A galvanic solid-state sensor for monitoring ozone and nitrogen dioxide

The sensor is based on silver and platinum electrodes with an intervening silver iodide disk as a solid electrolyte. The small disk (13 mm diameter) is easily made by pressing (7000 kg cm^-2) silver powder, silver iodide and a platinum gauze in layers in a die. The detector cell containing the disk is thermostated at 120 ± 0.1°C. When sample gas at 30 ml min^-1 impinges on the platinum cathode, the current flowing in the external circuit is linearly related to the concentration of ozone and/or nitrogen dioxide up to 0.5 ppm from the detection limit of 0.5 ppb for ozone or 1 ppb for nitrogen dioxide.     

Coulometric titration of bases in acetic acid and acetonitrile media

The working conditions and the results for coulometric titration of milligram amounts of some bases in 0.1M sodium perchlorate in a mixture of acetic acid and acetic anhydride (1:6), are given. Determinations were made both by coulometric back-titration or direct titration at the platinum anode. Back-titration was done in the catholyte, by coulometric titration of the excess of added perchloric acid. The titration end-point was detected photometrically with Crystal Violet as indicator. The direct titration of bases was done at the platinum anode, in the same electrolyte, to which hydroquinone was added as anode depolarizer and as the source of hydrogen ions, Malachite Green being used as indicator. Similarly, bases can be determined in acetonitrile if sodium perchlorate, hydroquinone and Malachite Green are added to the solvent. Errors are below 1 %, and the precision is satisfactory.     

Coulometric determination of organic substances using electrogenerated dipositive silver

Summary Conditions are described for the efficient generation of silver(II) and the titration of organic compounds by electrogenerated silver(II). An electrolyte of 0.1 M silver nitrate and 5 M nitric acid at –10°C is used, with a gold generating anode and a current density of 1.5–5 mA/cm². A potentiometric (platinum-S.C.E. pair) or biamperometric (platinum electrodes, 200 mV) end point detection is used. For potentiometric detection, the platinum electrode is preconditioned with AgO in nitric or by anodization. The compounds isoniazid, oxalyldihydrazide, hydroquinone, and resorcinol were titrated down to sub-milligram quantities with errors of 1–2%.

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Coulometrische Bestimmung von organischen Substanzen mit Hilfe von elektrolytisch erzeugtem zweiwertigem Silber

Zusammenfassung Der verwendete Elektrolyt besteht aus 0,1 M Silbernitrat in 5 M Salpetersäure bei –10°C. Die Generatoranode besteht aus Gold (Stromdichte 1,5–5 mA/cm²). Die Bestimmung des Endpunkts erfolgt potentiometrisch (Pt/SKE) oder biamperometrisch (Pt-Elektroden, 200 mV). Für die potentiometrische Bestimmung wird die Indicatorelektrode mit einer Lösung von AgO in Salpetersäure oder durch elektrochemische Anodisierung vorbehandelt. Folgende Substanzen wurden bis herab in den sub-Milligramm-Bereich mit Fehlern von 1–2% titriert: Isoniazid, Oxalyldihydrazid, Hydrochinon, Resorcin.

     

Carbon Dioxide Fixation Method for Electrosynthesis of Benzoic Acid from Chlorobenzene

Carbon dioxide fixation technique was developed as an alternative dechlorination method of chlorobenzenes.Electrolysis of chlorobenzene was carried out in a one-compartment cell fitted with an alu- minium anode and a platinum cathode.Electrolysis in N,N-dimethylformamide(DMF)solution contain- ing 0.1 M of tetrapropylammonium bromide(TPAB)at 0℃,100 ml/min of CO_2 flow rate and 120 mA/cm~2 of current density was found to be the optimum conditions of this electrocarboxylation,which gave 72% yield of benzoic acid from chlorobenzene.These conditions were then applied to 1,2-dichlorobenzene and 1,3-dichlorobenzene in order to convert them to their corresponding benzoic acids.     

Application de la methode polarovoltrique : Interprétation du dosage de L'acide maléique par des bases organiques en milieu n,n-diméthylformamide

The determination of the voltammetric curves, I=f(E), of maleic acid and of a basic titrant in N,N-dimethylformamide using 3 electrodes allowed interpretation of the polarovoltric titration curves of the neutralization of this acid by sodium methylate and tetrabutylammonium hydroxide. The different variations of the potential between 2 polarized platinum electrodes observed in such a neutralization reaction were identified and a notation was developed so that the origin of the observed potential variations could be established. The signal E_c^H+→S, which is related to the initial acidity, is given by the cathode and corresponds to a jump from the potential of the H⁺ reduction curves to that of the solvent reduction curves. The signal E_A^S→OH- characteristic of the second acidity, is given by the anode and is related to a jump from the potential of the solvent oxidation curves to that of the titrant oxidation curves.The effect of the use of unsymmetrical polarized electrodes (a rotating filament electrode and a large-surface, stationary electrode) on the shape of the titration curve was also examined: a rotating cathode gave rise to a curve resembling an inverted U, whereas a rotating anode gave rise to a curve resembling a deformed M.     

