Objective evaluation of the activity of electrocatalysts for water oxidation is of fundamental importance for the development of promising energy conversion technologies including integrated solar water-splitting devices, water electrolyzers, and Li-air batteries. However, current methods employed to evaluate oxygen-evolving catalysts are not standardized, making it difficult to compare the activity and stability of these materials. We report a protocol for evaluating the activity, stability, and Faradaic efficiency of electrodeposited oxygen-evolving electrocatalysts. In particular, we focus on methods for determining electrochemically active surface area and measuring electrocatalytic activity and stability under conditions relevant to an integrated solar water-splitting device. Our primary figure of merit is the overpotential required to achieve a current density of 10 mA cm–2 per geometric area, approximately the current density expected for a 10% efficient solar-to-fuels conversion device. Utilizing ...

Benchmarking Heterogeneous Electrocatalysts for the Oxygen Evolution Reaction

Dealloying is a common corrosion process during which an alloy is 'parted' by the selective dissolution of the most electrochemically active of its elements. This process results in the formation of a nanoporous sponge composed almost entirely of the more noble alloy constituents. Although considerable attention has been devoted to the morphological aspects of the dealloying process, its underlying physical mechanism has remained unclear. Here we propose a continuum model that is fully consistent with experiments and theoretical simulations of alloy dissolution, and demonstrate that nanoporosity in metals is due to an intrinsic dynamical pattern formation process. That is, pores form because the more noble atoms are chemically driven to aggregate into two-dimensional clusters by a phase separation process (spinodal decomposition) at the solid-electrolyte interface, and the surface area continuously increases owing to etching. Together, these processes evolve porosity with a characteristic length scale predicted by our continuum model. We expect that chemically tailored nanoporous gold made by dealloying Ag-Au should be suitable for sensor applications, particularly in a biomaterials context.

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Evolution of nanoporosity in dealloying

Introduction 1. Aqueous Corrosion 2. Environments and Application Examples 3. high-Temperature Corrosion 4. Modeling, Life Prediction, and Computer Applications 5. Corrosion Failures 6. Corrosion Maintenance Through Inspection And Monitoring 7. Acceleration and Amplification of Corrosion Damage 8. Materials Selection 9. Protective Coatings 10. Corrosion Inhibitors 11. Cathodic Protection 12. Anodic Protection

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Handbook of Corrosion Engineering

In recent years, near-nano (submicron) and nanostructured materials have attracted increasingly more attention from the materials community. Nanocrystalline materials are characterized by a microstructural length or grain size of up to about 100 nm. Materials having grain size of ∼0.1 to 0.3 μm are classified as submicron materials. Nanocrystalline materials exhibit various shapes or forms, and possess unique chemical, physical or mechanical properties. When the grain size is below a critical value (∼10–20 nm), more than 50 vol.% of atoms is associated with grain boundaries or interfacial boundaries. In this respect, dislocation pile-ups cannot form, and the Hall–Petch relationship for conventional coarse-grained materials is no longer valid. Therefore, grain boundaries play a major role in the deformation of nanocrystalline materials. Nanocrystalline materials exhibit creep and super plasticity at lower temperatures than conventional micro-grained counterparts. Similarly, plastic deformation of nanocrystalline coatings is considered to be associated with grain boundary sliding assisted by grain boundary diffusion or rotation. In this review paper, current developments in fabrication, microstructure, physical and mechanical properties of nanocrystalline materials and coatings will be addressed. Particular attention is paid to the properties of transition metal nitride nanocrystalline films formed by ion beam assisted deposition process.

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Nanocrystalline materials and coatings

Nanoporous Gold Leaf: “Ancient Technology”/Advanced Material

Characteristic features of alloy polarization curves

A mechanistic model has been developed which for the first time considers the effect of hydrogen entry into a metal on the kinetics of the hydrogen evolution reaction (h.e.r.). The model enables computation of (i) the hydrogen surface coverage and surface concentration; (ii) the hydrogen adsorption, absorption, discharge and recombination rate constants; and (iii) the h.e.r. coverage‐dependent transfer coefficient, α, and the exchange current density , from a knowledge of the steady‐state hydrogen permeation current, cathodic charging current, hydrogen overvoltage, and hydrogen diffusivity. The model predicts a linear relationship between the permeation flux and the square root of the hydrogen recombination flux, and provides an analytical method to determine the cathodic potential range for operation of a coupled discharge‐recombination mechanism of the h.e.r. With modifications the model can treat permeation data for which (i) the mechanics of the discharge step involve a (proposed) selvedge reaction, and (ii) surface hydrogen coverages are relatively high as in the presence of poisons (e.g., or ). Some of the existing literature data for hydrogen permeation in iron and nickel in acid and alkaline solutions are successfully analyzed.

Howard W. Pickering

Papers

Characteristic features of alloy polarization curves

Analysis of Hydrogen Evolution and Entry into Metals for the Discharge‐Recombination Process

The significance of the local electrode potential within pits, crevices and cracks

Significance of the local electrode potential within pits, crevices and cracks

Formation of New Phases during Anodic Dissolution of Zn‐Rich Cu ‐ Zn Alloys