Electrode Reaction Products Research Articles

Real-Time Mass Spectrometry for Simultaneous Monitoring of Electrode Dissolution and Reaction Product Distribution during Organic Electrosynthesis

An organic electrosynthesis is an emerging tool for modern chemical manufacturing fitting the environmental and sustainability agenda. It utilizes polarized electrode surfaces as “traceless” oxidants or reductants, whereas its heterogeneous nature and exceptional tunability enable easy access to radical intermediates and novel mechanistic pathways. In the line of further energy input improvement, there is a growing demand for appropriate catalytic materials devoted to organic molecule transformations, for which the activity and selectivity have so far been most studied. Although the investigation of electrodes’ and electrocatalysts’ stability in the field of electrochemical energy conversion is well-established, there is still a lack of attention to the symmetrical studies for organic electrosynthesis. Nevertheless, electrode material losses shorten the reactor’s lifetime and can cause metal cathodic re-depositions, severely altering reaction product selectivity and final product contaminations. Although some reports on the ex-cell metal dissolution analysis are available, no information about its mechanism can be gained in such a way. To highlight the issue numerically, an analytical method to characterize rates and mechanisms of catalyst dissolution within a real-time response-enabled potential-, temperature-, or time-resolved parametrization of the electrocatalyst is highly demanded.Herein we present a system to study organic electrosynthetic protocols under dynamic operations to quantitatively monitor the electrode dissolution aligned with reaction products during organic molecules transformations. The instrument comprises an electrochemical flow cell (EFC) with exchangeable working electrodes, the outlet of which is interfaced with an online quadrupole mass spectrometer (OQMS) for the analysis of extracted by solid membrane gaseous products and an inductively coupled plasma mass spectrometer (ICP-MS) for the detection of dissolved metals. The system is exemplified by a benchmark Kolbe electrolysis over platinum Pt anode, commonly considered a stable and inert electrode material. Based on the literature, methanol has been used as a solvent of choice, while partially neutralized acetic acids with different bases were studied as objects. The methodology shed some light on understanding the role of platinum oxide formation on the electrode surface and can be used to study time- and potential-resolved catalyst stability and the possibility for dissolved transition metal-catalyzed electroorganic transformations.

Development of a quasi-on-time ICP-OES for analyzing electrode reaction products

A quasi-on-time system for analyzing electrode reaction products was developed by combining inductively coupled plasma-optical emission spectrometry (ICP-OES) with a hydrodynamic electrochemical technique. Numerical calculations and experiments showed that the shorter the distance of the withdrawing flow channel from the electrode end to the OES detector, the shorter the time response and the detection efficiency is 98.1%, which enables the transient determination of the generation rate for products. Application of the combined system with sufficient time resolution to the analysis of reaction species generated from a Cu electrode in a chloride-containing aqueous solution showed that the addition of benzotriazole (BTA) above a critical concentration of 10 mol m–3 is effective in inhibiting the dissolution of Cu. The development of the quasi-on-time system of analysis would enable application to a wide range of non-steady-state electrochemical reactions including corrosion.

How to Improve the Performance of Electrochemical Sensors via Minimization of Electrode Passivation

It follows from critical evaluation of possibilities and limitations of modern voltammetric/amperometric methods that one of the biggest obstacles in their practical applications in real sample analysis is connected with electrode passivation/fouling by electrode reaction products and/or matrix components. This review summarizes possibilities how to minimise these problems in the field of detection of small organic molecules and critically compares their potential and acceptability in practical laboratories. Attention is focused on simple and fast electrode surface renewal, the use of disposable electrodes just for one and/or few measurements, surface modification minimising electrode fouling, measuring in flowing systems, application of rotating disc electrode, the use of novel separation methods preventing access of passivating particles to electrode surface and the novel electrode materials more resistant toward passivation. An attempt is made to predict further development in this field and to stress the need for more systematic and less random research resulting in new measuring protocols less amenable to complications connected with electrode passivation.

