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Relevant academic research and scientific papers

A Dual electrochrome of Poly-(3,4-Ethylenedioxythiophene) doped by N,N'-Bis(3-sulfonatopropyl)-4-4'-bipyridinium-redox chemistry and electrochromism in flexible devices

An electrochromic zwitterionic viologen, N,N'-bis(3-sulfonatopropyl)-4-4'-bipyridinium, has been used for the first time for doping poly (3,4-ethylenedioxythiopene) (PEDOT) films during electropolymerization. Slow and fast diffusional rates for the monomer at deposition potentials of +1.2 and +1.8 V, respectively yielded the viologen-doped PEDOT films with granular morphology and with dendrite-like shapes. The dual electrochrome formed at +1.8 V, showed enhanced coloration efficiency, larger electrochemical charge storage capacity, and superior redox activity in comparison to its analogue grown at +1.2 V, thus demonstrating the role of dendritic shapes in amplifying electrochromism. Flexible electrochromic devices fabricated with the viologen-doped PEDOT film grown at +1.8 V and Prussian blue with an ionic liquid-based gel electrolyte film showed reversible coloration between pale and dark purple with maximum coloration efficiency of 187cm2C-1 at λ = 693 nm. The diffusional impedance parameters and switching kinetics of the device showed the suitability of this dual electrochrome formed as a single layer for practical electrochromic cells.

Characterization of Intrinsic Amorphous Hydrogenated Silicon as a Thin-Film Photocathode Material. Efficient Photoreduction Processes in Aqueous Solution

Intrinsic amorphous hydrogenated silicon, a-Si:H, has been characterized as a thin-film (8000 Angstroem) a-Si:H material.The intrinsic a-Si:H is deposited onto a 200-Angstroem thick, heavily B-doped, layer of a-Si:H on stainless steel.The 200-Angstroem p+-a-Si:H layer ensures a back contact to the valence band to give as large a field across the 8000-Angstroem intrinsic layer as possible when the intrinsic layer is contacted on the other side by an electrolyte solution containing a redox couple.The a-Si:H photocathodes give good photovoltages in aqueous and nonaqueous media, up to 855 mV, depending on the E1/2 of the redox couple in contact with the electrode.A plot of photovoltage vs.E1/2 shows a slope of only 0.42.A zero photovoltage is extrapolated to obtain for E1/2 no more negative than +0.9 V vs.SCE; the photovoltage is constant for E1/2 more negative than ca. -0.8 V vs.SCE.The slope of less than 1.0 suggests a deleterious role for states situated between the valence and conduction bands of a-Si:H.The surface of a-Si:H can be derivatized with an N,N'-dialkyl-4,4'-bipyridinium reagent followed by deposition of Pd or Pt to effect H2 evolution at an electrode potential up to ca. 700 mV more positive than on a conventional electrode.The durability and photovoltage of a-Si:H photocathodes are superior to those of single-crystal p-Si photocathodes, but the wavelength response, rectangularity of current-voltage curves, and the quantum yield for electron flow offset the advantages of the thin-film photocathode.The sustained energy conversion efficiency for 632.8-nm light to electricity or H2 is about the same for a-Si:H and single-crystal p-Si under the same conditions.Importantly, constant output of electricity for 50 h at ca. 3.2 mA/cm2 has been obtained from a-Si:H photocathode-based cells employing an aqueous Eu3+/2+/KCl redox couple/electrolyte combination.

Kinetics and Thermodynamics of Binding between Zwitterionic Viologen Guests and the Cucurbit[7]uril Host

The host-guest binding interactions between a series of zwitterionic, symmetric viologens, and the cucurbit[7]uril host were investigated using NMR and UV-vis spectroscopic techniques. The nature of the viologen side arms had strong effects on the kinetics of association and dissociation and weaker, more uniform influence on the thermodynamic stability of the final 1:1 inclusion complexes, which can also be characterized as pseudorotaxanes.

Novel Effect of Man-Made Molecular Assemblies on Photoinduced Charge Separation. 3. Sensitized Photoreduction of Zwitterionic Viologen in the presence of Cationic Surfactants

Addition of cationic surfactant at concentrations above the cmc drastically increased the efficiency of photoreduction of zwitterionic propylviologenesulfonate as sensitized by tris(2,2'-bipyridine)ruthenium complex, Ru(bpy)32+, in the presence of triethanolamine (TEOA).The efficiency of net electron transfer in the quenching process was slightly improved by the addition of cationic surfactants.The lifetime of reduced viologens remarkably increased with increasing the concentrations of cationic surfactants.The electrostatic field due to the positively charged molecular assemblies such as micelles or lilayers were concluded to trap the reduced viologens and to prevent thermodinamically favored back-electron-transfer reactions.

