Hydrogen or hydrogen peroxide can be generated in liquid−liquid biphasic systems, where the organic phase contains sufficiently strong electron donor (whose redox potential is lower than the potential of reversible hydrogen electrode). H 2 O 2 generation with acidified aqueous phase occurs prior to H 2 evolution when oxygen is present. No other organic solvent than highly toxic 1,2-dichloroethane (DCE) has been reported in biphasic system for H 2 or H 2 O 2 generation. In this work, we have used trifluorotoluene (TFT) instead of carcinogenic DCE, and studied these reactions in TFT−water biphasic system. To evaluate H 2 flux, scanning electrochemical microscopy potentiometric approach curves to the TFT−water interface were recorded. H 2 O 2 was detected voltametrically at a microelectrode located in the vicinity of the interface. H 2 and H 2 O 2 are formed and both reactions occur also in the absence of a hydrophobic salt in the organic phase. Their thermodynamics was discussed on the basis of Gibbs energies determined electrochemically with droplet-modified electrodes. The results show that DCE can be replaced by a noncarcinogenic solvent and the biphasic system for H 2 and H 2 O 2 generation can be simplified by elimination of the uncommon hydrophobic salt from the organic phase.

Micro-domains of water molecules surrounded by organic solvent exhibit enhanced reactivity towards oxidation compared to highly hydrogen-bonded bulk water molecules.

In this paper, the electrochemical oxidation of hydrogen at the interface between single-crystal platinum electrodes and imidazolium-type room-temperature ionic liquids (RTILs) is studied. This is the first report about the electrochemical properties of single-crystal platinum electrodes in contact with ionic liquids. It was found that the imidazolium cation can be reduced to 1-alkyl-3-methylimidazol-2-ylidene species on the basal plane platinum electrodes and that the presence of hydrogen increases the reversibility of this process, suggesting that it is a proton-coupled electrontransfer reaction. On the other hand, it was found that the oxidation of H 2 is a surface structure-sensitive process on RTIL/Pt interfaces. The activity toward H 2 oxidation was found to increase in the order of Pt(100 100) is the best electrocatalytic electrode for this reaction. Finally, a complex kinetic behavior was observed upon potential cycling of [C 4 mim][OTf] saturated with H 2 in contact with Pt(110) as a working electrode. This is the first experimental example of an electrochemical oscillator in RTILs. The competitive adsorption of H 2 and carbenes and the electrode reconstruction, modulated by the adsorbates, can be at the origin of this electrochemical oscillatory behavior. The results presented here are expected to be useful for clarifying the complex nature of the platinum electrode/RTIL interface and to be of practical use for its possible applications in the electrosynthesis of carbenes, electrochemical sensors, and fuel cells.

No abstract

Photoexcited protonated tetrathiafulvalene (HTTF) was found to act as a photosensitizer, injecting electrons into Pt microparticles (floating electrocatalysts) to produce H and TTF in acidic acetonitrile. In addition, TTF was electrochemically reduced back to TTF on a carbon electrode, to be further protonated to continuously produce H photochemically. The onset potential for the electrochemical recycling of TTF on carbon was set at a potential 500 mV more positive than the potential required for the direct reduction of protons. HTTF showed no signs of decomposition after 51 h of continuous recycling and photoinduced production of H, proving stability and reversibility.

We report the in situ self-assembly of TTF, TTF•+, and BF4 – or PF6 – into p-type semiconductors on the surface of Pt microparticles dispersed in water/acetonitrile mixtures. The visible light photoactivation of these self-assemblies leads to water oxidation forming O2 and H+, with an efficiency of 100% with respect to the initial concentration of TTF•+. TTF•+ is then completely reduced to TTF upon photoreduction with water. The Pt microparticles act as floating microelectrodes whose Fermi level is imposed by the different redox species in solution; here predominantly TTF, TTF•+, and HTTF+, which furthermore showed no signs of decomposition in solution.

), moving from acidic to alkaline conditions. Bulk electrolysis experiments revealed that the IrO 2 /PDDA films were stable and adherent under acidic and neutral conditions but degraded in alkaline solutions. Oxygen was evolved with Faradaic efficiencies approaching 100% under acidic (pH 1) and neutral (pH 7) conditions, and 88% in alkaline solutions (pH 13).This layer-by-layer approach forms the basis of future large-scale OER electrode development using ink-jet printing technology.

[a] DedicatedtoProfessor Christian Amatore on occasion of his 65th birthdayThe water oxidationp rocess in acidified water/acetonitrile mixtures was studied by cyclic voltammetry using fluorinated tin oxide (FTO) electrodes modified layer-by-layer with deposited bilayerso fp ositivelyc harged poly(diallyldimethylammonium chloride) (PDDA) polymer andn egatively charged citrate-stabilized iridium oxide (IrO 2 )n anoparticles. The voltammetric profiles obtained at high water contents resemble those in aqueous mediaa nd remaina pproximately unchanged. However,a s the water content decreases below aw ater mole fraction (XH 2 O) of 0.6, at ipping point is reached and the onset potential for water oxidation gradually decreases. This reflects an enhanced reactivity,a nd therefore lower overpotential, of water molecules towards oxidation in water/acetonitrile mixtures. These lower kinetic barriers towards water oxidation are rationalized based on the degradation of the hydrogen bond network upon the formation of water/acetonitrile mixtures. Thus, as the ice-like structure of neat water transitions to clusters and low-bonded oligomers, these water molecules in more "free" states exhibit an enhanced susceptibility to water oxidation.Water is the ultimate source of electrons in idealized artificial photosynthetic schemes. These electrons may be released during water splitting, preferably utilizing solar energy in aphotoelectrochemical arrangement, and used to produce small molecules such as molecular hydrogen (H 2 ), as olar fuel. Importantly,t his route to H 2 avoids the generation of greenhouse gases. [1] Since the H 2 evolutionr eaction( HER) is much less energy-demanding than the water oxidation reaction (WOR), the later process is considered the limiting step in the overall water splitting scheme,r equiring the use of ac atalyst.M uch effort has been devoted to the development of such catalysts that can perform the WOR for long time periods and at moderate overpotentials.[2] However, little attention has been paid to the influence of the media within which the reaction takes place as aroute to enhance the reactivity of water.The physciochemical properties of water are expected to change in the presence of ions or organic molecules. Such changes can be advantageous as they can be translatedi nto modifications of reactivity.F or instance, Markovice tal. reported that the non-covalent interaction between ions in alkaline solutionsa nd the oxygenated species absorbed on the surface of Ir,R ua nd Ru 0.5 Ir 0.5 electrodes, play an importantr ole in the hydrogene volution reaction (HER), hydrogen oxidation reaction (HOR)a nd oxygen evolution reaction (OER).[3] Particularly, the reactivity towards the HER increasesi nt he order Ba 2 + > Li + > K + .T his trend is explained based on the higher ability of absorbedw ater to be dissociated into H ad and *OH, upon interaction with ions of higher specific charge density.S imilare ffects have been reported by Deng and co-workers,s uggesting that the increased acidity of the water...