Insight into CO activation over Cu(100) under electrochemical conditions

The reduction of CO2 on copper electrodes has attracted great attentions in the last decades, since it provides a sustainable approach for energy restore. During the CO2 reduction process, the electron transfer to COads is experimentally suggested to be the crucial step. In this work, we examine two possible pathways in CO activation, i.e. to generate COHads and CHOads, respectively, by performing the state-of-the-art constrained ab initio molecular dynamics simulations on the charged Cu(100) electrode under aqueous conditions, which is close to the realistic electrochemical condition. The free energy profile in the formation of COHads via the coupled proton and electron transfer is plotted. Furthermore, by Bader charge analyses, a linear relationship between C-O bond distance and the negative charge in CO fragment is unveiled. The formation of CHOads is identified to be a surface catalytic reaction, which requires the adsorption of H atom on the surface first. By comparing these two pathways, we demonstrate that kinetically the formation of COHads is more favored than that of CHOads, while CHOads is thermodynamically more stable. This work reveals that CO activation via COHads intermediate is an important pathway in electrocatalysis, which could provide some insights into CO2 electroreduction over Cu electrodes

Current developments of nanoscale insight into corrosion protection by passive oxide films

Oxide passive films are a key for the durability of metals and alloys components as well as a central issue in corrosion science and engineering. Herein, we discuss current developments of the nanometer and sub-nanometer scale knowledge of the barrier properties and adsorption properties of passive oxide films brought by recent model experimental and theoretical investigations. The discussed aspects include (i) the chromium enrichment and its homogeneity at the nanoscale in passive films formed on Cr-bearing alloys such as stainless steel, (ii) the corrosion properties of grain boundaries in early intergranular corrosion before penetration and propagation in the grain boundary network, and (iii) the interaction of organic inhibitor molecules with incompletely passivated metallic surfaces. In all three cases, key issues are highlighted and future developments that we consider as most relevant are identified.Comment: Current Opinion in Solid State and Materials Science, Elsevier, final accepted preprin

Electron affinity of liquid water.

Understanding redox and photochemical reactions in aqueous environments requires a precise knowledge of the ionization potential and electron affinity of liquid water. The former has been measured, but not the latter. We predict the electron affinity of liquid water and of its surface from first principles, coupling path-integral molecular dynamics with ab initio potentials, and many-body perturbation theory. Our results for the surface (0.8 eV) agree well with recent pump-probe spectroscopy measurements on amorphous ice. Those for the bulk (0.1-0.3 eV) differ from several estimates adopted in the literature, which we critically revisit. We show that the ionization potential of the bulk and surface are almost identical; instead their electron affinities differ substantially, with the conduction band edge of the surface much deeper in energy than that of the bulk. We also discuss the significant impact of nuclear quantum effects on the fundamental gap and band edges of the liquid

Environmentally Persistent Free Radicals (EPFRs). 3. Free versus Bound Hydroxyl Radicals in EPFR Aqueous Solutions

Additional experimental evidence is presented for in vitro generation of hydroxyl radicals because of redox cycling of environmentally persistent free radicals (EPFRs) produced after adsorption of 2-monochlorophenol at 230 °C (2-MCP-230) on copper oxide supported by silica, 5% Cu(II)O/silica (3.9% Cu). A chemical spin trapping agent, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), in conjunction with electron paramagnetic resonance (EPR) spectroscopy was employed. Experiments in spiked O17 water have shown that ∼15% of hydroxyl radicals formed as a result of redox cycling. This amount of hydroxyl radicals arises from an exogenous Fenton reaction and may stay either partially trapped on the surface of particulate matter (physisorbed or chemisorbed) or transferred into solution as free OH. Computational work confirms the highly stable nature of the DMPO–OH adduct, as an intermediate produced by interaction of DMPO with physisorbed/chemisorbed OH (at the interface of solid catalyst/solution). All reaction pathways have been supported by ab initio calculations

Double layer charging driven carbon dioxide adsorption limits the rate of electrochemical carbon dioxide reduction on Gold.

Electrochemical CO[Formula: see text] reduction is a potential route to the sustainable production of valuable fuels and chemicals. Here, we perform CO[Formula: see text] reduction experiments on Gold at neutral to acidic pH values to elucidate the long-standing controversy surrounding the rate-limiting step. We find the CO production rate to be invariant with pH on a Standard Hydrogen Electrode scale and conclude that it is limited by the CO[Formula: see text] adsorption step. We present a new multi-scale modeling scheme that integrates ab initio reaction kinetics with mass transport simulations, explicitly considering the charged electric double layer. The model reproduces the experimental CO polarization curve and reveals the rate-limiting step to be *COOH to *CO at low overpotentials, CO[Formula: see text] adsorption at intermediate ones, and CO[Formula: see text] mass transport at high overpotentials. Finally, we show the Tafel slope to arise from the electrostatic interaction between the dipole of *CO[Formula: see text] and the interfacial field. This work highlights the importance of surface charging for electrochemical kinetics and mass transport

Neutron and X-ray diffraction studies on complex liquids

The above examples illustrate the extent to which present day neutron and X-ray diffraction methods are being used to determine interatomic structure in a wide range of liquid and amorphous systems. The determination of pair radial distribution functions not only offers a means to characterise different structures in liquids, but also provides theorists with information to construct realistic model potentials that can be used to calculate macroscopic behaviour and structural properties in regimes not currently accessible to experiment.\ud The well-established NDIS difference methods remain superior to all other methods for the determination of interatomic pairwise structure. The relatively new AXD (or DAS) difference methods have the potential to answer long-standing questions about the structure around species with mass number greater than about 30. However, the relatively low X-ray scattering power from light elements such as hydrogen, carbon, nitrogen etc. means that it will never be possible to resolve completely structures of biologically important liquids by X-ray methods alone. EXAFS spectroscopy has the distinct advantage over both diffraction techniques as it can be used to study local structure around particular species at high dilution. Therefore studies which combine reference data from AXD or NDIS, with extensive EXAFS data, are likely to be useful in studies of structure in regimes which prove difficult for AXD and NDIS. \ud It is clear that no one method will be sufficient to resolve structure at the required level of detail around all species in a complex liquid. Instead one must rely on a full complement of diffraction and other techniques including computer simulation to determine the complete atomic structure of a complex liquid or amorphous system.\ud On the technical front, the construction and commissioning of new neutron diffractometers with higher count rates, such as D20 and D4C at ILL, and GEM at ISIS with an optimised sample environment for work at non-ambient conditions, will enable new and more extensive research to be undertaken. Additionally, the new custom-built X-ray diffractometer for liquids proposed for the DIAMOND synchrotron being established at RAL will provide a much-needed boost for wide-ranging AXD and EXAFS investigations of complex liquids. \ud Besides the many studies of immediate interest suggested at the end of some sections, there are several investigations that will become feasible in the longer term as the technology develops. These include 1. the use of isotopes such as 12C and 13C and 33S and 32S which will enable detailed and extensive structural studies to be carried out on a wide range of biologically significant materials, and 2. the exploitation of higher neutron and X-ray count rates to facilitate real time experiments to investigate changes of structure as a chemical or biochemical reaction occurs. \ud The one strong theme which emerges from all the work described in this paper is that diffraction, especially that based on difference techniques, remains the best means to determine structure at atomic resolution in complex liquids