Halide Concentration Research Articles

Enhanced Efficiency of Hot‐Cast Large‐Area Planar Perovskite Solar Cells/Modules Having Controlled Chloride Incorporation

Organic–inorganic perovskite photovoltaics are an emerging solar technology. Developing materials and processing techniques that can be implemented in large‐scale manufacturing is extremely important for realizing the potential of commercialization. Here we report a hot‐casting process with controlled Cl− incorporation which enables high stability and high power‐conversion‐efficiencies (PCEs) of 18.2% for small area (0.09 cm2) and 15.4% for large‐area (≈1 cm2) single solar cells. The enhanced performance versus tri‐iodide perovskites can be ascribed to longer carrier diffusion lengths, improved uniformity of the perovskite film morphology, favorable perovskite crystallite orientation, a halide concentration gradient in the perovskite film, and reduced recombination by introducing Cl−. Additionally, Cl− improves the device stability by passivating the reaction between I− and the silver electrode. High‐quality thin films deployed over a large‐area 5 cm × 5 cm eight‐cell module have been fabricated and exhibit an active‐area PCE of 12.0%. The feasibility of material and processing strategies in industrial large‐scale coating techniques is then shown by demonstrating a “dip‐coating” process which shows promise for large throughput production of perovskite solar modules.

Electrochemical dissolution of gold in presence of chloride and bromide traces studied by on-line electrochemical inductively coupled plasma mass spectrometry

Electrochemical dissolution of gold in the presence of halide ions is traditionally considered as a model case in metal corrosion and passivation studies. Due to a relatively low sensitivity of the conventional techniques, such studies were predominantly limited to electrolytes with high concentrations of halides. The current work employs a special electrochemical scanning flow cell with online inductively coupled plasma mass spectrometry (SFC-ICP-MS) that allows overcoming those limitations, enabling the quantification of gold dissolution in the presence of chloride and bromide traces (1μM≤[Cl−/Br−]≤100μM). Moreover, time- and potential-resolved gold dissolution profiles under different potential programs are provided. Based on the experimental results, a tentative mechanism of gold dissolution based on the catalyzing role of hydroxyl and halide anions is discussed.

Reemission of elemental mercury and mercury halides in wet flue gas desulfurization

The wet flue gas desulfurization process enables the removal of sulfur dioxide (SO2) and water soluble mercury compounds (e.g. HgCl2) from coal derived flue gas. The aim of this study is to improve the state of science about subsequent processes in the liquid phase of the slurry, leading to the undesired reemission of mercury. For that purpose, experiments are carried out on a continuously operated lab-scale wet flue gas desulfurization test-rig. The parameters investigated include slurry temperature, pH-value, individual halide concentration and slurry aeration flow rate. The results indicate that the reemission of elemental mercury results from the chemical reduction of dissolved oxidized mercury species with sulfite being the reducing agent. For increased slurry temperature and within individual concentration ranges of the halides bromide and iodide, simultaneous desorption of both, elemental mercury and oxidized mercury compounds into the clean gas is observed. The underlying mechanism is proposed to be the formation of the volatile uncharged oxidized mercury species HgBr2 and HgI2 respectively. Reemissions of both elemental and oxidized mercury species decrease with decreasing temperature and increasing share of charged halogenidomercurate(II)-complexes. Formation constants, inert redox character and volatility of halogenidomercurate(II)-complexes increase in the order Cl−<Br−<I−.

