Spontaneously Deposited Research Articles

(Invited) Zinc-Deposited Aluminum Electrode Prepared Using Spontaneous Deposition Method for Use in Aqueous Hybrid Capacitors

Aqueous electrolytes have advantages compared to nonaqueous electrolytes, such as high ionic conductivity, nonflammability, low environmental load, low cost, and so on. However, the maximum operating voltages of electric double-layer capacitors (EDLCs) with aqueous electrolytes are much lower than those with nonaqueous electrolytes, which can operate at voltages over 2.5 V, because the former are limited to 1.23 V, the theoretical decomposition voltage of water, leading to low energy and power densities. So, a key to improve energy and power densities is to increase the maximum operating voltage. Hybrid capacitors (HCs), which consists of activated carbon (AC) and redox electrodes, can greatly improve the energy and power densities of EDLCs because of widened potential windows. As for aqueous HCs, metal hydroxides/oxides as a redox positive electrode have realized the maximum operating voltages of 1.4–2.0 V because they have higher potential limits and higher oxygen overpotentials than AC,1-3 leading to higher energy and power densities. In the same manner, we reported that an HC with a Zn negative electrode whose hydrogen overpotential was larger than AC also increased the maximum operating voltage due to the extension of the negative potential limits, leading to low energy and power densities.4 A copper sheet was used as a substrate for zinc electrodeposition in the previous study.4 Aluminum is a light metal and cheap. Since the standard potential of Al is more negative than that of Zn, Zn can be spontaneously deposited on an Al sheet only by immersing it in a zincate solution. In this study, we prepared Zn-deposited Al sheet negative electrodes and evaluated their electrochemical properties and capacitor performance of a HC with the negative electrode.A polished Al sheet was immersed in a zincate solution to deposit Zn metal spontaneously. After the deposition, the mirror image of the Al sheet was cloudy due to zinc deposits. EDX and XPS analyses showed that Zn deposits covered almost the whole Al surface, indicating that spontaneous deposition of Zn occurred as follows.2Al + 3Zn(OH)4 2- → 3Zn + 4OH- + 2Al(OH)4 - Cyclic voltammograms of a Zn/Al electrode were recorded in 7 M KOH aqueous solution containing 0.6 M ZnO. A reduction peak due to Zn deposition and an oxidation peak due to Zn dissolution were observed in cyclic voltammograms, which was similar to a cyclic voltammogram of a Cu electrode in the same electrolyte.An aqueous HC cell with a Zn/Al negative electrode and AC positive electrode was assembled, and its capacitor performance will be reported. References V. Khomenko, E. Raymundo-Piñero, F. Béguin, J. Power Sources, 153, 183 (2006).T. Cottineau, M. Toupin, T. Brousse, D. Bélanger, Appl. Phys. A: Mater. Sci. Process., 82, 599 (2006).H. Inoue, Y. Namba, E. Higuchi, J. Power Sources, 195, 6239 (2010).H. Inoue, T. Morimoto, S. Nohara, Electrochem. Solid-State Lett., 10, A261 (2007).

Catalysis of Methanol Oxidation on Bimetallic Ir/Pt(poly) Electrodes.

Oxidation of methanol was studied in alkaline solution on bimetallic Ir/Pt(poly) catalysts prepared by the spontaneous deposition of Ir on polycrystalline Pt. Nano-scale surface properties of Ir/Pt(poly) catalysts were revealed by ex situ Atomic Force Microscopy imaging. Modified electrodes were characterized in situ electrochemically by cyclic voltammetry in 0.1 M KOH. Investigations of the methanol oxidation in the same alkaline solution showed that Ir/Pt(poly) electrode obtained after 1 minute Ir deposition, which is equivalent to 80% Ir coverage, showed improved activity with respect to both constitutive metals. The observed synergism on the methanol oxidation activity was ascribed to both bifunctional and electronic effects that are induced by the presence of spontaneously deposited Ir. The origin of the synergism and the possible methanol oxidation pathways were discussed on the basis of the activities of the Ir/Pt(poly) electrodes for the oxidation of the most probable reaction intermediates, CO and formaldehyde, in the same alkaline solution.

