Reduction Of I2 Research Articles

Shuttle-free zinc–iodine batteries enabled by a cobalt single atom anchored on N-doped porous carbon host with ultra-high specific surface area

Aqueous zinc‑iodine batteries are favorable solutions for grid-level energy storage owing to their cost-effective components and intrinsic safety. Nevertheless, the sluggish conversion kinetics and polyiodide shuttle effect have significantly hindered their practical applications. Herein, a Co single atom anchored on N-doped porous carbon nanosheets (Co-SAs@NPC) was produced through an efficient molten-salt engaged pyrolysis process and further utilized as the iodine host for aqueous zinc-iodine batteries. The large specific surface area (1741 m2 g−1) combined with abundant heteroatom-containing functional groups can afford a tight physical and chemical confinement towards iodine species. Meanwhile, the presence of Co single atoms exhibits high electrocatalytic activity towards I2 reduction reactions. According to the experimental results and DFT theoretical calculations, the resulting Co-SAs@NPC can simultaneously offer generous electrochemical active sites and electrocatalytic activity, which displays a high adsorption ability towards iodide species and boost the reversible redox reactions between iodine and iodides. Consequently, the as-assembled zinc-iodine batteries with Co-SAs@NPC/I2 cathodes can deliver a high specific capacity (295 mA h g−1 at 0.3 A g−1), good rate performance (199 mAh g−1 at 20 A g−1), and long cyclic stability over 10,000 cycles. Additionally, the absence of polyiodide shuttle was analyzed by a series of ex-situ spectrum analyses.

Dynamic Reversible Oxidation-Reduction of Iodide Ions for Operationally Stable Perovskite Solar Cells under ISOS-L-3 Protocol.

Despite rapid advancements in the photovoltaic efficiencies of perovskite solar cells (PSCs), their operational stability remains a significant challenge for commercialization. This instability mainly arises from light-induced halide ion migration and subsequent oxidation into iodine (I2). The situation is exacerbated when considering the heat effects at elevated temperatures, leading to the volatilization of I2 and resulting in irreversible device degradation. Mercaptoethylammonium iodide (ESAI) is thus incorporated into perovskite as an additive to inhibit the oxidation of iodide anion (I-) and the light-induced degradation pathway of FAPbI3→FAI+PbI2. Additionally, the formation of a thiol-disulfide/I--I2 redox pair within the perovskite film provides a dynamic mechanism for the continuous reduction of I2 under light and thermal stresses, facilitating the healing of iodine-induced degradations. This approach significantly enhances the operational stability of PSCs. Under the ISOS-L-3 testing protocol (maximum power point (MPP) tracking in an environment with relative humidity of ≈50% at ≈65°C), the treated PSCs maintain 97% of their original power conversion efficieney (PCE) after 300 h of aging. In contrast, control devices exhibit almost complete degradation, primarily due to rapid thermal-induced I2 volatilization. These results demonstrate a promising strategy to overcome critical stability challenges in PSCs, particularly in scenarios involving thermal effects.

Pyodine: an open, flexible reduction software for iodine-calibrated precise radial velocities

Context. Many telescopes use an iodine (I2) absorption cell to measure precise radial velocities (RVs), but their data reduction pipelines are all tailored to their respective instrumental characteristics and not openly accessible. Aims. For existing and future projects dedicated to measuring precise RVs, we have created an open-source, flexible data reduction software to extract RVs from échelle spectra via the I2 cell method. The software, called pyodine, is completely written in Python and has been built in a modular structure to allow for easy adaptation to different instruments. Methods. We present the fundamental concepts employed by pyodine, which build on existing I2 reduction codes, and give an overview of the software’s structure. We adapted pyodine to two instruments, Hertzsprung SONG located at Teide Observatory (SONG hereafter) and the Hamilton spectrograph at Lick Observatory (Lick hereafter), and demonstrate the code’s flexibility and its performance on spectra from these facilities. Results. Both for SONG and Lick data, the pyodine results generally match the RV precision achieved by the dedicated instrument pipelines. Notably, our code reaches a precision of roughly 0.69 m s−1 on a short-term solar time series of SONG spectra, and confirms the planet-induced RV variations of the star HIP 36616 on spectra from SONG and Lick. Using the solar spectra, we also demonstrate the capabilities of our software in extracting velocity time series from single absorption lines. A probable instrumental effect of SONG is still visible in the pyodine RVs, despite being a bit damped as compared to the original results. Conclusions. With pyodine we prove the feasibility of a highly precise, yet instrument-flexible I2 reduction software, and in the future the code will be part of the dedicated data reduction pipelines for the SONG network and the Waltz telescope project in Heidelberg.