Strong Correlations Between Structural Order and Passive State at Water-Copper Oxide Interfaces

Fundamental understanding of coupled electrochemical processes at metal-oxide/aqueous media interfaces, e.g., interfacial structure evolution, metal dissolution, and solvation dynamics at the atomic level are of immense interest to corrosion research, surface chemistry, and electrochemistry in general. Using reactive force field (ReaxFF) molecular dynamics (MD) simulations of CuOx passive thin film on Cu substrate, we investigated the impact of non-stoichiometry of passive oxide film on its breakdown, and aqueous corrosion (in sea water) of the underlying copper. Upon exposure to aqueous media (halide concentration similar to seawater), we find that halide ions adsorb on to the passive oxide layer, and cause dissolution of Cu atoms via formation of water-soluble Cu-halide complexes; eventually, this results in the breakdown of the passive oxide layer, and consequently leads to corrosion of underlying Cu. Our MD simulations indicate that oxygen rich CuOx films show enhanced resistance to breakdown via impeding halide ion adsorption as well as metal dissolution; for instance, increasing oxygen stoichiometry from 0.2 to 0.79 causes by halide adsorption to drop by half. Thus, O-rich Cu-oxide films provide better corrosion resistance than O-deficient ones. Interestingly, we find that high O-content in the oxide film promotes ordering of water molecules at the water/oxide interface leading to 2D “ice-like” layers. These ordered water layers inhibit the adsorption of halide ions via a phenomenon similar to brine rejection. These findings clearly indicate the oxygen stoichiometry, dissolution kinetics, and solvation dynamics at the water/oxide interface are strongly correlated to each other [Narayanan et al. Electrochimica Acta 179, 386 (2015)]. To validate the predictions of theory, and to probe the initiation of pits during aqueous corrosion of Cu, we employ coherent x-ray diffraction imaging. This imaging technique coupled with large scale molecular dynamics simulations identify localized strain fields that arise in the Cu nanoparticles; this in turn, provides atomic scale insights into pit formation during aqueous corrosion.

Observation of Enhanced Hole Extraction in Br Concentration Gradient Perovskite Materials.

Enhancing hole extraction inside the perovskite layer is the key factor for boosting photovoltaic performance. Realization of halide concentration gradient perovskite materials has been expected to exhibit rapid hole extraction due to the precise bandgap tuning. Moreover, a formation of Br-rich region on the tri-iodide perovskite layer is expected to enhance moisture stability without a loss of current density. However, conventional synthetic techniques of perovskite materials such as the solution process have not achieved the realization of halide concentration gradient perovskite materials. In this report, we demonstrate the fabrication of Br concentration gradient mixed halide perovskite materials using a novel and facile halide conversion method based on vaporized hydrobromic acid. Accelerated hole extraction and enhanced lifetime due to Br gradient was verified by observing photoluminescence properties. Through the combination of secondary ion mass spectroscopy and transmission electron microscopy with energy-dispersive X-ray spectroscopy analysis, the diffusion behavior of Br ions in perovskite materials was investigated. The Br-gradient was found to be eventually converted into a homogeneous mixed halide layer after undergoing an intermixing process. Br-substituted perovskite solar cells exhibited a power conversion efficiency of 18.94% due to an increase in open circuit voltage from 1.08 to 1.11 V and an advance in fill-factor from 0.71 to 0.74. Long-term stability was also dramatically enhanced after the conversion process, i.e., the power conversion efficiency of the post-treated device has remained over 97% of the initial value under high humid conditions (40-90%) without any encapsulation for 4 weeks.

Multifold Increases in Turing Pattern Wavelength in the Chlorine Dioxide-Iodine-Malonic Acid Reaction-Diffusion System.

Turing patterns in the chlorine dioxide-iodine-malonic acid reaction were modified through additions of sodium halide salt solutions. The range of wavelengths obtained is several times larger than in the previously reported literature. Pattern wavelength was observed to significantly increase with sodium bromide or sodium chloride. A transition to a uniform state was found at high halide concentrations. The observed experimental results are qualitatively well reproduced in numerical simulations with the Lengyel-Epstein model with an additional chemically realistic kinetic term to account for the added halide and an adjustment of the activator diffusion rate to allow for interhalogen formation.

