A self-assembled organic/metal junction for water photo-oxidation

We report the in situ self-assembly of TTF, TTF ·+ , and BF 4 - or PF 6 - 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 O 2 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.Fil: Olaya, Astrid J.. Swiss Federal Institute Of Technology Epfl; SuizaFil: Omatsu, Terumasa. Kyoto Institute Of Technology; JapónFil: Hidalgo-Acosta, Jonnathan C.. Swiss Federal Institute Of Technology Epfl; SuizaFil: Riva, Julieta Soledad. Swiss Federal Institute Of Technology Epfl; Suiza. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Bassetto, Victor Costa. Swiss Federal Institute Of Technology Epfl; SuizaFil: Gasilova, Natalia. Swiss Federal Institute Of Technology Epfl; SuizaFil: Girault, Hubert. Swiss Federal Institute Of Technology Epfl; Suiz

Catalysis of water oxidation in acetonitrile by iridium oxide nanoparticles

Water oxidation catalysed by iridium oxide nanoparticles (IrO2 NPs) in water–acetonitrile mixtures using [RuIII(bpy)3]3+ 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 (HClO4) 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% H2O (v/v)). The results can be rationalized based on the structure of water in water–acetonitrile mixtures. At high water fractions, water is present in highly hydrogen-bonded arrangements and is less reactive. As the water content decreases, water clustering gives rise to the formation of water-rich micro-domains, and the number of bonded water molecules decreases monotonically. The results presented herein indicate that non-bonded water present in the water micro-domains is considerably more reactive towards oxygen production. Finally, long term electrolysis of water–acetonitrile mixtures containing [RuII(bpy)3]2+ and IrO2 NPs in solution show that the amount of oxygen produced is constant with time demonstrating that the redox mediator is stable under these experimental conditions

Adsorption and first stages of polymerization of aniline on platinum single crystal electrodes

The present communication studies the adsorption of aniline on platinum single crystal electrodes and the electrochemical properties of the first layers of polyaniline(PANI) grown on those platinum surfaces. The adsorption process was studied in aqueous acidic solution (0.1 M HClO4) and the electrochemical properties of thin films of PANI in both aqueous (1 M HClO4) and non-aqueous media (tetrabutyl ammonium hexafluorophosphate (TBAPF6) with additions of methanesulphonic acid in acetonitrile). First of all, it was found that the adsorption of aniline on platinum single crystal surfaces is a surface sensitive process, and even more important that the adsorption features found at low concentrations (5 × 10−5 M) can be directly correlated to the electrochemical properties of thin films of PANI in the very early stages of polymerization. The Pt(1 1 0) surface was found to be more suitable to obtain polymers with more reversible redox transitions when studied in aqueous media (1 M HClO4). This is in good agreement with the higher polymerization rates found on this surface compared to Pt(1 0 0) and Pt(1 1 1). Finally the differences in ionic exchange rate were greatly enhanced when they were studied in organic media. The AC 250 Hz response in the case of the thin films synthesized on Pt(1 1 0) is about twice greater than that obtained in the other basal planes using polymer layers with the same thickness.Support from the Spanish MICYNN though projectCTQ2010–16271 and GV through PROMETEO/2009/045 (FEDER) are greatly acknowledged. J. C. H-A. acknowledges the Santiago Grisolía scholarship (GRISOLIA\2010\047)

Photosensitized Hydrogen Evolution on a Floating Electrocatalyst Coupled to Electrochemical Recycling

Photoexcited protonated tetrathiafulvalene (HTTF⁺) was found to act as a photosensitizer, injecting electrons into Pt microparticles (floating electrocatalysts) to produce H₂ 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 H₂ 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 H₂, proving stability and reversibility

Enhanced reactivity of water clusters towards oxidation in water/acetonitrile mixtures

The water oxidation process in acidified water/acetonitrile mixtures was studied by cyclic voltammetry using fluorinated tin oxide (FTO) electrodes modified layer-by-layer with deposited bilayers of positively charged poly(diallyldimethylammonium chloride) (PDDA) polymer and negatively charged citrate-stabilized iridium oxide (IrO2) nanoparticles. The voltammetric profiles obtained at high water contents resemble those in aqueous media and remain approximately unchanged. However, as the water content decreases below a water mole fraction (XH2O) of 0.6, a tipping point is reached and the onset potential for water oxidation gradually decreases. This reflects an enhanced reactivity, and 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.ACCEPTEDpeer-reviewe

