Catalytic Activity of Anisotropic Gold Nanoplates towards Oxygen Reduction

Glassy carbon electrode (GCE) coated with anisotropic gold nanoplates (aAuNPs) was used for the study of oxygen reduction reaction (ORR) in 0.5 M sulfuric acid instead of bulk gold electrodes. The electrode cleaning/activation procedure lead to the removal of any charged and uncharged residues on the gold nanoplates, leaving the nanostructured surface highly active towards oxygen reduction. The advantages: much lower overpotential and larger current densities of oxygen reduction are ascribed to the unique nanostructures present on the carbon electrode surface‐the gold nanoplates. They are rich in edges providing a large population of Au (100) sites with unsaturated coordination exposed to the solution, and catalytically active. Measurements performed using a rotating disc electrode, modified with the gold nanoplates, confirmed that ORR proceeds via two separate steps: oxygen is reduced to hydrogen peroxide, and the peroxide is further reduced in a two‐electron reduction to water.     

Au单晶电极上H2O2的氧化反应研究

本文利用旋转圆盘电极系统研究了酸性介质中H₂O₂在Au(100)和Au(111)电极表面的电化学行为. 实验发现在Au电极上H₂O₂难以发生还原,但是当电位稍微正于H₂O₂氧化为O₂的平衡电势时即可发生氧化. 在Au(111)上H₂O₂氧化的起始电位比在Au(100)正0.1 V左右. Au(100)上的双桥位位点能增强反应中间体*OOH的吸附,可能是导致Au(100)上H₂O₂氧化反应超电势比Au(111)低的主要原因. 在较正电位区(E>1.2 V), 当电极表面被氧物种覆盖时,H₂O₂在两个电极上的氧化都会受到一定程度的抑制,这种影响在Au(111)上比Au(100)上更加明显,这与Au(111)上氧物种的生成与逆向还原可逆性差的趋势一致. 最后还将Au与Pt单晶电极上H₂O₂氧化的行为进行了对比分析.     

Nanostructured catalysts for cathodes of oxygen-hydrogen fuel cells

Bimetallic catalysts platinum-cobalt, platinum-chromium, and platinum-tungsten, deposited onto highly dispersed carbon black from complex cluster-type compounds of corresponding metals with a 1: 1 atomic ratio of metals are developed. The catalysts are characterized by methods of x-ray diffraction analysis and energy dispersive analysis of x-rays. The procedure involving use of a thin-film rotating disk electrode is employed to probe kinetic parameters of the oxygen reduction reaction on the catalysts developed. The investigated binary catalysts exhibit specific electrochemical characteristics that are not inferior and, in some cases, are superior to the characteristics intrinsic to the commercial platinum catalyst E-TEK, when tested in the composition of a gas-diffusion electrode under conditions that are close to real conditions in which cathodes of oxygen-hydrogen fuel cells operate.     

Effect of the nature of carbonaceous supports on the bioelectrocatalytic activity of peroxidase, immobilized on the supports, in the hydrogen peroxide reduction reaction

Electrochemical properties of such disperse carbonaceous materials as acetylene black AD-100, finely divided colloidal graphite (FCG), ultradisperse diamond (UDD), and carbon nanotubes (CNT) are examined. Effect of the nature of disperse carbonaceous supports on bioelectrocatalytic activity of adsorbed peroxidase (POD) in the hydrogen peroxide reduction reaction is investigated. It is shown that the hydrogen peroxide reduction on the biocatalysts studied proceeds in conditions of direct bioelectrocatalysis independently of the disperse-support type. It is also demonstrated that the biocatalysts’ activity depends on the structure and properties of the surface of the supports defining the magnitude of the POD adsorption in an orientation favorable for direct bioelectrocatalysis. Maximum activity is inherent in the catalysts manufactured on the basis of materials with moderate hydrophobic and hydrophilic properties. By the magnitude of the activity in the hydrogen peroxide reduction reaction, depending on the nature of the carbonaceous support, the fabricated catalysts (carbonaceous material with adsorbed POD) form the series AD-100, CNT > FCG > UDD.     

