Mechanism Of Electrochemical Oxidation Research Articles

Mechanism of Electrochemical Oxidation of Nitroxide Radicals in Ethaline Deep Eutectic Solvent

Deep eutectic solvents (DESs) are emerging as promising electrolytes for electrochemical energy storage applications. Electroactive nitroxide-radical-containing organics can be dissolved in DESs to facilitate redox reactions; however, mechanistic know-how of their charge transfer kinetics at the electrode surface is rather limited. Here, we investigate the mechanism underlying the electrochemical oxidation of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) and 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (4-hydroxy-TEMPO). Using polarization measurements on a platinum rotating disk electrode and micro-electrode, we show that the anodic charge transfer coefficient () for one-electron transfer oxidations of TEMPO and 4-hydroxy-TEMPO approaches 0.9 in DES as well as in aqueous electrolytes, i.e., a significant deviation from α ≈ 0.5 expected for symmetric redox behavior. To explain this observation, a two-step oxidation mechanism is proposed wherein the nitroxide-containing species undergo fast charge transfer at an electrode surface followed by slow rate-limiting desorption of the adsorbed oxidized species. Numerical simulations are reported to characterize how the proposed two-step mechanism manifests in transient cyclic voltammetry behavior of the 4-hydroxy-TEMPO oxidation reaction, and good agreement with experiments is noted.

The coupling use of electro-chemical and advanced oxidation to enhance the gaseous elemental mercury removal in flue gas

A novel diffusion electro-chemical combined advanced oxidation reactor offers potential for elemental mercury (Hg0) removal in flue gas and shown excellent performance. This study introduced an ultraviolet light into the electric catalytic system to form an UV-electric oxidation system to strengthen Hg0 removal. Hg0 removal efficiency in the combined UV-electric oxidation system reached up to 65%. Hg0 is excited by UV lamp with a wavelength of 253.7 nm, and a very small amount of oxygen contained in high-purity nitrogen can still participate in Hg0 oxidation reaction. In addition, the Fenton method has also been introduced into the simple electrolysis system. Both the above combined system can improve the efficiency of Hg0 removal. The electro-chemical GDE was characterized by SEM, BET, and contact angle and gas permeability. The electro-chemical and advanced oxidation process (Fenton method and UV illumination) combined within a system or individually in series were explored the different influencing factors. The gaseous elemental mercury removal mechanism of the combined electro-chemical and advanced oxidation was investigated via combining the experimental data and theoretical reasoning. Electrochemical coupling with other advanced oxidation technologies is a promising technology.

A surfactant SDS modified carbon paste electrode as an enhanced and effective electrochemical sensor for the determination of doxorubicin and dacarbazine its applications: A voltammetric study

An electrochemical method has been described for the voltammetric oxidation and determination of anticancer drug doxorubicin (DOX) and dacarbzine (DTIC) were investigated by cyclic voltammetry (CV) and differential pulse voltammetric (DPV) techniques using in the presence of an enhancing agent sodium dodecyl sulfate (SDS) immobilizing at the carbon paste electrode. The solution conditions and operating parameters were optimized. We studied electrochemical parameters of DOX and DTIC like the effect of scan rate (diffusion controlled), heterogeneous rate constant, pH and from the concentration effect both drugs gives lower detection limit at SDS modified carbon paste electrode (SDS/MCPE). An analytical method was developed for the determination of DOX and DTIC in phosphate buffer solution (PBS) at pH 6.2 as a supporting electrolyte by CV and DPV techniques. A plausible electrochemical oxidation mechanism of DOX and DTIC was proposed. The results indicated that the voltammetric response of DOX and DTIC drugs were improved distinctly in the low concentration of SDS, suggesting that SDS exhibiting a noticeable enhancement effect to the electrocatalytic activity of DOX and DTIC drugs. The SDS/MCPE gives well separated four enhancement peaks for dopamine, serotonin, DOX and DTIC by CV and DPV system. The DOX and DTIC with excipients and interaction of DOX with DNA-time curve were also obtained by the established method. The developed sensor could be a successful monitor for clinical analysis, quality control and other therapeutic drugs.

