A detailed investigation has been carried out of the structure and electrochemical activity of electrodeposited Ni-Fe films for the oxygen evolution reaction (OER) in alkaline electrolytes. Ni-Fe films with a bulk and surface composition of 40% Fe exhibit OER activities that are roughly 2 orders of magnitude higher than that of a freshly deposited Ni film and about 3 orders of magnitude higher than that of an Fe film. The freshly deposited Ni film increases in activity by as much as 20-fold during exposure to the electrolyte (KOH); however, all films containing Fe are stable as deposited. The oxidation of Ni(OH)2 to NiOOH in Ni films occurs at potentials below the onset of the OER. Incorporation of Fe into the film increases the potential at which Ni(OH)2/NiOOH redox occurs and decreases the average oxidation state of Ni in NiOOH. The Tafel slope (40 mV dec(-1)) and reaction order in OH(-) (1) for the mixed Ni-Fe films (containing up to 95% Fe) are the same as those for aged Ni films. In situ Raman spectra acquired in 0.1 M KOH at OER potentials show two bands characteristic of NiOOH. The relative intensities of these bands vary with Fe content, indicating a change in the local environment of Ni-O. Similar changes in the relative intensities of the bands and an increase in OER activity are observed when pure Ni films are aged. These observations suggest that the OER is catalyzed by Ni in Ni-Fe films and that the presence of Fe alters the redox properties of Ni, causing a positive shift in the potential at which Ni(OH)2/NiOOH redox occurs, a decrease in the average oxidation state of the Ni sites, and a concurrent increase in the activity of Ni cations for the OER.

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An Investigation of Thin-Film Ni–Fe Oxide Catalysts for the Electrochemical Evolution of Oxygen

Since 2000, there has been an explosion of activity in the field of plasmon-enhanced Raman spectroscopy (PERS), including surface-enhanced Raman spectroscopy (SERS), tip-enhanced Raman spectroscopy (TERS) and shell-isolated nanoparticle-enhanced Raman spectroscopy (SHINERS). In this Review, we explore the mechanism of PERS and discuss PERS hotspots — nanoscale regions with a strongly enhanced local electromagnetic field — that allow trace-molecule detection, biomolecule analysis and surface characterization of various materials. In particular, we discuss a new generation of hotspots that are generated from hybrid structures combining PERS-active nanostructures and probe materials, which feature a strong local electromagnetic field on the surface of the probe material. Enhancement of surface Raman signals up to five orders of magnitude can be obtained from materials that are weakly SERS active or SERS inactive. We provide a detailed overview of future research directions in the field of PERS, focusing on new PERS-active nanomaterials and nanostructures and the broad application prospect for materials science and technology. Assisted by rationally designed novel plasmonic nanostructures, surface-enhanced Raman spectroscopy has presented a new generation of analytical tools (that is, tip-enhanced Raman spectroscopy and shell-isolated nanoparticle-enhanced Raman spectroscopy) with an extremely high surface sensitivity, spatial resolution and broad application for materials science and technology.

Nanostructure-based plasmon-enhanced Raman spectroscopy for surface analysis of materials

The nature and properties of surface-enhanced vibrational spectra of molecules adsorbed on surfaces that can enhance the absorption and the emission of electromagnetic radiation are discussed. Examples of surface-enhanced resonant Raman scattering, surface-enhanced Raman scattering in the near-infrared and surface-enhanced infrared are given. The rough surfaces used are metal island films coated with a nanometric organic film using the Langmuir-Blodgett technique or deposited by vacuum evaporation.

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Surface enhanced vibrational spectroscopy

Ni-(oxy)hydroxide-based materials are promising earth-abundant catalysts for electrochemical water oxidation in basic media. Recent findings demonstrate that incorporation of trace Fe impurities from commonly used KOH electrolytes significantly improves oxygen evolution reaction (OER) activity over NiOOH electrocatalysts. Because nearly all previous studies detailing structural differences between α-Ni(OH)2/γ-NiOOH and β-Ni(OH)2/β-NiOOH were completed in unpurified electrolytes, it is unclear whether these structural changes are unique to the aging phase transition in the Ni-(oxy)hydroxide matrix or if they arise fully or in part from inadvertent Fe incorporation. Here, we report an investigation of the effects of Fe incorporation on structure–activity relationships in Ni-(oxy)hydroxide. Electrochemical, in situ Raman, X-ray photoelectron spectroscopy, and electrochemical quartz crystal microbalance measurements were employed to investigate Ni(OH)2 thin films aged in Fe-free and unpurified (reagent-grade)...