Crystalline Mixed Halide Halobismuthates and Their Induced Second Harmonic Generation

Mixed halide coordination has been widely used to finely tune the properties of inorganic and inorganic–organic hybrid compounds, especially for emerging perovskites materials. Despite the increasing number of reports on preparation methods and the affected functionalities, the peculiar and precise role of the doping halogens in structural regulation of the crystals and the resulting variations on the basic properties remain to be addressed. Here, to shed light into the “black box”, a new series of [NH2(CH2CH3)2]3Bi(Cl1–xBrx)6 (x = 0, 0.135, 0.255, 0.385, 0.847, and 1) single crystals were grown from the mixed halide solvents by the temperature lowering method. The correlation between the inclusion amounts of Br in the final crystals with the halide concentrations in the precursors is discussed from different perspectives. The two kinds of halogens share the same position in the mixed halide system, with every crystallographically independent halide site possessing different halogen occupancies. The mixed...

Using Perovskite Nanoparticles as Halide Reservoirs in Catalysis and as Spectrochemical Probes of Ions in Solution.

The ability of cesium lead halide (CsPbX3; X = Cl(-), Br(-), I(-)) perovskite nanoparticles (P-NPs) to participate in halide exchange reactions, to catalyze Finkelstein organohalide substitution reactions, and to colorimetrically monitor chemical reactions and detect anions in real time is described. With the use of tetraoctylammonium halide salts as a starting point, halide exchange with the P-NPs was performed to calibrate reactivity, stability, and extent of ion exchange. The exchange of CsPbI3 with Cl(-) or Br(-) causes a significant blue-shift in absorption and photoluminescence, whereas reacting I(-) with CsPbBr3 causes a red-shift of similar magnitudes. With the high local halide concentrations and the facile nature of halide exchange in mind, we then explored the ability of P-NPs to catalyze organohalide exchange in Finkelstein like reactions. Results indicate that the P-NPs serve as excellent halide reservoirs for substitution of organohalides in nonpolar media, leading to not only different organohalide products, but also a complementary color change over the course of the reaction, which can be used to monitor kinetics in a precise manner. The merits of using P-NP as spectrochemical probes for real time assaying is then expanded to other anions which can react with, or result in unique, classes of perovskites.

Employing vibrational spectroscopy to confirm the catalytic activity of Ce(III) and Cr(III) towards amide bond cleavage

The dependence of the Ce(III) and Cr(III) halide concentration on the spectrum of formamide is investigated for the first time. The downshifts observed for the νCO mode in the IR spectra and the upshifts of the νCN vibration in the Raman spectra are consistent with the stabilization of the HO−CN+H2 form, which is directly involved in the amide bond cleavage reaction. The νCN region was used for the quantitative treatment and reveals that Ce(III) is surrounded by 8 formamide molecules, in a square prismatic arrangement, while 4 formamide molecules are around Cr(III) and the counter-ion occupies two vertices of the octahedron in the cis-configuration. The spectral changes in the region of the solvent are in excellent agreement with those observed for the metal-ligand vibrations.

Early stages of tin bronze corrosion in neutral aqueous chloride media: Electrochemical and FTIR investigations

The corrosion behavior of tin bronze alloy equivalent to a Punic one was investigated in aqueous 0.5 M chloride electrolyte using potentiodynamic measurements. The electrochemical results showed selective dissolution of the major alloy component reflecting a decuprification process. FTIR characterization of the patina anodic layers showed the presence of various dehydrated and hydrated tin compounds with a few copper species suggesting the patina type I formation on the Cu10Sn bronze alloy. A kinetic model for the Cu10Sn bronze alloy dissolution in the chloride solution was developed. The reaction order with respect to chloride content was determined for the Cl− halide concentration domains. The low order value (about 0.22) was attributed to the Cl− adsorption intermediate step. The high reaction order value (about 2) reflected two determining steps of cuprous chloride complex formation. Two behaviors for the material were evidenced when varying the temperature. The values of the activation energy Ea, activation enthalpy ΔH* and activation entropy ΔS* were calculated and discussed.

