Achieving Efficient Electrocatalytic Oxygen Evolution in Acidic Media on Yttrium Ruthenate Pyrochlore through Cobalt Incorporation

The development of electrocatalysts for the oxygen evolution reaction (OER) especially in acidic media remains the major challenge that still requires significant advances, both in material design and mechanistic exploration. In this study, the incorporation of cobalt in Y_2-xCo_xRu₂O_7−δ results in an ultrahigh OER activity because of the charge redistribution at e_g orbitals between Ru and Co atoms. The Y1.₇₅Co_0.25Ru₂O_7−δ electrocatalyst exhibits an extremely small overpotential of 275 mV in 0.5 m H₂SO₄ at the current density of 10 mA cm⁻², which is smaller than that of parent Y₂Ru₂O_7−δ (360 mV) and commercial RuO₂ (286 mV) catalysts. The systematic investigation of the composition related to OER activity shows that the Co substitution will also bring other effective changes, such as reducing the bandgap, and creating oxygen vacancies, which result in fast OER charge transfer. Meanwhile, the strengthening of the bond hybridization between the d orbitals of metal (Y and Ru) and the 2p orbitals of O will intrinsically enhance the chemical stability. Finally, theoretical calculations indicate that cobalt substitution reduces the theoretical overpotential both through an adsorbate evolution mechanism and a lattice oxygen-mediated mechanism.     

Modeling the point-spread function in helium-ion lithography

We present here a hybrid approach to modeling helium-ion lithography that combines the power and ease-of-use of the Stopping and Range of Ions in Matter (SRIM) software with the results of recent work simulating secondary electron (SE) yield in helium-ion microscopy. This approach traces along SRIM-produced helium-ion trajectories, generating and simulating trajectories for SEs using a Monte Carlo method. We found, both through simulation and experiment, that the spatial distribution of energy deposition in a resist as a function of radial distance from beam incidence, i.e. the point spread function, is not simply a sum of Gauss functions.     

Surface energy evaluation of casting and nanofiber polyurethane films by using different models

The components of the surface free energy (SFE) were determined from static contact angle measurements of five liquids using different methods. The two manufacturing techniques (casting and electrospinning) applied to obtain polyurethane (PU) membranes give surfaces with different wetting properties. The SFE data varied and were strongly dependent on calculations methods and liquids that were used for contact angle measurements. As a whole, the SFE of electrospun PU membrane (PU-N) (~24 mN/m) was slightly higher than that of casting PU membrane (PU-F) (~18 mN/m) with similar chemical compositions. The overall increase in the value of SFE is mainly due to the microstructures with increased surface area and modulations of nanofibers. The results evidence the impact of the PU membrane preparation on the properties of the biomaterial surface. Such structure–properties–function relationship is necessary to lay the groundwork for establishing a set of design criteria to guide the fabrication of synthetic materials.     

The extended generalized distance problem in discrete time

We obtain the class of all solutions to the extended (two block) generalized distance problem for discrete-time systems by employing the so-called ‘signature condition’—a generalized Popov theory type argument which parallels the J-spectral factorization approach. The novelty is that we derive explicit state-space formulae in terms of one Riccati and one Lyapunov equation while we remove the usual assumption in the discrete case on the time reversibility (invertibility of the state matrix) of the system to be approximated. © 1998 John Wiley & Sons, Ltd.     

Image sharpness measurement in scanning electron microscopy—part II

A method for qualitative and quantitative analysis of scanning electron microscope (SEM) images forthe determination of sharpness is presented in this paper. Described is a procedure for qualitative analysis based on a software program called SEM Monitor that can be applied to research or industrial SEMs for day-to-day performance monitoring. The idea is based on the fact that, as the electron beam scans the sample, the low-frequency changes in the video signal show information about the larger features and the high-frequency changes give data on finer details. The image contains information about the primary electron beam and about all the parts contributing to the signal formation in the SEM. If everything else is kept unchanged, with a suitable sample, the geometric parameters of the primary electron beam can be mathematically determined. An image of a sample, which has fine details at a given magnification, is sharper if there are more high frequency changes in it. In the SEM, a better focused electron beam yields a sharper image, and this sharpness can be measured. The method described is based on calculations in the frequency domain and can also be used to check and optimize two basic parameters of the primary electron beam, the focus, and the astigmatism.     

Nanowires and nanostructures fabrication using template methods: a step forward to real devices combining electrochemical synthesis with lithographic techniques

One of the great challenges of today is to find reliable techniques for the fabrication of nanomaterials and nanostructures. Methods based on template synthesis and on self organization are the most promising due to their easiness and low cost. This paper focuses on the electrochemical synthesis of nanowires and nanostructures using nanoporous host materials such as supported anodic aluminum considering it as a key template for nanowires based devices. New ways are opened for applications by combining such template synthesis methods with nanolithographic techniques.     

Spectroelectrochemical Investigations of the Spreading of 4-Pentadecyl Pyridine onto the Au(111) Electrode

The adsorption of 4-pentadecyl-pyridine (C15-4-Py) onto the Au(111) electrode was investigated with the help of electrochemical and spectroscopic techniques. Electrochemical studies demonstrated that a film of C15-4-Py spreads onto the metal surface at potentials close to the potential of zero charge (pzc) and desorbs from the electrode surface at potentials which are sufficiently negative. The character of C15–4-Py adsorption resembles adsorption of pyridine molecules at the Au(111) electrode, indicating that the film properties are to a large extent determined by the interaction between the pyridine moiety and the metal surface. Addition of 25 mol%) of 10-decyl-9-[2-(4-pyridyl)ethyl]anthracene(DPEA), a dye molecule, to the C15–4-Py film only slightly modified its properties but allowed the use of spectroscopic methods to study the film properties. Fluorescence spectroscopy and light scattering experiments were employed to study the potential-induced desorption and adsorption of the surfactant molecules. Using spectroelectrochemical techniques we have demonstrated that the desorption of the film and its readsorption involves the formation of micelles in the subsurface region and spreading of the micelles onto the electrode surface. A general mechanism of spreading of insoluble surfactants onto electrode surfaces has been proposed.     

Silica encapsulating lanthanum complexes using the sol–gel technique

BACKGROUND: Because of its properties, silica gel is an excellent host for different compounds. Many types of chemical species (organics, organometallics, proteins, enzymes, etc.) can be encapsulated in xerogels, and the sol–gel technique has been shown to be very useful for this aim. RESULTS: Some host–guest systems based on silica and complexed lanthanum were prepared in order to develop fluorescence properties. Three pathways were used to prepare such systems: (1) obtaining the lanthanum complex with a dimethylsiloxane‐based ligand and its incorporation into a silica network; (2) preparation of a silica network having hydroxyazomethine groups and in situ lanthanum complexation; and (3) preparation of polydimethylsiloxane (PDMS)/silica composites that possess hydroxyazomethine groups on the silica and in situ lanthanum complexation. The sol–gel technique was used in all cases. CONCLUSION: The photophysical properties of the prepared compounds were evaluated using fluorescence spectroscopy. The investigations revealed that the systems belonging to the second series are the most fluorescent. In the third series, the presence of PDMS provokes a decrease of the fluorescence intensity, until its complete quenching when the PDMS content exceeds a certain threshold value. However, there is a range of silica/PDMS ratio for which fluorescent free‐standing films can be obtained. The presence of complexed lanthanum induces changes in the morphology of the silica/PDMS matrix, as evidenced by scanning electron microscopy studies. Copyright © 2008 Society of Chemical Industry