Livain Breau

An organic redox electrolyte to rival triiodide/iodide in dye-sensitized solar cells

Dye-sensitized solar cells (DSCs) have achieved impressive conversion efficiencies for solar energy of over 11% with an electrolyte that contains triiodide/iodide as a redox couple. Although triiodide/iodide redox couples work efficiently in DSCs, they suffer from two major disadvantages: electrolytes that contain triiodide/iodide corrode electrical contacts made of silver (which reduces the options for the scale up of DSCs to module size) and triiodide partially absorbs visible light. Here, we present a new disulfide/thiolate redox couple that has negligible absorption in the visible spectral range, a very attractive feature for flexible DSCs that use transparent conductors as current collectors. Using this novel, iodide-free redox electrolyte in conjunction with a sensitized heterojunction, we achieved an unprecedented efficiency of 6.4% under standard illumination test conditions. This novel redox couple offers a viable pathway to develop efficient DSCs with attractive properties for scale up and practical applications.

Influence of the counter electrode on the photovoltaic performance of dye-sensitized solar cells using a disulfide/thiolate redox electrolyte

Strong scientific interests focus on the investigation of iodine-free redox couples for their application in dye-sensitized solar cells (DSCs). Recently, a disulfide/thiolate-based redox electrolyte has been proposed as a valuable alternative to the conventional I3−/I− system due to its transparent and non-corrosive nature. In the work presented herein, we systematically studied the influence of different counter electrode materials on the photovoltaic performance of DSCs employing this promising organic redox electrolyte. Our investigations focused on understanding the importance of electrocatalytic activity and surface area of the electroactive material on the counter electrode, comparing the conventional platinum to cobalt sulfide (CoS) and poly(3,4-ethylenedioxythiophene) (PEDOT). Electrochemical Impedance Spectroscopy has been used to study in detail the interfacial charge transfer reaction at the counter electrode. By using a high surface area PEDOT-based counter electrode, we finally achieved an unprecedented power conversion efficiency of 7.9% under simulated AM1.5G solar irradiation (100 mW cm−2) which, to the best of our knowledge, represents the highest efficiency that has so far been reported for an organic redox couple.

The Influence of the Range of Electroactivity and Capacitance of Conducting Polymers on the Performance of Carbon Conducting Polymer Hybrid Supercapacitor

Hybrid electrochemical supercapacitors based on carbon and conducting polymers as negative and positive electrodes, respectively, have been investigated. Poly-(3-fluorinatedphenyl)thiophene and poly(ethylenedioxythiophene) derivatives showing various ranges of electrochemical activity and capacitance values were evaluated as positive electrodes. It was shown that the mass and capacitance of the polymers have a significant effect on the charge/discharge characteristics and performance of such hybrid electrochemical supercapacitors. The experimental conditions that should be used to obtain specific charge/discharge curves are presented. A linear charge/discharge curve can be obtained between 0 and 3 V when the weight of conducting polymer is larger than that of the negative carbon electrode. In contrast, a battery-like charge/discharge curve is recorded when a smaller conducting polymer weight, relative to that of the carbon electrode, is used.

Synthesis and electrochemical polymerization of poly [3-(1-naphthylthiophene)]

Abstract 3-(1-naphthylthiophene) was synthesized by a coupling reaction of a 1-naphthyl Grignard reagent with 3-bromothiophene, catalyzed by Ni(II) catalyst. Cyclic voltammetry of a 17 mM 3-(1-naphthyithiophene), 0.1 M Et 4 NBF 4 /acetonitrile solution yields an oxidation wave at about 1.2 V which corresponds to the formation of the radical cation. Galvanostatic deposition of poly [3-(1-naphthylthiophene)] was carried out at a current density of 12.5 mA/cm 2 and the potential of the electrode reached a plateau value of about 1.1 V vs. Ag/Ag + after 50 s. The cyclic voltammogram of the resulting polymer in 1 M Et 4 NBF 4 /acetonitrile is characterized by anodic and cathodic waves at 0.9 and 0.8 V, respectively. The doping level of the polythiophene derivative was found to be equal to about 0.2 which indicates that every five thiophene units carry one positive charge. Cyclic voltammetry results indicates that poly [3-(1-naphthylthiophene)] cannot be n-doped very efficiently in the experimental conditions used in this work.

Chemical Synthesis and Electrochemical Properties of Poly(cyano-substituted-diheteroareneethylene) as Conducting Polymers for Electrochemical Supercapacitors

