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Query: UMLS:C1862200 (RHE)
 1,093 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The adsorption of hexahexylduodecithiophene (12T) on a Au(111) electrode was investigated by using cyclic voltammetry (CV) and in situ electrochemical scanning tunneling microscopy (EC-STM) in 0.10 M HClO(4). Potential control at 0.20 V (vs RHE) revealed adlayer structures of mostly folded and rarely angular (oblique) and extended conformations on a reconstructed Au(111)-(square root(3) x 22) surface. The angular and extended conformations predominate when the electrode potential is increased to 0.35 and 0.60 V. Folded structures are still evident, but dynamic STM studies showed unfolding of this conformation. With molecular STM imaging of 12T adlayers, we address the packing arrangement and conformational changes of 12T admolecules on the reconstructed Au(111) electrode surface.
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PMID:Direct observation of conformational changes of beta-substituted duodecithiophene on a Au(111)-(square root(3) x 22) substrate using in situ electrochemical STM in 0.1 M HClO4. 2006 11

The electrocatalytic properties of home-made Pt nanoparticles supported onto WO(x) were determined for the electrooxidation of a CO(ads) monolayer and compared with that of a commercial Pt/C having the same Pt particle size. By combining electrochemical and spectroscopic techniques, we found that Pt/WO(x) nanoparticles exhibit a very high tolerance to CO at low electrode potentials (E = 0.1 V vs. RHE), which was never reported in the literature before. CO adsorption at E = 0.1 V vs. RHE on Pt/WO(x) yields CO(2) production as observed by Fourier-transform infrared spectroscopy (FTIR). When the gas bubbling in solution changes from CO to Ar, the current attenuates and the CO(2) production vanishes. This points towards a limited number of "active sites" and a slow step in the electrocatalytic process. When H(2) is used to purge the electrolyte from CO, a steep and continuous increase of the H(2) electrooxidation current is observed pointing towards continuous liberation of the Pt catalytic sites. The high tolerance to CO of Pt/WO(x) is discussed in terms of strong metal-support interaction (SMSI), which involves formation of a metal-oxide film partially covering the Pt nanoparticles (encapsulation) and creation of W-OH groups upon H(+) insertion at low electrode potentials.
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PMID:The role of the support in CO(ads) monolayer electrooxidation on Pt nanoparticles: Pt/WO(x)vs. Pt/C. 2009 84

A cobalt-phosphate water oxidation catalyst ("Co-Pi") has been electrodeposited onto mesostructured alpha-Fe(2)O(3) photoanodes. The photoelectrochemical properties of the resulting composite photoanodes were optimized for solar water oxidation under frontside illumination in pH 8 electrolytes. A kinetic bottleneck limiting the performance of such photoanodes was identified and shown to be largely overcome by more sparse deposition of Co-Pi onto the alpha-Fe(2)O(3). Relative to alpha-Fe(2)O(3) photoanodes, a sustained 5-fold enhancement in the photocurrent density and O(2) evolution rate was observed at +1.0 V vs RHE with the Co-Pi/alpha-Fe(2)O(3) composite photoanodes. These results demonstrate that integration of this promising water oxidation catalyst with a photon-absorbing substrate can provide a substantial reduction in the external power needed to drive the catalyst's electrolysis chemistry.
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PMID:Photoelectrochemical water oxidation by cobalt catalyst ("Co-Pi")/alpha-Fe(2)O(3) composite photoanodes: oxygen evolution and resolution of a kinetic bottleneck. 2020 13

Silver atomic quantum clusters (AgAQCs), with two or three silver atoms, show electrocatalytic activities that are not found in nanoparticles or in bulk silver. AgAQCs supported on glassy carbon electrodes oxidize ethanol and other alcohols in macroscopic electrochemical cells in acidic and basic media. This electrocatalysis occurs at very low potentials (from approximately +200 mV vs RHE), at physiological pH, and at ethanol concentrations that are found in alcoholic patients. When mammalian cells are co-exposed to ethanol and AgAQCs, alcohol-induced alterations such as rounded cell morphology, disorganization of the actin cytoskeleton, and activation of caspase-3 are all prevented. This cytoprotective effect of AgAQCs is also observed in primary cultures of newborn rat astrocytes exposed to ethanol, which is a cellular model of fetal alcohol syndrome. AgAQCs oxidize ethanol from the culture medium only when ethanol and AgAQCs are added to cells simultaneously, which suggests that cytoprotection by AgAQCs is provided by the ethanol electro-oxidation mediated by the combined action of AgAQCs and cells. Overall, these findings not only show that AgAQCs are efficient electrocatalysts at physiological pH and prevent ethanol toxicity in cultured mammalian cells, but also suggest that AgAQCs could be used to modify redox reactions and in this way promote or inhibit biological reactions.
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PMID:Silver sub-nanoclusters electrocatalyze ethanol oxidation and provide protection against ethanol toxicity in cultured mammalian cells. 2021 76

