Electrocatalytic reduction of Nitrate on Copper single crystals in acidic and alkaline solutions

Catalysis and Surface Chemistr

Interconversions of nitrogen-containing species on Pt(100) and Pt(111) electrodes in acidic solutions containing nitrate

This work deals with the interconversions of various nitrogen-containing compounds on Pt(111) and Pt(100) electrodes in contact with acidic solutions of nitrate. Via its reduction, nitrate acts merely as the source of adsorbed nitrogen-containing intermediates, which then undergo complex oxidative or reductive transformations depending on the electrode potential. Nitrate reduction to ammonium is structure sensitive on Pt(111) and Pt(100) because it is mediated by *NO, the adsorption and reactivity of which is also structure sensitive. Accordingly, previous knowledge from *NO electrochemistry is useful to streamline nitrate reduction and elaborate a comprehensive picture of nitrogen-cycle electrocatalysis. Our overall conclusion for nitrate reduction is that the complete conversion to ammonium under prolonged electrolysis is possible only if the reduction of nitrate to nitric oxide, and the reduction of nitric oxide to ammonium are feasible at the applied potential. Among the two surfaces studied here, this condition is fulfilled by Pt(111) in a narrow potential region. (C) 2018 Elsevier Ltd. All rights reserved.Catalysis and Surface Chemistr

Unusual synergistic effect in layered Ruddlesden-Popper oxide enables ultrafast hydrogen evolution

Efficient electrocatalysts for hydrogen evolution reaction are key to realize clean hydrogen production through water splitting. As an important family of functional materials, transition metal oxides are generally believed inactive towards hydrogen evolution reaction, although many of them show high activity for oxygen evolution reaction. Here we report the remarkable electrocatalytic activity for hydrogen evolution reaction of a layered metal oxide, Ruddlesden-Popper-type Sr2RuO4 with alternative perovskite layer and rock-salt SrO layer, in an alkaline solution, which is comparable to those of the best electrocatalysts ever reported. By theoretical calculations, such excellent activity is attributed mainly to an unusual synergistic effect in the layered structure, whereby the (001) SrO-terminated surface cleaved in rock-salt layer facilitates a barrier-free water dissociation while the active apical oxygen site in perovskite layer promotes favorable hydrogen adsorption and evolution. Moreover, the activity of such layered oxide can be further improved by electrochemistry-induced activation

Determination of Specific Electrocatalytic Sites in the Oxidation of Small Molecules on Crystalline Metal Surfaces

The identification of active sites in electrocatalytic reactions is part of the elucidation of mechanisms of catalyzed reactions on solid surfaces. However, this is not an easy task, even for apparently simple reactions, as we sometimes think the oxidation of adsorbed CO is. For surfaces consisting of non-equivalent sites, the recognition of specific active sites must consider the influence that facets, as is the steps/defect on the surface of the catalyst, cause in its neighbors; one has to consider the electrochemical environment under which the “active sites” lie on the surface, meaning that defects/steps on the surface do not partake in chemistry by themselves. In this paper, we outline the recent efforts in understanding the close relationships between site-specific and the overall rate and/or selectivity of electrocatalytic reactions. We analyze hydrogen adsorption/desorption, and electro-oxidation of CO, methanol, and ammonia. The classical topic of asymmetric electrocatalysis on kinked surfaces is also addressed for glucose electro-oxidation. The article takes into account selected existing data combined with our original works.M.J.S.F. is grateful to PNPD/CAPES (Brazil). J.M.F. thanks the MCINN (FEDER, Spain) project-CTQ-2016-76221-P

Chemisorbed Oxygen at Pt(111): a DFT Study of Structural and Electronic Surface Properties

Simulations based on density functional theory are used to study the electronic and electrostatic properties of a Pt(111) surface covered by a layer of chemisorbed atomic oxygen. The impact of the oxygen surface coverage and orientationally ordered interfacial water layers is explored. The oxygen adsorption energy decreases as a function of oxygen coverage due to the lateral adsorbate repulsion. The surficial dipole moment density induced by the layer of chemisorbed oxygen causes a positive shift of the work function. In simulations with interfacial water layers, ordering and orientation of water molecules strongly affect the work function. It is found that the surficial dipole moment density and charge density are roughly linearly dependent on the oxygen surface coverage. Moreover, we found that water layers exert only a small impact on the surface charging behavior of the surface

The impact of chloride ions and the catalyst loading on the reduction of H₂O₂ on high-surface-area platinum catalysts

Minor electrolyte constituents that are present even in the best grade, and highly pure electrolytes can have a major impact on electrocatalytic reactions. In this work, we discuss particularly the influence of chloride adsorption on the interaction of hydrogen peroxide with carbon-supported platinum nanoparticle catalysts, as this is of high relevance for the oxygen reduction reaction (ORR). Under non-equilibrium conditions, the surface coverage of chloride at a certain time is determined by the ratio of the chloride flux within the diffusion layer to the number of surface sites. Therefore, by decreasing the catalyst loading, the same amount of chloride ions that reaches the surface under a given mass transport regime leads to a higher coverage. Similarly, by increasing the mass transport rates, chloride ions diffuse to the surface with a higher rate and thus cover a larger fraction of the surface at a given time. The increased coverage with chloride in both cases leads to an inhibition of the hydrogen peroxide reduction reaction (PRR), and concomitantly to desorption of the H2O2 intermediate during the ORR on Pt electrodes. The contribution of the electrolyte impurities to the macroscopic H2O2 release during the ORR on low-loading catalysts or under high mass transport rates is thus an important - if not the decisive - factor that needs to be taken into consideration, for instance during fuel cell operation or in the interpretation of experimental observations for mechanistic studies. (C) 2013 Elsevier Ltd. All rights reserved

Electrocatalytic nitrate reduction for sustainable ammonia production

Catalysis and Surface Chemistr