Improved Charge Separation and Photosensitized H2 Evolution from Water with TiO2 Particles on Colloidal SiO2 Carriers

Laser flash photolysis and steady-state photolysis studies show that electrostatic interactions have a dramatic influence on the kinetics for charge separation and hydrogen production in aqueous systems (pH 9.8) of 20-nm diameter TiO2-modified SiO2 colloids in various combinations with an electron relay, a photosensitizer, and a Pt catalyst.Either direct excitation of the semiconductor or the photosensitizer Ru(bpy)32+ (bpy= 2,2'-bipyridine), electrostatically adsorbed to the colloid, initiate electron transfer to either the zwitterionic electron relay, N,N'-bis(3-sulfonatopropyl)-4,4'-bipyridinium (PVS0), or N,N'-bis(3-sulfonatopropy l)-2,2'-bipyridinium (DQS0), or methyl viologen (MV2+).The rates and quantum yields for the formation of the radical PVS.- anion in both the TiO2-SiO2/PVS0 and the TiO2-SiO2/Ru(bpy)32+/PVS0 systems decline with increasing ionic strength.The rate and quantum yields for H2 production in both the TiO2-SiO2/DQS0/Pt and the TiO2-SiO2/Ru(bpy)32+/DQS0/Pt systems also show a similar ionic strength dependence.Kinetic analysis of data infers that repulsion of the reduced zwitterionic relay PVS.- and DQS.- from the negatively charged colloidal interface inhibits back electron transfer to both the semiconductor and the surface-attached oxidized photosensitizer Ru(bpy)33+.Formation of the cation MV.+ radical and its back electron transfer to the semiconductor are rapid and imply that the MV2+ electron relay is in close proximity to the colloid.Both the photogenerated valence-band holes and the oxidized photosensitizer Ru(bpy)33+ oxidize surface Ti-O- groups of TiO2.This redox process has the important effect of recycling the photosensitizer for further reaction.The addition of the superoxide dismutase enzyme to the oxidized TiO2-(SiO2) system regenerates, in part, the activity of the semiconductor to evolve H2 and to release molecular oxygen.

ASYMMETRIC METAL COMPLEX AS AN ACTIVE MATERIAL OF A FLOW BATTERY

The present invention teaches an asymmetrical metal complex comprising a metal center coordinated with between two and six hydrophilic ligands, wherein at least one of said hydrophilic ligands is chemically different than the other said hydrophilic ligands.

Spatial Structure Regulation: A Rod-Shaped Viologen Enables Long Lifetime in Aqueous Redox Flow Batteries

A stable rod-like sulfonated viologen (R-Vi) derivative is developed through a spatial-structure-adjustment strategy for neutral aqueous organic redox flow batteries (AORFBs). The obtained R-Vi features four individual methyl groups on the 2,2′,6,6′-positions of the 4,4′-bipyridine core ring. The tethered methyls confine the movement of the alkyl chain as well as the sulfonic anion, thus driving the spatial structure from sigmoid to rod shape. The R-Vi with weak charge attraction and large molecular dimension displays an ultralow membrane permeability that is only 14.7 % of that of typical sigmoid viologen. Moreover, the electron-donating effect of methyls endows R-Vi with the lowest redox potential of ?0.55 V vs. SHE among one-electron-storage viologen-based AORFBs. The AORFB with the R-Vi anolyte and a K4Fe(CN)6 catholyte exhibits an energy efficiency up to 87 % and extremely low capacity-fade rate of 0.007 % per cycle in 3200 continuous cycles.

Electrochemical investigation of structurally varied azinium scaffolds

Inspired by the successful utilization of aziniums as anolytes in redox-flow batteries, we have designed and prepared a systematically extended series of (di)azinium compounds based on pyrazine, bipyridine, 1,5-naphthyridine, 3,8-phenanthroline, (E)-4,4′-

Mesostructure organic-inorganic hybrid ionic liquids based on heteropoly acids: Effect of linkage on the molecular structure and catalytic activity

The new inorganic–organic hybrids based on SO3H-functionalized ionic liquids (ILs) and Keggin-type heteropoly acids (H3PW12O40, H3PMo12O40, and H4SiW12O40; HPAs) are prepared and characterized by FT-IR, NMR, XRD, CV, SEM/EDX, ICP-OES, BJH and UV. Different molecular structures according to the different inorganic part were also proved. Potentiometric titration showed a good relationship between catalytic activity and acidity of the catalysts. Electrochemical aspects showed electron transfer ability of the compounds. For understanding catalytic activities of the HPA-IL hybrids in N-formylation reaction, effect of catalyst composition, substrate, and reaction conditions were studied. The best SO3H-functionalized ionic liquid catalyst was readily recovered and reused for four runs. Easy preparation of the catalyst, simple and easy work-up, mild reaction conditions, low cost, excellent yields and short reaction times are the key features of this work.

MATERIALS FOR USE IN AN AQUEOUS ORGANIC REDOX FLOW BATTERY

Described herein are aqueous organic redox flow batteries that include a first redox active material that can include a metallocene or a salt thereof, and a second redox active material that can include a viologen or a salt thereof. The aqueous organic re