Amine-Thiol/Selenol Chemistry for Efficient and Stable Perovskite Solar Cells

Controlling the crystallization of perovskites is imperative to reduce defect densities in perovskite thin films and extend device lifetimes. In this work, combinations of amine and chalcogenide ligands were introduced in the sequential deposition method to fabricate highly crystalline and oriented formamidinium lead iodide thin films with reduced defect densities and increased charge carrier lifetimes. The dual additives can tune the perovskite intermediate state and control the crystallization, leading to devices with improved efficiencies and stabilities. While thiophenol failed to prevent the amine ligand from degrading the perovskite precursors, benzene selenol combinations with amine ligands drastically changed the solution chemistry to increase the PbI2 conversion to highly crystalline and oriented α-FAPbI3 films with lower defect densities. X-ray photoelectron spectroscopy studies reveal benzene selenol evaporates from the thin film, leaving behind a modified surface, which is associated with the amine additive. These results indicate the amine selection can be used to tune the surface properties. Lastly, we propose a highly tunable I2 reduction strategy using chalcogenide chemistry to help enable the realization of perovskite solar cells with high performance and stability.

Electrocatalytic Iodine Reduction Reaction Enabled by Aqueous Zinc‐Iodine Battery with Improved Power and Energy Densities

AbstractProposed are Prussian blue analogue hosts with ordered and continuous channels, and electrocatalytic functionality with open Co and Fe species, which facilitate maximum I2 utilization efficiency and direct I2 to I− conversion kinetics of the I2 reduction reaction, and free up 1/3 I− from I3−. Co[Co1/4Fe3/4(CN)6] exhibits a low energy barrier (0.47 kJ mol−1) and low Tafel slope (76.74 mV dec−1). Accordingly, the Co[Co1/4Fe3/4(CN)6]/I2//Zn battery delivers a capacity of 236.8 mAh g−1 at 0.1 A g−1 and a rate performance with 151.4 mAh g−1 achieved even at 20 A g−1. The battery delivers both high energy density and high‐power density of 305.5 Wh kg−1 and 109.1 kW kg−1, higher than I2//Zn batteries reported to date. Furthermore, solid‐state flexible batteries were constructed. A 100 mAh high capacity solid‐state I2//Zn battery is demonstrated with excellent cycling performance of 81.2 % capacity retained after 400 cycles.

Electrocatalytic Iodine Reduction Reaction Enabled by Aqueous Zinc-Iodine Battery with Improved Power and Energy Densities.

Proposed are Prussian blue analogue hosts with ordered and continuous channels, and electrocatalytic functionality with open Co and Fe species, which facilitate maximum I2 utilization efficiency and direct I2 to I- conversion kinetics of the I2 reduction reaction, and free up 1/3 I- from I3 - . Co[Co1/4 Fe3/4 (CN)6 ] exhibits a low energy barrier (0.47 kJ mol-1 ) and low Tafel slope (76.74 mV dec-1 ). Accordingly, the Co[Co1/4 Fe3/4 (CN)6 ]/I2 //Zn battery delivers a capacity of 236.8 mAh g-1 at 0.1 A g-1 and a rate performance with 151.4 mAh g-1 achieved even at 20 A g-1 . The battery delivers both high energy density and high-power density of 305.5 Wh kg-1 and 109.1 kW kg-1 , higher than I2 //Zn batteries reported to date. Furthermore, solid-state flexible batteries were constructed. A 100 mAh high capacity solid-state I2 //Zn battery is demonstrated with excellent cycling performance of 81.2 % capacity retained after 400 cycles.

