19 research outputs found
Photoproduction of Hydrogen by Decamethylruthenocene
Splitting water to produce hydrogen (H2) fuel appears very promising to address the challenges of solar energy storage and global warming as the only by-product generated is oxygen (O2). An alternative strategy, called batch water-splitting, based on Interfaces between Two Immiscible Electrolyte Solutions (ITIES) and artificial light-induced water-splitting is presented in the following thesis. This approach consists of two biphasic systems for the photo-production of H2 and O2. The following thesis focuses on the realisation of the H2 side. In first instance, the photo-induced hydrogen evolution reaction (HER) by decamethylruthenocene (Cp2*Ru(II)) is reported as a strategy to facilitate water splitting in biphasic systems. Hydrogen evolution by Cp2*Ru(II) was studied in detail. The study highlights that Cp2*Ru(II) is an attractive molecule capable of photo-reducing hydrogen without the need for an additional sensitizer. Electrochemical, gas chromatographic and spectroscopic (UV/vis, 1H and 13C NMR) measurements indicate that the production of hydrogen occurs by a two-step process. First, the decamethylruthenocene hydride ([Cp2*Ru(IV)(H)]+) is formed in the presence of acids, followed by the reduction of this complex via a hetero-dissociation reaction leading to a first release of hydrogen. Thereafter, the resultant decamethylruthenocenium ion ([Cp2*Ru(III)]+) is further reduced leading to a second release of hydrogen by subtraction of a proton from a methyl group of [Cp2*Ru(III)]+. Experimental results showed an excitation of [Cp2*Ru(IV)(H)]+ at ï¬ = 243 nm to evolve H2 for the first oxidation. [Cp2*Ru(III)]+ was produced from the reduction of protons by Cp2*Ru(II) at ï¬ = 365 nm and electrochemically regenerated in situ on a Fluorinated Tin Oxide (FTO) electrode surface. A promising internal quantum yield of 25 % was obtained for HER by Cp2*Ru(II) combined with electrochemical recycling. Thereafter, HER by Cp2*Ru(II) was performed at ITIES. Shake-flask experiments demonstrated the production of H2 only when the biphasic system was positively polarized, to favor proton transfer. Kinetics/thermodynamics for decamethylruthenocene hydride formation were electrochemically evaluated at liquidÇliquid interface. Simulated curves developed using COMSOL Multiphysics software and compared to experimental data, indicate a modified EC (electrochemicalâchemical) mechanism for the [Cp2*Ru(IV)(H)]+ formation at polarised interfaces. In the proposed pathway, [Cp2*Ru(IV)(H)]+ is sufficiently stable in dichloroethane to transfer at negative potentials to the aqueous phase where it quickly dissociates. Additionally, the SHG response of [Cp2*Ru(IV)(H)]+ as function of the polarisation applied confirmed this mechanism. Finally, an alternative method using homogeneous catalysts, Co(dmgh)2(py)Cl and Fe2(ï-SCH2C6H4CH2S)(CO)6 at liquidÇliquid interfaces was investigated. Coupled with a sacrificial electron donor and a sensitizer, H2 production was achieved for both catalysts. However, results showed the polarisation was not responsible for the proton transfer and the electron donor was identified as the dominant proton source. This study represents major progress in the development of the batch water splitting process as it overcomes the use of sacrificial electron donors. Moreover, these investigations provide substantial improvement in the general understanding of the photo-production of H2 by metallocenes and reactions and characterisations at ITIES
Mediated water electrolysis in biphasic systems
peer-reviewedThe concept of efficient electrolysis by linking photoelectrochemical biphasic H2 evolution and water
oxidation processes in the cathodic and anodic compartments of an H-cell, respectively, is introduced.