Mechanism of electrochemical reduction of hydrogen peroxide on copper in acidic sulfate solutions

Hydrogen peroxide is a commonly used oxidizer component in chemical mechanical planarization slurries, used in the processing of Cu metallization in microelectronics applications. We studied the electrochemical reduction of hydrogen peroxide on Cu in 0.1 M H2SO4 solutions using methods including cyclic voltammetry, rotating disk electrode experiments, surface-enhanced Raman spectroscopy, and density functional theory (DFT) calculations. The spectroscopy reveals that the hydrogen peroxide molecule is reduced at negative potentials to form a Cu-OH surface species in acidic solutions, a result consistent with the insight from Tafel slope measurements. DFT calculations support the instability of peroxide relative to the surface-coordinated hydroxide on both Cu(111) and Cu(100) surfaces.     

Electropolymerization of iron tetra(<Emphasis Type="Italic">o</Emphasis>-aminophenyl)porphyrin from aqueous solution and the electrocatalytic behavior of modified electrode

Stable electroactive iron tetra(o-aminophenyl)porphyrin (FeTAPP) films are prepared by electropolymerization from aqueous solution by cycling the electrode potential between −0.4 and 1.0 V vs Ag/AgCl at 0.1 V s⁻¹. The cyclic voltammetric response indicates that polymerization takes place after the oxidation of amino groups, and the films could be produced on glassy carbon (GC) and gold electrodes. The film growth of poly(FeTAPP) was monitored by using cyclic voltammetry and electrochemical quartz crystal microbalance. The cyclic voltammetric features of Fe(III)/Fe(II) redox couple in the film resembles that of surface confined redox species. The electrochemical response of the modified electrode was found to be dependent on the pH of the contacting solution with a negative shift of 57 mV/pH. The electrocatalytic behavior of poly(FeTAPP) film-modified electrode was investigated towards reduction of hydrogen peroxide, molecular oxygen, and chloroacetic acids (mono-, di-, and tri-). The reduction of hydrogen peroxide, molecular oxygen, and dichloroacetic acid occurred at less negative potential on poly(FeTAPP) film compared to bare GC electrode. Particularly, the overpotential of hydrogen peroxide was reduced substantially. The O₂ reduction proceeds through direct four-electron reduction mechanism.     

MnFeNi-Based Composite as a Case Study of a Bifunctional Oxygen Electrocatalyst under Dynamically Changing Electrode Potentials

High-performance bifunctional electrocatalysts for the oxygen reduction (ORR) and oxygen evolution reaction (OER) are essential components in energy conversion and storage technologies. Yet, their poor reversibility hinders their applicability. A highly active ORR/OER catalyst, consisting of multiwalled carbon nanotubes-supported MnFeNiOx nanoparticles, was subjected to sequences of chronoamperometric steps alternating between the ORR, the OER and highly cathodic potentials (E_c). Rotating ring disk electrode methods revealed that applying E_c leads to a small increase in the current and peroxide species yield during the ORR while enhancing substantially the OER. X-ray absorption spectroscopy showed irreversible changes in the chemical state of MnFeNiOx correlating with its catalytic properties. The complexity of changes that a composite catalyst may undergo under varying potentials, the importance of monitoring product formation, and the convenience of using dynamic electrochemical sequences for the assessment of catalyst reversibility, as well as for the activation and/or restoration of their catalytic properties, are highlighted.     

苯在旋转圆盘电极上的氧化过程动力学

Ｃｌａｒｋ等［１］研究苯阳极氧化过程,认为二氧化铅是最合适的电极,苯是二级反应,苯在阳极上首先氧化为产物对苯二醌,产物可进一步氧化成马来酸,直至氧化成二氧化碳．但Ｉｔｏ［２］等研究表明苯阳极氧化还有一个并行反应：苯直接氧化为马来酸．Ｆｌｅｓｚａｒ和Ｐ...     

Electrochemical Codeposition of Platinum and Molybdenum Oxides: Formation of Composite Films with Distinct Electrocatalytic Activity for Hydrogen Peroxide Detection

The electrochemical properties of gold electrode surfaces modified by molybdenum oxide films intercalated with platinum microparticles have been described. The incorporation of Pt microparticles at the oxide film was characterized by PIXE (particle induced X‐ray emission) spectroscopy. The modified electrode showed electrochemical activity at around ?0.5 V in 50 mmol L^?1 Na₂SO₄ supporting electrolyte (pH 3), corresponding to the reduction of protons at platinum sites and further transfer of hydrogen atoms to form reduced molybdenum oxides (bronzes). At 0.1 V, the MoO₃ / Pt electrode showed a better performance for hydrogen peroxide oxidation than on platinized gold electrodes. The solution pH has a marked effect on the voltammetric profile and best responses for hydrogen peroxide were obtained at the 5.0 to 6.0 pH range. The activation of the electrode by polarization at negative potentials was also studied and a mechanism by which more platinum sites are available as a consequence of this process was proposed. Calibration plots for hydrogen peroxide were highly linear (r=0.9989) in the 0.2 to 1.6 mmol L^?1 concentration range, with a relative standard deviation (RSD)<1%.     

