Electrolyte Modification Research Articles

Experimental insight into the performance characteristics of Ni-mesh semiconductor photo-electrochemical cells

The performance characteristics of two photo-electrochemical cells with different cell configurations were investigated at 25°C and within the illumination range of 70–100 W/m 2. These cells included a jacketed single cell (JSC) and a jacketed two-compartment cell (JTC). Ni-mesh was used as a counter electrode and as a backing material for semiconductor electrodes. Semiconductor electrodes were prepared by silk-screen painting technique using TiO 2, WO 3, PbO, Sb 2S 3, ZnO, Al 2O 3 or CuO powder mixed with Teflon. The electrolyte contained aqueous methylene blue (MB) and Fe (II)/Fe(III) compounds. Voltage–current characteristics of the cells were measured at 25°C. Energy conversion efficiencies were calculated. A best-performing cell was selected from each cell configuration. The effects of Ni-mesh, semiconductor properties, and electrolyte modification on cell performance were studied. Experimental observations are compared with those in the literature, and the performance of each cell configuration is discussed. The best performance was obtained from Ni–TiO 2-MB/MB, Fe(II)//MB, Fe(II)/Ni–C cell configuration with 13% efficiency from JTC, Ni-PbO/MB, Fe(II)/Ni cell configuration with 24% efficiency from JSC.

2-β-Dinitrostyrene as a cathode material in a magnesium/zinc- based primary battery

The efficiency of 2-β-dinitrostyrene as a cathode material in a magnesium/zinc-based primary battery is examined. The discharge performance of the cell is investigated under different parametric variations such as temperature, nature of electrolyte, current drain and zeolite modification. A seven-electron reduction seems to be responsible for the discharge of the cell. The end-of-discharge product is anthranilic acid. Participation of oxygen in the reduction process is indicated. The chemical reaction responsible for discharge involves electroreductive cyclization of 2-β-dinitrostyrene to indole, which is further converted into anthranilic acid by oxygen.

2-Nitrophenylpyruvic acid as a cathode material in a magnesium/zinc-based primary battery

The efficiency of 2-nitrophenylpyruvic acid as a cathode material in a magnesium/zinc based primary battery is examined. The discharge performance of the cell is investigated under different parametric variations such as temperature, nature of electrolyte, current drain and zeolite modification. A 7e reduction seems to be responsible for the electrochemical reaction causing the reduction of 2-nitrophenylpyruvic acid to an indole intermediate which is oxidatively cleaved to form anthranilic acid as the end-of-discharge product. Participation of oxygen in the reduction process is indicated. The discharge capacity is 1.03 Ah g−1, the highest value ever observed in organic batteries.

Effect of Electrode and Electrolyte Modification on the Performance of One‐Chamber Solid Oxide Fuel Cell

A one‐chamber solid oxide fuel cell (working in a methane‐air mixture) with yttria‐stabilized zirconia (YSZ) electrolyte was modified by adding oxide to the anode (Pt) and cathode (Au). It was determined that the addition of to both electrodes significantly improved the cell discharge characteristics. The short‐circuit current density of a cell using 15 wt % added to the Pt and 20 wt % added to the Au was about 50 times larger than that of a cell using Pt and Au electrodes. Moreover, the cell performance was enhanced further when 1 wt % was doped into the YSZ electrolyte. Microstructural observations of the YSZ electrolyte/electrodes interfaces indicated that both the electrode porosity and the contact areas between electrodes and YSZ electrolyte increased markedly for the Pt and Au electrodes. In addition, the electrocatalytical property of added in the electrodes may also contribute to the improved cell performance. © 1999 The Electrochemical Society. All rights reserved.

Competitive Intermolecular Energy Transfer and Electron Injection at Sensitized Semiconductor Interfaces

Sensitization of nanocrystalline TiO{sub 2} electrodes with molecular chromophores forms the basis for efficient solar energy conversion in regenerative photoelectrochemical cells. The study of interfacial electron-transfer dynamics in these solar cells is an area of intense and active investigation. The nanocrystalline materials also have the potential to act as supports for molecular reagents and could increase the efficiency of reactions that are otherwise limited by diffusive encounters in fluid solution. The ability to photoinduce interfacial electron transfer coupled with exploitation of lateral reaction chemistry will produce materials that have applications that extend beyond solar energy conversion. Here the authors report an unprecedented example of molecular excited states that can be switched from lateral energy transfer across a nanocrystalline TiO{sub 2} surface to orthogonal interfacial electron injection by electrolyte modification or with an externally applied potential. Significantly, the process is reversible and serves as a molecular charge-energy transfer switch.