(Invited) Electrocatalysis of Hydrogen Evolution on Single Crystal Gold Electrodes Decorated By Palladium and Rhodium Nanoislands

Single crystal gold electrodes, Au(hkl), modified by submonolayer deposit of highly active metals from platinum group are convenient bimetallic model systems for fundamental studies of the electrocatalytic activity of various nanostructures for fuel cell reactions. Preparation of such bimetallic electrodes was carried out by spontaneous deposition method, which was monitored by chronopotentiometric measurement of open circuit potential. Surface characterization of the modified bimetallic electrodes, as well as base substrate electrodes, were performed ex situ by atomic force microscopy Simultaneously recorded topographic and phase images provided insight into different characteristics of the bimetallic surfaces, such as the dimensions of the deposited islands, occurrence of the preferential deposition along specific surface sites and the substrate coverage with deposited islands. Phase AFM images display an obvious chemical contrast between two materials, independent of the surface topography enabling thus quite accurate estimation of the surface coverage, particularly important in the cases when the conventional ways are not accurate enough or not applicable. X-ray photoelectron spectroscopy has shown the oxidation state of the surface constituents of the as prepared bimetallic electrodes. Pronounced catalytic activity for hydrogen evolution reaction (HER) of gold single crystals decorated by palladium nanoislands with submonolayer coverage has been reported so far for different Pd/Au(111) nanostructures in acid [1] and alkaline [2] media. Rh/Au(111) bimetallic electrodes, obtained by the same spontaneous deposition method have shown even better catalytic activity for HER in acid solution [3]. The activity was in agreement to the one theoretically predicted for Au(111) surface covered with Rh overlayers, which was comparable to that of Pt(111) [4]. It was shown that among different Rh/Au(111) nanostructures, the one with 50% Rh coverage has shown the highest activity for HER in acid media, starting at approx. 100 mV more positive potential than the most active Pd/Au(111) [1], and very close to the activity of Pt(111), although not exceeding it. Similar order of activity has been reported for HER in alkaline solution [2,5]. Comparison of the catalytic activity of the most active Pd/Au(111) and Rh/Au(111) in acid and alkaline media is shown in Fig. 1. The research is extended to the use of Au(100) electrode as the substrate for the same foreign metals deposition. The comparison of the catalytic activity of bimetallic surfaces consisting of Pd or Rh islands spontaneously deposited with the same coverage on differently oriented gold single crystals have shown that those bimetallic surfaces having Au(111) as substrate is more active than the ones deposited on Au(100) as substrate. The improved catalytic activity of the hereby explored bimetallic electrodes was interpreted by means of geometric and electronic effects of the substrates, which are responsible for different electrocatalytic properties with respect to both constitutive metals. We belive that these results contribute to the current search for the efficient catalyst for HER. [1] M.Smiljanić, I. Srejić, B. Grgur, Z. Rakočević, and S. Štrbac, Electrocatal. 3, 369 (2012). [2] M.Smiljanić, I. Srejić, B. Grgur, Z. Rakočević, and S. Štrbac, Electrochim. Acta 88, 589 (2013). [3] M.Smiljanić, I. Srejić, B. Grgur, Z. Rakočević, and S. Štrbac, Electrochem. Commun. 28, 37 (2013). [4] G. Soldano, E.N. Schulz, D.R. Salinas, E. Santos, and W. Schmickler, Phys. Chem. Chem. Phys. 13, 16437 (2011). [5] S. Štrbac, M. Smiljanić, and Z. Rakočević, J. Electrochem. Soc. 163, D3027 (2016). Figure 1

Effect of pH on the spontaneous synthesis of palladium nanoparticles on reduced graphene oxide

Palladium (Pd) nanoparticles were spontaneously deposited on reduced graphene oxide (rGO) without any external reducing agents. The prepared Pd/rGO composites were then characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Spontaneous deposition occurred because of a redox reaction between the Pd precursor and rGO, which involved reduction of bivalent Pd to metallic Pd0 and oxidation of the sp2 carbon of rGO to oxygen-containing functional groups. The amount of Pd deposited on rGO varied with pH, and this was attributed to electrostatic interactions between the Pd precursor and rGO based on the results of zeta potential measurements. The importance of the redox reaction in the spontaneous deposition was demonstrated in the experiment with Zn, Ni, Cu, Ag, Pt, Pd, and Au.

