Anodic Contact Glow Discharge Electrolysis Research Articles

Nanoporous Au Formation on Au Substrates via High Voltage Electrolysis.

Nanoporous Au (NPG) films have promising properties, making them suitable for various applications in (electro)catalysis or (bio)sensing. Tuning the structural properties, such as the pore size or the surface-to-volume ratio, often requires complex starting materials such as alloys, multiple synthesis steps, lengthy preparation procedures or a combination of these factors. Here we present an approach that circumvents these difficulties, enabling for a rapid and controlled preparation of NPG films starting from a bare Au electrode. In a first approach a Au oxide film is prepared by high voltage (HV) electrolysis in a KOH solution, which is then reduced either electrochemically or in the presence of H2 O2 . The resulting NPG structures and their electrochemically active surface areas strongly depend on the reduction procedure, the concentration and temperature of the H2 O2 -containing KOH solution, as well as the applied voltage and temperature during HV electrolysis. Secondly, the NPG film can be prepared directly by applying voltages that result in anodic contact glow discharge electrolysis (aCGDE). By carefully adjusting the corresponding parameters, the surface area of the final NPG film can be specifically controlled. The structural properties of the electrodes are investigated by means of XPS, SEM and electrochemical methods.

Using auxiliary electrochemical working electrodes as probe during contact glow discharge electrolysis: A proof of concept study

Plasma in-liquid by means of anodic contact glow discharge electrolysis (aCGDE) is a growing research field allowing the selective modification of the electrode and the electrolyte. The aim of this proof of concept study is to demonstrate that auxiliary electrochemical electrodes placed in the vicinity of the plasma electrode can be modified by aCGDE (ignited at the anode by applying a DC voltage between the driving electrodes). Furthermore, we illustrate in how far such auxiliary electrodes can be used as a probe to detect products (in particular, H2, H2O2, and O2) formed in the solution by aCGDE via electrochemical techniques. In this work, aCGDE is achieved by applying a voltage of 580 V to a small Pt wire (plasma electrode) versus a large stainless steel counter electrode. An auxiliary Pt electrochemical working electrode, operated in a three electrode configuration, is placed at different distances from the plasma working electrode. Depending on the distance, we find small changes in the working electrode structure. More importantly, we will show that, in principle, the local H2O2 concentration in the electrolyte can be monitored operando. After aCGDE, the concentration changes with time and depends on the distance from the plasma electrode.

Simultaneous Degradation of Aqueous Trichloroacetic Acid by the Combined Action of Anodic Contact Glow Discharge Electrolysis and Normal Electrolytic Processes at the Cathode

To enhance the removal of trichloroacetic acid (TCA) by anodic contact glow discharge electrolysis (CGDE), the combined degradation of TCA by the action of anodic CGDE, denoted anodic degradation, and normal electrolytic processes at the cathode, denoted cathodic degradation, was investigated. Here, this overall process is termed simultaneous degradation. Compared to anodic degradation, in simultaneous degradation, the reduction rates for TCA and total organic carbon (TOC) increased from 65.32% and 62.03% to 91.82% and 73.03%, respectively. Meanwhile, the dechlorination rate rose from 64.6 to 80.12%. For simultaneous degradation, the disappearance of TCA, the reduction in the TOC, and the dechlorination of TCA, followed first-order kinetics. The reaction intermediates were detected and, based on the intermediates and the observed kinetics, the effects of the simultaneous degradation of TCA, TOC, and dechlorination of TCA are discussed. The cathode materials, length of the anode dipped into the electrolyte, and Pd loading on the Ni cathode all affected the simultaneous degradation of TCA significantly. The effect of the addition of Fe2+ was also investigated. The additive and synergistic effects of the combination of anodic and cathodic degradations on simultaneous degradation are discussed. Based on these results, an analysis of the degradation of TCA suggests that ·OH and ·H/e aq − generated by the action of anodic CGDE, as well as the ·Hads generated on the Pd-loaded Ni cathode surface, are the key species responsible for the dechlorination of TCA. Furthermore, possible mechanistic routes for the simultaneous degradation of TCA are proposed.