Highly selective and sensitive iodide sensor based on carbon paste electrode modified with nanosized sulfate-doped α-[formula omitted

Sulfate-doped α-Fe2O3 nanoparticles-modified carbon paste electrode (CPE) was demonstrated to be an efficient and highly selective sensor for iodide concentration determination. The detection process was characterized by studying the redox behavior of I2/I− couple at both modified and unmodified carbon paste electrodes via cyclic voltammetry and electrochemical impedance spectroscopy. It was shown that α-Fe2O3-incorporated CPE is better than bare CPE for I− oxidation as well as I2 reduction. However, Sulfate-doped α-Fe2O3-CP electrode led to the highest efficiency for I− oxidation among all examined electrode, suggesting that modification of the hematite with sulfate improves the electrocatalytic performance of hematite for iodide ion oxidation. The effect of electrode composition (sulfated α-Fe2O3, carbon, binder) as well as electrochemical determination conditions (including pH and accumulation time) on the response of Sulfate-doped α-Fe2O3-CPE was investigated and the optimum conditions were chosen. A good linear correlation was obtained between iodide concentration and cyclic voltammetry response, in a concentration range of 2.5 × 10−7 to 1.5 × 10−3 mol L−1. The detection limit of the developed sensor for iodide ion was calculated to be 0.1 μmol L−1 (S/N = 3) for an accumulation time of 15 min. The relative standard deviation (RSD) was found to be 3.5% (n = 5). Determination of iodide by the sensor in real samples, such as sea water and soil, led to satisfactory results.

Synergistic impact of humic acid on the photo-reductive decomposition of perfluorooctanoic acid

Perfluorooctanoic acid (PFOA) is a stable perfluoro-surfactant due to the contribution of electronegative fluorine atoms and the high strength of CF bonds (116 kcal/mol). However, UV irradiation of iodide at 254 nm produces hydrated electrons (eaq−) that react with PFOA to initiate its photo-reductive decomposition. In this study, we investigate the role of humic acid (HA) during the decomposition of PFOA at λmax = 254 nm as mediated by the formation of eaq−. Results show that, in UV/iodide/HA system, the decomposition and defluorination ratios of PFOA at 1.5 h were increased to 67.5% and 23.5%, respectively, compared with iodide-photolysis alone results as 8.7% and 3.3%, respectively, at room temperature (25 °C) and pH 10.0 under anaerobic conditions. Kinetic analysis indicated that the PFOA decomposition fit the first-order kinetics with a rate constant of 0.822 h−1. Reaction mechanism accounting for the effects of HA on the photo-reductive decomposition of PFOA is proposed that the aromatic rings of HA react with I2 to form π-complexes, which effectively inhibits the reactive quenching of eaq− by I2. After adduct formation and subsequent oxidation of phenolic hydroxy groups by I2, I− is regenerated, which allows for the continuous photo-production of eaq−. The quinone moieties in HA effectively act as electron shuttles leading to the reduction of I2 back to 2 I−. The reaction sequence involving HA provides a catalytic cycle that leads to the continuous production of eaq−, which in turn drives the decomposition and defluorination of PFOA.

Impact of humic acid on the photoreductive degradation of perfluorooctane sulfonate (PFOS) by UV/Iodide process

Iodide photolysis under UV illumination affords an effective method to produce hydrated electrons (eaq–) in aqueous solution. Therefore, UV/Iodide photolysis can be utilized for the reductive degradation of many recalcitrant pollutants. However, the effect of naturally occurring organic matter (NOM) such as humic and fulvic acids (HA/FA), which may impact the efficiency of UV/Iodide photoreduction, is poorly understood. In this study, the UV photoreductive degradation of perfluorooctane sulfonate (PFOS) in the presence of I− and HA is studied. PFOS undergoes a relatively slow direct photoreduction in pure water, a moderate level of degradation via UV/Iodide, but a rapid degradation via UV/Iodide/HA photolysis. After 1.5 h of photolysis, 86.0% of the initial [PFOS] was degraded in the presence of both I− and HA with a corresponding defluorination ratio of 55.6%, whereas only 51.7% of PFOS was degraded with a defluorination ratio of 4.4% via UV/Iodide illumination in the absence of HA. The relative enhancement in the presence of HA in the photodegradation of PFOS can be attributed to several factors: a) HA enhances the effective generation of eaq– due to the reduction of I2, HOI, IO3− and I3− back to I−; b) certain functional groups of HA (i.e., quinones) enhance the electron transfer efficiency as electron shuttles; c) a weakly-bonded association of I− and PFOS with HA increases the reaction probability; and d) absorption of UV photons by HA itself produces eaq–. The degradation and defluorination efficiency of PFOS by UV/Iodide/HA process is dependent on pH and HA concentration. As pH increases from 7.0 to 10.0, the enhancement effect of HA improves significantly. The optimal HA concentration for the degradation of 0.03 mM PFOS is 1.0 mg L−1.