Oxygen reduction electrocatalyst of Pt on Au nanoparticles through spontaneous deposition.

A straightforward one-step spontaneous deposition approach for growth of Pt atomic shell on Au nanoparticles and the superior activity and durability of the resulted Pt-on-Au nanoparticles for the oxygen reduction reaction (ORR) are reported. Transmission electron microscopy, X-ray photoelectron spectroscopy, energy-dispersive spectrometry, and electrochemical measurements indicate that Pt can be spontaneously deposited on Au surface upon simply dispersing carbon-supported Au nanoparticles in PtCl42–-containing solution, without introducing any extraneous reducing agents or any pre/post-treatments. The deposited Pt atoms are uniformly distributed on the surface of Au nanoparticles, with coverage tunable by the concentration of PtCl42– and temperatures. An approximate monolayer of Pt forms at temperature of ca. 80 °C and PtCl42– concentrations of above 10–4 mol/L. The obtained Pt-on-Au core–shell nanoparticles catalyze the ORR with specific and mass activities of Pt that are 3.5 times higher than that of pure Pt nanoparticles. Moreover, they exhibit no visible activity degradation after undergoing long-term oxidization/reduction cycling in O2-saturated acid media, therefore showing great prospect as durable cathode electrocatalysts in proton-exchange membrane fuel cells.

Influence of buffering on the spontaneous deposition of cerium conversion coatings for corrosion protection of AA2024-T3 aluminum alloy

Cerium-based conversion coatings were spontaneously deposited on AA2024-T3 alloy at 60 °C using buffered and non-buffered CeCl3 solutions in the presence of H2O2. Malonic acid or amino-acetic acid (glycine) was used as buffering additives. The deposition process and the properties of the coatings obtained were followed by linear voltammetry and electrochemical impedance spectroscopy. The surface morphology was studied by scanning electron microscopy. It was found that buffering complicates the conversion process and hampers the deposition rate. The coatings deposited using buffered baths had lower barrier ability and corrosion durability in 3.5 % NaCl corrosive medium compared to those deposited in the absence of buffers.

In situ surface-enhanced Raman spectroscopic study of formic acid electrooxidation on spontaneously deposited platinum on gold

Present formic acid fuel cell efficiency is limited by low kinetics at the anode, indicating the need for effective catalysts to improve the formic acid oxidation. As a prerequisite, the nature of adsorbed species and specifically the reaction intermediates formed in this process needs to be examined. This work focuses on the electrooxidation of formic acid and the nature of the intermediates at a platinum-modified gold surface prepared through spontaneous deposition using a combination of electrochemistry and in situ surface enhanced Raman spectroscopy (SERS). This Pt-modified gold electrode surface assists in oxidizing formic acid at potentials as low as 0.0 V vs. Ag/AgCl which is 0.15 V more negative than a bare Pt surface. The oxidation current obtained on the Pt-modified gold electrode is 72 times higher than on a bare Au surface and 5 times higher than on a bare Pt surface at the same potential. In situ SERS has revealed the involvement of formate at a low frequency as the primary intermediate in this electrooxidation process. While previous studies mainly focused on the formate mode at ca. 1322 cm(-1), it is the first time that a formate peak at ca. 300 cm(-1) was observed on a Pt or Pt-associated surface. A unique relationship has been observed between the formic acid oxidation currents and the SERS intensity of this formate adsorbate. Furthermore, the characteristic Stark effect of the formate proves the strong interaction between the adsorbate and the catalyst. Both electrochemical and spectroscopic results suggest that the formic acid electrooxidation takes place by the dehydrogenation pathway involving a low frequency formate intermediate on the Pt-modified gold electrode catalyst.