A study of the phase-structural engineering possibilities of coatings on D16 alloy during micro-arc oxidation in electrolytes of different types

The effect of electrolysis conditions with different electrolyte compositions on the growth kinetics, phase-structural state, and hardness of coatings obtained by microarc oxidation (MAO) on the D16 aluminum alloy (base – aluminum, main impurity Cu) was studied. An analysis of the results obtained showed that the choice of the type of electrolyte and the conditions for the MAO process makes it possible to vary the growth kinetics and phase-structural state of the coating on the D16 aluminum alloy within a wide range. For all types of electrolytes, with an increase in the content of KOH, Na 2 SiO 3 , or KOH+Na 2 SiO 3 , the growth rate of MAO coatings increases. It was found that in MAO coatings obtained in an alkaline (KOH) electrolyte, a two-phase (γ−Al 2 O 3 and α−Al 2 O 3 phases) crystalline state is formed. An increase in the KOH concentration leads to an increase in the relative content of the α–Al 2 O 3 phase (corundum). During the formation in a silicate electrolyte, the phase composition of MAO coatings with an increase in the content of liquid glass (Na 2 SiO 3 ) changes from a mixture of the γ−Al 2 O 3 phase and mullite (3Al 2 O 3 ∙2SіO 2 ) to an X-ray amorphous phase. The use of a complex electrolyte leads to a two-phase state of the coating with a large (compared to an alkaline electrolyte) shift of the γ−Al 2 O 3 →α−Al 2 O 3 transformation towards the formation of the α−Al 2 O 3 phase. It was determined that the value of hardness correlates with the content of the α−Al 2 O 3 phase in the MAO coating, reaching the maximum value of 1620 kg/mm 2 at the highest content (about 80 vol. %) of the α−Al 2 O 3 phase. Two types of dependences of the coating thickness on the amount of electricity passed were revealed. For the amount of passed electricity 10–50 A-h/dm 2 , the thickness dependence is determined as 4.2 μm/(A-h/dm 2 ), which suggests the basic mechanism of electrochemical oxidation during the formation of a coating. For the amount of electricity transmitted 50–120 A-hour/dm 2 , the thickness dependence is determined by a much smaller value of 1.1 μm/(A-hour/dm 2 ). This suggests a transition to a different mechanism of coating formation − the formation of a coating with the participation of electrolysis components

Reprint of "Genotoxic permanent hair dye precursors p-aminophenol and p-toluenediamine electrochemical oxidation mechanisms and evaluation in biological fluids"

The p-toluenediamine (PTD) and p-aminophenol (PAP), genotoxic precursor agents widely used in permanent hair dyeing formulations, electrochemical mechanisms and evaluation in biological fluids, at a glassy carbon electrode, in a wide pH range, by cyclic, differential pulse, and square wave voltammetry, were investigated. The oxidation of both PTD and PAP is reversible. The PTD two electrons and two protons transfer diffusion-controlled reaction occurs at the molecule nitrogen atoms in the amine groups. Also PAP oxidation is a two electrons and two protons transfer diffusion-controlled reactions, and occur at the nitrogen and oxygen atoms of the molecule amine and hydroxyl groups. An electrochemical oxidation mechanism for PTD and PAP is proposed. The PTD and PAP diffusion coefficients, DPTD = 1.57 × 10−5 cm2 s−1 for PTD, and DPAP = 1.03 × 10−5 cm2 s−1 for PAP, were determined. The electrochemical quantification in 0.10–1.00 μM concentration range showed a detection limit of 0.12 μM for PTD and 0.17 μM PAP. A new electroanalytical method for the determination of PTD and PAP in fetal bovine serum biological fluid, and in artificial urine samples, using differential pulse voltammetry, was also developed.

Investigation of Electrochemical Oxidation Behaviors and Mechanism of Single-Crystal Silicon (100) Wafer under Potentiostatic Mode

Electrochemical oxidation (ECO) has been used widely to oxidize single crystal Si wafers. Aiming at optimizing the ECO assisted machining methods, the oxidation behaviors of single- crystal silicon (100) wafer under potentiostatic mode are experimentally investigated. It is shown that the Si wafer can be electrochemically oxidized and the oxidized film thickness reaches to 239.6 nanometers in 20 min. The hardness of the oxidized surface is reduced by more than 50 percent of the original surface. The results indicate that the oxide thickness and the hardness can be controlled by changing the voltage. Based on the experimental findings, a hypothesis on the ECO mechanism under potentiostatic mode was proposed to explain the fluctuations of current density under specific applied voltage. The occurrence of the multiple peaks in the current density curve during the oxidation process is due to the formation of discharge channels, which was initiated from the defects at the interface between the oxide bottom and the substrate. This breaks the electrical isolation and leads to the discontinuous growth of the electrochemical oxide layer. The present work contributes to the fundamental understanding of the ECO behaviors for the single-crystal Si (100) wafer under potentiostatic mode.

