Photoproduction of Hydrogen by Decamethylruthenocene Combined with Electrochemical Recycling.

The photoinduced hydrogen evolution reaction (HER) by decamethylruthenocene, Cp *Ru (Cp*=C Me ), is reported. The use of a metallocene to photoproduce hydrogen is presented as an alternative strategy to reduce protons without involving an additional photosensitizer. The mechanism was investigated by (spectro)electrochemical and spectroscopic (UV/Vis and H NMR) measurements.

Boosting water oxidation layer-by-layer.

Electrocatalysis of water oxidation was achieved using fluorinated tin oxide (FTO) electrodes modified with layer-by-layer deposited films consisting of bilayers of negatively charged citrate-stabilized IrO2 NPs and positively charged poly(diallyldimethylammonium chloride) (PDDA) polymer. The IrO2 NP surface coverage can be fine-tuned by controlling the number of bilayers. The IrO2 NP films were amorphous, with the NPs therein being well-dispersed and retaining their as-synthesized shape and sizes.

Charging and discharging at the nanoscale: Fermi level equilibration of metallic nanoparticles.

The redox properties of metallic nanoparticles are discussed, in particular the relationships between excess charge, size and the Fermi level of the electrons. The redox potentials are derived using simple electrostatic models to provide a straightforward understanding of the basic phenomena. The different techniques used to measure the variation of Fermi level are presented.

Catalysis of water oxidation in acetonitrile by iridium oxide nanoparticles.

Water oxidation catalysed by iridium oxide nanoparticles (IrO NPs) in water-acetonitrile mixtures using [Ru(bpy)] as oxidant was studied as a function of the water content, the acidity of the reaction media and the catalyst concentration. It was observed that under acidic conditions (HClO) and at high water contents (80% (v/v)) the reaction is slow, but its rate increases as the water content decreases, reaching a maximum at approximately equimolar proportions (≈25% HO (v/v)). The results can be rationalized based on the structure of water in water-acetonitrile mixtures.

Selective electrocatalytic oxidation of a re-methyl complex to methanol by a surface-bound Ru(II) polypyridyl catalyst.

The complex [Ru(Mebimpy)(4,4'-((HO)2OPCH2)2bpy)(OH2)](2+) surface bound to tin-doped indium oxide mesoporous nanoparticle film electrodes (nanoITO-Ru(II)(OH2)(2+)) is an electrocatalyst for the selective oxidation of methylrhenium trioxide (MTO) to methanol in acidic aqueous solution. Oxidative activation of the catalyst to nanoITO-Ru(IV)(OH)(3+) induces oxidation of MTO. The reaction is first order in MTO with rate saturation observed at [MTO] > 12 mM with a limiting rate constant of k = 25 s(-1).

Gold metal liquid-like droplets.

Simple methods to self-assemble coatings and films encompassing nanoparticles are highly desirable in many practical scenarios, yet scarcely any examples of simple, robust approaches to coat macroscopic droplets with continuous, thick (multilayer), reflective and stable liquid nanoparticle films exist. Here, we introduce a facile and rapid one-step route to form films of reflective liquid-like gold that encase macroscopic droplets, and we denote these as gold metal liquid-like droplets (MeLLDs). The present approach takes advantage of the inherent self-assembly of gold nanoparticles at liquid-liquid interfaces and the increase in rates of nanoparticle aggregate trapping at the interface during emulsification.

Photoreduction of CO2 using [Ru(bpy)2(CO)L]n+ catalysts in biphasic solution/supercritical CO2 systems.

The reduction of CO2 in a biphasic liquid-condensed gas system was investigated as a function of the CO2 pressure. Using 1-benzyl-1,4-dihydronicotinamide (BNAH) as sacrificial electron donor dissolved in a dimethylformamide-water mixture and [Ru(bpy)2(CO)L](n+) as a catalyst and [Ru(bpy)3](2+) as a photosensitizer, the reaction was found to produce a mixture of CO and formate, in total about 250 μmol after just 2 h. As CO2 pressure increases, CO formation is greatly favored, being four times greater than that of formate in aqueous systems.