Carbon Nanohorn and Ionic Liquid Mixture: Towards High Performance Organic Catholyte for Rechargeable Lithium Metal Battery

Recenlty, several novel prototypes of lithium metal battery that use lithium metal as anode and soluble halogen redox couple (such as Br2/Br- and I2/I-) as catholyte have been developed.1-3 These emerging prototypes have several advantages compared with existing lithium-oxygen (Li-O2) and lithium-sulfur (Li-S) batteries. The high solubility of redox couple circumvents the deposition of insoluble and electrical-insulating product on the carbon anode that has caused large overpotential for Li-O2 batteries. And the cell potentials of these prototypes are much larger than those of Li-S batteries, because of the high redox potential (vs Li+/Li) of the halogen redox couples: 3.6 V for I2/I- and 4.1 V for Br2/Br-, compared with 2-2.4 V for polysulfide. Probably the most distinct feature of these new lithium metal battery is the use of an aqueous solution as cathode that provides much higher ion conductivity and thus better power performance than solid-state cathodes. However, the aqueous electrolyte also poses several challenges to other components of the battery. First, a strictly water-tight ion exchange membrane is needed to protect the lithium metal anode from the catholyte and any water leakage will cause safety issues considering the violent reaction between lithium and water. Secondly, corrosive I2 or Br2 has to be added to the electrolyte to ensure reversible redox reactions. Finally, the small electrochemical window of water limit the further improvement on cell potential. To address these issues with existing aqueous catholyte, this paper proposes an organic catholyte with acetonitrile as solvent, I2-free ionic liquid as redox active species, and carbon nanohorn as additives. Compared with aqueous electrolyte, organic electrolyte has much higher voltage window and poses less safety threat to the lithium metal anode, but unfortunately, it also has lower ion conductivity. The carbon nanohorn additives mitigate the low conductivity problems by forming a percolating nanoscale conductive network inside the organic electrolyte.4 This network extend the reaction site from the surface of the carbon current collector into the bulk of the organic catholyte, hence it reduces the I- ion diffusion length to compensate for the lower ion conductivity of organic electrolyte. The good electrical conductivity of the carbon nanohorn also reduce the internal resistance of the battery to improve power formances. Last but not the least, the carbon nanohorn has catalytic effect towards the reduction of I2 to I-. As a result, even without adding corrosive I2 to the electrolyte, the I- to I2 reduction reaction can still proceed with low overpotential. Based on the aforementioned analysis, we developed a novel organic catholyte by mixing carbon nanohorn (CNH) into 37 mg/ml acetonitrile solution of 1-ethyl-3-methylimidazolium iodide ([EMIM]I) ionic liquid. The weight ratio between CNH and [EMIM]I is 1:1. The CNH is from Graphene Laboratories Inc. Calverton, NY, USA and the [EMIM]I (97%) and acetonitrile (anhydrous, 99.8%) are from Sigma Aldrich, Milwaukee, WI, USA. All materials and chemicals are used without further processing or purification. To elucidate the effect of CNH additives, 37 mg/ml [EMIM]I in acetonitrile solution are used as a reference catholyte. These two catholyte systems are studied inside a glovebox using a three-electrode beaker cell with glassy carbon of 7.07 mm2 area as working electrode, silver wire as non-aqueous reference electrode, and platinum mesh as counter electrode. In cyclic voltammetry study, the cell using CNH-added electrolyte has higher cathodic current (corresponding to reduction of I2 to I-) than that of CNH-free cell, demonstrating that this reduction reaction is more facile in the CNH-added cell. Electrochemical impedance spectroscopy of CNH-added electrolyte at 0.1Hz-100kHz demonstrates lower impedance at high frequency region and lower charge transfer resistance in mid-frequency region, which proves that the CNH can reduce the internal resistance of the cell and facilitate the I-/I2 redox reaction as expected. Ongoing work is to assemble the CNH-added electrolyte with lithium metal anode and evaluate the lithium metal battery performance. Reference Lu, Yuhao, John B. Goodenough, and Youngsik Kim. "Aqueous cathode for next-generation alkali-ion batteries." Journal of the American Chemical Society 133.15 (2011): 5756-5759.Zhao, Yu, et al. "A reversible Br 2/Br− redox couple in the aqueous phase as a high-performance catholyte for alkali-ion batteries." Energy & Environmental Science 7.6 (2014): 1990-1995.Zhao, Yu, Lina Wang, and Hye Ryung Byon. "High-performance rechargeable lithium-iodine batteries using triiodide/iodide redox couples in an aqueous cathode." Nature communications 4 (2013): 1896.Fan, Frank Y., William H. Woodford, Zheng Li, Nir Baram, Kyle C. Smith, Ahmed Helal, Gareth H. McKinley, W. Craig Carter, and Yet-Ming Chiang. "Polysulfide flow batteries enabled by percolating nanoscale conductor networks." Nano letters 14, no. 4 (2014): 2210-2218.