Probing phosphoric acid redistribution and anion migration in polybenzimidazole membranes

Micro platinum electrodes embedded in a laminated phosphoric acid doped polybenzimidazole membrane are employed to monitor the acid migration during hydrogen pump mode operation. Upon application of a constant current, an immediate ohmic resistance decrease of the membrane near the anode is observed, accompanied by a corresponding increase near the cathode side. This is a direct evidence of migration of the acid anions via the vehicle conducting mechanism, resulting in an accumulation of acid at the anode side and depletion at the cathode side. Both resistances reach a steady state value after a prolonged period of measurement, apparently balanced by the back diffusion of the acid molecules. The phenomenon is magnified at higher current densities and with increased thickness of the overall membrane, which is of significance in quantitative understanding of the proton conductivity mechanism e.g. for determination of the anionic transference number. The finding provides a technique to monitor the acid redistribution within the membrane as a basis for an engineering solution to address the long-term durability of fuel cells built around phosphoric acid doped polymer membranes.     

自动电位滴定法测定铜冶炼分银渣中的银量刘秋波

铜冶炼分银渣是铜阳极泥冶炼过程的副产品,但其还有一定量的银等贵金属,准备测定银的含量具有重要的意义。由于分银渣中除含有大量的银外,还含有铅、碲、铋、金、铂等元素,造成后续的处理比较复杂。本实验采用自动电位滴定法直接测定分银渣中的银量,避免了处理合粒复杂过程。实验讨论了硅酸度、氧化铅用量、杂志干扰等因素对银含量测定结果的影响。银的加标回收率在98.4%～99.3%之间,方法精密高,可满足分析检测的需要。     

An electrochemical amplification immunoassay using bi-electrode signal transduction system

An electrochemical immunoassay technique has been developed based on the sensitive detection of the enzyme-generated product with a bi-electrode signal transduction system. The system uses two separate electrodes, an immunoelectrode and a detection electrode to form a galvanic cell to implement the redox reactions on two different electrodes, that is the enzyme-generated reductant in the anode region is electrochemically oxidized by an oxidant (silver ions) in the cathode apartment. Based on a sandwich procedure, after immunoelectrode with antibody immobilized on its surface bound with the corresponding antigen and alkaline phosphatase conjugated antibody successively, the immunoelectrode was placed in enzyme reaction solution and wired to the detection electrode which was immerged into a silver deposition solution. These two solutions are connected with a salt bridge. Thus a bi-electrode signal transduction system device is constructed in which the immunoelectrode acts as anode and the detection electrode serves as cathode. The enzyme bound on the anode surface initiates the hydrolysis of ascorbic acid 2-phosphate to produce ascorbic acid in the anode region. The ascorbic acid produced in the anodic apartment is electrochemically oxidized by silver ions coupled with the deposition of silver metal on the cathode. Via a period of 30 min deposition, silver will deposited on the detection electrode in an amount corresponding to the quantity of ascorbic acid produced, leading to a great enhancement in the electrochemical stripping signal due to the accumulation of metallic silver by enzyme-generated product. Compared with the method using chemical deposition of silver, the electrochemical deposition of silver on a separate detection electrode apartment avoids the possible influence of silver deposition on the enzyme activity.     

Combining phosphate species and stainless steel cathode to enhance hydrogen evolution in microbial electrolysis cell (MEC)

Microbial electrolysis cells (MEC) must work around neutral pH because of microbial catalysis at the anode. To develop a hydrogen evolution cathode that can work at neutral pH remains a major challenge in MEC technology. Voltammetry performed at pH 8.0 on rotating disk electrodes showed that the presence of phosphate species straightforwardly multiplied the current density of hydrogen evolution, through the so-called cathodic deprotonation reaction. The mechanism was stable on stainless steel cathodes whereas it rapidly vanished on platinum. The phosphate/stainless steel system implemented in a 25 L MEC with a marine microbial anode led to hydrogen evolution rates of up to 4.9 L/h/m² under 0.8 V voltage, which were of the same order than the best performance values reported so far.     

