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The surface wettability of catalysts is typically controlled via surface treatments that promote catalytic performance. Here we report on potential-regulated hydrophobicity/hydrophilicity at cobalt-based oxide interfaces with an alkaline solution. The switchable wetting of single particles, directly related to their activity and stability towards the oxygen evolution reaction, was revealed by electrochemical liquid-phase transmission electron microscopy. Analysis of the movement of the liquid in real time revealed distinctive wettability behaviour associated with specific potential ranges. At low potentials, an overall reduction of the hydrophobicity of the oxides was probed. Upon reversible reconstruction towards the surface oxyhydroxide phase, electrowetting was found to cause a change in the interfacial capacitance. At high potentials, the evolution of molecular oxygen, confirmed by operando electron energy-loss spectroscopy, was accompanied by a globally thinner liquid layer. This work directly links the physical wetting with the chemical oxygen evolution reaction of single particles, providing fundamental insights into solid–liquid interfacial interactions of oxygen-evolving oxides., Surface treatments can tune catalysts’ wettability, which can be used to promote their catalytic performance. Now, a potential-dependent dynamic wetting behaviour of cobalt-based oxide catalysts is identified before and during the oxygen evolution reaction.

Among the perovskites used to catalyze the oxygen evolution reaction (OER), Ba0.5Sr0.5Co0.8Fe0.2O3−δ (BSCF) exhibits excellent activity which is thought to be related to dynamic reconstruction at t...

Perovskites have been widely studied for electrocatalysis due to the exceptional activity they exhibit for surface-mediated redox reactions. To date, descriptors based on density functional theory calculations or experimental measurements have assumed a bulk-like configuration for the surfaces of these oxides. Herein, we probed an initial exposed surface and the screened subsurface of LaMnO3 particles, demonstrating that their augmented activity toward the oxygen reduction reaction (ORR) can be related to a spontaneous surface reconstruction. Our approach involves high energy resolution electron energy loss spectroscopy for the fine structure probing of oxygen and manganese ionization edges under electron beam conditions that leave the structure unaffected. Atomic multiplet and density functional theory calculations were used to compute the theoretical energy loss spectra for comparison to the experimental data, allowing to quantitatively demonstrate that the particle surface layers are La-deficient. This deficiency is linked to equivalent tetrahedral Mn2+ sites at the reconstructed surface, leading to the coexistence of +3 and +2 oxidation states of Mn at the surface layers. This electronic and structural configuration of the as-synthesized particles is indirectly linked to strong adsorption pathways that promote the ORR on LaMnO3, and thus, it could prove to be a valuable design feature in the engineering of catalytic surfaces.

Among the perovskites used to catalyze the oxygen evolution reaction (OER), Ba

A microstructural investigation of epitaxial CoFe 2 O 4 films grown by pulsed laser deposition on single crystal SrTiO 3 substrates was performed. We quantitatively analysed the microscopic mechanisms for structural mismatch compensation and the mode of the film growth. X-ray diffraction revealed very low microstrain in all three crystallographic directions of the film, which together with the lattice strain is not large enough to compensate effectively for the mismatch. Quantitative high-resolution transmission electron microscopy showed that most of the compensation occurs by formation of (4 0 0) edge dislocations in the film. These dislocations are concentrated within a critical layer above which a change from layer-by-layer growth to island growth was observed. These observations closely correspond to characteristics of the Stranski–Krastanov growth mode. Atomic force microscopy studies confirmed that during the post-annealing long-range mass diffusion takes place, which facilitates the relaxation of the microstrain during this treatment.

Structures comprising single-crystal, iron-carbon-based nanowires encapsulated by multiwall carbon nanotubes self-organize on inert substrates exposed to the products of ferrocene pyrolysis at high temperature. The most commonly observed encapsulated phases are Fe3C, α-Fe, and γ-Fe. The observation of anomalously long-period lattice spacings in these nanowires has caused confusion since reflections from lattice spacings of ≥0.4 nm are kinematically forbidden for Fe3C, most of the rarely observed, less stable carbides, α-Fe, and γ-Fe. Through high-resolution electron microscopy, selective area electron diffraction, and electron energy loss spectroscopy we demonstrate that the observed long-period lattice spacings of 0.49, 0.66, and 0.44 nm correspond to reflections from the (100), (010), and (001) planes of orthorhombic Fe3C (space group Pnma). Observation of these forbidden reflections results from dynamic scattering of the incident beam as first observed in bulk Fe3C crystals. With small amounts of beam tilt these reflections can have significant intensities for crystals containing glide planes such as Fe3C with space groups Pnma or Pbmn.

Silicon supplementation has been shown to play an important role in skeleton development, however, the potential role that silicon plays in mediating bone formation, and an understanding of where it might localise in the resulting bone tissue remain elusive. An improved understanding of these processes could have important implications for treating pathological mineralisation. A key aspect of defining the role of silicon in bone is to characterise its distribution and coordination environment, however, there is currently almost no information available on either. We have combined a sample-preparation method that simultaneously preserved mineral, ions, and the extracellular matrix (ECM) with secondary ion mass spectroscopy (SIMS) and electron energy-loss spectroscopy (EELS) to examine the distribution and coordination environment of silicon in murine osteoblasts (OBs) in an in vitro model of bone formation. SIMS analysis showed a high level of surface contamination from polydimethysiloxane (PDMS) resulting from sample preparation. When the PDMS was removed, silicon compounds could not be detected within the nodules either by SIMS or by energy dispersive X-ray spectroscopy (EDX) analysis. In comparison, electron energy-loss spectroscopy (EELS) provided a powerful and potentially widely applicable means to define the coordination environment and localisation of silicon in mineralising tissues. We show that trace levels of silicon were only detectable from the mineral deposits located on the collagen and in the peripheral region of mineralised matrix, possibly the newly mineralised regions of the OB nodules. Taken together our results suggest that silicon plays a biological role in bone formation, however, the precise mechanism by which silicon exerts its physicochemical effects remains uncertain. Our analytical results open the door for compelling new sets of EELS experiments that can provide detailed and specific information about the role that silicates play in bone formation and disease.