Formic acid oxidation at spontaneously deposited palladium on polyaniline modified carbon fibre paper

Extended reaction zone anodes for formic acid oxidation have been prepared by the spontaneous deposition of Pd on polyaniline coated carbon fibre paper. The PANI supports, deposited on carbon fibre paper either galvanostatically, potentiostatically, or potentiodynamically, were characterized by electron microscopy, cyclic voltammetry and impedance spectroscopy. Pd was deposited on them by spontaneous reduction of Pd(II) by the reduced form of the PANI in order to preserve the characteristics of each type of PANI layer. It was found that galvanostatically deposited PANI produced electrodes that were much more active for formic acid oxidation than PANI produced under potential control. The morphology and mean particle size of Pd was found to depend strongly on the way in which the PANI was prepared and also correlated with the resistance and capacitance of the PANI at low potentials. It is proposed that the electrochemical characteristics of the PANI play a significant role in determining the morphology, particle size, and electrocatalytic activity for formic acid oxidation of the spontaneously deposited Pd.

Spontaneous deposition of gold nanoparticle nanocomposite on polymer surfaces throughsol–gel chemistry

A aminosilica nanocomposite layer containing a monolayer of gold nanoparticles (d = 18–22 nm) with a well-defined spacing was spontaneously deposited on an unmodifiedpolystyrene surface via a sol–gel reaction when the reduction reaction was carried outunder 1:8 molar ratio (gold(III):aminosilane). The amount of aminosilica and spacingbetween gold nanoparticles were found to be a function of the aminosilane:water molarratio, which contributes to the plasmonic property of the films with its absorptionwavelength ranging between 701 and 548 nm. Furthermore, the nanocomposite film thatconsists of a monolayer of nanoparticles in aminosilica has also been deposited on thesurface of polystyrene beads. This core–shell structure was found capable of storingelectrostatic charges and forming a well-separated 2D array.

Catalytic graphitization of PAN-based carbon fibers by spontaneously deposited manganese oxides

A simple method for the spontaneous deposition of manganese oxides on the surface of polyacrylonitrile (PAN)-based carbon fibers by a direct redox reaction between carbon fibers and permanganate ions is described. Catalytic graphitization of the PAN-based carbon fibers coated with manganese oxides was investigated by X-ray diffraction, Raman spectroscopy, and scanning electron microscopy. The results indicate that the graphitization of the PAN-based carbon fibers was accelerated in the presence of the manganese oxides even at the relatively low temperature of 1,600 °C.

Spontaneous deposition of Pt and Ir on Ru: Reduction to intermediate oxidation states

X-ray photoelectron spectroscopy (XPS) was used to study the spontaneous deposition of Pt and Ir on Ru(0 0 0 1). The spontaneous deposition experiments were performed in a combined ultra high vacuum/electrochemistry (UHV–EC) system allowing sample transport between UHV and electrochemical environments under controlled conditions. The Ru(0 0 0 1) electrode surface was cleaned in UHV and then brought into contact with either a Pt-containing solution(10 mM K 2PtCl 6 + 0.1 M H 2SO 4 or 10 mM (NH 4) 2PtCl 4 + DI water) or with solutions containing 10 mM (NH 4) 2IrCl 6 in varying concentrations of H 2SO 4 corresponding to pH values of 0.5, 1 and 7 in the electrochemistry chamber for 30 min without an externally applied potential. XPS data acquired after rinsing in DI water indicated that each metal is present in intermediate oxidation states. Pt is found spontaneously deposited as Pt(II) on Ru(0 0 0 1) at pH 1. Similarly, intermediate states of Ir are observed, with higher binding energies, characteristic of higher oxidation states, observed at higher pH values. Annealing the spontaneously deposited adlayer in UHV to >500 K in each case results in the reduction of the Pt or Ir adsorbate to the metallic state. Typical metal surface coverages, determined by XPS, varied with number of immersions and solution conditions, but in all cases was observed to be <0.3 monolayers average thickness.