Detailed kinetic study of the electrochemical Bunsen reaction in the sulfur–iodine cycle for hydrogen production

The electrochemical Bunsen reaction has been proposed as an innovative and promising method compared with the traditional Bunsen reaction for the sulfur–iodine cycle, and its kinetics were studied in this work. Polarization curves were measured using platinum electrode in the different concentrations of SO2–H2SO4–H2O and I2–HI–H2O solutions at a temperature range of 303–353K. Fundamental kinetic parameters, namely exchange current density, Tafel slope, asymmetry factor, were determined for anodic SO2 oxidation reaction and cathodic I2 reduction reaction according to the Tafel plots. The activation energy and pre-exponential factor for the electrode reactions were also analyzed using Arrhenius relation. Results indicated that an increase in the SO2 concentration in the anolyte and the I2 concentration in the catholyte reduced the activation energy, contributing to the easier anode and cathode reaction. Take high electrode reaction rate and easier electrode reactions into account, the initial SO2 concentration of 1.509mol/L and the I2/HI molar ratio of 0.5 could be optimal.

Reduction of I2/I3− by Titanium Dioxide

A photoelectrochemical cell was designed that allowed the reactivity of oxidized iodide species with mesoporous nanocrystalline (anatase) TiO2 thin films to be quantified spectroscopically on nanosecond and longer time scales in half molar iodide acetonitrile solutions. Under forward bias conditions, TiO2 did not react with photogenerated iodine radical anions, I2−•, that were found instead to disproportionate with a rate constant that was within experimental error the same as that measured in fluid acetonitrile solution, k = 3 × 109 M−1 s−1. The absence of reactivity with I2−• was unexpected. It appears that the reduction of I2−• by TiO2(e−) does not complete kinetically with rapid I2−• disproportionation. In contrast, TiO2(e−) was found to decrease the concentration of tri-iodide, I3−, and presumably molecular iodine, I2, that was expected to be present in low equilibrium concentrations. The findings have relevance to unwanted charge recombination processes in dye sensitized solar cells.

Synthesis, Characterization, and Conducting Properties of Heterobimetallic Salts of Cyanoiminomethanedithiolate Ligand

Abstract Heterobimetallic ion-pair complexes of the type [M(bpy)3][M′(cdc)2] (M = Fe2+, Co2+, and Ni2+; M′ = Ni2+ and Cu2+; bpy = 2,2′-bipyridine, cdc2− = cyanoiminomethanedithiolate (C2N2S22−)) have been synthesized by reacting a solution of K2[M′(cdc)2] with [M(bpy)3]X2 (X = Cl− and SO42−) in equimolar ratio. These complexes have been characterized by elemental analysis, solution conductance, and magnetic susceptibility measurements, IR, 1H and 13C NMR, ESR, and UV–visible spectroscopies and pressed pellet conductivity technique. Three of these salts show behavior of semiconductors in the 295–443 K temperature range while the remaining are insulators. The lowering of the ν(C≡N) frequency in I2-doped products of these complexes as compared to the parent complexes clearly reveals interaction of the C≡N group of the ligand cdc2− resulting in decrease in ν(C≡N) bond order and in turn partial reduction of I2. The I2-doped products of the majority of the complexes show enhanced room-temperature conductivity and exhibit semiconducting behavior.