Coordination chemistry of single-site catalyst precursors in reductively electropolymerized vinylbipyridine films.

Reductive electropolymerization of [Ru(II)(PhTpy)(5,5'-dvbpy)(Cl)](PF6) and [Ru(II)(PhTpy)(5,5'-dvbpy)(MeCN)](PF6)2 (PhTpy is 4'-phenyl-2,2':6',2″-terpyridine; 5,5'-dvbpy is 5,5'-divinyl-2,2'-bipyridine) on glassy carbon electrodes gives well-defined films of poly{[Ru(II)(PhTpy)(5,5'-dvbpy)(Cl)](PF6)} (poly-1) or poly{[Ru(II)(PhTpy)(5,5'-dvbpy)(MeCN)](PF6)2} (poly-2). Oxidative cycling of poly-2 with added NO3(-) results in the replacement of coordinated MeCN by NO3(-) to give poly{[Ru(II)(PhTpy)(5,5'-dvbpy)(NO3)](+)}, and with 0.1 M HClO4, replacement by H2O occurs to give poly{[Ru(II)(PhTpy)(5,5'-dvbpy)(OH2)](2+)} (poly-OH2).

LEPA: from proteomics to energy conversion.

This review article summarizes the different fields of research at the Laboratoire d'Electrochimie Physique et Analytique at the Ecole Polytechnique Fédérale de Lausanne. The research areas covered include charge transfer reactions at soft interfaces, bio-analytical microchips and electrophoretic methods, electrochemical ionization methods for mass spectrometry and Scanning Electrochemical Microscopy (SECM).

Melittin adsorption and lipid monolayer disruption at liquid-liquid interfaces.

Melittin, a membrane-active peptide with antimicrobial activity, was investigated at the interface formed between two immiscible electrolyte solutions (ITIES) supported on a metallic electrode. Ion-transfer voltammetry showed well-defined semi-reversible transfer peaks along with adsorptive peaks. The reversible adsorption of melittin at the liquid-liquid interface is qualitatively discussed from voltammetric data and experimentally confirmed by real-time image analysis of video snapshots.

Hydrogen evolution catalyzed by electrodeposited nanoparticles at the liquid/liquid interface.

Aqueous protons reduction by decamethylferrocene in 1,2-dichloroethane can be catalyzed efficiently by platinum and palladium nanoparticles electrogenerated in situ at the liquid-liquid interface.

Formation and study of single metal ion-phospholipid complexes in biphasic electrospray ionization mass spectrometry.

Single metal ion-phospholipid complexes are observed in biphasic electrospray ionization mass spectrometry (BESI-MS) using a dual-channel microsprayer. Such a microsprayer makes it possible to put into contact two immiscible liquids within the Taylor cone. Thus, L-α-dipalmitoyl phosphatidylcholine (DPPC) dissolved in 1,2-dichloroethane (DCE) reacts with aqueous metal cations (M = Na(+), K(+), Ca(2+), Cu(2+), La(3+)) yielding the formation of [M-DPPC(n)](z+) complexes.

Copper(I) and copper(II) binding to β-amyloid 16 (Aβ16) studied by electrospray ionization mass spectrometry.

Copper-β-amyloid 16 (Aβ16) complexes were investigated by electrospray ionization mass spectrometry (ESI-MS). Copper(i) and (ii) complexes were formed on-line in a microchip electrospray emitter by using a sacrificial copper electrode as the anode in positive ionization mode. In the presence of ascorbic acid in the peptide solution, the amount of Cu(i)-Aβ16 generated electrochemically was even higher.

Molecular electrocatalysis at soft interfaces.

The fundamental aspects of electrochemistry at liquid-liquid interfaces are introduced to present the concept of molecular electrocatalysis. Here, a molecular catalyst is adsorbed at the interface to promote a proton coupled electron transfer reaction such as hydrogen evolution or oxygen reduction using lipophilic electron donors.

Oxygen reduction catalyzed by a fluorinated tetraphenylporphyrin free base at liquid/liquid interfaces.

