Mediated Oxygen Reduction Research Articles

Hyperoxidation active species produced by seawater electro membrane reactor assisted electrolytic cell system for simultaneous decyanation and carbon removal

Herein, a novel triple-layered heterojunction catalytic cathode membrane (PVDF/rGO/TFe/MnO2, TMOHccm) was reported and applied in seawater electro membrane reactor assisted electrolytic cell system (SEMR-EC), achieving increased properties for cyanide wastewater treatment. Hydrophilic TMOHccm exhibits higher electrochemical activity (qT* 1.11 C cm−2, qo* 0.03 C cm−2), indicating excellent electron transfer efficiency. Further analysis shows a one-electron redox cycle of exposed transition metal oxides (TMOs) on rGO support mediated oxygen reduction reaction (ORR) process, and calculated results of density functional theory (DFT) demonstrates positive Bader charge (72 |e|) of synthesized catalyst. The developed SEMR-EC was implemented in intermittent-stream operation for treating cyanide wastewater, the system achieved optimized decyanation and carbon removal performance (CN− 100%, TOC 88.49%). Hyperoxidation active species produced SEMR-EC including hydroxyl, sulfate, and reactive chlorine species (RCS) was confirmed. The proposed mechanistic explanation indicated multiple removal pathways relevant to cyanide, organic matter, and iron were elucidated, and the engineering applications prospects were highlighted by cost (5.61 $) and benefit (Ce 399.26 mW m−2 $−1, EFe 248.11 g kWh−1) analysis of the system.

Evidence of Sulfur Non-Innocence in [CoII (dithiacyclam)]2+ -Mediated Catalytic Oxygen Reduction Reactions.

In many metalloenzymes, sulfur-containing ligands participate in catalytic processes, mainly via the involvement in electron transfer reactions. In a biomimetic approach, we now demonstrate the implication of S-ligation in cobalt mediated oxygen reduction reactions (ORR). A comparative study between the catalytic ORR capabilities of the four-nitrogen bound [Co(cyclam)]2+ (1; cyclam=1,5,8,11-tetraaza-cyclotetradecane) and the S-containing analog [Co(S2 N2 -cyclam)]2+ (2; S2 N2 -cyclam=1,8-dithia-5,11-diaza-cyclotetradecane) reveals improved catalytic performance once the chalcogen is introduced in the Co coordination sphere. Trapping and characterization of the intermediates formed upon dioxygen activation at the CoII centers in 1 and 2 point to the involvement of sulfur in the O2 reduction process as the key for the improved catalytic ORR capabilities of 2.

(Invited) The Electrochemical Synthesis of Hydrogen Peroxide with Homogeneous Copper Systems

Hydrogen peroxide is an important bulk chemical that current is produced via the non-catalytic anthraquinone process. Separation of hydrogen peroxide from organic material is cumbersome and energy intensive and therefore the synthesis of hydrogen peroxide is only economical in a concentration form at large factories and at a very large scale. Given that hydrogen peroxide is typically consumed in diluted form, a continuous sustainable electrochemical method to produce hydrogen peroxide in small quantities is advantageous.Recently we have shown that Cu-tmpa can catalyze the oxygen reduction reaction with record breaking reaction rates of 1.8 million turnovers per second.[1] Hydrogen peroxide is formed as an obligatory intermediate that accumulates providing that the overall oxygen reduction reaction is not heavily mass transport limited in dioxygen. The reduction of hydrogen peroxide is significantly slower, and with a solvent kinetic isotope effect of 1.5, it is expected to proceed via formation of hydroxyl radicals.[2] We have shown that the key to obtaining such a high activity lies with the low reorganization energy required to cycle between the Cu(I) and Cu(II) oxidation states in case of the tmpa ligand system.[3]Currently we are exploring the longevity, selectivity and activity of these homogeneous copper systems during long term chronoamperometry measurements to produce hydrogen peroxide with good Faradaic efficiencies.[1] M. Langerman, D. G H. Hetterscheid, Fast Oxygen Reduction Catalyzed by a Copper(II) Tris(2‐pyridylmethyl)amine Complex through a Stepwise Mechanism, Angew. Chem. Int. Ed., 2019, 58, 12974.[2] M. Langerman, D. G. H. Hetterscheid, Mechanistic study of the activation and the electrocatalytic reduction of hydrogen peroxide by Cu-tmpa in neutral aqueous solution, ChemElectroChem, 2021, DOI: 10.1002/celc.202100436[3] N. W. G. Smits, B. Van Dijk, I. De Bruin, S. L. T. Groeneveld, M. A. Siegler, D. G. H. Hetterscheid, Influence of Ligand Denticity and Flexibility on the Molecular Copper Mediated Oxygen Reduction Reaction, Inorg. Chem. 2020, 59, 16398. Figure 1