Preparation of monodisperse poly(vinyl alcohol) microspheres by heterogeneous surface saponification and iodine complex formation

AbstractMonodisperse poly(vinyl acetate) (PVAc) microspheres with high molecular weight obtained by suspension polymerization of vinyl acetate were saponified in alkaline aqueous solution to keep their spherical structure. The saponification was restricted on the surface of the PVAc microspheres and obtained particles had skin/core structure. Various poly(vinyl alcohol) (PVA) microspheres with different diameters and degrees of saponification (DSs) were obtained. The conversion of PVAc to PVA during the heterogeneous surface saponification time were examined by nuclear magnetic resonance spectroscopy and after 72 h hydrogel type PVA microspheres completely saponified were obtained. The crystal melting temperatures of the microspheres obtained by the saponification were measured a constant value of 238°C irrespective of varying DS, and the peaks became enlarged as reaction time. Iodine complexes were formed in saponified microspheres with DS of 41% and 99% by immersing them in I2/KI aqueous solution and decomposed by the reduction of I2 in the complexes to 2I− using sodium sulfite to confirm whether the skin formed through the saponification was composed of PVA with high VA content. Obviously, characteristic blue color developments owing to I5−‐PVA complexes were observed in both saponified regions and a red in the PVAc core. Consequently, it was concluded that the PVA skins formed by heterogeneous surface saponification had high DSs. Such complexes endowed polymeric microspheres a good radiopacity which would be useful in clinical treatment of vascular diseases and were examined by X‐ray irradiation image. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Transient Absorption Studies and Numerical Modeling of Iodine Photoreduction by Nanocrystalline TiO2 Films

We have used transient absorption spectroscopy to study the reaction between photogenerated electrons in a dye-free nanocrystalline titanium dioxide film and an iodine/iodide redox couple. Recombination kinetics was measured by recording the transient optical signal following band gap excitation by a UV laser pulse. In the presence of a methanol hole scavenger in the electrolyte, a long-lived (0.1-1 s) red/infrared absorbance is observed and assigned to photogenerated electrons forming Ti(3+) species. In the presence of iodine and excess iodide in the electrolyte, the signal decays on a millisecond-microsecond time scale, assigned to reduction of the redox couple by photogenerated electrons in the TiO(2). The electron lifetime decreases inversely with increasing iodine concentration, indicating that the back reaction is first order in [I(2)]. No evidence for I(2)(-) is observed, indicating that the reaction mechanism does not involve the formation of I(2)(-) as an intermediate. The shape of the kinetics evolves from monoexponential at low [I(2)] to stretched-exponential as [I(2)] increases. A Monte Carlo continuous-time random walk model is implemented to simulate the kinetics and its [I(2)] dependence and used to address the order of the recombination reaction with respect to electron density, n. The model incorporates the diffusion of oxidized species from the electrolyte toward the TiO(2) surface as well as electron trapping and transport in the TiO(2). In the limit of low [I(2)], the monoexponential kinetics is explained by the recombination reaction being rate limited by the diffusion of the oxidized species in the electrolyte. The stretched-exponential behavior at high [I(2)] can be explained by the reaction being rate limited by the transport of electrons through a distribution of trap states toward reactive sites at the TiO(2)-electrolyte interface, similar to the mechanism proposed previously for the kinetics of electron-dye cation recombination. Such trap-limited recombination can also explain the superlinear dependence of electron recombination rate on electron density, which has been reported elsewhere, without the need for a reaction mechanism that is second order in n. In contrast, a second-order reaction mechanism in a trap-free medium cannot explain the observed kinetics, although a second-order mechanism incorporating electron trapping cannot be conclusively ruled out by the data. We propose that the most likely reaction scheme, that is first order in both [I(2)] and n, is the dissociative reduction of I(2) onto the metal oxide surface, followed by a second electron reduction of the resulting adsorbed iodine radical, and that empirical second-order behavior of the electron lifetime is most likely explained by electron trapping rather than by a second-order recombination mechanism.