A Coverage-Dependent Study of Pt Spontaneously Deposited onto Au and Ru Surfaces: Direct Experimental Evidence of the Ensemble Effect for Methanol Electro-Oxidation on Pt

Direct experimental evidence that can be unambiguously attributed to the need of an ensemble of a minimum number of neighboring Pt atoms for methanol electro-oxidation has been observed for the first time. This was realized by a Pt coverage-dependent investigation of methanol and CO electro-oxidation on Pt sites generated via spontaneous deposition onto both Au and Ru surfaces. CO stripping voltammograms also show clear evidence of a substantially strengthened CO-Pt bonding for submonolayer Pt deposited on the Au substrate over a range of ca. 0.22 to 0.77, which is in qualitative agreement with the theoretical prediction based on the Hammer-Nørskov d-band center model. However, the degree of the bond strengthening depends on the Pt coverage, being stronger for lower coverage. Additionally, evidence of an Ostwald ripening process for Pt islands formation has also been observed.

Methanol electrooxidation on platinum spontaneously deposited on unsupported and carbon-supported ruthenium nanoparticles

Using an inverted spontaneous deposition method, unsupported Ru and carbon-supported 40% Ru nanoparticles were decorated with platinum after surface Ru oxides were reduced in the hydrogen atmosphere at 25 °C for 1 h. All samples that we produced in this way yielded high catalytic activity towards methanol oxidation at an electrode potential of interest to DMFC fuel cells. In the chronoamperometric experiment, the activity increased with the uptake of platinum to high Pt packing density values. The 40% C/Ru/Pt catalyst with an optimized packing density shows higher reactivity than that of an equivalent commercial, carbon-supported Pt/Ru catalyst. Reduction of Ru (and Ru/Pt) nanoparticles at higher than ambient temperature induced unacceptable level of sintering, and was avoided.

In situ STM study of nanosized Ru and Os islands spontaneously deposited on Pt(1 1 1) and Au(1 1 1) electrodes

We provide an overview of structure and reactivity of selected bimetallic single crystal electrodes obtained by the method of spontaneous deposition. The surfaces that are described and compared are the following: Au(1 1 1)/Ru, Pt(1 1 1)/Ru and Pt(1 1 1)/Os. Detailed morphological information is presented and the significance of this work in current and further study of nanoisland covered surfaces in the catalytic and spectroscopic perspective is highlighted. All surfaces were investigated by in situ STM and by electroanalytical techniques. The results confirm our previous data that nanosized Ru islands are formed with specific and distinctive structural features, and that the Ru growth pattern is different for Au(1 1 1) and Pt(1 1 1). For Au(1 1 1), Ru is preferentially deposited on steps, while a random and relatively sparse distribution of Ru islands is observed on terraces. In contrast, for Ru deposited on Pt(1 1 1), a homogeneous deposition over all the Pt(1 1 1) surface was found. Os is also deposited homogeneously, and at a much higher rate than Ru, and even within a single deposition it forms a large proportion of multilayer islands. On Au(1 1 1), the Ru islands on both steps and terraces reach the saturation coverage within a short deposition time, and the Ru islands grow to multilayer heights and assume hexagonal shapes. On Pt(1 1 1), the Ru saturation coverage is reached relatively fast, but when a single deposition is applied, Ru nanoislands of mainly monoatomic height are formed, with the Ru coverage not exceeding 0.2 ML. For Ru deposits on Pt(1 1 1), we demonstrate that larger and multilayer islands obtained in two consecutive depositions can be reduced in size––both in height and width––by oxidizing the Ru islands and then by reducing them back to a metallic state. A clear increase in the Ru island dispersion is then obtained. However, methanol oxidation chronoamperometry shows that the surface with such a higher dispersion is less active to methanol oxidation than the initial surface. A preliminary interpretation of this effect is provided. Finally, we studied CO stripping reaction on Pt(1 1 1)/Ru, Au(1 1 1)/Ru and on Pt(1 1 1)/Os. We relate CO oxidation differences observed between Pt(1 1 1)/Ru and Pt(1 1 1)/Os to the difference in the oxophilicity of the two admetals. In turn, the difference in the CO stripping reaction on Pt(1 1 1)/Ru and Au(1 1 1)/Ru with respect to the Ru islands is linked to the effect of the substrate on the bond strength and/or adlayer structure of CO and OH ads species.