Design and Performance of a Full Functional Electrochemical Cell for Lab Scale in-Situ GI-XRD Instruments

In-situ XRD may support electrochemical measurements by delivering analytical information about electrochemical processes. Since structural changes at the electrode/electrolyte interface are of specific interest, measurements are done usually in small angle reflection mode geometry. The surface sensitive grazing incidence – XRD (GI-XRD) in-situ technique allows the detection of short-lived electrode reaction products or products sensitive to ambient atmosphere exposure. This method finds applications for quite a number of investigations of electrochemical processes including corrosion, film growth and deposition, reconstruction of superficial regions, ion insertion battery materials, etc. The common cell designs for lab scale XRD equipment use thin electrolyte layers to avoid unacceptable beam intensity loss through water. The use of synchrotron radiation would reduce this shortcoming to some extent but is much less accessible.In 1986, Fleischmann et al. presented an in-situ XRD thin layer cell in reflection as well as in transmission mode, where a X-ray transparent Mylar foil was used as window material [1]. However, this geometry restricts the positioning of counter and reference electrodes and therefore has unfavorable current density distribution, has very small electrolyte volume, is vulnerable to side reactions with gas evolution and does not allow high flow rates for the solution. Thus, the general applicability is limited.In our proposed in-situ cell design for GI-XRD, the electrochemical cell is fully functional, avoiding all of the above mentioned drawbacks [2]. The solution of this issue is the "backside-illumination" (or "inverse" illumination) of a thin film working electrode applied on a thin polymer foil as a support by the X-ray beam at a small incident angle. On the opposite side a conventional electrochemical cell with reference electrode and counter electrode and sufficient solution volume can be used. The big advantage of this design is that the X-ray only has to penetrate the foil and the thin layer of electrode material resulting in high signals from the region of interest. It is used with a conventional laboratory X-ray source and does not need high intensity synchrotron radiation. With this cell design, problems with bulk solution resistance, inhomogeneous current-density distribution, insufficient bath agitation or gas evolution as side reaction are eliminated.In this contribution, details of the cell design, analysis of current density distribution within the thin current collector and the electrochemical cell, results of calibration measurements and measurements on copper as an example for a galvanic deposition/dissolution process are presented.[1] M. Fleischmann, A. Oliver, and J. Robinson, ‘In Situ X-ray diffraction studies of electrode solution interfaces’, Electrochimica Acta, vol. 31, no. 8, pp. 899–906, (1986)[2] S. Reither, W. Artner, A. Eder, S. Larisegger, M. Nelhiebel, C. Eisenmenger-Sittner, G. Fafilek, ‘On the In-Situ Grazing Incidence X-Ray Diffraction of Electrochemically Formed Thin Films’, ECS Transactions, 80 (10) 1231-1238, (2017) 10.1149/08010.1231ecst Figure 1

Two-dimensional porous transition metal organic framework materials with strongly anchoring ability as lithium-sulfur cathode

Lithium-sulfur (Li-S) batteries are regarded as promising candidates for energy storage devices due to their high theoretical energy density. An ideal Li-S batteries cathode should effectively prevent polysulfide dissolution in order to achieve longer cycle life and higher rate performance. Herein, a new 2D transition metal organic framework material, hexaaminobenzene-based coordination polymers (HAB-CPs), has been systematically investigated as cathode candidate materials for Li-S batteries. First principles calculations combined with the vdW interaction and solvent model reveal that V-HAB-CP has the best ability to hinder the shuttle effect of lithium polysulfides among the three polymers (V, Cr and Fe-HAB-CPs). Quantum conduction (G) and density of states (DOS) calculations indicate that HAB-CPs maintain excellent conductivity during the whole charging process. Moreover, a very small volume change (about 3.06%) of V-HAB-CP before and after the electrode reaction can well deal with the volume expansion problem of Li-S batteries. Meanwhile, the energy density reaches 808.465 W h kg-1 when the electrode reaction product is Li16S8/V-HAB-CP. Attributed to these benefits, V-HAB-CP is a suitable cathode material, which is expected to be used in future Li-S battery systems. The computational method adopted in this paper can provide a guidance for considering the influence of electrolytes on the Li-S batteries in the future and be widely used in other simulation calculations involving the solution effect.