Mechanism and thermodynamic study of electrochemical oxidation of Caffeic acid in the presence of Thiols: Electro-organic synthesis of new Caffeic acid thioethers

In the current study, the electrochemical oxidation of caffeic acid (CA) has been studied in the presence of 2-mercaptobenzoxazole (2) and 2-mercaptobenzimidazole (3). It is demonstrated that electrochemically produced o-benzoquinone is removed by 2 and 3 to give final products via an EC mechanism pathway. The ΔGtot of studied species calculated by the use of a general thermodynamic cycle, were used to mechanism study of the electrochemical oxidation of CA in the presence of both nucleophiles. It was found that ΔGtot of the products is more than that of CA. The computational data were obtained using a DFT (Bp86) level of theory and 6-31G (d, p) basis set. In this work, we introduce new compounds with good yields through a catalyst-free and environmentally friendly method at room temperature under green conditions.

Electrochemical oxidation of synthetic amino-substituted benzamides with potential antioxidant activity

Amino-substituted benzamide derivatives are very attractive compounds due to their capacity to act as powerful antioxidants by scavenging free radicals. Knowledge on electrochemical oxidation mechanisms plays an important role in understanding the free radical scavenging activity of antioxidants. In this paper, the electrochemical oxidation of four amino-substituted derivatives [N-(4-aminophenyl)-2-hydroxybenzamide (1), N-(4-aminophenyl)-2-hydroxy-4-methoxybenzamide (2), N-(4-aminophenyl)-2-methoxybenzamide (3), N-(4-aminophenyl)-3,4,5-trihydroxybenzamide (4)] in an aqueous buffer solution was studied by means of cyclic and square-wave voltammetry, and probable reaction mechanisms have been proposed. In compounds 1–3, the primary amino group was found to be the main electroactive centre undergoing a complex, pH-dependent oxidation process with the transfer of two electrons and two protons. This reaction occurs in one step or in two separate steps, depending on the pH of the medium. A possible explanation for this electrochemical behaviour is discussed. The final products of initial electrochemical oxidation of amino-substituted benzamides 1–3 are quinonediimine derivatives that undergo further chemical transformation into electroactive forms. Oxidation of compound 4 proceeds through two sequential reactions; the first anodic reaction is the oxidation of the trihydroxyphenyl group to the corresponding o-quinone, followed by the oxidation of a primary amino group. Considering the oxidation potentials, and bearing in mind that lower/less positive potential implies better radical scavenging activity, the order of antioxidant activity of the here studied amino-substituted benzamides is: 4 >2 >1 >3.

Efficient removal of radioactive iodide by three-dimensional Cu@Cu2O: An adsorption and electrocatalytic oxidation coupling process

Electrochemical promotion technology, an environmentally friendly and facile strategy, is becoming increasingly attractive to researchers. In this work, a novel Cu@Cu2O foam block composite material was constructed through a one-step hydrothermal method. The product was then employed as the anode and electrified to catalyse removal of radioactive iodide ions (I−) in the liquid phase. The removal rate of I− sharply increased to 96.65 % under electrification, which is a 4.5-fold increase over that without electrification. The current strength had an impact on this result, and the removal was still relatively high in a wide range of pH values. The composite material had good reusability and could maintain good performance after simple separation. Therefore, based on X-ray diffraction and X-ray photoelectron spectroscopy analysis, we proposed a mechanism of electrochemical oxidation and adsorption coupling for the iodine removal. As Cu@Cu2O adsorbed I− to form CuI, the current flow oxidised I− to I2, which finally was adsorbed by the formed CuI. Therefore, the current provides services of accelerating I− movement and oxidation. This coupling model of electrocatalytic oxidation and adsorption provides us with a new research method to remove iodide from water.