Electroreduction of molecular oxygen on dispersed copper in an ion-exchange matrix

Electrochemical reduction of molecular oxygen was studied on a [dispersed copper]-[macroporous KU-23 15/100S sulfocation exchanger with various metal concentrations] composite electrode. It was found that a high proton concentration in the ion-exchange matrix causes a decrease in the oxygen reaction overvoltage. The nanostructured state of copper particles causes stabilization of the intermediate product, i.e., hydrogen peroxide. Using the rotating disk electrode method, it was detected that the process is limited by external diffusion of oxygen to composite grains. The oxygen reaction is mostly concentrated on the grain surface and surface layers; oxygen is reduced in the bulk due to dispersed copper oxidation.     

Electrocatalytic Dioxygen Reduction at Glassy Carbon Electrode Modified with Polyaniline Grafted Multiwall Carbon Nanotube Film

The work details the electrocatalysis of oxygen reduction reaction (ORR) in 0.5 M H₂SO₄ medium on a modified electrode containing a film of polyaniline (PANI) grafted multi‐wall carbon nanotube (MWNT) over the surface of glassy carbon electrode. We have fabricated a novel modified electrode in which conducting polymer is present as connected unit to MWNT. The GC/PANI‐g‐MWNT modified electrode (ME) is fabricated by electrochemical polymerization of a mixture of amine functionalized MWNT and aniline with GC as working electrode. Cyclic voltammetry and amperometry are used to demonstrate the electrocatalytic activity of the GC/PANI‐g‐MWNT‐ME. The GC/PANI‐g‐MWNT‐ME exhibits remarkable electrocatalytic activity for ORR. A more positive onset potential and higher catalytic current for ORR are striking features of GC/PANI‐g‐MWNT‐ME. Rapid and high sensitivity of GC/PANI‐g‐MWNT‐ME to ORR are evident from the higher rate constant (7.92×10² M^?1 s^?1) value for the reduction process. Double potential chronoamperometry and rotating disk and rotating ring‐disk electrode (RRDE) experiments are employed to investigate the kinetic parameters of ORR at this electrode. Results from RDE and RRDE voltammetry demonstrate the involvement of two electron transfer in oxygen reduction to form hydrogen peroxide in acidic media.     

Electrocatalysis of the Oxygen Reaction by Pyropolymers of N4 Complexes

Results of research into structural and electrocatalytic properties of metalloporphyrins and metallophthalocyanines pyrolyzed on carbon supports of various dispersion degree in the oxygen electroreduction reaction (OER) are analyzed. The pyrolysis products (pyropolymers) that form at T 800° in inert atmosphere contain centers Co(Fe)–N surrounded by carbon particles. The oxygen electroreduction reaction on pyropolymers in acid and alkali solutions is studied on a model gas-diffusion electrode and a rotating ring–disk electrode. The slopes of Tafel plots in an acid solution are 60 and 120 mV. On a disk electrode covered with a pyropolymer, the intermediate product of OER, hydrogen peroxide, is fixed on the ring electrode throughout the entire range of OER potentials. The activity of pyropolymers in the hydrogen peroxide electroreduction reaction in an acid solution is insignificant. In an acid environment, OER occurs via a parallel–successive mechanism with a slow stage of the attachment of the first electron. In alkali media, slopes of Tafel plots equal 40 and 120 mV at low and high polarizations, respectively. The amount of hydrogen peroxide fixed on the ring electrode corresponds to 2–5% of the disk electrode current. A pyropolymer is active in the hydrogen peroxide reduction. The slow stage in OER in an alkali environment is the attachment of the second electron at a low polarization and the attachment of the first electron, at a high polarization. In acid and alkali solutions a pyropolymer is methanol-tolerant.     

Oxygen reduction and hydrogen evolution–oxidation reactions on Cu(hkl) surfaces

Taking advantage of the ring collection properties of the rotating ring–disk electrode with a single-crystal copper disk, we have shown that the oxygen reduction reaction and the hydrogen evolution–oxidation reactions on Cu(111) and Cu(100) surfaces in sulfuric acid are structure-sensitive processes. An interpretation of the structural sensitivity is presented, based on the premise of the structure-sensitive adsorption of (bi)sulfate anions. We have observed that the ordering kinetics of the (bi)sulfate on Cu(hkl) have an important role in the mechanism of the oxygen reduction reaction.     