Ion-exchange membranes in gold electowinning processes on flow-through carbon fiber electrodes

The change in the properties of ion-exchange membranes preventing the negative effect of anodic reaction products on the electrowinning of gold on carbon fiber cathodes from (1) sulfuric acid thiourea eluates formed during the extraction of gold from ores and (2) citrate–phosphate washing solutions from gold plating of electronic components has been studied. By using electron microscopy, microanalysis, and atomic absorption spectroscopy, it has been shown that the main cause of the change in the properties of the membranes during their operation is the inclusion of components of the solutions subjected to treatment and the products of electrode reactions in the membrane. The service life of the membranes in said processes has been determined.

A chip-type thin-layer electrochemical cell coupled with capillary electrophoresis for online separation of electrode reaction products

A coupling technique of thin-layer electrolysis with high-performance capillary electrophoresis/UV–vis technique(EC/HPCE/UV–vis) is developed for online separation and determination of electrode reaction products. A chip-type thin-layer electrolytic (CTE) cell was designed and fabricated, which contains a capillary channel and a background electrolyte reservoir, allowing rapid electrolysis, direct sampling and online electrophoretic separation. This chip-type setup was characterized based on an electrophoresis expression of Nernst equation that was applied to the redox equilibrium of o-tolidine at different potentials. The utility of the method was demonstrated by separating and determining the electro-oxidation products of quercetin in different pH media. Two main products were always found in the studied time, potential and pH ranges. The variety of products increased not only with increasing potential but also with increasing pH value, and in total, at least 13 products were observed in the electropherograms. This work illustrates a novel example of capillary electrophoresis used online with thin-layer electrolysis to separate and detect electrode reaction products.

THE CONSTRUCTION OF A NOVEL ELECTROCHEMICAL MEASURING SYSTEM FOR ENHANCED ROTATING RING-DISK ELECTRODE EXPERIMENTS

Based on the cutting-edge technology provided by National Instruments' data acquisition cards and on the LabVIEW graphical programming language, a new electrochemical measuring system has been designed, developed, and presented in this paper. The main objective of the development was to design a workstation which is capable of conducting advanced rotating ring-disk electrode experiments that are based on the simultaneous dynamic potential control of both the disk and the ring electrodes. Our system provides great flexibility in defining the perturbing waveforms and visualizing the measured data. By the use of this system, several new experimental methods have been developed; for example, the construction of three dimensional maps of electrode reaction products has become possible.

Feasibility investigation of methanol generation by CO2 reduction using Pt/C-based membrane electrode assembly for a reversible fuel cell

In this study, we investigated the viability of a reversible fuel cell which uses methanol as the candidate liquid fuel. This fuel cell consists of methanol oxidation and its coupled carbon dioxide (CO2) reduction reaction. The CO2 electrode reaction using a membrane electrode assembly (MEA) with a carbon-supported platinum (Pt/C)-based anode and cathode was evaluated. First, the electrode potential of the CO2 reduction at the MEA cathode was measured by linear sweep voltammetry. The resulting voltammograms show that the CO2 reduction occurs within the electrode potential region of 0.06–0.4 V vs. the dynamic hydrogen electrode (DHE) in a CO2 atmosphere. Products of the CO2 electrode reaction were then analyzed by gas chromatograph–mass spectrometry, and a small amount of methanol was detected. Stripping voltammetry for CO and methanol was conducted, revealing that CO2 is reduced to methanol and almost all of it strongly adsorbs onto the Pt/C cathode. Finally, the CO2 electroreduction was shown to occur with a relatively high Coulombic efficiency of 30–50% at 0.06–0.25 V vs. DHE. Our study showed that the CO2 reduction was able to produce methanol in an MEA with Pt/C electrodes, which may have applications in future fuel cell development.

Effect of the doping level on the biological stability of hydrogenated boron doped diamond electrodes

Fouling of electrode surfaces by electrode reaction products or by biological spectator species is known to inactivate electrochemical sensors and thus limit their use in biological conditions. Here we present an investigation on the stability of boron doped diamond (BDD) electrodes with different levels of doping. Three different doping levels were used (0.1, 1 and 5% in the carbon phase). The highly doped (5%) BDD is of particular interest as it is here used for the first time for biological applications. Three different redox reactions were examined based on their electrode reaction characteristics: ruthenium(III) hexaammine (outer sphere), ferrocyanide (surface dependent), dopamine (adsorption mediated). The effect of albumin at blood concentration was studied. All results were compared with glassy carbon. There were no significant differences for the outer sphere electrochemistry, but all the BDDs showed improved resistance to fouling for the ferrocyanide oxidation. The electrocatalytic activity of BBD towards dopamine oxidation increased with increased boron content. However, this appears to be due to a larger number of defect sites which also increases the vulnerability to fouling by albumin and by electrode reaction products and the 5% BDD had similar properties to glassy carbon in this regard. These results suggest that it is possible to optimise the BDD performance for specific applications and that the large potential window for BDD may be due, at least in part, to its relatively poor electrocatalytic activity.