CO2/ SOx-sensors with different β“-aluminas as solid electrolytes

Sensors with solid electrolytes provide the possibility of correct and fast measurements of partial pressures of various gases. By modification of the solid electrolyte, sensors with specific performances may be manufactured. Layers of Na+-, Li+-, Ca2+- and Sr2+-β“-alumina on top of polycrystalline α-alumina substrates were produced by an in-situ formation process and were used as solid electrolytes for CO2 and SOx sensors. Carbonates and sulphates were applied as measuring electrodes and oxidic mixtures of SiO2 and silicates were used as reference electrodes. The different performance of these sensors was investigated over a wide temperature range and the results were compared with theoretical data. Different solid electrolyte / electrode combinations were applied, which all showed different characteristic cross sensitivities against water and organic components.

Electrolytic modification of a buffer during a capillary electrophoresis run

The electrolyte composition and pH changes in the electrode reservoirs caused by the electric current in a capillary electrophoresis system are analyzed. Parameters determining the pH, electric conductivity and the ionic strength variations are the initial electrolyte composition, applied voltage, the capillary dimensions, volume of the reservoirs, and the electroosmotic flow. Equations for the pH and molarities of the electrolyte components as functions of time are derived. Experimentally measured pH shifts in the electrode reservoirs are in good agreement with the predicted values. The time interval after which the electrode buffer needs to be replenished is determined as a function of the electric field strength, mobilities of the buffer ions, capillary cross-section and volume of the buffer in the reservoir.

Modification of LiCl-LiBr-KBr Electrolyte for LiAl/FeS2 Batteries

The bipolar LiAl/FeS{sub 2} battery is being developed to achieve the high performance and long cycle life needed for electric vehicle application. The molten-salt (400 to 440 C operation) electrolyte composition for this battery has evolved to support these objectives. An earlier change to LiCl-LiBr-KBr electrolyte is responsible for significantly increased cycle life (up to 1,000 cycles). Recent electrolyte modification has significantly improved cell performance; approximately 50% increased power, with increased high rate capacity utilization. Results are based on power-demanding EV driving profile test at 600 W/kg. The effects of adding small amounts (1--5 mol%) of LiF and LiI to LiCl-LiBr-KBr electrolyte are discussed. By cyclic voltammetry, the modified electrolytes exhibit improved FeS{sub 2} electrochemistry. Electrolyte conductivity is little changed, but high current density (200 mA/cm{sup 2}) performance improved by approximately 50%. A specific feature of the LiI addition is an enhanced cell overcharge tolerance rate from 2.5 to 5 mA/cm{sup 2}. The rate of overcharge tolerance is related to electrolyte properties and negative electrode lithium activity. As a result, the charge balancing of a bipolar battery configuration with molten-salt electrolyte is improved to accept greater cell-to-cell deviations.

Blood volume regulating hormones, fluid and electrolyte modifications during 21 and 198-day space flights (Altair-MIR 1993)

During the Altair MIR' 93 mission we studied several parameters involved in blood volume regulation. The experiment was done on two cosmonauts before (B-60, B-30), during (D6, D12, D18 for French and D7, D12, D17 for Russian) and after the flight (R+1, R+3 and R+7). Space flight durations were different for two cosmonauts: for the Russian the flight duration was 198 days and for the French 21 days. On board the MIR station only urinary (volume and electrolytes, atrial natriuretic peptide (ANP), cyclic guanosine monophosphate (cGMP) and catecholamines) and salivary (cGMP and cortisol) samples were collected, centrifuged and stored in freezer. Lithium was used as a tracer to know exactly the 24 h urine output (CNES urine collection Kit). Before and after flight, blood was drawn with an epicite needle and vacutainer system for hormonal assays (renin, antidiuretic hormone, cGMP, ANP and aldosterone) in two positions: after 30 min rest in upright seated position and after 90 min of supine position. Salivary samples were collected simultaneously. During flight a decrease of diuresis and ANP and an increase of osmolality were found. No modifications of hematocrit, but an increase of salivary cGMP and cortisol were also observed. The decrease of urinary ANP is in favor of hypovolemia as described in previous flights. The postflight examinations revealed changes in fluid-electrolyte metabolism which indicate a hypohydration status and a stimulation of hormonal system responsible for water and electrolyte retention in order to readapt to the normal gravity.