Modeling of mass and charge transfer in an inverted rotating disk electrode (IRDE) reactor

In this work, the validation of a newly constructed inverted rotating disk electrode (IRDE) reactor is reported. Compared to the rotating disk electrode (RDE) reactor, the working electrode is changed in position from the top to the bottom of the electrochemical cell. The IRDE reactor is designed to facilitate the actual study of gas evolution reactions. It is studied whether the first-order analytical expression for the velocity field in an RDE reactor is also acceptable for an IRDE configuration. To that purpose, the kinetic parameters of the well-known ferri/ferro cyanide redox system are determined in both configurations and compared. This is done qualitatively by comparing the polarization curves obtained in the inverted and the conventional RDE configuration. Additionally, a statistically founded fitting algorithm is used to quantitatively determine the model parameters of the oxidation and reduction reaction. Not only the diffusion coefficients of Fe²⁺ and Fe³⁺ are calculated, but also the rate constants (k_ox and k_red) and the transfer coefficients (α_ox and α_red) are quantified and compared together with their respective standard deviation. It is found that the parameters of mass and charge transfer in both configurations agree well. So it is concluded that the same analytical equations of mass and charge transfer can be used in both the RDE and the IRDE reactor.     

Catalytic decomposition of hydrogen peroxide in alkaline solutions

Catalytic activity of carbon, platinum-supported on high-area carbon, platinum, lead ruthenate, and ruthenium oxide towards hydrogen peroxide decomposition in alkaline solution is investigated using the rotating disk electrode technique. The heterogeneous rate constant for peroxide decomposition on these catalysts is determined from the slope of log(i_L) versus time, where i_L is the diffusion-limiting current corresponding to the concentration of peroxide at a given time. The order of catalytic activity is found to be platinum>lead ruthenate>ruthenium oxide>carbon. A general reaction mechanism for the peroxide decomposition on these catalysts is also proposed.     

Hidden in plain sight: unlocking the full potential of cyclic voltammetry with the thin-film rotating (ring) disk electrode studies for the investigation of oxygen reduction reaction electrocatalysts

Cyclic voltammetry conducted with a thin-film rotating disk electrode, or ring-disk electrode (CV-TF-R(R)DE) is a very popular ‘ex situ’ tool for the rapid screening of electrocatalysts for their activity in oxygen reduction reaction. Despite its popularity and broad use, in most instances only a small part of the information that could be accessed by CV-TF-R(R)DE is actually used by scientists in their research. This work outlines both innovative and more traditional (but half-forgotten) ways of using CV-TF-R(R)DE to its optimal or full potential in the ongoing quest to study the most relevant features of oxygen reduction reaction electrocatalysts and quickly identify the most promising candidates for their applications in fuel cells or other electrochemical devices.     

Silver nanoparticle assemblies supported on glassy-carbon electrodes for the electro-analytical detection of hydrogen peroxide

Electrochemical detection of hydrogen peroxide using an edge-plane pyrolytic-graphite electrode (EPPG), a glassy carbon (GC) electrode, and a silver nanoparticle-modified GC electrode is reported. It is shown, in phosphate buffer (0.05 mol L^–1, pH 7.4), that hydrogen peroxide cannot be detected directly on either the EPPG or GC electrodes. However, reduction can be facilitated by modification of the glassy-carbon surface with nanosized silver assemblies. The optimum conditions for modification of the GC electrode with silver nanoparticles were found to be deposition for 1 min at –0.5 V vs. Ag from 5 mmol L^–1 AgNO₃/0.1 mol L^–1 TBAP/MeCN, followed by stripping for 2 min at +0.5 V vs. Ag in the same solution. A wave, due to the reduction of hydrogen peroxide on the silver nanoparticles is observed at –0.68 V vs. SCE. The limit of detection for this modified nanosilver electrode was 2.0×10^–6 mol L^–1 for hydrogen peroxide in phosphate buffer (0.05 mol L^–1, pH 7.4) with a sensitivity which is five times higher than that observed at a silver macro-electrode. Also observed is a shoulder on the voltammetric wave corresponding to the reduction of oxygen, which is produced by silver-catalysed chemical decomposition of hydrogen peroxide to water and oxygen then oxygen reduction at the surface of the glassy-carbon electrode.     