DC and AC Performance of Graphite Films Supercapacitors Prepared by Contact Glow Discharge Electrolysis

In the present work, we fabricate and characterize carbon graphite films by high-voltage cathodic and anodic contact glow discharge electrolysis (CGDE) for supercapacitor applications. Transmission electron microscopy revealed that the carbon films obtained by anodic CGDE, in which a carbon graphite is used as the positive electrode, are in the form of two-dimensional, relatively large lateral size sheets without major fractures or structural distortions. Whereas with the cathodic configuration, tiny and elongated flakes of graphite attached to larger sheets are obtained. We observed negative Raman wavenumber shifts of the G peak and the appearance of the T peak at ca. 1100 cm− 1, which are attributed to thermal-induced strains and structural damages in the graphite crystal lattice, as well as to some C-C sp3 bonds content. In addition to the aforementioned results and optical emission spectroscopy, it is proposed that both formation mechanisms by electrochemical exfoliation and material evaporation occur depending on the used polarization. All-solid-state symmetric supercapacitors using polyvinyl alcohol/H3PO4 as gel electrolyte were fabricated and tested under dc and ac frequencies. We found two different behaviors: at dc and close-to-dc, the material prepared with cathodic CGDE showed close-to-ideal behavior with higher capacitance at different charging/discharging rates, which makes it more suitable for energy storage applications, whereas at higher frequencies ( ⩾ 100 Hz), the material prepared with anodic CGDE performed better for ac filtering applications that has been verified using an inverting integrator circuit.

Defluorination and Mineralization of Difluorophenols in Water by Anodic Contact Glow Discharge Electrolysis

Anodic contact glow discharge electrolysis (CGDE) is a DC-excited atmospheric pressure discharge, in which a steady non-thermal plasma is generated locally between the surface of an electrolytic solution and an anode in contact with it. The I–U characteristics of CGDE were investigated. The plasma temperatures were estimated to be in the range, 1373–2045 K. Hydroxyl radicals and hydrogen peroxide were the main oxidants generated by CGDE. The hydrogen peroxide concentration reached 31.2 mmol/L (mM) in a phosphate buffer solution without organic substrates. During CGDE, the DFPs and the corresponding total organic carbon (TOC) in water were consumed. Most of the fluorine atoms in the DFPs were converted to fluoride ions, and the fluoride concentration increased steadily. An analysis of the hydroxylation of DFPs suggested that the hydroxyl radicals generated by CGDE were the key species responsible for the degradation of DFPs, and the possible mechanistic routes of the mineralization of DFPs are proposed. The disappearance of DFPs and the TOC as well as the defluorination of the DFPs followed first-order kinetics. The rate of TOC disappearance was relatively constant: 1.00 ± 0.05 × 10−2 min−1. The order of disappearance of the DFPs was 2,6-DFP > 2,3-DFP > 2,5-DFP > 2,4-DFP > 3,4-DFP > 3,5-DFP. In contrast, the order of defluorination of the DFPs was 2,5-DFP > 2,3-DFP > 2,6-DFP > 2,4-DFP > 3,4-DFP > 3,5-DFP. Overall, the order of the reaction rates for each DFP was kDFP > kdF > kTOC.

A Kinetic and Mechanismic Study of Plasma-Induced Degradation of Monochloropropionic Acids in Water by Means of Anodic Contact Glow Discharge Electrolysis

Decomposition of aqueous monochloropropionic acids (MCPAs) was investigated by means of anodic contact glow discharge electrolysis (CGDE). With the decay of MCPAs, the corresponding total organic carbon (TOC) also decreased smoothly. Furthermore, it was found that chlorine atoms in the MCPAs were released as chloride ions. As the main by-products, oxalic acid and formic acid were detected. The acetic acid (CA), monochloroacetic acid (MCA), and propanedioic acid (PDA) were also detected as the primary intermediates for decomposition of the corresponding MCPAs. The decay of both MCPAs and TOC obeyed the first-order kinetics, respectively. The apparent rate constant for the decay of MCPAs increased with the increase inpKavalues of MCPAs, while that for the decay of TOC was substantially unaffected. The reaction pathway involving the successive attack of hydroxyl radical and the carbon chain cleavage were discussed based on the products and kinetics.