Electroreduction of tetra-coordinate phosphonium derivatives; one-pot transformation of triphenylphosphine oxide into triphenylphosphine

Electroreduction of triphenylphosphine dichloride in acetonitrile was performed successfully in an undivided cell fitted with an aluminium sacrificial anode and a platinum cathode, wherein Al³⁺, which was electrogenerated at the anode would react as a Lewis acid with triphenylphosphine dichloride to afford tetra-coordinate chlorotriphenylphosphonium species and subsequent two-electron reduction at the cathode would give triphenylphosphine. One-pot transformation of triphenylphosphine oxide to triphenylphosphine was achieved successfully by the treatment of triphenylphosphine oxide with oxalyl chloride and subsequent electroreduction. In a similar manner, some tetra-coordinate triphenylphosphonium species derived from triphenylphosphine oxide were reduced electrochemically to triphenylphosphine in moderate yields.     

Progress in pulsed-current Karl Fischer coulometry using diaphragm-free cells

Factors influencing the accuracy of water determinations using diaphragm-free, pulsed current Karl Fischer (KF) coulometry were investigated with the new Metrohm 756 instrument. Results obtained with commercially available reagents from Riedel-deHaën and Merck were compared with home-made ones that were especially designed to minimize the formation of iodine-consuming reduction products generated in the cathode reaction. Positive errors in the range 2–5% were found for the commercial reagents as compared to 0.2–1% for the home-made ones which were buffered at about pH 10 containing modifiers like chloroform, hexanol or ethylene glycol. Except for the composition of the KF-reagent, the cathode current density and the titration rate were found to be critical parameters for the accuracy of the determinations. For all reagents investigated, the best results were obtained for the maximum generator current 400 mA (corresponding to a current density of 1400 mA cm^–2) in combination with a maximum titration rate of 2000 μg min^–1. Surprisingly, the errors found under optimum conditions for the pulse technique were always somewhat larger than the corresponding values obtained with continuous coulometry.     

Improvement in performance of a direct ethanol fuel cell: Effect of sulfuric acid and Ni-mesh

A direct ethanol fuel cell (DEFC) is developed with low catalyst loading at anode and cathode compared to that reported in the literature. Pt/Ru (40%:20% by wt.)/C and Pt-black were used as anode and cathode catalyst with loadings in the range of 0.5–1.2 mg/cm². The temperatures of anode and cathode were varied from 34 °C to 110 °C, and the pressure was maintained at 1 bar. Although low catalyst loading was used, the cell performance is enhanced by 40–50% with the use of low concentration of sulfuric acid in ethanol and Ni-mesh as current collector at the anode. The power density 15 mW/cm² at 32 mA/cm² of current density is obtained from the single cell with 0.5 mg/cm² loading of Pt–Ru/C at anode (90 °C) and Pt-black at cathode (110 °C). The performance of DEFC increases with the increase in ethanol and sulfuric acid concentrations, electrocatalyst loadings up to 1 mg cm⁻² at anode and cathode. However, the performance of DEFC decreases with further increase in electrocatalyst loading.     

Coulometric generation of molybdenum(v)

Molybdenum (V) was generated at a platinum cathode from 0.7 M molybdenum(VI) in 4 M sulfuric acid. A current efficiency of 99.9% was attained. A limiting current density of 0.05 mA/cm²/mM was found. The formal potential of the Mo(VI)–Mo(V) couple in 4 M sulfuric acid was determined to be ca. 0.55 V vs. N.H.E. Chromium(VI) solutions were titrated over a wide range of sample size and generating current. Amperometric titration curves were interpreted from current-voltage curves. Titrations could be performed in the presence of oxygen at the 1μeq. level. The effect of nitrate, perchlorate, orthophosphate, and chloride ions on the titration was determined.     

Sequential and rapid determination of Po-210, Bi-210 and Pb-210 in natural waters

A sequential and rapid separation method for the determination of radon daughter nuclides, Pb-210, Bi-210 and Po-210 has been developed for application to natural waters. Rapid separation is attained by the use of the same hydrochloric acid solution. After isolation of the three radionuclides from the sample by co-precipitation with added Fe³⁺, polonium isotopes are first spontaneously deposited onto a silver disc from a 0.5N hydrochloric acid solution. Next, bismuth isotopes are electrodeposited onto a platinum net cathode coupled with a platinum coil anode at 1.2 V. Finally, lead isotopes are electrodeposited onto a platinum net cathode at 1.8 V from the remaining solution by adding hydroxylamine hydrochloride as an anodic depolarizer. This method can be applied to meteorological precipitation samples where these three nuclides are separated within 10 hr after the sampling with chemical yields of more than 80% for Po-210 and Bi-210 and more than 70% for Pb-210. This method is applicable to other environmental water samples.     

Electrochemical microbioassay of vitamin b1

A microbioassay of vitamin B₁ is possible with a new electrode assembly consisting of a platinum anode and a silver peroxide cathode. The response time of the electrode decreases with increasing amount of the bacterial suspension (L. fermenti) injected. A linear relationship is obtained between the steady-state current and the concentration of vitamin B₁ in the culture broth. The microbioassay can be completed within 6 h, with relative errors of ±8%. A possible mechanism of the current generation is discussed.     

