Objective comparisons of electrocatalyst activity and stability using standard methods under identical conditions are necessary to evaluate the viability of existing electrocatalysts for integration into solar-fuel devices as well as to help inform the development of new catalytic systems. Herein, we use a standard protocol as a primary screen for evaluating the activity, short-term (2 h) stability, and electrochemically active surface area (ECSA) of 18 electrocatalysts for the hydrogen evolution reaction (HER) and 26 electrocatalysts for the oxygen evolution reaction (OER) under conditions relevant to an integrated solar water-splitting device in aqueous acidic or alkaline solution. Our primary figure of merit is the overpotential necessary to achieve a magnitude current density of 10 mA cm–2 per geometric area, the approximate current density expected for a 10% efficient solar-to-fuels conversion device under 1 sun illumination. The specific activity per ECSA of each material is also reported. Among HER...

Benchmarking Hydrogen Evolving Reaction and Oxygen Evolving Reaction Electrocatalysts for Solar Water Splitting Devices

Work function, electronegativity, and electrochemical behaviour of metals: III. Electrolytic hydrogen evolution in acid solutions

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respect, dislocation pile-ups cannot form, and the Hall–Petch relationship for conventional coarse-grained materials is no longer valid.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

Measurements show that monolayers of graphene and hexagonal boron nitride are unexpectedly highly permeable to thermal protons and that their conductivity rapidly increases with temperature, but that no proton transport is detected for few-layer crystals. A perfect graphene sheet is impermeable to all atoms and molecules: even hydrogen, the smallest of atoms, is not expected to penetrate through graphene's dense electronic cloud within billions of years. This characteristic is thought to extend to other two-dimensional crystals such as hexagonal boron nitride and molybdenum disulphide. Sheng Hu and colleagues now show that, surprisingly, monolayers of graphene and hexagonal boron nitride (but not molybdenum disulphide) are highly permeable to protons. In combination with their stability, this establishes these monolayers as promising candidates for use in many hydrogen-based technologies. Graphene is increasingly explored as a possible platform for developing novel separation technologies1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19. This interest has arisen because it is a maximally thin membrane that, once perforated with atomic accuracy, may allow ultrafast and highly selective sieving of gases, liquids, dissolved ions and other species of interest2,9,10,11,12,13,14,15,16,17,18,19. However, a perfect graphene monolayer is impermeable to all atoms and molecules under ambient conditions1,2,3,4,5,6,7: even hydrogen, the smallest of atoms, is expected to take billions of years to penetrate graphene’s dense electronic cloud3,4,5,6. Only accelerated atoms possess the kinetic energy required to do this20,21. The same behaviour might reasonably be expected in the case of other atomically thin crystals22,23. Here we report transport and mass spectroscopy measurements which establish that monolayers of graphene and hexagonal boron nitride (hBN) are highly permeable to thermal protons under ambient conditions, whereas no proton transport is detected for thicker crystals such as monolayer molybdenum disulphide, bilayer graphene or multilayer hBN. Protons present an intermediate case between electrons (which can tunnel easily through atomically thin barriers24) and atoms, yet our measured transport rates are unexpectedly high4,5 and raise fundamental questions about the details of the transport process. We see the highest room-temperature proton conductivity with monolayer hBN, for which we measure a resistivity to proton flow of about 10 Ω cm2 and a low activation energy of about 0.3 electronvolts. At higher temperatures, hBN is outperformed by graphene, the resistivity of which is estimated to fall below 10−3 Ω cm2 above 250 degrees Celsius. Proton transport can be further enhanced by decorating the graphene and hBN membranes with catalytic metal nanoparticles. The high, selective proton conductivity and stability make one-atom-thick crystals promising candidates for use in many hydrogen-based technologies.

http://www.condmat.physics.manchester.ac.uk/media/eps/condensedmatterphysicsgroup/publications/2014protoncurrents.pdf

Proton transport through one-atom-thick crystals

The real condition of electrochemically oxidized platinum surfaces

Des courbes de polarisation en regime permanent et des voltammogrammes cycliques ont ete realises avec des microelectrodes en platine dans des solutions a concentrations variables en ions Ni pour mettre en evidence le role de l'acide borique sur la deposition du nickel Dans l'acide sulfurique, H 2 est depose avant le nickel sur la surface de platine Dans le bain de Watts (contenant l'acide borique) la couche de nickel est deposee avant La presence de l'acide borique abaisse la surtension necessaire au depot du nickel

On the Role of Boric Acid in the Watts Bath

Donnees sur les etudes de voltammetrie cyclique dans le cas d'un lit de microelectrodes d'or, dans des solutions de H 2 SO 4 1N et de HF1N agitees par N 2 , en fonction de la vitesse de balayage et du domaine de potentiels balaye. On montre que H 2 et O 2 sont tres legerement adsorbes sur Au et que rien n'est dissous dans le metal en masse. Ces faits indiquent que l'electrode d'or est une electrode indicatrice plus stable que Pt, qui dissout l'oxygene

James P. Hoare

Papers

On the Role of Boric Acid in the Watts Bath

A Cyclic Voltammetric Study of the Gold‐Oxygen System

Rest Potentials in the Platinum‐Oxygen‐Acid System

Boric Acid as a Catalyst in Nickel Plating Solutions

On the Mechanisms of Chromium Electrodeposition