Redox Electrolyte Solution Research Articles

Magnetohydrodynamic flow of RedOx electrolyte

Magnetohydrodynamic (MHD) flow of a RedOx electrolyte in a straight conduit is investigated theoretically. Inert electrodes are deposited along segments of the opposing walls of a straight conduit that is filled with a RedOx electrolyte solution. The conduit is positioned in a uniform magnetic field. When a potential difference is applied across the opposing electrodes, the resulting current interacts with the magnetic field to induce Lorentz forces. The species’ mass transport and the momentum equation are coupled and must be solved simultaneously. We compute the various species’ concentration distributions, the current flux distribution, and the liquid’s motion in the absence and presence of pressure gradients. The pressure gradients may either assist or oppose the MHD flow. At low potential differences, the current and the induced MHD flow increase nearly linearly as the potential difference increases. When the potential difference exceeds a certain critical value, the current and the flow rate saturate. We demonstrate that it is advantageous to use multiple electrode pairs with dielectric gaps between adjacent electrodes rather than a single electrode pair with an equivalent length. Finally, MHD flow with RedOx solution in the presence of abundant supporting electrolyte under limiting current conditions is analyzed using boundary layer theory. The approximate analytical solutions for the ions’ concentrations and the current agree well with the numerical solutions.

Solid type dye-sensitized solar cell using polysaccharide containing redox electrolyte solution

The liquid of a dye-sensitized solar cell composed of a nanoporous titanium dioxide (TiO 2) film and a bipyridine–Ru complex dye (N3 dye) was solidified by utilizing a tight and elastic solid polysaccharide (κ-carrageenan or agarose) containing excess liquid. The solid type cell exhibited similar characteristics and light-to-electricity conversion efficiency as a conventional liquid type cell. The electric resistance of the solid containing the solution of redox electrolytes (I −/I 3 −) was of the same order of magnitude as a liquid, and the charge transfer resistance on the electrode surface was even smaller for the solid than for the liquid. The increase of the polysaccharide solid hardness did not greatly affect the conversion efficiency. On exchanging the water of the polysaccharide solid with an organic medium solution containing redox electrolytes, the soaking time (from 1 to 3 h) and the repeated change to a fresh solution did not greatly affect the performance of the solid type cell. For both the solid and liquid type cells the thinner electrolyte layer gave a higher conversion efficiency. The investigation of both the solid and liquid type cells by alternating current impedance spectroscopy showed almost similar behavior in every step of the charge transfer event.

Influence of pyrazole derivatives in I−/I3− redox electrolyte solution on Ru(II)-dye-sensitized TiO2 solar cell performance

Abstract The influence of pyrazole additives in an I − /I 3 − redox electrolyte solution on the performance of a bis(tetrabutylammonium) cis -bis(thiocyanato)bis(2,2′-bipyridine-4-carboxylic acid, 4′-carboxylate)ruthenium(II) (N719) dye-sensitized TiO 2 solar cell was studied. The current–voltage characteristics of the cell were measured using 18 different pyrazole derivatives. All of the pyrazole additives enhanced the open-circuit photovoltage ( V oc ) and the solar energy conversion efficiency ( η ), but reduced the short-circuit photocurrent density ( J sc ). Most of the pyrazoles improved fill factor (ff). The physical and chemical properties of the pyrazoles were computationally calculated in order to elucidate the reasons for the additive effects on cell performance. The greater the partial charge of the nitrogen atom at position 2 in the pyrazole group, the larger the V oc, but the smaller the J sc values. As the dipole moment of the pyrazole derivatives increased, the V oc value increased, but the J sc value decreased. The V oc of the cell also increased as the ionization energy of the pyrazoles decreased. These results suggest that the electron donicity of the pyrazole additives affected the interaction with the nanocrystalline TiO 2 photoelectrode, the I − /I 3 − electrolyte, and the acetonitrile solvent, which changed the Ru(II)-dye-sensitized solar cell performance.