Effect of electrolyte composition in the capillary electrophoretic separation of inorganic/organic anions in the presence of cationic polymers

Abstract Electrolyte modification with two cationic polyelectrolytes has been investigated for the separation of inorganic anions, aliphatic and aromatic carboxylic acids, and sulphonic acids. Changes in migration rates and separation selectivity, arising from hydrophobic interactions, ion exchange, and changes in electroosmotic flow were studied for benzoate, chromate and phosphate + chloride counter-ions as a function of pH, and for the addition of methanol and acetonitrile. Large changes in separation selectivity, for aliphatic and sulphonic acids, were observed with benzoate electrolytes as compared to chromate electrolytes. In addition, electroosmotic flow was faster in the former separation electrolytes by about 65%. Changes in selectivity as a result of hydrophobic interactions were investigated with a series of aromatic acids where shifts in migration order were observed as function of polyelectrolyte concentration. For inorganic anions, in chromate electrolytes at a constant concentration of polyelectrolyte, the addition of methanol or acetonitrile decreased migration rates by as much as 67%. The analytical merits of the methodology were examined for a potash (concentrated KCl) sample and a simulated decontamination solution containing EDTA, Fe 3+ (EDTA) and oxalate.

Solution aspects of photoelectrochemistry

studies on polysulfide, ferrocyanide, polyselenide and polyiodide electrolyte modification of photoelectrochemical solar cells were presented

Electrolyte modified photoelectrochemical solar cells

Rationale electrolyte modification of photoelectrochemical systems can be used to (i) enhance facile charge transfer, (ii) suppress competing reactions and suppress both (iii) electrode and (iv) electrolyte decomposition products, as well as (v) substantially effect the open-circuit photovoltage. Studies on polysulfide, ferrocyanide, polyselenide and polyiodide electrolyte modification of photoelectrochemical solar cells are discussed. Electrolyte modification of semiconductor/electrolyte systems entails investigation of the primary photo-re-dox species, the nature of the counter ion, the distribution of species in solution, and related competing reactions. The examples presented emphasize the fundamental and practical importance of probing the active electrolytic constituents pertinent to overall photoelectrochemical energy conversion.

Modification of Solid Polymeric Electrolytes from PEO-Nal System by the Addition of Finely Dispersed Aluminum Powder

Modification of Solid Polymeric Electrolytes from PEO-Nal System by the Addition of Finely Dispersed Aluminum Powder

Novel photochemical/photoelectrochemical systems based on metal hexacyanoferrates

Abstract Electrolyte modification is realized to be a promising route to achieve better efficiencies in solar energy conversion in photoelectrochemical cells. Recent reports by Bocarsly et al. [1,2] and Licht et al. [3,4] have amply demonstrated this aspect wherein maximum efficiency received so far viz. 16.4% has been reported using chalcogenides of Cd as semiconductors in contact with a solution of a mixture of ferro/ferricyanide containing added cyanide ions. Surface modification of the semiconductor, cadmium sulphide/selenide, that takes place as a result of interaction with the redox, giving rise to cadmium hexacyanoferrate, has been considered important in yielding the improved energy efficiency. But interestingly, no attempt to ascertain the role of modifying hexacyanoferrate film formed as a possible photo-energy converter (also) has been made. Many metal hexacyanoferrates themselves semiconductors, being intervalent compounds, are subjects of intensive current research as they hold promise in several applications of sensors, electrochromic devices, catalysis, and most importantly in photo-energy conversion. In this context we report the results of photoresponse studies on indium hexacyanoferrate films on conducting carbon in contact with solutions of Fe(CN) −3 6 . We conclude from these studies that such interfaces under light irradiation indeed give rise to measurable and significant photocurrents whose nature is distinctly different from that obtained in the absence of a redox in solution. The article describes the observations and explains them taking into account photo/photoelectrochemical effects.