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Effects of Fe Electrolyte Impurities on Ni(OH)2/NiOOH Structure and Oxygen Evolution Activity

Ordered anion adlayers on metal electrode surfaces.

: Surface-enhanced Raman spectra of benzene and eight mono substituted benzenes adsorbed at gold electrodes have been examined in order to probe the nature of adsorbate-surface bonding for simple aromatic molecules. Benzene appears to adsorb flat via pi adsorbate-surface interactions as evidenced by the significant (20-30/cm) downshifts in the symmetric rig breathing mode (v sub 1) and the absence of other ring modes in the SER spectra. Similar results were obtained using gold surfaces prepared by electroplating or anodic-cathodic potential sweeps in chloride, although much more stable SERS was obtained by using the latter procedure. The ring substituents -CHD3, -CH(CH3)2, -C(CH3)3, - Cl, -Br, -CN, -NO2, -COO(-) and -CHO were chosen so to provide steric perturbations or alternative binding modes to the metal surface. With the alkyl, benzoate, and aldehyde substituents, small yet significant (ca. 5-15/cm) decreases in the v sub 12 and v sub 18a characteristic ring modes along with band broadening were observed upon adsorption, consistent with attachment via the benzene ring; For the halogen substituents, smaller such downshifts were obtained along with the appearance of low-frequency modes associated with halogen-surface vibrations, implicating the role of substituent bonding in the adsorption. For the nitrile and nitro substituents, the ring modes were unaltered in frequency or band shape upon adsorption while intense internal substituent modes were observed.

Surface-enhanced Raman spectroscopy as a probe of adsorbate-surface bonding: benzene and monosubstituted benzenes adsorbed at gold electrodes

Surface-enhanced Raman scattering at gold electrodes: dependence on electrochemical pretreatment conditions and comparisons with silver

Les frequences des vibrations adsorbat-surface du metal dans le cas des vibrations des couches monomoleculaires de chlorure, bromure, iodure thiocyanate et cyanure adsorbes sur des electrodes d'or, obtenues par diffusion Raman augmentee en surface, sont comparees a des donnees correspondantes obtenues sur des electrodes d'Ag, en vue d'elucider la nature des liaisons de surface

Metal-adsorbate vibrational frequencies as a probe of surface bonding: halides and pseudohalides at gold electrodes

Etude par spectrometrie SERS et par voltammetrie cyclique de l'adsorption et de la reduction electrochimique de l'azobenzene et du nitrobenzene sur une electrode d'or

Surface-enhanced raman spectroscopy as a probe of electroorganic reaction pathways. 1. Processes involving adsorbed nitrobenzene, azobenzene, and related species

On propose un procede fonde sur des cycles d'oxydation et de reduction de balayage du potentiel, permettant de preparer des surfaces d'or legerement rugueuses, donnant des spectres Raman augmentes en surface intenses pour une serie d'adsorbats a l'interface or-solution aqueuse. On propose des spectres representatifs pour des adsorbats halogenures, pseudohalogenures et oxyanions, pour les complexes metalliques redox actifs et pour l'ethylene adsorbe

Ping Gao

Papers

Surface-enhanced Raman spectroscopy as a probe of adsorbate-surface bonding: benzene and monosubstituted benzenes adsorbed at gold electrodes

Surface-enhanced Raman scattering at gold electrodes: dependence on electrochemical pretreatment conditions and comparisons with silver

Metal-adsorbate vibrational frequencies as a probe of surface bonding: halides and pseudohalides at gold electrodes

Surface-enhanced raman spectroscopy as a probe of electroorganic reaction pathways. 1. Processes involving adsorbed nitrobenzene, azobenzene, and related species

Gold as a ubiquitous substrate for intense surface-enhanced Raman scattering