Influence of Ligand Denticity and Flexibility on the Molecular Copper Mediated Oxygen Reduction Reaction.

To date, the copper complex with the tris(2-pyridylmethyl)amine (tmpa) ligand (Cu-tmpa) catalyzes the ORR with the highest reported turnover frequency (TOF) for any molecular copper catalyst. To gain insight into the importance of the tetradentate nature and high flexibility of the tmpa ligand for efficient four-electron ORR catalysis, the redox and electrocatalytic ORR behavior of the copper complexes of 2,2′:6′,2″-terpyridine (terpy) and bis(2-pyridylmethyl)amine (bmpa) (Cu-terpy and Cu-bmpa, respectively) were investigated in the present study. With a combination of cyclic voltammetry and rotating ring disk electrode measurements, we demonstrate that the presence of the terpy and bmpa ligands results in a decrease in catalytic ORR activity and an increase in Faradaic efficiency for H2O2 production. The lower catalytic activity is shown to be the result of a stabilization of the CuI state of the complex compared to the earlier reported Cu-tmpa catalyst. This stabilization is most likely caused by the lower electron donating character of the tridentate terpy and bmpa ligands compared to the tetradentate tmpa ligand. The Laviron plots of the redox behavior of Cu-terpy and Cu-bmpa indicated that the formation of the ORR active catalyst involves relatively slow electron transfer kinetics which is caused by the inability of Cu-terpy and Cu-bmpa to form the preferred tetrahedral coordination geometry for a CuI complex easily. Our study illustrates that both the tetradentate nature of the tmpa ligand and the ability of Cu-tmpa to form the preferred tetrahedral coordination geometry for a CuI complex are of utmost importance for ORR catalysis with very high catalytic rates.

Oxygen Reduction: Biaxial Strains Mediated Oxygen Reduction Electrocatalysis on Fenton Reaction Resistant L10‐PtZn Fuel Cell Cathode (Adv. Energy Mater. 29/2020)

Oxygen Reduction: Biaxial Strains Mediated Oxygen Reduction Electrocatalysis on Fenton Reaction Resistant L1₀‐PtZn Fuel Cell Cathode (Adv. Energy Mater. 29/2020)

Biaxial Strains Mediated Oxygen Reduction Electrocatalysis on Fenton Reaction Resistant L10‐PtZn Fuel Cell Cathode

AbstractPtM alloy catalysts (e.g., PtFe, PtCo), especially in an intermetallic L10 structure, have attracted considerable interest due to their respectable activity and stability for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). However, metal‐catalyzed formation of ·OH from H2O2 (i.e., Fenton reaction) by Fe‐ or Co‐containing catalysts causes severe degradation of PEM/catalyst layers, hindering the prospects of commercial applications. Zinc is known as an antioxidant in Fenton reaction, but is rarely alloyed with Pt owing to its relatively negative redox potential. Here, sub‐4 nm intermetallic L10‐PtZn nanoparticles (NPs) are synthesized as high‐performance PEMFC cathode catalysts. In PEMFC tests, the L10‐PtZn cathode achieves outstanding activity (0.52 A mgPt−1 at 0.9 ViR‐free, and peak power density of 2.00 W cm−2) and stability (only 16.6% loss in mass activity after 30 000 voltage cycles), exceeding the U.S. DOE 2020 targets and most of the reported ORR catalysts. Density function theory calculations reveal that biaxial strains developed upon the disorder‐order (A1L10) transition of PtZn NPs would modulate the surface PtPt distances and optimize PtO binding for ORR activity enhancement, while the increased vacancy formation energy of Zn atoms in an ordered structure accounts for the improved stability.