Influence of quinoline derivatives in I −/I 3− redox electrolyte solution on the performance of Ru(II)-dye-sensitized nanocrystalline TiO 2 solar cell

The influence of quinoline additives in an I −/I 3 − redox electrolyte solution on the performance of a bis(tetra-butylammonium) cis-bis(thiocyanato)bis(2,2′-bipyridine-4-carboxylic acid, 4′-carboxylate)ruthenium(II) (N719) dye-sensitized TiO 2 solar cell was studied. The I– V characteristics were measured for the cells with 20 types of quinoline derivatives. All of the quinoline additives enhanced the open-circuit photovoltage ( V oc) and fill factor (ff), but reduced the short circuit photocurrent density ( J sc) of the solar cell. Most of the quinolines also improved the solar energy conversion efficiency ( η). The physical and chemical properties of the quinolines were computationally calculated in order to elucidate the reasons for the additive effects on the cell performance. The greater the lowest partial charge of the atoms in the quinoline derivatives, namely nitrogen, the larger the V oc, but the smaller the J sc values. As the dipole moment of the quinoline derivatives increased, the V oc value increased, but the J sc value decreased. The V oc of the cell also increased as the ionization energy of the quinolines decreased. These results suggest that the electron donicity of the quinoline additives affected the interaction with the nanocrystalline TiO 2 photoelectrode, the I −/I 3 − electrolyte, and the acetonitrile solvent, which changed the Ru(II)-dye-sensitized solar cell performance.

Influence of aminothiazole additives in I−/I3− redox electrolyte solution on Ru(II)-dye-sensitized nanocrystalline TiO2 solar cell performance

Abstract The influence of aminothiazole additives in acetonitrile solution of an I−/I3− redox electrolyte on the performance of a bis(tetrabutylammonium)cis-bis(thiocyanato)bis(2,2′- bipyridine-4-carboxylic acid, 4′-carboxylate)ruthenium(II) (N719) dye-sensitized TiO2 solar cell was studied. The current–voltage characteristics were investigated under AM 1.5 (100 mW/cm2) for nine different aminothiazole compounds. The aminothiazole additives tested had varying influences on the solar cell performance. Most of the additives enhanced the open-circuit photovoltage (Voc), but reduced the short circuit photocurrent density (Jsc) of the solar cell. Both the physical and chemical properties of the aminothiazoles were computationally calculated in order to determine the reasons that the additive influenced solar cell performance. The larger the calculated partial charge of the nitrogen atom in the thiazole, the higher the Voc value. The Voc value increased as the dipole moment of aminothiazoles in acetonitrile increased. Moreover, the Voc of the solar cell also increased as the size of the aminothiazole molecules decreased. These results suggest that the electron donicity of the aminothiazole additives influenced the interaction with the TiO2 photoelectrode, which altered the dye-sensitized solar cell performance.

Synthesis, structure and photoelectrochemical performance of micro/nano-textured ZnO/eosin Y electrodes

Micro/nano-textured ZnO thick films were synthesized through deposition and pyrolysis of layered hydroxide zinc acetate (LHZA), Zn 5(OH) 8(CH 3COO) 2·2H 2O. LHZA films having a unique, rose-like morphology were initially deposited on conducting glass sheets in a chemical bath composed of methanol and zinc acetate dihydrate at 60 °C under neutral conditions. Pyrolysis of the LHZA films resulted in formation of ZnO without destroying the original morphology. Pyrolysis temperatures were found to greatly influence grain sizes and specific surface areas of the ZnO films. Photoelectrochemical performance of the films as ZnO/eosin Y electrodes was investigated in dye-sensitized solar cells using an I −/I 3 − redox electrolyte solution. The cell using the ZnO film pyrolyzed at 150 °C exhibited overall light to electricity conversion efficiencies of 2.0 and 3.3% under an AM-1.5 illumination at 100 and 10 mW cm −2, respectively. While microscale pores in the electrodes facilitated mass transfer of fluid electrolytes in the depth direction, nanoscale pores contributed to an increase in the amount of adsorbed dye. The maximum incident photon-to-current conversion efficiency (IPCE) of the electrode reached 84.9% at a wavelength of 530 nm.