Can electrochemical oxidation techniques really decontaminate saline dyes wastewater?

Formation of toxic chlorinated organic byproducts is of great concern when selecting electrochemical oxidation (EO) as decontamination technology for saline dye wastewater, but still not verified. To test the applicability of EO, methyl orange (MO) was used as a model dye for anodic contact glow discharge electrolysis (CGDE) and conventional electrolysis (CE) in the presence of chloride. The degradation kinetics and organic intermediates were analyzed. In the presence of chloride, the rates of dye degradation were significantly increased as CGDE and CE were applied. CE resulted in higher mineralization efficiency than CGDE which needs much energy input. Several refractory chlorinated aromatic and even aliphatic compounds were identified during MO degradation, as well as the other anthraquinone dye, alizarin red S (AR). Therefore, the issues of toxic chlorinated byproducts and energy cost should be preferentially evaluated prior to the selection of EO technologies.

Plasma-Induced Decomposition of Dichlorophenols and Trichlorophenols in Water by Means of Anodic Contact Glow Discharge Electrolysis

Decomposition of aqueous dichlorophenols and trichlorophenols was investigated by means of contact glow discharge electrolysis. With the decay of chlorophenols (CPs), the amount of total organic carbon (TOC) in water also decreased smoothly, indicating that carbon atoms of benzene nucleus could be eventually converted to inorganic carbons. And, it was found that chlorine atoms in the CPs were released as chloride ions. As the by-products, oxalate and formate were formed. The chlorine derivatives of 1,4-hydroquinone and 1,4-benzoquinone were detected as the primary intermediates in the initial stage of decomposition of each of CPs. The decay of both CPs and TOC obeyed the first-order rate law, respectively. The apparent rate constants for the decay of CPs increased with the decrease in pKa values of CPs, while those for the decay of TOC were substantially unaffected.

Destruction of 4-phenolsulfonic acid in water by anodic contact glow discharge electrolysis

Destruction of 4-phenolsulfonic acid (4-PSA) in water was carried out using anodic contact glow discharge electrolysis. Accompanying the decay of 4-PSA, the amount of total organic carbon (TOC) in water correspondingly decreased, while the sulfonate group of 4-PSA was released as sulfate ion. Oxalate and formate were obtained as minor by-products. Additionally, phenol, 1,4-hydroquinone, hydroxyquinol and 1,4-benzoquinone were detected as primary intermediates in the initial stages of decomposition of 4-PSA. A reaction pathway involving successive attacks of hydroxyl and hydrogen radicals was assumed on the basis of the observed products and kinetics. It was revealed that the decay of both 4-PSA and TOC obeyed a first-order rate law. The effects of different Fe ions and initial concentrations of 4-PSA on the degradation rate were investigated. It was found that the presence of Fe ions could increase the degradation rate of 4-PSA, while initial concentrations lower than 80 mmol/L had no significant effect on kinetic behaviour. The disappearance rate of 4-PSA was significantly affected by pH.

Enhancement of Phenol Degradation by Electron Acceptors in Anodic Contact Glow Discharge Electrolysis

Effects of several electron acceptors (Fe3+, Cu2+, Cr(VI), and H2O2) on phenol degradation in anodic contact glow discharge electrolysis have been investigated. Results show that the electron acceptors have positive effects on phenol removal, with the sequence of Fe3+ > Cr(VI) > H2O2 > Cu2+. Under conditions of voltage 500 V and current 100 mA, 100 mg/L phenol can be removed with 10 min of discharge treatment in the presence of 1.0 mmol/L Fe3+, while without any additive only 35 % of phenol is removed in 30 min. The mechanism of the degradation enhancement was discussed based on the reactions taking place in the presence of the different additives.