Oxygen is electroreduced to water on a "wired" enzyme electrode at a lesser overpotential than on platinum

The first enzyme-based catalyst that is superior to platinum in the four-electron electroreduction of oxygen to water is reported. The smooth Pt cathode reached half and 90% of the mass transport-limited current density at respective overpotentials of -0.4 and -0.58 V in 0.5 M sulfuric acid, and only at even higher overpotentials in pH 7.2 phosphate buffer. In contrast, the smooth "wired" bilirubin oxidase cathode reached half and 90% of the mass transport-limited current density at respective overpotentials as low as -0.2 and -0.25 V. The mass transport-limited current density for the smooth "wired" enzyme cathode in PBS was twice that with smooth Pt in 0.5 M sulfuric acid. Under 1 atm O2 pressure, O2 was electroreduced to water on a polished carbon cathode, coated with the "wired" BOD film, in pH 7.2 saline buffer (PBS) at an overpotential of -0.31 V at a current density of 9.5 mA cm-2. At the same overpotential, the current density of the polished platinum cathode in 0.5 M H2SO4 was 16-fold lower, only 0.6 mA cm-2.     

A Membrane-Free Neutral pH Formate Fuel Cell Enabled by a Selective Nickel Sulfide Oxygen Reduction Catalyst

Polymer electrolyte membranes employed in contemporary fuel cells severely limit device design and restrict catalyst choice, but are essential for preventing short-circuiting reactions at unselective anode and cathode catalysts. Herein, we report that nickel sulfide Ni₃S₂ is a highly selective catalyst for the oxygen reduction reaction in the presence of 1.0 m formate. We combine this selective cathode with a carbon-supported palladium (Pd/C) anode to establish a membrane-free, room-temperature formate fuel cell that operates under benign neutral pH conditions. Proof-of-concept cells display open circuit voltages of approximately 0.7 V and peak power values greater than 1 mW cm⁻², significantly outperforming the identical device employing an unselective platinum (Pt) cathode. The work establishes the power of selective catalysis to enable versatile membrane-free fuel cells.     

Voltammetry of Formaldehyde at Mechanically Renewable Solid Electrodes

The electrochemical behavior of formaldehyde (CH₂O) at solid electrodes made of platinum, gold, silver, cobalt, nickel, copper, and graphite was studied. The working surface of the electrodes was renewed by cutting a thin layer (0.5 m) immediately in the test solution. It was found that, in alkaline solutions, CH₂O was oxidized at all electrodes other than cobalt and graphite ones while scanning the potential to the anode and cathode regions. The peaks of CH₂O oxidation at platinum and gold electrodes using potential scanning in the anode and cathode directions, as well as at nickel, copper, and silver electrodes using potential scanning in the anodic direction, are suitable for analytical purposes.     

活性炭纤维电极生成羟基自由基降解酸性红B

分别采用具有吸附催化性能的活性炭纤维(ACF)作为阳极和阴极对水中偶氮染料酸性红B (ARB)的电化学降解情况进行了系统研究. 研究表明两种体系均可较好降解ARB, 可达到色度完全去除, 但ACF作为阴极电芬顿对有机物的矿化程度远远高于以ACF作为阳极时的矿化程度, 其TOC去除率达到70%, 高于阳极体系的30% TOC去除率. 通过电子自旋捕集技术(ESR)检测两种反应体系中产生的活性中间体, 发现在两种体系中均有高活性的羟基自由基生成, ACF阴极体系中产生的羟基自由基的量远远高于阳极体系产生量, 这是阴极体系有机物矿化效果较好的根本原因. 还对电流强度和初始pH的影响进行了研究, 并对两个体系反应机理进行了讨论.     

From Bad Electrochemical Practices to an Environmental and Waste Reducing Approach for the Generation of Active Hydrogen Evolving Electrodes

The electrodeposition of noble metals using corresponding dissolved metal salts represents an interesting process for the improvement of the electrocatalytic hydrogen evolution reaction (HER) properties of less active substrate materials. The fact that only a small fraction of the dissolved noble metals reaches the substrate represents a serious obstacle to this common procedure. We therefore chose a different path. It was found that the HER activity of Ni42 alloy drastically increased (η=140 mV at j=10 mA cm^?2; pH 1) when a platinum counter electrode was used during polarization experiments in acid. This improvement was caused by a platinum transfer from the platinum anode to the steel cathode, a process which occurred simultaneously to the hydrogen evolution. The negligible accumulation of Pt (26 μg) in the electrolyte turns this straight‐forward transfer procedure into a highly cost‐effective, environmentally friendly, and waste reducing approach for the generation of cheap, stable and effective HER electrodes.