Ligand, cation and speciation effects on [formula omitted] photoelectrochemistry

Electrolyte modification is shown to have a substantial effect on the understanding and optimization of nCdSe ferricyanide photoelectrochemical solar cells. A series of pentacyanoferrate(II) complexes, [Fe(CN) 5L] 3− aqueous are prepared (L = CN −, NH 3, (CH 3) 2SO, H 2O, NO +, NO 2 − and Fe(CN 5 3−), and their substantial variation in photoelectrochemical activities at n-CdSe are correlated to their spectral and electrochemical properties. Investigation into ferro ferricyanide speciation showed that in the alkaline pH region where ferrocyanides are most photoelectroactive, monocation ferrocyanide and ferricyanide species dominate, MFe(CN) 6 3−/2−. These cation derivatives ( M = Mg 2+, Ca 2+, Li +, Na +, K +, Cs +, NH 4 +) are varied, and the potassium derivative was shown to result in both high photopotentials and facile kinetics.

Two-dimensional electrophoresis of basic proteins with equilibrium isoelectric focusing in carrier ampholyte-pH gradients.

A modified procedure for the two-dimensional electrophoretic analysis of basic polypeptides is described. This method uses isoelectric focusing with carrier ampholytes in the first dimension, and sodium dodecyl sulfate-electrophoresis in the second dimension. Counteraction of the cathodic drift is achieved by glass tube treatment (silanization), electrolyte modification (use of weak bases and acids), protection of the catholyte from carbon dioxide, and the addition of glycerol to the gel mix. Better resolution and reproducibility are obtained than with nonequilibrium pH gradient electrophoresis, since quasi equilibrium focusing can be obtained.

Trial of antihypertensive intervention and management: Greater efficacy with weight reduction than with a sodium-potassium intervention

The Trial of Antihypertensive Intervention and Management evaluated nine diet-drug combinations in 878 mildly hypertensive, moderately obese participants using a 3 × 3 factorial design. Drugs evaluated were placebo, diuretic (chlorthalidone), and β-blocker (atenolol); diets were usual (no intervention), weight reduction, and low sodium/high potassium (NaK). This article reports 6-month dietary changes and the effect of dietary change on blood pressure. Six-month mean weight change was −4.7 kg in the weight reduction group, −0.3 kg in the NaK group, and −0.5 kg in the usual-diet group. At 6 months, daily electrolyte excretion had changed in the NaK intervention group. Daily sodium excretion decreased from 138.0 to 112.0 mmol in the NaK group and increased from 134.1 to 138.4 mmol in the weight reduction group and from 129.1 to 137.0 mmol in the usual-diet group. Daily potassium output increased from 58.7 to 71.4 mmol in the NaK group, from 57.0 to 60.5 mmol in the weight reduction group, and from 55.3 to 59.1 mmol in the usual diet group. Analysis of 3-day food records indicated that sodium intake decreased from 141.1 to 85.8 mmol and potassium intake increased from 76.4 to 90.5 mmol. Our results indicate that the goal for weight reduction was more easily achieved than the goal for electrolyte modification.

Electrolytic Surface Modification of Copper Foil for Printed Circuit Use

Electrolytic Surface Modification of Copper Foil for Printed Circuit Use

Surface modification of solid electrolytes for gas sensors

Surface modifications allow to use fast solid ionic conductors for gas sensors without requiring the transfer of the gaseous species (or their presence as an immobile component). A mixed ionically and electronically conducting layer directs the cell reaction in such a way that both the gaseous species and the electroactive component become involved. Examples are given for Cl 2, O 2 and NO 2 partial-pressure measurements. The reaction may be controlled by kinetic parameters which leads to deviations from thermodynamically expected values. Kinetic phenomena may be employed advantageously to discriminate between several gases. Selectivity, stability ranges and response times of surface modified gas sensors are discussed.

The modification of aromatic electrolytes for electrodeposition of aluminium

With the purpose of obtaining finer-grained and more-compact aluminium coatings from aromatic solutions, the influence of some organic additives was studied. It was found that only the presence of dipyridyl (0.1–0.3 wt%) in the solution improved the coating resistance against corrosion. A small amount of SnBr2 added to the solution and the use of reverse-pulse deposition also increased the protective properties of the coatings.