Relation between Overall Rate of ATRP and Rates of Activation of Dormant Species

The rate of atom transfer radical polymerization (ATRP) depends on the rate constant of propagation (kp) and concentration of growing radicals. The latter is related to the ATRP equilibrium constant (KATRP) and concentrations of alkyl halides, activators, and deactivators. Activation of alkyl halides by CuI/L and deactivation of radicals by X–CuII/L are vital processes providing good control in ATRP. Rates of these reactions are typically identical throughout polymerization, since the ATRP equilibrium is maintained in essentially all ATRP systems. There are new ATRP processes carried out with ppm of Cu catalysts, such as activators regenerated by electron transfer (ARGET), initiators for continuous activator regeneration (ICAR), supplemental activators and reducing agents (SARA), and electrochemically or photochemically mediated ATRP (eATRP, photoATRP). In these processes, as in conventional radical polymerization (or in RAFT), concentration of radicals is established by balancing rates of radical generat...

Cesium Lead Halide Perovskites with Improved Stability for Tandem Solar Cells.

A semiconductor that can be processed on a large scale with a bandgap around 1.8 eV could enable the manufacture of highly efficient low cost double-junction solar cells on crystalline Si. Solution-processable organic-inorganic halide perovskites have recently generated considerable excitement as absorbers in single-junction solar cells, and though it is possible to tune the bandgap of (CH3NH3)Pb(BrxI1-x)3 between 2.3 and 1.6 eV by controlling the halide concentration, optical instability due to photoinduced phase segregation limits the voltage that can be extracted from compositions with appropriate bandgaps for tandem applications. Moreover, these materials have been shown to suffer from thermal degradation at temperatures within the processing and operational window. By replacing the volatile methylammonium cation with cesium, it is possible to synthesize a mixed halide absorber material with improved optical and thermal stability, a stabilized photoconversion efficiency of 6.5%, and a bandgap of 1.9 eV.

Influence of Halide Ions on Anodic Oxidation of Ethanol on Palladium

Ethanol oxidation on polycrystalline palladium electrodes in alkaline media was studied in the presence of halide ions. Addition of halide ions decreased the ethanol oxidation peak current monotonically as a function of increasing halide concentration. The extent of poisoning was found to be in the order I− > Br− > Cl−. Thus, Cl− ions show appreciable inhibition of ethanol oxidation peak current at [Cl−] ~ 10−3 M, whereas Br− and I− inhibit ethanol oxidation even at [Br−] or [I−] ~ 10−6 M. The potential of the ethanol oxidation peak shifted positive with increasing halide ion concentration. The extent of the shift was found to be in the order I− > Br− > Cl−. This study is relevant due to the widespread use of palladium halide complexes in the production of Pd electrocatalysts for ethanol oxidation and other electrocatalytic reactions.

All-inorganic cesium lead halide perovskite nanocrystals for photodetector applications.

Herein, we describe simple, fast and reproducible halide ion exchange reactions in CsPbX3 (X = Cl, Br, I) nanocrystals (NCs) at room temperature. Through the simple adjustment of the halide ion concentration, the photoluminescence of these NCs can be tuned over the entire visible region (425-655 nm). Photodetector devices based on entirely inorganic CsPbI3 NCs are demonstrated for the first time. The photodetectors exhibited a good on/off photocurrent ratio of 10(5).

A yolk–shell structured Pd@void@ZrO2 catalyst for direct synthesis of hydrogen peroxide from hydrogen and oxygen

In this study, we prepared a yolk–shell structured Pd@void@ZrO2 catalyst and tested its activity in direct hydrogen synthesis from hydrogen and oxygen. The catalyst was prepared by first encapsulating the nano Pd crystal with SiO2 and then, the Pd core–silica shell composite (Pd@SiO2) was encapsulated again with ZrO2 (Pd@SiO2@ZrO2). The yolk–shell structure was obtained by etching the silica layer of Pd@SiO2@ZrO2 using 0.2M KOH solution. Compared to the core–shell structured Pd@SiO2, the void space in the yolk–shell structure allowed more gases to access the core Pd surface. In reaction tests, the production rate of gram Pd-specific H2O2 with Pd@void@ZrO2 was approximately 1.2 times higher than with Pd@SiO2. It was found that the optimum level of halide ion concentration in the reaction medium was between 0.1 and 0.3mM for Pd@void@ZrO2 catalyst.