Effects of Alkaline Ferrocyanide on Non-faradaic Yields of Anodic Contact Glow Discharge Electrolysis: Determination of the Primary Yield of OH· Radicals

Non faradaic yields of anodic contact glow discharge electrolysis (CGDE) originate through H· and OH· radical generated during the process. Scavenging effects of Fe(CN)64− on OH· radicals, in alkaline media have been investigated. A kinetic analysis of the competing reactions of O− with different species in the system leads to an yield of 9.8 mol mol electron−1 of OH· and H· radicals each in the liquid phase reaction zone of anodic CGDE in good agreement with the yield reported from a study involving H· radical scavengers.

Degradation of reactive dyes by contact glow discharge electrolysis in the presence of Cl − ions: Kinetics and AOX formation

The plasma generated around the anode during contact glow discharge electrolysis (CGDE) is a rich source of hydroxyl ( OH) radicals that can efficiently degrade organic contaminants in aqueous solutions. The degradation of textile azo dyestuffs, Reactive Yellow 176 (Y3RS), Reactive Red 239 (R3BS) and Reactive Black 5 (B5), by anodic CGDE was investigated in the presence of chloride (Cl −) ions. The degradation kinetics of the dyes was dependent on the concentration of Cl − ions and on the respective dye being treated. R3BS degradation was inhibited by Cl − ions in the range of 0–0.01 M. When the Cl − ion concentration was less than 0.02 M, the dyes followed pseudo first-order degradation kinetics. For concentrations greater than 0.02 M, the degradation of Y3RS and B5 was significantly enhanced compared to the degradation of R3BS and deviated from first-order reaction kinetics. The presence of Cl − ions (0.03 M) did not appear to improve dye mineralization but resulted in the formation of adsorbable organic halogens (AOX). The results indicated that the AOX could be abated with prolonged electrolytic treatment. This observation is significant for the assessment of the environmental impact of this technology for wastewater treatment.

Mineralization of aqueous pentachlorophenolate by anodic contact glow discharge electrolysis

Exhaustive mineralization of pentachlorophenolate ion (PCP) in phosphate buffer was carried out using anodic contact glow discharge electrolysis (CGDE), in which plasma was sustained between the electrolyte and anode. During CGDE, PCP degraded smoothly. The amount of total organic carbon decreased significantly, indicating the eventual conversion of the carbon atoms of benzene nucleus to inorganic carbons. Furthermore, chlorine atoms in PCP were liberated as chloride ions. As a primary intermediate product, 2,3,5,6-tetrachloro-1,4-benzoquinone was detected, and oxalate and formate as byproducts were also found. It was revealed that disappearance of PCP obeyed first-order kinetics. The reaction rate was generally unaffected by both O 2 and inert gases in the cell, although it decreased by raising initial pH of solution. In addition, a plausible reaction pathway involving hydroxyl radical was proposed.

Scavenging Effects of Aliphatic Alcohols and Acetone on H• Radicals in Anodic Contact Glow Discharge Electrolysis: Determination of the Primary Yield of H• Radicals

A study of scavenging effects of iso-propanol, n-propanol, n-butanol and acetone on H• radicals, precursors for nonfaradaic products of anodic contact glow discharge electrolysis (CGDE) in aqueous media, has been carried out. A kinetic analysis of the competing reactions of H• with different species in the system leads to a primary yield of 9.8 mol (mol electron)−1 each of H• and OH• radicals in the liquid-phase reaction zone of anodic CGDE. The method is considerably more convenient to apply than those reported earlier based on the use of OH• scavengers.