Cathodic Electrodeposition of ZnO/Eosin Y Hybrid Thin Films from Oxygen-Saturated Aqueous Solution of ZnCl2 and Eosin Y

Electrodeposition of ZnO/eosin Y hybrid thin films from aqueous mixed solution of zinc chloride and eosin Y as promoted by reduction of oxygen has been studied. Highly oriented crystalline hybrid thin films with two distinctive structures have been obtained depending on the redox state of eosin Y. Deposition at potentials more positive than that of eosin Y reduction resulted in a formation of compact ZnO crystals into which eosin Y molecules are entrapped, while that accompanied with the reduction of eosin Y yielded a film consisting of sponge-like ZnO crystals with internal nanoporous structure to which eosin Y molecules are adsorbed. The addition of eosin Y accelerated the film growth both in oxidized and reduced forms due to its catalysis toward the reduction of oxygen. Photoelectrochemical measurement in an redox electrolyte solution revealed that the hybrid thin film in the latter structure performed as an efficient sensitized photoelectrode because of its porous nature. © 2003 The Electrochemical Society. All rights reserved.

Cathodic electrodeposition of oxide semiconductor thin films and their application to dye-sensitized solar cells

Cathodic electrodeposition of titanium dioxide (TiO 2) and zinc oxide (ZnO) thin films has been studied in the aim of developing cost-effective alternative routes to the photoelectrode materials for dye-sensitized solar cells (DSCs). Preparation of porous anatase TiO 2 thin film modified by cis-dithiocyanato bis(4,4′-dicarboxylic acid-2,2′-bipyridine)ruthenium(II) (N3) dye has been achieved by a three-step process: cathodic electrodeposition of a Ti hydroxide thin film from an acidic aqueous solution containing TiOSO 4, H 2O 2 and KNO 3, heat treatment of the film at 400 °C and chemical adsorption of dyes from solution. The photocurrent action spectrum measured at the N3-modified TiO 2 thin film electrode in contact with I −/I 3 − redox electrolyte solution revealed incident photon to current conversion efficiency (IPCE) of 37% in the visible range. While TiO 2 needed heat treatment for crystallization, direct electrodeposition of crystalline ZnO was possible from an aqueous solution of Zn(NO 3) 2. Addition of N3 to the deposition bath made it possible to synthesize porous ZnO/N3 hybrid thin film in one step. IPCE of 24% has been achieved for this film. A sandwich cell using the electrodeposited ZnO/N3 hybrid thin film photoelectrode measured I sc=0.61 mA/cm 2, V oc=0.46 V, F.F.=0.46 and η=0.13% under illumination by an artificial light source (500-W Xe lamp equipped with a <420-nm and an IR cutoff filters, intensity=100 mW cm −2), being the first example of a real working DSC fabricated without any heat treatment.

The Photovoltage-Determining Mechanism in Dye-Sensitized Solar Cells

The authors attempt to distinguish between two competing models of the photovoltage-determining mechanism in dye-sensitized solar cells. One model does not consider the equilibrium potential difference at the TiO{sub 2}/substrate interface to be a significant factor in determining the photovoltage; the other claims that this potential difference sets the upper limit to the achievable photovoltage. The authors deposit dye-sensitized TiO{sub 2} films on four different substrates that have vacuum work functions spanning a 1.4 eV range and measure the photovoltage obtained from these films in three different redox electrolyte solutions. No significant differences in photovoltage are obtained on the different substrates, not even on Pt where the interfacial potential should oppose electron transfer. The authors suggest that the interfacial potential barrier may be smaller than expected and/or too thin to have a significant influence on cell performance. The authors conclude that the photovoltage is determined by photoinduced chemical potential gradients, not by equilibrium electric fields.

Disposable reference electrode

In this paper we present a new low-cost disposable reference electrode. The construction of the electrode is based on a microfibre matrix, e.g., filter paper, which is filled with a redox electrolyte solution. The disposable reference electrode shows a reproducible and stable potential, which is little affected by the composition of the measuring solution.