Osmium nanoislands spontaneously deposited on a Pt(111) electrode: an XPS, STM and GIF-XAS study

Scanning tunneling microscopy (STM) characterized adlayers of spontaneously deposited osmium on a Pt(111) electrode were investigated using ex-situ X-ray photoemission spectroscopy (XPS) and in-situ grazing incidence fluorescence X-ray absorption spectroscopy (GIF-XAS). After a single spontaneous deposition, monoatomic (or nearly monoatomic) nanoislands of osmium are formed. The island diameter varies from 2 to 5 nm depending on the Os coverage, which in turn is adjusted by varying the concentration of the Os precursor salt (OsCl3) in the deposition bath and/or by the deposition time. XPS reveals three oxidation states: a metallic Os (the 4f7/2 core level binding energy of 50.8 eV), Os(IV) (51.5 eV) and Os(VIII) (52.4 eV). The metallic osmium exists at potentials below 500 mV (vs. RHE) while above 500 mV osmium is oxidized to Os(IV). Electrodissolution of osmium begins above 900 mV and occurs simultaneously with platinum oxidation. At ca. 1200 mV V versus the RHE reference, the oxidation state of some small amounts of osmium that survive dissolution is the Os(VIII). We demonstrate, for the first time, that mixed or odd valencies of osmium exist on the platinum surface at potentials higher that 800 mV. In-situ GIF-XAS measurements of an Os LIII edge also reveal the presence of three Os oxidation states. Namely, below the electrode potential of 400 mV, the X-ray fluorescent energy at maximum absorption is 10.8765 keV, and is characteristic of the metallic Os. In the potential range between 500 and 1000 mV this energy is gradually shifted to higher values, assignable to higher valencies of osmium, like Os(IV). This tendency continues to higher potentials consistent with the third, highly oxidized osmium form present, most likely Os(VIII). The variation of the “raw edge jump height” of Os with the electrode potential, which is equivalent to a drop in osmium surface concentration, demonstrates that the electrochemical stripping of Os begins below 1.0 V versus RHE, as expected from voltammetry. Also, the observed intensity of the white line of Os in the 100–400 mV region is larger than the value reported for metallic bulk Os. This discrepancy may result from the difference in the electronic properties of the metallic Os layers on Pt(111) and the metallic bulk Os: in the potential region between 100 and 400 mV, the 5d electrons in Os and Pt form a mixed electronic band, and the density of electronic states near the Fermi level, the main factor determining the white line intensity, may not be the same as in metallic bulk. The presented results on osmium adlayers are much more comprehensive than those available in our previous work due to the combined STM, GIF-XAS and XPS investigations. A nearly perfect convergence of the in situ and ex situ data is one of the main research outcomes of this project. Finally, platinum XPS spectra taken in the context of Os electrooxidation from the electrode surface are also presented and conclusions are made, that up to 900 mV platinum remain metallic, irrespective of a significant osmium oxidation on its surface.

In situ STM imaging of spontaneously deposited ruthenium on Au( [formula omitted

Spontaneous deposition of ruthenium on Au(1 1 1) surfaces from 1.0 mM RuCl 3+0.5 M H 2SO 4 (or 0.1 M HClO 4) solutions was investigated by in situ STM and cyclic voltammetry, focusing on the morphology of the resulting submonolayer Ru modified surfaces. STM results show a pronounced step decoration, indicating that the steps are active sites for the nucleation of Ru monolayer islands, while a random distribution of Ru nuclei is observed on terraces. During deposition, the open circuit potential rapidly increases from 0.38 to above 0.72 V vs. (Ag/AgCl). Experiments with different deposition times show that deposition from sulfuric acid solution saturates after 3 min deposition, the island size reaches its saturation value of 2.8 nm after 1 min. Significantly higher deposition activities and saturation coverages are found for deposition from perchlorate solution and for deposition on highly stepped surfaces/surface areas, indicative of a pronounced anion effect and reflecting the higher activity of steps for Ru deposition, respectively. In both cases, in particular for deposition in perchlorate solution, islands grow to multilayer heights and assume hexagonal shapes. Finally it is shown that multiple deposition can be utilized to reach higher coverages, attaining step saturation also in sulfuric acid solution. The Ru modified Au(1 1 1) electrode was found to be inert for hydrogen adsorption, and the electrochemical results indicate that the ruthenium islands inhibit long-range ordering of the sulfate adlayer on the substrate.