Overpotentials at the cathode and anode are minimised by incorporating light-driven elements into
both biphasic reactions. The concepts viability is demonstrated by electrochemical H2 production from
water splitting utilising a polarised water-organic interface in the cathodic compartment of a
prototype H-cell. At the cathode the reduction of decamethylferrocenium cations ([Cp2*Fe(III)]+) to
neutral decamethylferrocene (Cp2*Fe(II)) in 1,2-dichloroethane (DCE) solvent takes place at the solid
electrode/oil interface. This electron transfer process induces the ion transfer of a proton across the
immiscible water/oil interface to maintain electroneutrality in the oil phase. The oil-solubilised proton
immediately reacts with Cp2*Fe(II) to form the corresponding hydride species, [Cp2*Fe(IV)(H)]+.
Subsequently, [Cp2*Fe(IV)(H)]+ spontaneously undergoes a chemical reaction in the oil phase to evolve
hydrogen gas (H2) and regenerate [Cp2*Fe(III)]+, whereupon this catalytic Electrochemical, Chemical,
Chemical (ECC’) cycle is repeated. During biphasic electrolysis, the stability and recyclability of the
[Cp2*Fe(III)]+/Cp2*Fe(II) redox couple were confirmed by chronoamperometric measurements and,
furthermore, the steady-state concentration of [Cp2*Fe(III)]+ monitored in situ by UV/vis spectroscopy.
Post-biphasic electrolysis, the presence of H2 in the headspace of the cathodic compartment was
established by sampling with gas chromatography. The rate of the biphasic hydrogen evolution
reaction (HER) was enhanced by redox catalysis in the presence of floating catalytic molybdenum
carbide (Mo2C) microparticles at the immiscible water/oil interface. The use of a superhydrophobic
organic electrolyte salt was critical to ensure proton transfer from water to oil, and not anion transfer
from oil to water, in order to maintain electroneutrality after electron transfer. The design, testing and
successful optimisation of the operation of the biphasic electrolysis cell under dark conditions with
Cp2*Fe(II) lays the foundation for the achievement of photo-induced biphasic water electrolysis at low
overpotentials using another metallocene, decamethylrutheneocene (Cp2*Ru(II)). Critically, Cp2*Ru(II)
may be recycled at a potential more positive than that of proton reduction in DCE
Redox electrocatalysis of floating nanoparticles: determining electrocatalytic properties without the influence of solid supports
peer-reviewedRedox electrocatalysis (catalysis of electron transfer reactions by floating
conductive particles) is discussed from the point-of-view of Fermi level equilibration, and an
overall theoretical framework is given. Examples of redox electrocatalysis in solution, in
bipolar configuration and at liquid-liquid interfaces are provided, highlighting that bipolar
and liquid-liquid interfacial systems allow the study of the electrocatalytic properties of
particles without effects from the support, but only liquid-liquid interfaces allow
measurement of the electrocatalytic current directly. Additionally, photo-induced redox
electrocatalysis will be of interest, for example to achieve water splittin
Machine Learning Bio-molecular Interactions from Temporal Logic Properties
With the advent of formal languages for modeling bio-molecu\-lar interaction systems, the design of automated reasoning tools to assist the biologist becomes possible. The biochemical abstract machine BIOCHAM software environment offers a rule-based language to model bio-molecular interactions and an original temporal logic based language to formalize the biological properties of the system. Building on these two formal languages, machine learning techniques can be used to infer new molecular interaction rules from temporal properties. In this context, the aim is to semi-automatically correct or complete models from observed biological properties of the system. Machine learning from temporal logic formulae is quite new however, both from the machine learning perspective and from the Systems Biology perspective. In this paper we present an ad-hoc enumerative method for structural learning from temporal properties and report on the evaluation of this method on formal biological models of the literature
Decamethylruthenocene Hydride and Hydrogen Formation at Liquid|Liquid Interfaces