Bio-electrocatalytic reduction of dissolved oxygen by whole blood chemically modified electrode and its application

Studies related to interaction of whole blood with dissolved oxygen with a new analytical method is a continued research interest in the interdisciplinary areas of biomedical, biochemistry and analytical chemistry. There has been significant number of reports for spectroscopic and electrochemical investigation for the interaction of heme/hemoglobin with dissolved oxygen. Indeed, there is no direct study relating to electron-transfer behaviour of whole blood and oxygen reduction reaction. Complex nature of the blood and difficulty in transferring the electron from the buried hemoglobin in the blood cell are the limitations for the observation. Herein, we report, a human whole blood modified electrode system using graphitized mesoporous carbon and Nafion as a matrix for direct-electron-transfer reaction with dissolved oxygen in physiological solution. The blood modified electrode exhibits a specific redox peak at an apparent standard electrode potential, E°′=−0.38V vs Ag/AgCl corresponding to the electron-transfer reaction of hemoglobin-Fe(III)/Fe(II) redox system and shows a mediated oxygen reduction reaction similar to a commercial Hb modified electrode response. Using the new bio-analytical system, interaction between the blood and dissolved oxygen was studied in terms of oxygen reduction reaction (ORR). Cyclic voltammetry, rotating disc electrode and flow injection analysis coupled with a dual electrode system, wherein, blood and MnO2 modified electrode systems are used for signals corresponding to the oxygen reduction and H2O2 oxidation reactions, kinetics and mechanism. As an extension to practical applicability, quantification of dissolved oxygen using the blood modified electrode was demonstrated with result comparable to that of a commercial dissolved oxygen measurement kit.

High-Capacity and High-Rate Discharging of a Coenzyme Q10 -Catalyzed Li-O2 Battery.

Discharging of the aprotic Li-O2 battery relies on O2 reduction to insulating solid Li2 O2 , which can either deposit as thin films on the cathode surface or precipitate as large particles in the electrolyte solution. Toward realizing Li-O2 batteries with high capacity and high rate capability, it is crucially important to discharge Li2 O2 in the electrolyte solution rather than on the cathode surface. Here, a soluble electrocatalyst of coenzyme Q10 (CoQ10 ) that can efficaciously drive solution phase formation of Li2 O2 in current benchmark ether-based Li-O2 batteries is reported, which would otherwise lead to Li2 O2 surface-film growth and premature cell death. In the range of current densities of 0.1-0.5 mA cm-2areal , the CoQ10 -catalyzed Li-O2 battery can deliver a discharge capacity that is ≈40-100 times what the pristine Li-O2 battery could achieve. The drastically enhanced electrochemical performance is attributed to the CoQ10 that not only efficiently mediates the electron transfer from the cathode to dissolve O2 but also strongly interacts with the newly formed Li2 O2 in solution retarding its precipitation on the cathode surface. The mediated oxygen reduction reaction and the bonding mechanism between CoQ10 and Li2 O2 are understood with density functional theory calculations.

Investigation on electrochemical behavior and its catalytic effect on oxygen reduction reaction of 3-Ferrocenyl dihydropyrazole derivative as electron relay

Amino group surface tailored multi-wall carbon nano-tubes were covalently tethered to the gold disk electrode and Laccase molecules were covalently coupled to nano-tubes to prepare Lac-based electrode. Derivative of 3-ferrocenyl dihydropyrazole (FDPFFP) was proposed to be electron mediator for mediated oxygen reduction reaction. Investigation in electro-chemical behavior and catalytic performance to enzymatic reaction of FDPFFP indicated that it displayed quasi-reversible characteristics of electro-chemical reaction with rapid dynamics of electron shuttle and had apparent catalytic effect in oxygen reduction (onset potential for catalysis at 450mV vs NHE). This enzymatic catalysis was restrained by the step in diffusion of substrate.

