx moieties and Fe3C particles in the fresh catalyst. NEXAFS reveals the presence of two groups of (Fe)NxCy ensembles, namely (Fe)Nx-pyridinic and (Fe)Nx-pyrrolic. The architecture of the FeNxCy ensembles and their evolution during the ORR has been analysed by XAS, NEXAFS, and identical locations TEM. NxCy, FeNxCy and Fe3C species are partially removed during the ORR, resulting in the formation of Fe2O3 and Fe3O4 particles with different morphologies. The process is more severe in acid electrolyte than in alkaline one. (Fe)Nx-pyrrolic moieties are the main ones in the fresh catalysts, but (Fe)Nx-pyridinic groups are more stable after the ORR. The correlation between the evolution of the ORR activity and that of the FeNxCy ensembles indicates that FeNx-pyridinic ensembles are responsible for the ORR activity.

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Abstract: Amorphous alloys consisting of elements present in the human body, such as magnesium, zinc and calcium, are currently extensively studied in order to utilize them as a material for biodegradable orthopaedic implants. amongst all Mg-Zn-Ca alloys investigated up to date, the Mg66Zn30Ca4 composition has the greatest potential for applications. Its critical casting thickness reaches a value of 5 mm, the compressive strength (716–854 MPa) is about 4 times the limit of human cortical bone while elastic modulus is (31 GPa) is only 3 times higher than that of human bone. During dissolution the alloy shows only marginal hydrogen evolution. Here we present a detailed, experiment-based structural investigation of Mg66Zn30Ca4. Structural and topological analysis of its atomic structure reveals a high number of predominantly icosahedral densely packed Zn-centred clusters. It is believed that the existence of these structural units is responsible for the suppression of internal diffusion and thus greatly improves glass formability.

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Abstract: Porosity is the term used to describe the voids in a rock. This porosity is made up of many pores which form a pore network. Pore scale displacement in fluid flow is relevant to a number of industrial and environmental applications. The characteristics of the pore network control the way in which fluid flow occurs throughout the network. Carbonate rocks have particularly complex pore networks due a range of post-depositional processes that modify pore size, shape and connectivity. Although the contributions of factors such as pore throat size and pore network connectivity on fluid flow are reasonably well understood, there is a limited understanding of the effect of pore topology. This research aims to provide a pore-scale picture of the dynamics of fluid flow in both single and multiphase immiscible flow through the use of digital image analysis of fluid flow experiments. The dynamics and patterns of interface displacement as well as the size distribution of trapped oil ganglia were visualised using 2D microfluidic experiments. Different pore topologies resulted in different oil recoveries, however the effect of pore topology was not constant across fluid pairs with different viscosity ratios. Pore size was shown to be a key factor in the recovery efficiency of polymer flooding. This demonstrates that microfluidic experiments offer a methodology to quickly assess a number of different pore topologies under different fluid flow conditions. A range of rock types were imaged in 3D using X-Ray micro-computed tomography to visualise and quantify the range of pore topologies which exist in carbonates. These pore systems were used to assess the reliability of using 2D digital image analysis for permeability prediction, and show that 3D digital image analysis is a far superior technique for reliable pore topological characterisation and permeability prediction. A highly correlated multi-linear regression between permeability and pore topological parameters shows the relevance of pore topologies in predicting permeability. In addition to the investigation of single phase flow in a range of different carbonate pore systems, an investigation into multiphase immiscible displacement in a single carbonate pore system has been conducted. Through the use of synchrotron X-Ray tomographic imaging of an experimental core-flood (oil-brine drainage followed by imbibition) insights into the dynamics of multiphase flow have been gained. The pathway followed by the non-wetting fluid during drainage is strongly linked to the pore topological parameters measured during the analysis of the experiment. Oil initially invades simple pores with low elongation, which are aligned with the flow direction, before invading increasingly complex pores, less aligned to the flow direction. A channelization of flow occurs associated with an area of large, elongate pores. This research demonstrates that pore topology, particularly elongation and orientation to flow direction, has a clear influence on flow and warrants further investigation.

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Abstract: Ternary lanthanide indium oxides LnInO3 (Ln = La, Pr, Nd, Sm) were synthesized by high-temperature solid-state reaction and characterized by X-ray powder diffraction. Rietveld refinement of the powder patterns showed the LnInO3 materials to be orthorhombic perovskites belonging to the space group Pnma, based on almost-regular InO6 octahedra and highly distorted LnO12 polyhedra. Experimental structural data were compared with results from density functional theory (DFT) calculations employing a hybrid Hamiltonian. Valence region X-ray photoelectron and K-shell X-ray emission and absorption spectra of the LnInO3 compounds were simulated with the aid of the DFT calculations. Photoionization of lanthanide 4f orbitals gives rise to a complex final-state multiplet structure in the valence region for the 4fn compounds PrInO3, NdInO3, and SmInO3, and the overall photoemission spectral profiles were shown to be a superposition of final-state 4fn–1 terms onto the cross-section weighted partial densities of states from the other orbitals. The occupied 4f states are stabilized in moving across the series Pr–Nd–Sm. Band gaps were measured using diffuse reflectance spectroscopy. These results demonstrated that the band gap of LaInO3 is 4.32 eV, in agreement with DFT calculations. This is significantly larger than a band gap of 2.2 eV first proposed in 1967 and based on the idea that In 4d states lie above the top of the O 2p valence band. However, both DFT and X-ray spectroscopy show that In 4d is a shallow core level located well below the bottom of the valence band. Band gaps greater than 4 eV were observed for NdInO3 and SmInO3, but a lower gap of 3.6 eV for PrInO3 was shown to arise from the occupied Pr 4f states lying above the main O 2p valence band.

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Abstract: The controlled arrangement of N-heterocyclic carbenes (NHCs) on solid surfaces is a current challenge of surface functionalization. We introduce a strategy of using Ru porphyrins in order to control both the orientation and lateral arrangement of NHCs on a planar surface. The coupling of the NHC to the Ru porphyrin is a facile process which takes place on the interface: we apply NHCs as functional, robust pillars on well-defined, preassembled Ru porphyrin monolayers on silver and characterize these interfaces with atomic precision via a battery of experimental techniques and theoretical considerations. The NHCs assemble at room temperature modularly and reversibly on the Ru porphyrin arrays. We demonstrate a selective and complete functionalization of the Ru centers. With its binding, the NHC modifies the interaction of the Ru porphyrin with the Ag surface, displacing the Ru atom by 1 Å away from the surface. This arrangement of NHCs allows us to address individual ligands by controlled manipulation with the tip of a scanning tunneling microscope, creating patterned structures on the nanometer scale.