Chemical effects of anodic contact glow discharge electrolysis Formation of amino acid

In Contact Glow Discharge Electrolysis (CGDE), a plasma is sustained by d.c. glow discharges between an electrode and the electrolyte around it. The chemical results of CGDE are significantly non faradaic. With the anodic plasma in an aqueous electrolyte, non-faradaic results originate mainly from break-up of liquid water molecules near the plasma | anolyte interface by sufficiently energized H 2 O + gas ions coming out of the plasma into H and OH in yields as high as 13 moles per mol electron of electricity. The radical generating potentiality of anodic CGDE in high local concentration in liquid phase has been explored as a tool for synthesizing amino acids from ammoniacal solution of carboxylates. The results show that amino acids such as glycine from ammoniacal acetate electrolyte and α-alanine from ammoniacal propionate electrolyte are formed in yields exceeding the Faraday law value. The formation of amino acid by anodic CGDE has been explained by radical scavenging action of ammonia and carboxylates on H and OH radicals and by mutual interaction between NH 2 and RC HCOO - radicals formed. The present technique requires 0.1- 0.2 kcal for production of 10 -5 mol of glycine as compared to 24 kcal by spark discharge and 50 kcal by X-ray for glycine production from constituents of reducing atmosphere.

A study on acrylamide polymerization by anodic contact glow‐discharge electrolysis: A novel tool

AbstractContact glow‐discharge electrolysis (CGDE) is an unconventional electrolytic phenomenon in which a plasma is sustained by a direct current (dc) glow‐discharge between an electrode and the liquid electrolyte around it. A remarkable feature of CGDE is highly nonfaradaic chemical effects at the glow‐discharge electrode. During anodic CGDE of an aqueous electrolyte, non‐Faradaic yields originate mainly from reactions triggered by H• and OH• radicals generated in high local concentrations near the anodic plasma/liquid electrolyte interface during the process. The radical‐generating potentiality of anodic CGDE was explored for the polymerization of acrylamide in aqueous media. The percentage of monomer conversion, rate of polymerization, charge efficiency, and viscometric average molar mass of the polymers produced were measured as functions of the quantities of electricity passed. The charge efficiency of the polymerization of acrylamide by anodic CGDE was at least 1 order of magnitude higher than that of ordinary electrochemically initiated polymerization. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1584–1588, 2001

A Study on the Origin of Nonfaradaic Behavior of Anodic Contact Glow Discharge Electrolysis: The Relationship Between Power Dissipated in Glow Discharges and Nonfaradaic Yields

Chemical effects of contact glow discharge electrolysis (CGDE) at an electrode where a plasma is sustained by dc glow discharges between the electrode and the surrounding electrolyte, are remarkably nonfaradaic. A critical analysis of the chemical results of anodic CGDE at varying voltages, currents, power supplies, and pHs clearly shows that nonfaradaic yields originate in two separate reaction zones: the plasma around the anode and the liquid anolyte near the plasma‐anolyte interface. The yields from the former zone appear from 250 V onward (the beginning of the onset of partial glow discharge) and vary linearly with the power dissipated in the glow discharge. The yields from the latter zone appear from 410 V onward (the beginning of the full glow discharge) and are independent of the power dissipated in the glow discharge. The relative contribution of the two zones to the total nonfaradaic yields is dependent on the voltage applied: the plasma zone having a share of 100% up to 400 V, followed by 20% up to 450 V, and thereafter rising steadily to 57% at 500 V.

Contact glow discharge electrolysis: a study of its chemical yields in aqueous inert-type electrolytes

A study of the chemical yields of contact glow discharge electrolysis (CGDE) at the anode in aqueous inert electrolytes at various quantities of electricity, applied voltages and electrolyte compositions shows that, for the passage of each mole of electrons, 0.25 mol of O2 and more than 1.0 mol of both H2 and H2O2 plus O2 are produced at the anode when the glow discharges there are fully grown. Non-faradaic yields may originate in two reaction zones: the anolyte near the plasma where liquid water molecules are broken up into H2O2, O2 and H2, and the plasma around the anode where gas phase dissociation of water molecules into H2 and O2 occurs. The former is important for anodic CGDE. Hickling's radiolytic mechanism has been applied to interpret the chemical results of the liquid phase reaction zone. A comparative study of the chemical yields of anodic and cathodic CGDE indicates that the breakup of water molecules occurs entirely in the plasma during cathodic CGDE, but primarily in the liquid anolyte and partly in the plasma during the anodic phenomenon.