Enhancement of the Activity of Electrochemical Oxidation of BPS by Nd-Doped PbO2 Electrodes: Performance and Mechanism

The electrochemical oxidation processes have attracted tremendous attention on the destruction of toxic and non-biodegradable organics. A series of neodymium (Nd)-doped PbO2 electrodes (Ti/PbO2-Nd) were synthesized through a pulse electrodeposition method, and its activity of bisphenol S (BPS) removal was further examined. The morphologies and structures were characterized by the X-ray diffraction (XRD), scanning electron microscopy (SEM) and an energy dispersive spectrometer (EDS). The performance, energy consumption and mechanism of electrochemical oxidation of BPS by Ti/PbO2-Nd electrode were also discussed. Compared to the traditional Ti/PbO2 electrode, the Ti/PbO2-Nd enables finer crystal particles, facilitating the oxygen evolution overpotential (OEP) from 1.41V to 1.55V and the generation of hydroxyl radicals (•OH). Moreover, lower duty cycles during the preparation of the electrode also contribute to the tapering size of crystals. The results show that the Ti/PbO2-Nd electrode exhibits relatively high activity in the anodic oxidation of BPS. Over 95% of BPS could be removed with the current density of 15 mA cm−2. Moreover, the energy consumption of BPS degradation on Ti/PbO2-Nd electrode is 60.26 kWh m−3, much lower than that on Ti/PbO2 electrode (95.45 kWh m−3). To conclude, the Ti/PbO2-Nd electrode has been proven to be a promising material for BPS removal.

Electrochemical filtration carbon membrane derived from coal for wastewater treatment: Insights into the evolution of electrical conductivity and electrochemical performance during carbonization

A novel electrochemical filtration carbon membrane (ECM) was developed from caking coal via self-bonding in this work. The evolutions of chemical structure, morphology, carbon microstructure from nonconductive precursor membrane to conductive ECM during carbonization were systemically investigated by FTIR, SEM, Raman and XRD. The evolution mechanism of electrical conductivity and electrochemical performance of ECM was proposed and discussed. The electrochemical filtration performance of ECM was evaluated by using the phenol as simulated pollutant in wastewater treatment. It was found that the precursor membrane underwent the violent thermal decomposition and condensation during carbonization. The electrical conductivity and electrochemical performance of ECM depended strongly on carbonization temperature (CT), which was attributed to the evolution of carbon microstructure such as the growth of the conductive carbon clusters and defect graphite lattices (active sites) as CT increased. The electrochemical filtration performance of ECM on phenolic water was strongly correlated to its electrochemical properties. The higher electrochemical activity of ECM would result in the better electrochemical filtration performance. The ECM obtained at 950 °C exhibited the optimal overall performance, and its phenol and COD removal rates were up to 91.65% and 81.89% under the applied voltage of 2.0 V, respectively. The mechanism of electrochemical oxidation involved in ECM included the direct oxidation and indirect oxidation, in which the indirect oxidation was caused by the electro-catalytic activity of minerals existed in ECM.

Electrocatalytic degradation of dibenzoazepine drugs by fluorine doped β-PbO2 electrode: New insight into the electrochemical oxidation and mineralization mechanisms

In this paper, we achieve two important goals. First, we have developed an efficient electrocatalytic oxidation method using a nanostructured graphite/fluorine doped β-PbO2 electrode to remove difficult-to-oxidize dibenzoazepine drugs (imipramine, desipramine and clomipramine). The prepared electrode has a wide electrochemical potential window, high removal percentage and ability to operate under ambient conditions. The experimental results show that the proposed method for the mineralization of dibenzoazepine drugs has high removal percentage, so that the average removal percentage of these drugs is 95%. The second goal of this paper is to study the electrochemical behavior of dibenzoazepine drugs in aqueous solutions with different pH values to propose comprehensive mechanisms for the electrooxidation and mineralization of imipramine on the GC and G/F-PbO2 electrodes, respectively.

Electrocatalysis and simultaneous determination of hydroquinone and acetaminophen using PN[sbnd]COF/graphene oxide modified electrode

In this present study, a new porphyrin based covalent organic framework material (PNCOFs) is synthesized by the imidization reaction of tetraminophenyl porphyrin (TAPP) and 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTCDA), and then the obtained COFs were combined graphene oxide (GO) to prepare PNCOFs/GO modified electrode for the simultaneous determination of hydroquinone (HQ) and acetaminophen (AC). The composite material displays a well synergistic effect of high electrocataytic activity of the COFs and good conductivity of GO. Catalytic process and electrochemical oxidation mechanism are discussed. Under the optimum conditions, the detection limits are 1.1 × 10−8 mol L − 1 and 9.0 × 10−9 mol L − 1 for AC and HQ, respectively. The linear ranges are 2.0 × 10−7 mol L − 1 to 1.5 × 10−4 mol L − 1 for AC and 1.0 × 10−7 mol L − 1 to 1.0 × 10−4 mol L − 1 for HQ. This work is beneficial to the electrochemical application of COFs.