Monodisperse Pt nanoparticles supported on a graphitized carbon black (GC; 150 m(2) g(-1)), which exhibits higher resistance to carbon corrosion than a conventional high-surface-area carbon black (CB; 800 m(2) g(-1)), were prepared by the nanocapsule method. Three kinds of 50 wt%-Pt loaded catalysts (our nanocapsule Pt/GC, a commercial Pt/GC, and a commercial Pt/CB) were subjected to the durability test by a standard potential step protocol (E = 0.9 V <--> 1.3 V vs. RHE, holding 30 s at each E, 1 min for one cycle) in N(2)-saturated 0.1 M HClO(4) solution at 25 degrees C. The oxygen reduction reaction (ORR) activities at these catalysts were evaluated from the hydrodynamic voltammograms in O(2)-saturated 0.1 M HClO(4) solution at 25 degrees C by the rotating ring-disk electrode technique. The kinetically-controlled mass activities (MA) for the ORR at these catalysts at E = 0.85 to 0.70 V vs. RHE were found to decrease in proportion to log [number of potential step cycles] from 100 to 5000 cycles. It was found that our nanpcapsule Pt/GC showed the highest durability; the time elapsed for the reduction of MA(0.8V) to 700 A g(-1) (ca. 1/2 of the initial MA(0.8V)) at our Pt/GC was 30 and 60 times longer than those for the commercial Pt/GC and Pt/CB, respectively. It was found that the most important factor leading to both high MA and high durability is highly dispersed state of Pt nanoparticles with uniform size over the whole surface of the corrosion-resistant GC support, to which our nanocapsule method has contributed greatly.
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PMID:Durability of Pt/graphitized carbon catalysts for the oxygen reduction reaction prepared by the nanocapsule method. 2035 74

In the present study, we have performed in situ STM observation of the surface oxidation-reduction process at Pt(111) surface in 10 mM HF solution under N(2) atmosphere in a stainless-steel chamber. We have for the first time demonstrated the dynamic process of the roughening of the Pt(111) surface during the potential cycles. At E < 0.8 V vs. RHE, no distinct change was observed in the positive-going potential sweep, even though surface oxidation is expected to commence in the so-called butterfly peak region at 0.6 V. At E > or = 0.9 V, tiny spots with a height of 0.08 nm appeared on the terraces, which can be attributed to adsorbed oxygen species rather than Pt ad-atoms. When the electrode potential reached 1.3 V, the electrode surface became bumpy with small corrugations (<0.1 nm) due to oxygen atoms becoming incorporated into the subsurface, without any additional layer formation. In the negative-going potential sweep, the electrode surface was suddenly covered with monoatomic islands, as well as pits, while the tiny spots disappeared at the moment that the electrode potential reached 0.5 V, at which the surface reduction was completed. During the repetitive potential cycles, the formation and growth of the Pt islands were found to occur only around 0.5 V in each negative-going potential sweep back from 1.3 V.
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PMID:In situ STM observation of morphological changes of the Pt(111) electrode surface during potential cycling in 10 mM HF solution. 2037 11

Sustainable hydrogen production through photoelectrochemical water splitting using hematite (alpha-Fe(2)O(3)) is a promising approach for the chemical storage of solar energy, but is complicated by the material's nonoptimal optoelectronic properties. Nanostructuring approaches have been shown to increase the performance of hematite, but the ideal nanostructure giving high efficiencies for all absorbed light wavelengths remains elusive. Here, we report for the first time mesoporous hematite photoelectodes prepared by a solution-based colloidal method which yield water-splitting photocurrents of 0.56 mA cm(-2) under standard conditions (AM 1.5G 100 mW cm(-2), 1.23 V vs reversible hydrogen electrode, RHE) and over 1.0 mA cm(-2) before the dark current onset (1.55 V vs RHE). The sintering temperature is found to increase the average particle size, and have a drastic effect on the photoactivity. X-ray photoelectron spectroscopy and magnetic measurements using a SQUID magnetometer link this effect to the diffusion and incorporation of dopant atoms from the transparent conducting substrate. In addition, examining the optical properties of the films reveals a considerable change in the absorption coefficient and onset properties, critical aspects for hematite as a solar energy converter, as a function of the sintering temperature. A detailed investigation into hematite's crystal structure using powder X-ray diffraction with Rietveld refinement to account for these effects correlates an increase in a C(3v)-type crystal lattice distortion to the improved optical properties.
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PMID:Photoelectrochemical water splitting with mesoporous hematite prepared by a solution-based colloidal approach. 2044 99