Polymers derived from diheteroaryl-(cyanovinylene), synthesized by chemical polymerization of the monomers in the presence of 6 equivalents of FeCl 3 in chloroform, were characterized by elemental analysis, energy-dispersive analysis by X-ray, and X-ray photoelectron spectroscopy. The electrochemical performances of composite electrodes prepared from chlorinated poly-(E)-α-[(2-thienyl)methylene]-2-thiopheneacetonitrile (poly-1), poly-(E)-α-[(3-methyl-2-thienyl)methylene]-2-thiopheneacetonitrile (poly-2), and poly-(E)-α-[(2-furanyl)methylene]-2-thiopheneacetonitrile (poly-3), with acetylene black (A.B., 45 wt %) and polytetrafluoroethylene (5 wt %) have been investigated in 1 M Et 4 NBF 4 /acetonitrile using cyclic voltammetry, electrochemical impedance spectroscopy, and galvanostatic charge/discharge cycling. The effect of the structure of the polymers on their electrochemical properties is in good agreement with anticipated effects for methyl and furan groups. The results indicated p- and n-doping levels up to 0.3 electrons per heterocycle for the three polymers. These values make those polymers interesting candidates for use in electrochemical supercapacitors in which specific capacity and energy of about 30 Ah/kg and 55 Wh/kg of polymer may be achieved. The best cyclahility was demonstrated with poly-1 and poly-2. in particular during cycling in their n-doping state with a doping level of 0.16 and 0.17 electrons per thiophene unit, respectively, maintained after 1000 cycles. Preliminary charge/ discharge galvanostatic cycling with a poly-1-based supercapacitor yielded specific energy and power of 42 Wh/kg and 11 kW/kg of polymer, respectively, during the first 60 cycles and 30 Wh/kg and 9 kW/kg after 1800 cycles, for a discharge time of about 10 s. Moreover, cycling experiments performed separately on negative and positive electrodes have shown that the capacity loss is associated essentially with the n-doping process at the negative electrode.

Synthesis of 2-isoxazolines from olefins derived from norephedrine and pulegone

Abstract In this communication we report the use of (±)-norephedrine and (−)-8-benzylaminomenthol (derived from (+)-pulegone) as chiral adjuvants for the cycloaddition of α,β-unsaturated 1,3-dipolarophiles. 2-Isoxazolines were obtained with low stereoselectivity from the reaction of nitrile oxides with the N-tosyl norephedrine derivative as the dipolarophile. Cycloaddition of nitrile oxide with 2-vinyl-N-benzyl-4,4,7α-trimethyl- trans -octahydro-1,3-benzoxazine produced stereoisomeric 2-isoxazolines in a ratio of about 95:5.

2-Vinyl-trans-octahydro-1,3-benzoxazine: Cyclization and 1,3-dipolar cycloaddition of nitrile oxides

Abstract A study of the stereochemistry of the acid-catalyzed cyclization between (−)-8-tosylaminomenthol (derived from (+)-pulegone) and acrolein diethyl acetal afforded two novel chiral perhydro-1,3-benzoxazine isomers 4a and 4b . Catalyst type as well as the reaction conditions dramatically affected the isomeric ratio. An X-ray crystal structure of 4a established a chair-boat conformation. The usefulness of this auxiliary was demonstrated by highly diastereoselective (i.e. 90% de ) 1,3-dipolar cycloadditions with nitrile oxides.

Synthesis of 17α-substituted ethynylestradiols: Potential ligands for drug vectors

17alpha-substituted ethynylestradiols, derived from estrone, were converted to their corresponding 17 alpha-(bromo- or iodo-propargyl)estrone intermediates. Nucleophilic substitution onto these moieties with malonate diester followed by hydrolysis and complexation with cis-Pt(Me(2)en)I(2) (Me(2)en=N,N-dimethylethylenediamine) gave cis-Pt(Me(2)en)(2-(3-(17beta-estradiol-17 alpha-yl)-prop-2-ynyl)malonato) 7, thus demonstrating that these estrogen-derived compounds can be used to synthesize stable Pt(II) complexes. The 3-(17beta-estradiol-17 alpha-yl)-prop-2-ynyl-1-sulfanylethylthiol 23 was also prepared.

Diastereoselective synthesis of 2-isoxazolines via silaketal tethered 1,3-dipolar cycloadditions

Abstract The use of silaketals derived from allylic alcohols and 1-substituted nitroethanols for the stereocontrolled synthesis of 3,4,5-trisubstituted 2-isoxazolines via intramolecular 1,3-dipolar cycloaddition is demonstrated. High levels of stereoselectivity (70–92% de ) were obtained from the reaction involving nitrile oxides with dipolarophiles having a stereocenter located at the allylic position. Intramolecular cycloaddition of precursors having only a stereocenter in α-position to the nitrile oxide moiety, produced 2-isoxazolines with moderate diastereoselectivities. The use of silyl nitronates increased the level of selectivity, albeit at the expense of conversion yields.

Synthesis of Novel Alkyl- and Aryl Sulfides and Thiols as Precursors for Self-Assembled Monolayers on Gold

A series of 4-alkyl-1-bromosulfanylbenzenes having S-methyl 2, S-t-butyl 3, S-trityl 4, S-benzyl 5, and S-silylethoxymethyl 6 substituents were prepared and evaluated for their ability to form a monolayer consisting of anS-aryl adsorbate on Au (111) surface. The monolayer was formed via the selective hydrolytic removal of an alkyl group protecting the sulfur functionality upon adsorbtion onto the gold surface. Thiols having variable carbon chain length and a peripheral thiophene moiety 9, 10, 17, 18 and 23-26 were also prepared.