Carbon monoxide oxidation on a Au(111) surface modified by spontaneously deposited Ru

The spontaneous deposition of Ru on Au(111) was performed in 10-3MRuCl3 + 0.5MH2SO4 solution. The obtained surface was characterized by STM under potential control in 0.5MH2SO4 solution. The coverage of the Au(111) terraces by deposited Ru was estimated by STM to be 0.02 ML. Step decoration could be noticed in the STM images, which indicates that the steps, as lined defects, are active sites for the nucleation of Ru monolayer islands, while the random distribution of Ru nuclei, observed on the terraces indicates point defects as active sites. The electrocatalytic activity of Au(111) surface modified by spontaneously deposited Ru was studied towards CO oxidation. The significant enhancement in the reaction rate compared to CO oxidation on a pure Au(111) surface, indicated that the edges of the deposited Ru islands were the active sites for the reaction.

Preparation and Characterization of Metal Nanoparticles on a Diamond Surface

The deposition of metal nanoparticles (such as Ag, Cu, Au, Pd, and Pt) on boron-doped, polycrystalline diamond thin films grown on silicon substrates was investigated using Raman spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and X-ray diffraction. Nanometer-size metal particles with preferred crystalline textures can be spontaneously deposited on the diamond thin film after a simple immersion in an acidic solution containing metal ions or metal complex ions. The size and distribution of metal deposits can be controlled by adjusting the metal ions concentration, the solution acidity, and the deposition time. The diamond/silicon interfacial ohmic contact was found to be the critical factor for achieving the observed spontaneous metal deposition on the diamond surface. Significant enhancement of hydrogen evolution activity was observed on a diamond electrode modified by 9% coverage of Pd nanoparticles. The results demonstrate a novel route for depositing nanometer-size metal catalysts on a highly corrosion resistant and dimensionally stable polycrystalline diamond support.

Ultrathin Films of Ruthenium on Low Index Platinum Single Crystal Surfaces: An Electrochemical Study

We report on electrochemical properties of ultrathin films of ruthenium on platinum single crystal surfaces, Pt(100), Pt(111) and Pt(110), and demonstrate that such films can be obtained by spontaneous deposition. We also show that the spontaneously deposited ruthenium coverage is surface structure dependent. Using the spontaneous deposition process and a constant potential electrolysis, a variety of Pt/Ru surfaces up to ca. 0.4 monolayer of ruthenium were prepared. All such Ru films are stable in the electrode potential range that precedes platinum oxidation. A strong surface structure effect in the electrochemical properties of these thin films was found. On Pt(100)/Ru at a fixed Ru coverage, there is a transition from a reversible to irreversible surface redox behavior that is not observed on other platinum single crystal faces. In contrast to Pt(100)/Ru and Pt(110)/Ru, the individual voltammetric phases of the Pt(111)/Ru electrode are not resolved, and ruthenium surface oxides appear to be the most st...

The electrical conductivity of thin films of the alkali metals spontaneously deposited on glass surfaces

A description is given of an investigation of the electrical conductivity of the invisible thin films of the alkali metals which are deposited spontaneously on the walls of an enclosure in which they are sealed in vacuo. The resistivity of the films decreases in the order potassium, rubidium, caesium. The resistivity of the rubidium film is in reasonable agreement with a previous measurement given by Ives and Johnsrud. Some evidence is adduced in support of the view reached by the above workers that the thicknesses of these spontaneous deposits are of the order of those of monatomic layers.