The aim of the present work is to provide a deeper understanding of gold catalysis for CO electrooxidation in alkaline media, through a combined electrochemical, spectroscopic, and DFT study. Voltammetric and spectroscopic measurements evidence that the amount of CO irreversibly adsorbed on gold increases as the adsorption potential becomes more negative (vs SHE). This explains why higher CO coverages can be achieved in more alkaline solutions, since the value of adsorption potential vs RHE becomes more negative vs SHE with increasing pH. On the other hand, the combination of FTIRRAS experiments and DFT calculations shows that the adsorption site of irreversibly adsorbed CO on Au(111) depends on the value of the adsorption potential. It is concluded that CO adsorption on top sites takes place at all studied potentials, and hollow and bridge sites also become occupied for adsorption potentials lower and higher than 0 V vs RHE, respectively. However, it should be noted that our DFT calculations give values of the CO binding energies that are not strong enough to explain CO irreversible adsorption. This may be partly attributed to the fact that OH coadsorption is not included in the calculations. Indeed, this work presents two experimental facts that suggest that CO adsorption on gold promotes the coadsorption of OH species: (i) CO irreversibly adsorbed on Au(111) and Au(100) leads to an unusual voltammetric feature, whose charge indicates the stabilization of one OH species per adsorbed CO species; (ii) the apparent transfer coefficient of this unusual state is close to unity, suggesting that it is due to a presumed structural transformation coupled to OH adsorption. Finally, the effect of the adsorption potential on the bulk CO electrooxidation is also studied. It is found that, on Au(111), an increased occupation of CO on multifold (hollow) sites seems to result in a less efficient catalysis. However, on Au(110), an increased coverage of CO on top sites does not produce any significant change in catalysis.
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PMID:CO electroxidation on gold in alkaline media: a combined electrochemical, spectroscopic, and DFT study. 2056 May 79

The electrochemical adsorption of underpotential deposited hydrogen (upd-H(ad)) and OH(ad) on structurally well-defined Pt(x)Ru(1-x)/Ru(0001) surface alloys was investigated by cyclic voltammetry and density functional theory (DFT) calculations. The adsorption energies of both upd-H(ad) and OH(ad) decrease with increasing Pt content in the adsorption ensemble, shifting the onset of upd-H(ad) and OH(ad) formation to increasingly cathodic and anodic potentials, respectively. For bare Ru(0001) and for Ru(3) sites in the surface alloy, the stability regions of these two species overlap or almost overlap, respectively. Similar to previous findings for upd-H(ad) adsorption/desorption on partly Pt monolayer island covered Ru(0001) surfaces (J. Phys. Chem. B 2004, 108, 14780), we find a sharp peak at approximately 100 mV vs. RHE in each scan direction, which is attributed to a Pt catalyzed OH(ad)<--> upd-H(ad) replacement on Ru(3) sites, via adsorption on Pt rich sites and spill-over to Ru(3) sites. The decrease of the integrated charge in these peaks with the third power of the Ru surface concentration, which for a random distribution of surface atoms reflects the availability of Ru(3) sites, supports the above assignment.
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PMID:Pt promotion and spill-over processes during deposition and desorption of upd-H(ad) and OH(ad) on Pt(x)Ru(1-x)/Ru(0001) surface alloys. 2059 65

The current materials used in proton-exchange membrane fuel cells (PEMFCs) are not sufficiently durable for commercial deployment. One of the major challenges lies in the development of an inexpensive, efficient, and CO-tolerant anode catalyst. Here we report the unique CO-tolerant property of Pt nanoparticles supported on Ti(0.7)W(0.3)O(2). The Ti(0.7)W(0.3)O(2) nanoparticles (50 nm) were synthesized via a sol-gel process and platinized using an impregnation-reduction technique. Electrochemical studies of Pt/Ti(0.7)W(0.3)O(2) show unique CO-tolerant electrocatalytic activity for hydrogen oxidation compared to commercial E-TEK PtRu/C catalysts. Differential electrochemical mass spectrometry measurements show the onset potential for CO oxidation on Pt/Ti(0.7)W(0.3)O(2) to be below 0.1 V (vs RHE). Pt/Ti(0.7)W(0.3)O(2) is a promising new anode catalyst for PEMFC applications.
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PMID:Highly stable and CO-tolerant Pt/Ti0.7W0.3O2 electrocatalyst for proton-exchange membrane fuel cells. 2066 94


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