Electrochemical oxidation mechanisms for selective products due to C-O and C-C cleavages of β-O-4 linkages in lignin model compounds.

Electrochemical oxidation is a promising and effective method for lignin depolymerization owing to its selective oxidation capacity and environmental friendliness. Herein, the electrooxidation of non-phenolic alkyl aryl ether monomers and β-O-4 dimers was experimentally (by cyclic voltammetry, in situ spectroelectrochemistry, and gas chromatography-mass spectroscopy) and theoretically (by DFT calculations) explored in detail. Compared to the reported literature (T. Shiraishi, T. Takano, H. Kamitakahara and F. Nakatsubo, Holzforschung, 2012, 66(3), 303-309), 1-(4-ethoxyphenyl)ethanol showed a distinguishable oxidation pathway, where the resulting carbonyl product surprisingly underwent a bond cleavage on alkyl-aryl ether to ultimately produce a quinoid like compound. In contrast, β-O-4 dimers, like 2-phenoxy-1-phenethanol and 2-phenoxyacetophenone also demonstrated electrochemical oxidation induced by Cβ-O and Cα-Cβ bond cleavages. For the oxidation products, the presence of the Cα-hydroxyl group in dimers was the key to selectively generate aldehyde-containing species under mild electrochemical conditions, otherwise it produces alcohol-containing products following a different mechanism compared to the Cα[double bond, length as m-dash]O containing dimers.

Investigation into electrochemical oxidation behavior of 4H-SiC with varying anodizing conditions

Electrochemical-assisted hybrid machining has been widely utilized for processing of single crystal SiC, which is a very promising next-generation semiconductor material for high power, high frequency and high temperature applications. With the aim of optimizing the machining process to achieve both high efficiency and high surface integrity, the electrochemical oxidation behaviors of 4H-SiC were experimentally investigated with varying the anodizing conditions from the aspects of electrolyte types, ionic concentration, potentials etc. in this study. Experimental results demonstrated that neutral solutions showed higher oxidation ability of 4H-SiC in comparison to acidic and alkaline electrolytes. 4H-SiC could be electrochemically oxidized in an extremely low concentration electrolyte, and mass concentration 1–2% could achieve highest film thickness of 197 nm and initial oxidation rate of 4.9 nm/s. The oxidation rate increased exponentially at the initial stage of anodization before reaching saturation. Meanwhile, the oxidation process exhibited significant anisotropy, with the oxidation rate of C-face 5–15 times higher that of Si-face. On the other hand, the hardness of the electrochemically-oxidized 4H-SiC surface was reduced by more than 90%. It was also noticed that the micro morphology of oxidized surface was significantly influenced by the ion types in the electrolytes. Furthermore, the electrochemical oxidation mechanism of 4H-SiC were discussed based on the experimental findings. The OH. radical was considered the main factor determining the oxidation process of SiC. The research results deepen the understanding of the electrochemical oxidation of SiC and provide insights for optimizing the electrochemical-assisted hybrid machining process.

Genotoxic permanent hair dye precursors p-aminophenol and p-toluenediamine electrochemical oxidation mechanisms and evaluation in biological fluids

The p-toluenediamine (PTD) and p-aminophenol (PAP), genotoxic precursor agents widely used in permanent hair dyeing formulations, electrochemical mechanisms and evaluation in biological fluids, at a glassy carbon electrode, in a wide pH range, by cyclic, differential pulse, and square wave voltammetry, were investigated. The oxidation of both PTD and PAP is reversible. The PTD two electrons and two protons transfer diffusion-controlled reaction occurs at the molecule nitrogen atoms in the amine groups. Also PAP oxidation is a two electrons and two protons transfer diffusion-controlled reactions, and occur at the nitrogen and oxygen atoms of the molecule amine and hydroxyl groups. An electrochemical oxidation mechanism for PTD and PAP is proposed. The PTD and PAP diffusion coefficients, DPTD = 1.57 × 10−5 cm2 s−1 for PTD, and DPAP = 1.03 × 10−5 cm2 s−1 for PAP, were determined. The electrochemical quantification in 0.10–1.00 μM concentration range showed a detection limit of 0.12 μM for PTD and 0.17 μM PAP. A new electroanalytical method for the determination of PTD and PAP in fetal bovine serum biological fluid, and in artificial urine samples, using differential pulse voltammetry, was also developed.