Removal of Chlorine and Chlorinated Organic Compounds from Aqueous Media Using Substrate-Anchored Zero-Valent Bimetals

Chlorine added to drinking water as a disinfectant is a concern of this generation. This is because chlorine reacts with dissolved organic compounds to form polychlorinated complexes that are carcinogenic. Available methods for the removal of chlorine and chlorinated compounds include adsorption, precipitation, electrolysis and ozonation, but some result in the generation of more toxic compounds. This study explored the use of zero-valent bimetals Fe/Zn for the degradation of chlorinated compounds in water which did not generate toxic by-products. The zero-valent bimetallic material was anchored on a polystyrene waste material as a green method of cleaning the environment. It was prepared through nitration, amination, complexation and reduction. The resulting solid material was characterised using Fourier transform infrared (FTIR). The material was also characterised using XPS which confirmed the presence of metals anchored on the material through complexation. The metals were also found to be present upon reduction to zero valence and even after the degradation process of the chlorinated organic compounds. It was then applied for the removal process. Optimization parameters such initial halide concentration, effect of time and bimetal dosage variation were established using synthetic water samples. It was found that the substrate-anchored ZVB material had a degradation capacity of 4.532, 5.362 and 4.513 μmol l−1 for 1,2-dichloroethane, 2-chloro-2-methylpropane and 1-chlorobutane, respectively. The material was then applied on real samples sourced from Nairobi. Quantification of chlorine was done using potentiometric methods and the results confirmed that the degradation was first order. The degradation capacities were found to be 2.37 ± 0.01, 3.55 ± 0.01 and 3.72 ± 0.01 in that order.

Comparison of UV/hydrogen peroxide and UV/peroxydisulfate processes for the degradation of humic acid in the presence of halide ions.

This study compared the behaviors of two classic advanced oxidation processes (AOPs), hydroxyl radical-based AOPs ((•)OH-based AOPs) and sulfate radical-based AOPs (SO4 (•-)-based AOPs), represented by UV/ hydrogen peroxide (H2O2) and UV/peroxydisulfate (PDS) systems, respectively, to degrade humic acid (HA) in the presence of halide ions (Cl(-) and Br(-)). The effects of different operational parameters, such as oxidant dosages, halide ions concentration, and pH on HA degradation were investigated in UV/H2O2/Cl(-), UV/PDS/Cl(-), UV/H2O2/Br(-), and UV/PDS/Br(-) processes. It was found that the oxidation capacity of H2O2 and PDS to HA degradation in the presence of halides was nearly in the same order. High dosage of peroxides would lead to an increase in HA removal while excess dosage would slightly inhibit the efficiency. Both Cl(-) and Br(-) would have depressing impact on the two AOPs, but the inhibiting effect of Br(-) was more obvious than that of Cl(-), even the concentration of Cl(-) was far above that of Br(-). The increasing pH would have an adverse effect on HA decomposition in UV/H2O2 system, whereas there was no significant impact of pH in UV/PDS process. Furthermore, infrared spectrometer was used to provide the information of degraded HA in UV/H2O2/Cl(-), UV/PDS/Cl(-), UV/H2O2/Br(-), and UV/PDS/Br(-) processes, and halogenated byproducts were identified in using GC-MS analysis in the four processes. The present research might have significant technical implications on water treatment using advanced oxidation technologies.