Discharge of a copper-magnesium galvanic cell in the presence of a weak electromagnetic field

The effect of weak periodic electromagnetic pulses with a repetition rate of 250 kHz on the discharge of a copper-magnesium galvanic cell is studied experimentally. Comparative characteristics of the electrochemical process and scanning electron microscopy images of electrode reaction products are presented.

A solid-phase microextraction device for the analysis of electrochemical reaction products by gas chromatography/mass spectrometry.

Presented is a solid-phase microextraction syringe-electrode assembly that may be used to identify electrode reaction products. After an electrochemical experiment, the electrode within this syringe-electrode assembly can be introduced into the injection port of a gas chromatograph. Electrochemical reaction products can be analyzed, provided they adhere to the electrode surface and are amenable to gas chromatographic/mass spectrometric analysis. We highlight the potential usefulness of this device using well-known electrochemical reaction of quinones.

A Study of Composition and Structure of Aluminozirconium Hydroxides Obtained by Coprecipitation in Membrane Electrolyzer

Fundamental aspects of formation of aluminum and zirconium hydroxides in their coprecipitation under the action of products of electrode reactions in a membrane electrolyzer were studied. The influence exerted by precipitation conditions (temperature and pH value) on the phase composition and porous structure of coprecipitated systems was analyzed.

Fiber-optic infrared reflectance spectroelectrochemistry: isomerization of a manganese pyranyl complex

A simple apparatus for fiber-optic reflectance FTIR spectroelectrochemical measurements is described. The method is useful for observing the products of electrode reactions generated in steady-state at an electrode surface, and the problem of large thin-layer resistance in non-aqueous solvents is minimized. Cyclic voltammetry (CV) and FTIR spectroelectrochemical measurements on five compounds ([(η 5-C 5H 5)Fe(CO) 2] 2 (Fp 2), Fp(CCPh), Mn 2(CO) 10, BrMn(CO) 5 and (η 5-2,4-diphenyl-6-methylpyranyl)tricarbonylmanganese (PyrMn(CO) 3) are presented. As expected, Mn 2(CO) 10 and BrMn(CO) 5 are both reduced to the known Mn(CO) 5 − anion, but Fp 2 is reduced in CH 2Cl 2 to form FpCH 2Cl, and Fp(CCPh) forms a [μ 2–η 1:η 2-Fp 2CCPh] + cation. Upon oxidation of the PyrMn(CO) 3 complex, the Mn(CO) 3 + unit undergoes migration from the pyranyl ring to a phenyl ring to form an η 6-arene complex which has a pyrylium ion as a substituent on the arene ligand.

Generalized theory of steady-state voltammetry without a supporting electrolyte. Effect of product and substrate diffusion coefficient diversity.

A generalized theory of the steady-state voltammetric response of a microelectrode in the absence of supporting electrolyte and for any values of diffusion coefficients of the substrate and the product of an electrode process is presented. The treatment applies to any reasonable combination of the charge numbers of the substrate, its counterion, and the product. A way to incorporate the activation polarization into the model is also demonstrated. It has been shown that the height, position, and shape of the migrational voltammogram are affected by the ratio of the product to substrate diffusivity (theta). In particular, for the electrode processes with sign retention, unequal diffusivities of electroactive species influence both characteristic points of the voltammogram (the limiting current and the half-wave potential). For charge neutralization processes (uncharged product), the changes in theta parameter are accompanied only by a shift in the half-wave potential. The most dramatic changes in the I-E relation can be observed for the charge reversal processes. In this case, a consecutive increase in theta results in the transition of the voltammogram shape from rapid exponential growth (theta < 1), through ramp shape (theta = 1), to common wave shape (theta > 1). On the basis of the expressions derived for the limiting current (exact and linearized), a possibility of the determination of the diffusion coefficient of the electrode reaction product is demonstrated. In addition, the ranges of theta where the assumption of equal diffusivities of the substrate and the product is obeyed within an insignificant error have been determined quantitatively. The theory has been experimentally verified using voltammetric oxidation of hexacyanoferrate(II).