The formation and the dissociation of metal hydrides are key steps within the hydrogen evolution reaction (HER) pathway for photochemical water splitting, but also impacts a wide range of other catalytic, industrial, and biochemical reactions. Herein, we describe our recent work studying HER at the interface between two immiscible electrolyte solutions (ITIES), between water|1,2-dichloroethane. This is a unique platform for evaluating the kinetics/thermodynamics for metallocene hydride formation using decamethylruthenocene. In this approach, an aqueous acid serves as the proton source and is pumped across the ITIES via an externally applied potential or the use of a phase transfer catalyst. Simulated curves developed using COMSOL Multiphysics software and compared to experimental ones, indicate a modified EC′ (electrochemical–chemical) mechanism for the decamethylruthenocene hydride formation. In the proposed pathway, decamethylruthenocene hydride is metastable in 1,2-dichloroethane and persists on the time scale of the recorded cyclic voltammograms long enough to transfer to the aqueous phase where it quickly dissociates. This is evidenced through an asymmetric, ion transfer wave observed experimentally and concluded to be hydride transfer. Shake-flask experiments with head space gas sampling demonstrated that hydrogen production was observed only when the biphasic system was positively polarized, to favor proton transfer, and decamethylruthenocene was photoactivated. This approach, combining electrochemical, simulation, and chromatographic methods, brings new insight into the factors that underlie the mechanism and rates of hydride formation/dissociation at soft interfaces
Effect of Chaotropes on the Transfer of Ions and Dyes across the Liquid–Liquid Interface
Chaotropes such as urea can break the structure of water, weakening the hydrophobic effect and reducing aggregation. Here, we investigated how the addition of urea affects the transfer of ions and cationic dyes across the interface between immiscible electrolyte solutions, both water-1,2-dichloroethane and water-trifluorotoluene. For most cations, their half-wave potential of transfer shifted toward more negative values, indicating that it is easier to transfer these ions from the aqueous phase with urea to the organic phase, showing that the addition of urea decreases the solvation of ions in the aqueous phase. However, the half-wave potentials for a series of cationic phenothiazine dyes shifted toward more positive potentials, indicating improved solvation in urea solution. The effect of urea was investigated also by differential capacitance and electrocapillary curves, as well as by molecular dynamics simulations. Finally, electrochemistry at liquid–liquid interfaces allows determination of the transfer energies of ions between water and aqueous solutions of urea via a thermodynamic cycle
Effect of Chaotropes on the Transfer of Ions and Dyes across the Liquid–Liquid Interface
Chaotropes such as
urea can break the structure of water, weakening
the hydrophobic effect and reducing aggregation. Here, we investigated
how the addition of urea affects the transfer of ions and cationic
dyes across the interface between immiscible electrolyte solutions,
both water-1,2-dichloroethane and water-trifluorotoluene. For most
cations, their half-wave potential of transfer shifted toward more
negative values, indicating that it is easier to transfer these ions
from the aqueous phase with urea to the organic phase, showing that
the addition of urea decreases the solvation of ions in the aqueous
phase. However, the half-wave potentials for a series of cationic
phenothiazine dyes shifted toward more positive potentials, indicating
improved solvation in urea solution. The effect of urea was investigated
also by differential capacitance and electrocapillary curves, as well
as by molecular dynamics simulations. Finally, electrochemistry at
liquid–liquid interfaces allows determination of the transfer
energies of ions between water and aqueous solutions of urea via a
thermodynamic cycle
Cerebral sinovenous thrombosis associated with head/neck infection in children: Clues for improved management
International audienceAim: To compare paediatric patients with cerebral sinovenous thrombosis (CSVT) with and without head/neck infection to improve management of the condition.Method: We conducted a bicentric retrospective study of consecutive children (neonates excluded) with radiologically confirmed CSVT, comparing children with a concurrent head/neck infection and children with other causes.Results: A total of 84 consecutive patients (46 males and 38 females) with a median age of 4 years 6 months (range 3 months–17 years 5 months) were included. Associated head/neck infection was identified in 65.4% of cases and represented the main identified CSVT aetiology. Children in the head/neck infection group displayed a milder clinical presentation and less extensive CSVT. Median time to complete recanalization was significantly shorter in this group (89 days [interquartile range 35–101] vs 112.5 days [interquartile range 83–177], p = 0.005). These findings were even more pronounced in the subgroup of patients with otogenic infection and no neurological sign.Interpretation: As CSVT in the setting of an otogenic infection and no neurological sign seems to represent a milder condition with a shorter course, these results suggest adapting current recommendations: consider earlier control imaging in paediatric otogenic CSVT, and shorter anticoagulant treatment if recanalization is obtaine