Investigation in Mediated Heterogeneous Oxygen Reduction of Immobilized Laccase

Dynamics of heterogeneous catalysis on oxygen reduction for Lac based electrode capped with a layer of Chitosan-multi-wall carbon nano-tubes complex in the presence of dissolved mediator, was investigated on the basis of precondition that the detainment of substrate and mediator could be neglected. Rates of steps involved in the whole catalytic cycle were determined by the means of UV–Vis spectroscopy, atomic adsorption spectroscopy, linear sweeping voltammetry and cyclic voltammetry in combination with rotating disk electrode technique. These kinetic parameters were normalized under the same dimension. Thus rate determining step was verified to be the diffusion of external mediator. Results also revealed the fact from analysis in changes of morphology and electric conductivity after protein incorporation into nano-composite that random adsorption of enzyme molecules on the conductive support resulted in the decrease in conductive area of nano-composite and hindered the direct electron transfer between active sites in enzyme molecules and conductive matrix. Non-oriented arrangement of protein molecules on the matrix also crippled the mechanical stability of nano-complex with enzyme resulting from weak interaction between incorporated protein molecules and carrier. Catalytic effect on dissolved oxygen reduction reaction for electrode which was over-coated by a layer of nano-complex with immobilized Laccase consisting of Chitosan and multi wall carbon nano-tubes, were found to be restrained by diffusion of electron relay.

Oxygen Reduction Mediated by Single Nanodroplets Containing Attomoles of Vitamin B12: Electrocatalytic Nano‐Impacts Method

AbstractWe report the use of single Vitamin B12 nanodroplets to mediate the reduction of oxygen in neutral buffer. Electron transfer to single Vitamin B12 nanodroplets is observed using the nano‐impacts method and shown to be quantitative. The mechanism of mediated oxygen reduction by single VB12 droplets is revealed as via both CoII and CoI reduced from CoIII in VB12 through one or two electron transfer followed by the four‐electron reduction of oxygen.

Oxygen reduction mediated by single nanodroplets containing attomoles of vitamin B12: electrocatalytic nano-impacts method.

We report the use of single Vitamin B12 nanodroplets to mediate the reduction of oxygen in neutral buffer. Electron transfer to single Vitamin B12 nanodroplets is observed using the nano-impacts method and shown to be quantitative. The mechanism of mediated oxygen reduction by single VB12 droplets is revealed as via both Co(II) and Co(I) reduced from Co(III) in VB12 through one or two electron transfer followed by the four-electron reduction of oxygen.

Methyl Viologen Mediated Oxygen Reduction in Ethanol Solvent: the Electrocatalytic Reactivity of the Radical Cation

Abstract: The study of methyl viologen (MV 2+ ) mediated oxygen reduction in electrolytic ethanol media possesses potential application in the electrochemical synthesis of hydrogen peroxide mainly due to the advantages of the much increased solubility of molecular oxygen (O 2 ) and high degree of reversibility of MV 2+/•+ redox couple. The diffusion coefficients of both MV 2+ and O 2 were investigated via electrochemical tech-niques. For the first time, MV 2+ mediated O 2 reduction in electrolytic ethanol solution has been proved to be feasible on both boron-doped diamond and micro-carbon disc electrodes. The electrocatalytic response is demonstrated to be due to the radical cation, MV •+ . The homogeneous electron transfer step is suggested to be the rate determining step with a rate constant of (1 ± 0.1) × 10 5 M − 1 s − . With the aid of a simulation program describing the EC’ mechanism, by increasing the concentration ratio of MV 2+ to O 2 electrochemical catalysis can be switched from a partial to a ‘total catalysis’ regime.Keywords: Methyl viologen, mediated oxygen reduction, ethanolic solution, diffusion coefficient and concentration of oxygen, homogeneous rate constant

Methyl Viologen Mediated Oxygen Reduction in Ethanol Solvent: the Electrocatalytic Reactivity of the Radical Cation

Methyl Viologen Mediated Oxygen Reduction in Ethanol Solvent: the Electrocatalytic Reactivity of the Radical Cation

Use of ‘split waves’ for the measurement of electrocatalytic kinetics: methyl viologen mediated oxygen reduction on a boron-doped diamond electrode

The mediated reduction of oxygen via the reduced form of methyl viologen is studied voltammetrically. The investigation is facilitated through the use of a boron-doped diamond electrode, allowing the catalytic response to be clearly delineated from that of the direct oxygen reduction process at the electrode surface. From simulation a high homogeneous electron transfer rate (6 × 10(9) M(-1) s(-1)) is found for the one-electron reduction of oxygen to superoxide. This value is in close agreement with that found using non-electrochemical methods and is significantly higher than the values previously reported in electrochemical studies. In the latter case it is demonstrated that the underestimation of the electron transfer rate arises due to oversimplification of the reaction mechanism.

