Preparation of highly dispersed Pt+Ru alloy clusters and the activity for the electrooxidation of methanol

Organic molecules and semiconductors have been proposed as active part of a large variety of nonvolatile memory devices, including resistors, diodes and transistors. In this review, we focus on electrically reprogrammable nonvolatile memories. We classify several possible devices according to their operation principle and critically review the role of the π-conjugated materials in the device operation. We propose specifications for applications for organic nonvolatile memory and review the state of the art with respect to these target specifications. Conclusions are drawn regarding further work on materials and device architectures.

Polymer and Organic Nonvolatile Memory Devices

Superionic conductors are compounds that exhibit exceptionally high values of ionic conductivity within the solid state. Indeed, their conductivities often reach values of the order of 1 Ω−1 cm−1, which are comparable to those observed in the molten state. Following Faraday's first observation of high ionic conductivity within the solids β-PbF2 and Ag2S in 1836, a fundamental understanding of the nature of the superionic state has provided one of the major challenges in the field of condensed matter science. However, experimental and theoretical approaches to their study are often made difficult by the extensive dynamic structural disorder which characterizes superionic conduction and the inapplicability of many of the commonly used approximations in solid state physics. Nevertheless, a clearer picture of the nature of the superionic state at the ionic level has emerged within the past few decades. Many different techniques have contributed to these advances, but the most significant insights have been provided by neutron scattering experiments and molecular dynamics simulations. This review will summarize the state of current knowledge concerning the crystal structures and conduction processes of superionic conductors, beginning with a comparison of the behaviour of two of the most widely studied binary compounds, AgI and β-PbF2. Each can be considered a parent of two larger families of highly conducting compounds which are related by either chemical or structural means. These include perovskite-structured oxides and Li+ containing spinel-structured compounds, which have important commercial applications in fuel cells and lightweight batteries, respectively. In parallel with these discussions, the relative importance of factors such as bonding character and the properties of the mobile and immobile ions (charge, size, polarizability, etc) in promoting the extensive lattice disorder which characterizes superionic behaviour will be assessed and the possibilities for predicting a priori which compounds will display high ionic conductivity discussed.

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Superionics: crystal structures and conduction processes

Nickel oxyhydroxide (NiOOH) is extensively used for energy storage and it is a very promising catalyst for the oxygen evolution reaction (OER). However, the processes occurring on the NiOOH surface during charge accumulation and OER are not well understood. This work presents an in situ Surface Enhanced Raman Spectroscopy (SERS) study of the pH dependent interfacial changes of the NiOOH catalyst under the working conditions used for OER. We demonstrate the important effect of the electrolyte pH on the degree of surface deprotonation of NiOOH, which crucially affects its OER activity. Our results show that the deprotonation of NiOOH produces negatively charged (or proton-deficient) surface species, which are responsible for the enhanced OER activity of NiOOH in highly alkaline pH. Moreover, we provide spectroscopic evidence obtained in an 18O-labeled electrolyte that allows us to assign this surface species to a superoxo-type species (Ni–OO−). Furthermore, we propose a mechanism for the OER on NiOOH which is consistent with the observed pH-sensitivity, and that also explains why NiOOH is not a suitable catalyst for applications in neutral or moderately alkaline pH (in the range 7–11), apart from the lower stability of the catalyst under these conditions.

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The importance of nickel oxyhydroxide deprotonation on its activity towards electrochemical water oxidation

Controlling the structure of colloidal nanocrystals (NCs) is key to the generation of their complex functionality This requires an understanding of the NC surface at the atomic level The structure of colloidal PbS NCs passivated with oleic acid has been studied theoretically and experimentally We show the existence of surface OH(-) groups, which play a key role in stabilizing the PbS(111) facets, consistent with x-ray photoelectron spectroscopy as well as other spectroscopic and chemical experiments The role of water in the synthesis process is also revealed Our model, along with existing observations of NC surface termination and passivation by ligands, helps to explain and predict the properties of NCs and their assemblies

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Hydroxylation of the surface of PbS nanocrystals passivated with oleic acid

X-ray photoelectron spectroscopic studies of electrode surfaces using a new controlled transfer technique: Part II. Results for a molybdenum electrode and the curve fitting procedure

The oxide films produced by anodic oxidation of gold and platinum have been studied by X-ray photoelectron spectroscopy. The change in the amount of each species present, with electrode potential, has been investigated. It is demonstrated that X-ray reduction occurs for these systems but that it can be minimised by a suitable choice of experimental conditions.A study of the intensities of the photoelectron peaks demonstrates how the thickness of an oxide layer and the true surface area of the electrode may be determined.

X-ray photoelectron spectroscopic studies of oxide films on platinum and gold electrodes

The presence and nature of surface species formed on a nickel electrode after polarisation in 0.5 mol dm–3 sulphuric acid and 0.5 mol dm–3 sulphuric acid + 0.005 mol dm–3 nickel sulphate has been investigated by X-ray photoelectron spectroscopy. The film produced in the active, prepassive, passive and transpassive regions was studied. Nine different species were detected including two sulphur species. In all cases the electrode was transferred to the spectrometer under nitrogen to minimise air oxidation of the metal or film.The binding energies and intensities of the photoelectron peaks were analysed and showed the presence of NiO and Ni(OH)2. The thickness of the film in the passive and transpassive regions was calculated, assuming a continuous layer, as 10–20 A.

T. Dickinson

Papers

X-ray photoelectron spectroscopic studies of electrode surfaces using a new controlled transfer technique: Part II. Results for a molybdenum electrode and the curve fitting procedure

X-ray photoelectron spectroscopic studies of oxide films on platinum and gold electrodes

Dissolution and passivation of nickel. An X-ray photoelectron spectroscopic study

X‐Ray Photoelectron Spectroscopic Studies of Tin Electrodes after Polarization in Sodium Hydroxide Solution

Quantitative use of the angular variation technique in studies of tin by X-ray photoelectron spectroscopy