Solvothermal routes to capped oxide and chalcogenide nanoparticles

Abstract We review our recent contributions to the use of solvothermal methods for the preparation of different oxide and chalcogenide nanoparticles. We have prepared sub 10-nm g-Fe2O3, ZnFe2O4, and CoFe2O4 particles by the decomposition of the corresponding cupferron complexes in the presence of n-octylamine or n-dodecylamine in solvothermal toluene. Similarly, dodecanethiol-capped chalcogenide nanoparticles of CdSe have been prepared by reacting cadmium stearates with H2Se under solvothermal conditions. The H2Se is generated in situ by the reduction of Se by tetralin. Using this latter technique, we have also been able to prepare PbSe and PbI2 in toluene under solvothermal conditions, albeit in bulk (rather than nanocrystalline) form. In the preparation of PbI2, HI is prepared by the in situ reduction of I2 by tetralin.

The reduction of I2 by H2O2 in aqueous solution

The reduction of I2 by hydrogen peroxide, a primary water radiolysis product, has been identified as a key reaction that would influence iodine volatility in nuclear reactor accident conditions (1–3). Although there have been a number of studies of the reduction of I2, there exists a great degree of controversy regarding the intermediates involved, the effect of buffers, and the general rate law (1–9). Because the rates and the mechanism of this reaction are important in predicting the pH dependence of iodine behaviour in reactor containment building after a postulated reactor accident, we have undertaken a kinetic study of I2 reduction by H2O2 in aqueous solution over a pH range of 6–9. The experiments were performed using stopped-flow instrumentation and monitoring the decay of I–3 spectrophotometrically. The effects of buffer catalysis have been examined by comparison of kinetic data obtained in sodium barbital (5,5-diethylbarbituric acid), disodium citrate, and disodium hydrogen phosphate buffers. The effect of buffers, combined with the complex acid dependence of the rate law, explains many of the discrepancies reported in earlier literature.Key words: hydrogen peroxide, molecular iodine, kinetics, iodine volatility.

Interfacial Recombination Processes in Dye-Sensitized Solar Cells and Methods To Passivate the Interfaces

Conventional dye-sensitized solar cells function efficiently only with a single redox couple, I-/I2, because of the unusually slow kinetics for I2 reduction on SnO2 and TiO2 surfaces. When faster redox couples such as ferrocene/ferrocenium are employed, the rapid interfacial recombination of photoinjected electrons with the oxidized half of the redox couple eliminates the photovoltaic effect. To make use of other, perhaps more appropriate, redox couples in these cells, the interfacial recombination processes must be understood and controlled. Charge recombination at the SnO2/solution interface is clearly distinguishable from recombination at the nanoporous TiO2/solution interface. Dark current measurements probe mainly the former reaction, although the latter may be the dominant recombination mechanism under illumination. We introduce two methods for passivating the interfaces that decrease the recombination rates by orders of magnitude. One method involves electropolymerization of an insulating film of p...

Dye Sensitization of Nanocrystalline Titanium Dioxide with Osmium and Ruthenium Polypyridyl Complexes

A series of osmium polypyridyl complexes having various ground-state reduction potentials has been synthesized and used to sensitize nanoporous titanium dioxide electrodes to solar illumination. The spectral response and current vs potential properties of electrodes modified with these dyes have been compared with the behavior of their ruthenium analogues. The trends can be explained by the differences in absorption spectra and ground-state redox potentials. The osmium complexes appear to be promising candidates for further optimization in operating photoelectrochemical cells for solar energy conversion applications. Of the materials studied, all complexes having ground-state redox potentials in methanol more positive than ∼0.4 V vs aqueous SCE were able to sustain oxidation of I-/I3- with a high steady-state quantum yield. For electrodes with very low dye coverages, the open-circuit voltage was mainly determined by the rate of reduction of I2, whereas for high dye coverages, the open-circuit voltage depended on the nature of the complex and on the dye loading level.

ヨウ化カリウム浴からの銀めっきの電流効率に及ぼすＩ２の影響

I2 effects on silver deposition current efficiency were investigated using a potassium iodide bath. Cathodic polarization curves in the I2 bath and Pt electrode rest potential in the aged KI solution were measured to clarify the I2 reduction mechanism.The following results were obtained:(1) In the lower pH range, I2 concentration in the bath increases with time in the presense of air according to equation (i):4H++4I-+O2_??_2I2+2H2O……(i)(2) Silver deposition current efficiency decreased as I2 increased in the bath. This suggests that I3- is reduced in agreement with equation (ii) as silver is deposited:I3-+2e-→3I-……(ii)