Lifetime Prediction of Electrochemical Ion Migration with Various Surface Finishes of Printed Circuit Boards

Electrochemical ion migration (ECM) can be generated by the electrochemical reaction between the anodic and cathodic electrodes of an electric circuit in the case of temperature, humidity and applied voltage. ECM can finally induce a malfunction of electronics due to precipitation of metallic ions in the cathode. In this work, we study the failure mechanism based on the identifying stress factor of ECM to occur and the accelerated life prediction of ECM occurrence. The modified Eyring model, which includes a stress model (temperature, humidity and voltage), is utilized to accelerate the life prediction of ECM. To obtain the temperature and humidity coefficient factors of ECM failure, an accelerated life test is conducted with a more than 50% failure of five types of test conditions, namely, 85°C/75% RH, 65°C/85% RH, 85°C/85% RH, 75°C/85% RH and 85°C/95% RH. The failure criterion of insulation resistance between the conductors is less than or equal to 107 Ω. In situ monitoring of surface insulation resistance is performed throughout the temperature-humidity-bias tests for over 2600 h. From these results, we deduce the temperature and humidity coefficients of the acceleration model for predicting ECM time-to-failure in electroless nickel-immersion gold (ENIG) surface finish conductors covered with a solder mask. In addition, the electrochemical oxidation and reduction mechanisms of ECM are examined by physics-of-failure. Finally, we predict the B10 life for ECM to occur on a FR-4 printed circuit board with an ENIG surface finish in use environment.

Synthesis and Characterization of Electrocatalysts for the Hydrogen Evolution and Hydrogen Oxidation Reactions in Alkaline Environment

The development of catalysts for the electrochemical processes of hydrogen systems (e.g. fuel cells and electrolyzer systems) continues to be a significant area of research for renewable energy technologies. One significant challenge has been the development of hydrogen catalysts that can be utilized in alkaline environments as the kinetics of hydrogen reactions decrease by two orders of magnitude in alkaline environments compared to acidic[1,2]. Chemical vapor deposition (CVD) is a conventional tool used in the synthesis of such catalysts[3,4]. This presentation discusses the extending work being done using a variant CVD process known as “Poor Man’s” CVD (PMCVD), to further its impact in electrochemical catalyst application[5]. PMCVD is utilizes an inexpensive vacuum oven to sublime commercially available metal-organic precursors; lowering synthesis cost while providing increased control of particle size and distribution. This work describes the work done to assess the PMCVD mechanisms as well as its use to develop catalysts for the hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER) in alkaline environments. Preliminary studies have shown that PMCVD can develop catalysts with highly dispersed nanoparticles on various supports. As depicted in Figure 1, PMCVD synthesized Pt/C and PtRu/C catalysts have shown to have improved kinetics over commercial developed catalysts exhibiting approximately a 40% and 45% increase in average exchange current densities respectively when compared to Tanaka Kikinzoku catalysts of the same loading. An extended function of the PMVCD process is the ability to synthesize alloyed catalysts in a single deposition process. By understanding the parametric effects of temperature and pressure on the deposition process with respect to particle size and distribution, we can optimize the PMCVD process to develop highly active catalysts that can be used in alkaline hydrogen systems. [1] Durst, J. et al. New insights into the electrochemical hydrogen oxidation and evolution reaction mechanism. Energ. Environ. Sci. 7, 2255–2260 (2014). [2]Sheng, W. et al. Hydrogen Oxidation and Evolution Reaction Kinetics on Platinum: Acid vs Alkaline Electrolytes. . Electrochem. Soc. 2010 volume 157, issue 11, B1529-B1536 [3] Garcia, Vargas, et al. “Chemical Vapor Deposition of Iridium, platinum, Rhodium, and Palladium.” Materials Transactions, Vol. 44, No. 9 (2003) pp. 1717-1728 [4] Serp, Philppe, et. al. “Chemical Vapor Deposition Methods for the Controlled Preparation of Supported Catalytic Materials.” Chem. Rev. 2002, 102, 3085−3128 [5] Papandrew, A. et al. Advanced Electrodes for Solid Acid Fuel Cells by Platinum Deposition on CsH2PO4. Chem. Mater. 2011, 23, 7, 1659-1667 Figure 1