Comparing a silver-impregnated activated carbon with an unmodified activated carbon for disinfection by-product minimisation and precursor removal

During disinfection, bromide, iodide and natural organic matter (NOM) in source waters can lead to the formation of brominated and/or iodinated disinfection by-products (DBPs), which are often more toxic than their chlorinated analogues. The objective of this study was to compare the efficiency of a silver-impregnated activated carbon (SIAC) with the equivalent unimpregnated granular activated carbon (GAC) for the removal of bromide, iodide and NOM from a matrix of synthetic waters with variable NOM, halide, and alkalinity concentrations, and to investigate the impact on DBP formation. An enhanced coagulation (EC) pre-treatment was employed prior to sample exposure to either carbon adsorbent. Excellent halide removals were observed by the SIAC treatment across the sample matrix, with iodide concentrations consistently reduced to below the method reporting limit (<2μg/L) from as high as 25μg/L, and 95±4% removal of bromide achieved. Bromide removal by unimpregnated GAC was poor, however iodide removal was comparable to that achieved by SIAC. The combination of EC with SIAC treatment removed 77±8% of the dissolved organic carbon (DOC) present, across the sample matrix, which was similar to removals by EC/GAC (67±14%). Combined EC/SIAC treatment reduced both total trihalomethanes (tTHMs) and total dihaloacetonitriles (tDHANs) formation by 97±3%, while also achieving a greater than 74% removal of two chloropropanones and a 92±8% decrease in chloral hydrate (CH), compared to untreated samples, regardless of the sample's starting water quality (bromide, alkalinity and NOM concentration). Combined EC/GAC treatment led to similar DBP removals to EC/SIAC for the fully chlorinated DBPs, however, brominated DBPs were less efficiently removed, or experienced concentration increases.

The impact of commercially treated oil and gas produced water discharges on bromide concentrations and modeled brominated trihalomethane disinfection byproducts at two downstream municipal drinking water plants in the upper Allegheny River, Pennsylvania, USA

In 2010, a dramatic increase in the levels of total trihalomethane (THM) and the relative proportion of brominated species was observed in finished water at several Pennsylvania water utilities (PDW) using the Allegheny River as their raw water supply. An increase in bromide (Br−) concentrations in the Allegheny River was implicated to be the cause of the elevated water disinfection byproducts. This study focused on quantifying the contribution of Br− from a commercial wastewater treatment facility (CWTF) that solely treats wastes from oil and gas producers and discharges into the upper reaches of the Allegheny River, and impacts on two downstream PDWs. In 2012, automated daily integrated samples were collected on the Allegheny River at six sites during three seasonal two-week sampling campaigns to characterize Br− concentrations and river dispersion characteristics during periods of high and low river discharges. The CWTF discharges resulted in significant increases in Br− compared to upstream baseline values in PDW raw drinking water intakes during periods of low river discharge. During high river discharge, the assimilative dilution capacity of the river resulted in lower absolute halide concentrations, but significant elevations Br− concentrations were still observed at the nearest downstream PDW intake over baseline river levels. On days with active CWTF effluent discharge the magnitude of bromide impact increased by 39ppb (53%) and 7ppb (22%) for low and high river discharge campaigns, respectively. Despite a declining trend in Allegheny River Br− (2009–2014), significant impacts from CWTF and coal-fired power plant discharges to Br− concentrations during the low river discharge regime at downstream PDW intakes was observed, resulting in small modeled increases in total THM (3%), and estimated positive shifts (41–47%) to more toxic brominated THM analogs. The lack of available coincident measurements of THM, precursors, and physical parameters limited the interpretation of historical trends.

Halide-Gated Molecular Release from Nanoporous Gold Thin Films

Nanoporous materials have attracted significant attention as drug delivery platforms in which interfacial phenomena are often more influential than fluid mechanics in defining molecular loading capacity and release kinetics. This study employs nanoporous gold (np-Au) as a model material system to investigate physical mechanisms of molecular release of fluorescein (a small molecule drug surrogate) from the submicron-thick np-Au coatings. Specifically, the study reveals an interfacial mechanism where halide ion–gold surface interactions dictate the loading capacity and release kinetics of fluorescein. We systematically study the effect of halide concentration and species on release kinetics from sputter-deposited np-Au films with a combination of quantitative electron microscopy, fluorospectrometry, and electrochemical surface characterization techniques. The results suggest that the interplay of halide–gold interaction probability and affinity determine the nature of release kinetics. The former mechanism ...