Photoelectrochemical processes at an n-type CdS: I single-crystal electrode as studied by photothermal laser beam deflection: Energy conversion efficiencies and Peltier heats

An expression is given for the potential dependence of the photothermal laser beam deflection signal (PDS) at a periodically illuminated n-type semiconductor electrode in a redox electrolyte solution. The expression can be used to obtain the maximal efficiencies of conversion of absorbed monochromatic optical energy to chemical or electrical energy ( n e m and L G m referring to the heat of reaction and to the Gibbs energy respectively for the hydrogen-producing photoelectrolysis mode, and light to electrical power conversion efficiency L G m for regenerative systems), the Peltier heat Q PE,e at the semiconductor-electrolyte junction and the internal quantum efficiency n a s of the photocurrent. Values of these quantities have been determined for oxidation of sulfite ( n e m = 0.21 and L G m = 0.12 for photoelectrolysis, n a s = 0.88 and Q PE,e, = -0.35 eV) and polysulfide ( n e m = 0.04, n a s = 0.74, Q PE,e = 0.13 eV and L G m = 0.07 for light to electrical power conversion) at the (0001) face of an approx. 3 mm 3 iodine-doped n-CdS single-crystal photoanode at 488 nm. The Peltier heat at the n-CdS-metal (In + Ga, Cu) contact was estimated as approx. 0.1 eV. The attempt to determine efficiency data by PDS for photoanodic oxidation of hexacyanoferrate(II) failed because of photocorrosion of the electrode. Results are discussed and compared with data from related photothermal studies employing various front- and back-surface techniques.

Liquid/Solid Polyelectrolyte Diodes and Semiconductor Analogs

Liquid or semisolid redox polymer electrolytes can be organized to show many characteristics of conventional solid‐state semiconductor diodes. Fermi levels of redox electrolyte solutions provide a rational comparison of redox electrolyte solution mixtures at equivalence, redox ions in fixed‐site polymers, corresponding redox polymer mixed conductor electrolytes, and intrinsic electronic semiconductors. Moving the Fermi levels by redox doping compares with aliovalent semiconductor doping. However the ionic mobility almost always leads to a breakdown of the analogy, and it is difficult to immobilize ions while maintaining electronic conductivity. Conditions for construction of chemical diodes that mimic p‐n junctions are deduced, and reported chemical diodes are analyzed as equivalent to p‐n junctions, or more nearly comparable with discharged battery cells that also show rectification.

A photochargeable device composed of bilayer membranes of poly(3-methylthiophene) and prussian blue

A photochargeable device which can be charged under irradiation and discharged in the dark should open a new field of photoenergy conversion and storage. Such a device can be used also for information storage. Such a device can be used also for information storage. Some model cells for photoenergy conversion and storage have been constructed by using liquid-junction inorganic semiconductors in contact with a redox electrolyte solution [l-5]. Recently, organic semiconductors such as poly(acetylene) [6,7], poly(pyrrole) [&lo], poly(aniline) [ll], and poly(thienylene) [12,13] were reported to give photocurrents in the form of a Schottky type device. Although the light-to-electricity conversion efficiency of these organic semiconductor devices is inferior to that of inorganic semiconductor ones, they have merits in their easy fabrication, utilization as a film, and fairly high stability, except for poly(acetylene), in contrast to the corrosive narrow bandgap inorganic semiconductors. Prussian Blue (PB) is a polynuclear iron cyanide complex with the composition, Fe~‘[Fe”(CN),]~-. The electrochemical behavior of PB has been well characterized [14-161. Since PB is both oxidized and reduced reversibly, it can work as both the anode and cathode active material of a secondary battery [17-191. PB can be used as a fihn because of its high molecular weight structure. The photoelectrochemical reaction of a PB film coated on a TiO, liquid-junction photoanode was reported in ref. 20. In the present paper we will report the first example of an organic bilayer device composed of poly(3-methylthiophene) and PB which can be charged under irradiation and discharged in the dark reversibly.

Electrochemical Properties of the Semiconducting TiO2(Rutile) Single Crystal Electrode

AbstractThe electrochemical behaviour of semiconducting TiO2electrodes has been investigated by means of impedance, current and potential measurements in darkness, and as well in indifferent electrolyte as in redox electrolyte solutions. The results allow the determination of the flat‐band potential and of the position of the energy band edges at the TiO2surface. The data obtained on electrochemical reactivity, both anodically and cathodically, appear to be qualitatively interpretable on the basis of the accepted theories for direct electron transfer at the semiconductor/electrolyte interface. Some particular features inherent to the TiO2/electrolyte system are discussed.