The mechanism of the electrochemical oxidation in the constant current mode of the porous silicon

In order to clarify the mechanism of the electrochemical oxidation (ECO) in the constant current mode of porous silicon (PS), the ECO process of PS in different concentration of electrolyte was studied in detail. According to the experiment facts, a hypothesis based on the mechanism of ‘electrical break’ was first proposed to explain the oxidation interruption that tends to occur in the lower concentration of the electrolyte. The experiment results show that the bottom of the porous layer is preferential oxidized in the ECO process since the oxidation process was governed by the holes injected from the substrate and supplied to the silicon-electrolyte interface. The appearance of the oxidation interruption during the ECO process is due to the electrical isolation between the Si substrate and electrolyte by the formation of a continuous oxide film at the bottom of the porous layer. The results obtained in this work indicated that it is easy to control the thickness of the oxide film by adjusting the concentration of electrolyte, which made the ECO method appears to be more attractive when incomplete oxidation is required. This present work is also contributes to the fundamental understanding of the ECO mechanism in the constant current mode of the PS material.

Direct Glucose Fuel Cell: Carbon Support Effect on the Anode Nanocatalysts Efficiency

Glucose is a promising fuel for new implantable electrochemical power sources due to its abundance in the human body. The selective oxidation of this sugar to gluconic acid requires an active and efficient catalyst surface. Platinum is the reference catalyst, but displays a fast deactivation due to the poisoning effect of strongly chemisorbed intermediates during glucose electro-oxidation1. On the other hand, gold is well known for its exceptional electrochemical activity and selectivity on aldehydes and hemiacetals conversion in a large pH window2. Combining these two metals as unique electrocatalyst for glucose oxidation, becomes a way to overcome poisoning issue. Furthermore, the nature of the support also plays an important role in the enhancement of the catalyst activity and stability. Recently, researches on graphene-like materials have shown the benefit of their utilization as support for electrocatalysts3. In the present work, gold and platinum monometallic and bimetallic nanoparticles have been synthesized on different carbon supports: amorphous carbon Vulcan XC 72R and reduced graphene oxide (rGO). Physicochemical and electrochemical characterizations show that i) Bromide Anion Exchange (BAE) synthesis method provides good anchorage and dispersion of the nanoparticles (particle mean size < 10 nm) on supports, ii) glucose electro-oxidation on gold monometallic catalysts starts at 0.3 V/RHE in alkaline media and before 0.1 V/RHE for platinum monometallic and bimetallic catalysts, iii) rGO supported platinum, and gold-platinum alloys (Au70Pt30 and Au50Pt50 ) exhibit higher power density than the corresponding nanocatalysts supported on Vulcan when used as anode in an alkaline glucose/oxygen fuel cell (Figure 1). The electrochemical study in near-biological conditions confirms and even accentuates the differences between the supports in terms of efficiency, stability and compatibility. The chromatographic and mass spectrometry analyses of the reactions products from the operation of this direct glucose fuel cell in alkaline medium demonstrate the presence of gluconate as a major product. Moreover, glucuronate considered as a high value added compound, has been clearly identified. References Kerzenmacher, S.; Ducree, J.; Zengerle, R.; von Stetten, F., An abiotically catalyzed glucose fuel cell for powering medical implants: Reconstructed manufacturing protocol and analysis of performance. Journal of Power Sources 2008, 182 (1), 66-75. Pasta, M.; La Mantia, F.; Cui, Y., Mechanism of glucose electrochemical oxidation on gold surface. Electrochim. Acta 2010, 55 (20), 5561-5568. Yadav, R.; Subhash, A.; Chemmenchery, N.; Kandasubramanian, B., Graphene and Graphene Oxide for Fuel Cell Technology. Ind. Eng. Chem. Res. 2018. Figure 1: Polarization and power density curves of different nanocatalysts used as anode in a glucose/oxygen fuel cell recorded in 0.1 mol L-1 KOH + 50 mmol L-1 glucose. All catalysts have a metal loading of 20 wt. % on carbon substrates. Pt/Vulcan is used as cathode catalyst. Figure 1