Glassy carbon tubular electrodes for the reduction of oxygen to hydrogen peroxide

The oxygen reduction reaction (ORR) to produce hydrogen peroxide (H2O2) is of great industrial interest. Herein, a hydrodynamic electrochemical method is explored for use as a continuous method to produce H2O2 at the point-of-use. The ORR was studied in a tubular glassy carbon flow cell under a laminar flow regime. A generalised theoretical model was developed to explore the conditions, such as volume flow rates and tubular lengths etc., for which a near-full electrolysis may be achieved. The parameters probed, transfer coefficient, half-wave potentials, volume flow rates, etc., provide physical insights into the irreversible oxygen reduction process. Thereafter, the surface modification of the tubular electrode with an electrocatalyst, 2-anthraquinonyl group (AQ-), is investigated for the mediated reduction of oxygen. This is shown to usefully decrease the required overpotential for the reduction process.

Surface modification imparts selectivity, facilitating redox catalytic studies: quinone mediated oxygen reduction

Modifying a gold electrode surface with hydroxy-alkyl-thiols significantly reduces the observed rate of electron transfer. This designed and controlled decrease in electron transfer rate readily allows reversible and irreversible electrode processes to be more clearly delineated. Separation of such voltammetric responses can facilitate the direct study of redox catalytic processes, which would, under other experimental conditions be obscured. The reduction of oxygen by anthraquinone hydroxy derivatives are used as a paradigmatic example, demonstrating the importance of the hydroxyl groups in the reduction process. Specifically, the reduced form of 1,8-dihydroxy-anthraquinone is shown to be significantly more reactive towards oxygen reduction than the 1,4-dihydroxyl analogue.

The anthraquinone mediated one-electron reduction of oxygen in acetonitrile

We report the use of a boron-doped diamond electrode and the selection of an optimal anthraquinone derivative, to unambiguously investigate the one-electron mediated oxygen reduction mechanism, in an anhydrous acetonitrile solution. Cyclic voltammetric results were simulated and the rate of the electron transfer between the semi-quinone and oxygen species was found to be 7(±3)×106M−1s−1.

The electrochemistry of quinizarin revealed through its mediated reduction of oxygen

After 35 years the hunt for improved anthracycline antibiotics is unabated but has yet to achieve the levels of clinical success desired. Electrochemical techniques provide a large amount of kinetic and thermodynamic information, but the use of such procedures is hindered by issues of sensitivity and selectivity. This work demonstrates how by harnessing the mechanism of catalytic reduction of oxygen by the quinone functionality present within the anthracycline structure it is possible to study the reactive moiety in nanomolar concentration. This methodology allows electrochemical investigation of the intercalation of quinizarin into DNA and, in particular, the quinone oxidation and degradation mechanism. The reversible reduction of the quinizarin, which in the presence of oxygen leads to the formation of reactive oxygen species, is found to occur at -0.535 V (vs. SCE) pH 6.84 and the irreversible oxidation leading to the molecules degradation occurs at +0.386 V (vs. SCE) pH 6.84.

Evaluation of performance and stability of biocatalytic redox films constructed with different copper oxygenases and osmium-based redox polymers

We are interested in investigating the applications of biocatalytic mediated reduction of oxygen by oxygenases in films on electrode surfaces, as such reactions can form the basis for biosensors or biocatalytic fuel cell development. Here we present approaches aimed at improving the stability and signal output of such films. These include selection of oxygen reducing biocatalysts which are active under physiological conditions and development of redox mediators which offer the opportunity to tailor the mediator to each enzyme. It was found that for each enzyme Melanocarpus albomyces laccase (MaL), Trametes hirsutus laccase (ThL) or bilirubin oxidase (MvBOD) it was the biocatalytic films mediated by Os(2,2′-bipyridine) 2Cl·PVI that not only generated the highest current densities compared to Os(4,4′-dimethyl-2,2′-bipyridine) 2Cl·PVI and Os(4,4′-dichloro-2,2′-bipyridine) 2Cl·PVI, but also proved to be the most stable over 48 h. Under physiological conditions electrodes constructed from MvBOD generated the highest initial current densities for each of the osmium redox polymers, however these films proved to be the least stable over 48 h. Stability could be improved using surface pre-treatment.