Large-scale layer-by-layer inkjet printing of flexible iridium-oxide based pH sensors

none7siMetal oxide based pH sensors are used in various applications, especially when the conventional glass electrode is unsuitable due to its fragility or when the applications require disposable sensors, e.g. for biomedical, clinical or food process monitoring. Generally, such pH sensors are produced by thermal oxidation or electrochemical deposition, neither suited for mass production nor miniaturization. Herein, we report on the fabrication of reliable and sensitive pH sensors based on the nano-assembly of iridium oxide (IrOx) nanoparticles and polydiallyldimethylammonium (PDDA) polymer layers. Such potentiometric sensors were very reproducibly fabricated on a large-scale via a layer-by-layer inkjet printing (LbL IJP) methodology. The obtained results indicated the ability of the LbL IJP technique to easily manipulate the NP coverage by the number of printed bilayers, leading to a swift sensor optimization. Open-circuit potentials were recorded to evaluate the pH sensitivity, response time, and reproducibility of the pH electrodes, which exhibit a rapid, linear and near-Nernstian pH response of about 59 mV/pH. Moreover, an RSD of 0.6% for five different electrodes from the same printing batch showed the excellent reproducibility of the IJP process with a correlation coefficient of 0.99 for all measurements. The insights gained in this study could be the basis for a new approach of developing scalable, patterned and flexible pH sensors with improved performance and a wide range of applications.mixedJović, Milica; Hidalgo-Acosta, Jonnathan C.; Lesch, Andreas; Costa Bassetto, Victor; Smirnov, Evgeny; Cortés-Salazar, Fernando; Girault, Hubert H.*Jović, Milica; Hidalgo-Acosta, Jonnathan C.; Lesch, Andreas; Costa Bassetto, Victor; Smirnov, Evgeny; Cortés-Salazar, Fernando; Girault, Hubert H.

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. UV/vis spectroscopic and spectro-electrochemical studies confirmed that the total surface coverage and electrochemically addressable surface coverage of IrO2 NPs increased linearly with the number of bilayers up to 10 bilayers. The voltammetry of the modified electrode was that of hydrous iridium oxide films (HIROFs) with an observed super-Nernstian pH response of the Ir(III)/Ir(IV) and Ir(IV)–Ir(IV)/Ir(IV)–Ir(V) redox transitions and Nernstian shift of the oxygen evolution onset potential. The overpotential of the oxygen evolution reaction (OER) was essentially pH independent, varying only from 0.22 V to 0.28 V (at a current density of 0.1 mA cm 2), moving from acidic to alkaline conditions. Bulk electrolysis experiments revealed that the IrO2/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.ACCEPTEDpeer-reviewe

Hydrogen and Hydrogen Peroxide Formation in Trifluorotoluene–Water Biphasic Systems

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). H₂O₂ generation with acidified aqueous phase occurs prior to H₂ evolution when oxygen is present. No other organic solvent than highly toxic 1,2-dichloroethane (DCE) has been reported in biphasic system for H₂ or H₂O₂ generation. In this work, we have used trifluorotoluene (TFT) instead of carcinogenic DCE, and studied these reactions in TFT–water biphasic system. To evaluate H₂ flux, scanning electrochemical microscopy potentiometric approach curves to the TFT–water interface were recorded. H₂O₂ was detected voltametrically at a microelectrode located in the vicinity of the interface. H₂ and H₂O₂ 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 H₂ and H₂O₂ generation can be simplified by elimination of the uncommon hydrophobic salt from the organic phase

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. UV/vis spectroscopic and spectro-electrochemical studies confirmed that the total surface coverage and electrochemically addressable surface coverage of IrO2 NPs increased linearly with the number of bilayers up to 10 bilayers. The voltammetry of the modified electrode was that of hydrous iridium oxide films (HIROFs) with an observed super-Nernstian pH response of the Ir(III)/Ir(IV) and Ir(IV)–Ir(IV)/Ir(IV)–Ir(V) redox transitions and Nernstian shift of the oxygen evolution onset potential. The overpotential of the oxygen evolution reaction (OER) was essentially pH independent, varying only from 0.22 V to 0.28 V (at a current density of 0.1 mA cm 2), moving from acidic to alkaline conditions. Bulk electrolysis experiments revealed that the IrO2/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