An analysis of radial dispersion effects in certain undivided cylindrical electrolysers

Radial dispersion in high geometric aspect ratio, thin cylindrical electrolytic cells is analysed with respect to controlling the reconversion of an electrode reaction product at the opposite electrode. Design aspects related to electrode process time (batch operation) and electrolyte residence time (flow-through operation) are also discussed.

The hanging meniscus contact: geometry induced diffusional overpotential. The reduction of oxygen in dimethylsulphoxide at Au(111)

Mass transport in the hanging meniscus configuration has been studied. The effects of this geometry on an electrochemical reaction of a gas phase species with a high solubility in the electrolyte phase have been investigated, both numerically and experimentally. The steady-state process is modelled in cylindrical polar coordinates using a fully implicit finite-difference numerical method and solved with a preconditioned Krylov subspace method. The numerical method incorporates an expanding mesh technique to optimise electrode flux error-cancelling. The nature of the meniscus boundary such as to permit the ingress of electroactive material mentioned, but not the egress of electrode reaction products is shown to result in a diffusional overpotential in the steady-state voltammogram. This observation has been examined experimentally by using the reduction of O 2 in dimethylsulphoxide solution on a Au(111) single crystal electrode.

Determination of diffusion coefficients of the electrode reaction products by the double potential step chronoamperometry at small disk electrodes

We propose an easy method for determining the diffusion coefficients of electrode reaction products by double potential step chronoamperometry at small disk electrodes. The necessary theoretical relationship between current and time for this method was obtained by digital simulation of a hopscotch algorithm. We quantified the digital results and showed the routine of the measurement. The method was verified successfully by an experiment in which the diffusion coefficients of both the elements of the [Fe(CN)6]4−/[Fe(CN)6]3− redox couple were determined by the usual potential step chronoamperometry and by this method.

Anion exchange chromatography and integrated amperometric detection of amino acids.

AbstractDuring the 1980s and 1990s, electrochemical detection has gained acceptance as a method of choice for some important biomolecules. Initially, the technique was utilized with glassy carbon electrodes and in the mode of constant potential amperometry. The first widely used applications were for catecholamines and their derivatives (1). Today, most laboratories around the world still rely on electrochemical detection when it comes to analyzing catecholamines in biological fluids. Although that approach has been highly successful, the next important advance came in the form of pulsed amperometric detection (PAD). The introduction of voltage pulses broadens the scope of electrochemical detection by regenerating the electrode in time for each new detection measurement. Gradual or sudden fouling of the electrode surface by the products of electrode reaction and the corresponding decreased detection response is eliminated with properly designed PAD techniques. The first important application of PAD was for carbohydrates following their separation by anion exchange (2,3).KeywordsSodium HydroxideAmino SugarCysteic AcidAutosampler VialPulse Amperometric DetectionThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Linear sweep voltammetry of 9-β- d-ribofuranosyluric acid 5′-monophosphate in aqueous and micellar media

Linear sweep voltammetric behaviour of 9-β- d-ribofuranosyluric acid 5′-monophosphate (UA-9R-5′-P) has been studied in phosphate buffers of pH 3.0 and 7.0 at the pyrolytic graphite electrode in aqueous and micellar media. At pH 3.0 in the presence of non-ionic and anionic surfactants, UA-9R-5′-P exhibited a single well-defined 2e, 2H + oxidation peak, whereas in the presence of cationic surfactant (CTAB) the oxidation peak I a showed a tendency to split into two peaks indicating that the 2e, 2H + oxidation of UA-9R-5′-P in peak I a reaction occurs in two 1e steps. The effect of cationic surfactant at pH 3.0 is explained on the basis of hydrophobic penetration of cationic species in cationic micelles. The products of electrode reaction in micellar medium were found as alloxan, urea and ribosyl phosphate at pH 3.0 and ribose, allantoin and 5-hydroxyhydantoin 5-carboxamide at pH 7.0 and were similar to those observed in aqueous media.