Sensitive Flow-Injection Electrochemical Determination of Hydrogen Peroxide at a Palladium Nanoparticle-Modified Pencil Graphite Electrode

A novel flow-injection amperometric method was proposed for the sensitive and enzymeless determination of hydrogen peroxide based on its electrocatalytic reduction at a palladium nanoparticle-modified pretreated pencil graphite electrode in a laboratory-constructed electrochemical flow cell. Cyclic voltammograms of the unmodified and modified electrodes were recorded in pH 7.0 phosphate buffer containing 0.10 M KCl at a scan rate of 50?mV s^?1 for the investigation of electrocatalytic reduction of hydrogen peroxide at the palladium nanoparticle-modified pretreated pencil graphite electrode. Cyclic voltammograms of the pretreated pencil graphite electrode revealed an irreversible oxidation peak and a weak reduction peak of hydrogen peroxide at +1100?mV and –450?mV vs. an Ag/AgCl/KCl saturated reference electrode. However, the reduction of hydrogen peroxide was observed at –100?mV with an increase in current in the cyclic voltammograms of the palladium nanoparticle-modified pretreated pencil graphite electrode compared to the unmodified electrode. These results indicate that the palladium nanoparticle-modified pretreated pencil graphite electrode exhibits efficient electrocatalytic activity for the reduction of hydrogen peroxide. A linear concentration range was obtained between .01 and 10.0?mM hydrogen peroxide with a detection limit of 3.0 µM from flow injection amperometric current–time curves recorded in pH 7.0 phosphate buffer at –100?mV and a 2.0?mL min^?1 flow rate. The novelty of this work relies on its use of a laboratory-constructed flow cell constructed for the pencil graphite electrode using these inexpensive, disposable, and electrochemically reactive modified electrodes for the amperometric determination of hydrogen peroxide in a flow injection analysis system.     

Electrocatalytic reduction of molecular oxygen at electrodes coated with a new cobalt(II)–platinum(II) bimetallic porphyrin

Cobalt(II) inserts into 5-(4-pyridyl)-10,15,20-(3,4-dimethoxyphenyl)porphyrin (1) by reaction of the porphyrin with the cobalt(II) acetate salt in refluxing N,N′-dimethylformamide solutions. When the porphyrin and the cobalt porphyrin are reacted with PtCl₂(DMSO)₂ in dichloromethane at ambient temperatures the platinum complex coordinates to the peripheral pyridyl group of the porphyrin. Roughened EPG electrodes coated with the cobalt(II)–platinum(II) bimetallic porphyrin, complex (4), show a 500?mV shift in the reduction of molecular oxygen in acidic media when compared to the bare electrode. Oxidation of the bimetallic porphyrin coated electrodes at 1.20?V versus saturated calomel electrode (SCE) results in an additional shift of ca 100?mV for the reduction of molecular oxygen when compared to the bimetallic porphyrin coated electrode prior to oxidation. In addition the oxidized surface shows the ability to reduce approximately 50% of the oxygen to water and the other 50% to hydrogen peroxide according to rotating disk electrode measurements.     

The role of anions in oxygen reduction in neutral and basic media on gold single-crystal electrodes

Oxygen reduction on well-defined single-crystal electrodes in different basic and neutral media has been studied using the impinging jet system. The results obtained with this system in 0.1 M NaOH are comparable to those reported in the literature for rotating disk electrodes, indicating that the impinging jet system behaves as a system in which the thickness of the diffusion layer is stationary. The activity of the Au(100) electrode is considerably higher than the rest of the basal planes in all media and yields water when E>–0.2 V and hydrogen peroxide for E<–0.2 V on the SHE scale. For Au(111) and Au(110) the activity of the electrode is much smaller and the final product is always hydrogen peroxide. The transition between both mechanisms for the Au(100) is, essentially, independent of the solution pH. In acid media the final product is always hydrogen peroxide for all the electrodes studied. The differences between the activities of the electrodes have been explained in the light of the different adsorption properties of the surfaces in relation to HO₂ ^–. In the case of the Au(100) electrode, the existence of a negative charge density on the metal inhibits further reduction of HO₂ ^–.Dedicated to Prof. Dr. Wolf Vielstich on the occasion of his 80th birthday in recognition of his numerous contributions to interfacial electrochemistry