The diprotonated form of a fluorinated free base porphyrin, namely 5-(p-aminophenyl)-10,15,20-tris(pentafluorophenyl)porphyrin (H(2)FAP), can catalyze the reduction of oxygen by a weak electron donor, namely ferrocene (Fc). At a water/1,2-dichloroethane interface, the interfacial formation of H(4)FAP(2+) is observed by UV-vis spectroscopy and ion-transfer voltammetry, due to the double protonation of H(2)FAP at the imino nitrogen atoms in the tetrapyrrole ring. H(4)FAP(2+) is shown to bind oxygen, and the complex in the organic phase can easily be reduced by Fc to produce hydrogen peroxide as studied by two-phase reactions with the Galvani potential difference between the two phases being controlled by the partition of a common ion.

Interfacial complexes between a protein and lipophilic ions at an oil-water interface.

The interaction between an intact protein and two lipophilic ions at an oil-water interface has been investigated using cyclic voltammetry, impedance based techniques and a newly developed method in which the biphasic oil-water system is analyzed by biphasic electrospray ionization mass spectrometry (BESI-MS), using a dual-channel electrospray emitter. It is found that the protein forms interfacial complexes with the lipophilic ions and that it specifically requires the presence of the oil-water interface to be formed under the experimental conditions. Furthermore, impedance based techniques and BESI-MS with a common ion to polarize the interface indicated that the Galvani potential difference across the oil-water interface significantly influences the interfacial complexation degree.

Dioxygen reduction by cobalt(II) octaethylporphyrin at liquid|liquid interfaces.

Oxygen reduction catalyzed by cobalt(II) (2,3,7,8,12,13,17,18-octaethylporphyrin) [Co(OEP)] at soft interfaces is studied by voltammetry and biphasic reactions. When Co(OEP) is present in a solution of 1,2-dichloroethane in contact with an aqueous acidic solution, oxygen is reduced if the interface is positively polarized (water phase versus organic phase). This reduction reaction is facilitated when an additional electron donor, here ferrocene, is present in excess in the organic phase.

Proton-coupled oxygen reduction at liquid-liquid interfaces catalyzed by cobalt porphine.

Cobalt porphine (CoP) dissolved in the organic phase of a biphasic system is used to catalyze O(2) reduction by an electron donor, ferrocene (Fc). Using voltammetry at the interface between two immiscible electrolyte solutions (ITIES), it is possible to drive this catalytic reduction at the interface as a function of the applied potential difference, where aqueous protons and organic electron donors combine to reduce O(2). The current signal observed corresponds to a proton-coupled electron transfer (PCET) reaction, as no current and no reaction can be observed in the absence of either the aqueous acid, CoP, Fc, or O(2).

Peptide-phospholipid complex formation at liquid-liquid interfaces.

Two peptides known to interact with receptors embedded in cell membranes, angiotensin III (Ang III) and Leu-enkephalin (LeuEnk), were studied electrochemically at the interface formed between two immiscible electrolyte solutions modified by an adsorbed monolayer of dipalmitoylphosphatidylcholine (DPPC). The results indicate that cationic angiotensin III transfer can be facilitated by the interfacial formation of a complex with DPPC. The complexation constant was determined by voltammetry and found to be equal to 5.

Biphasic electrospray ionization for the study of interfacial complexes.

Biphasic electrospray ionization (BESI) mass spectrometry is achieved by using a dual-channel microsprayer, where channels filled with different immiscible phases meet at the Taylor cone. Two types of interfacial complexation reactions have been studied: the interfacial complexation of aqueous lead ions by thioether crown molecules, and the interfacial complexation of an aqueous dipeptide by dibenzo-18-crown-6 as ionophore. The mass spectra also give valuable information on the stoichiometry of the complexation reaction.

Sonophotocatalytic oxidation of elemental sulphur on titanium dioxide.

The effect of ultrasound on the photocatalytic oxidation kinetics of elemental sulphur particles catalyzed by titanium dioxide was studied using a conductivity method to follow the reaction. The simultaneous use of photocatalyst and ultrasound have a positive effect on the reaction. The zero-order oxidation rate constant of sulphur, reached after an activation period of approximately 150 min, was about 20 times higher when the reactor was sonicated, using an ultrasonic processor of 30 kHz, compared to the rate found in its absence.