Electrocatalytic Reduction Of Molecular Oxygen Research Articles

Electrocatalytic reduction of Molecular Oxygen with a Copper (II) Coordination Polymer

Oxygen reduction at the polarized water/1,2‐dichloroethane (DCE) interface catalyzed by a Cu (II) coordination polymer (Cu–pol) was studied with two lipophilic electron donors ferrocene (Fc) and tetrathiafulvalene (TTF). The results of the ion transfer voltammetry and two‐phase shake flask experiments suggest proceeding of the catalytic reaction as proton‐coupled electron transfer reduction of oxygen to hydrogen peroxide and water. In this process, while the protons supplied from the aqueous phase, the electrons provided from the organic phase by the weak electron donor, Fc. The O2 molecule takes a superoxide structure with Cu–pol which resulted to hydrogen peroxide or water on reduction. Furthermore, the results revealed that the apparent rate constant of TTF + Cu‐pol is higher than that of Fc + Cu‐pol system due to the faster kinetic reaction of TTF with respect to Fc.

Factors Determining the Rate and Selectivity of 4e-/4H+ Electrocatalytic Reduction of Dioxygen by Iron Porphyrin Complexes.

Reactivity as well as selectivity are crucial in the activation and electrocatalytic reduction of molecular oxygen. Recent developments in the understanding of the mechanism of electrocatalytic O2 reduction by iron porphyrin complexes in situ using surface enhanced resonance Raman spectroscopy coupled to rotating disc electrochemistry (SERRS-RDE) in conjunction with H/D isotope effects on electrocatalytic current reveals that the rate of O2 reduction, ∼104 to 105 M-1 s-1 for simple iron porphyrins, is limited by the rate of O-O bond cleavage of an intermediate ferric peroxide species (FeIII-OOH). SERRS-RDE probes the system in operando when it is under steady state such that any intermediate species that has a greater rate of formation relative to its rate of decay, including the rate determining species, would accumulate and can be identified. This technique is particularly well suited to investigate iron porphyrin electrocatalysts as the intense symmetric ligand vibrations allow determination of the oxidation and spin states of the bound iron with high fidelity. The rate of O2 reduction could be tuned up by 3 orders of magnitude by incorporating residues in the catalyst design that can exert "push" or "pull" effects, that is, axial phenolate and thiolate ligands and distal arginine residues. Similarly the rate of O-O bond cleavage can be enhanced by several orders of magnitude upon incorporating a distal Cu site and installing the active site in a hydrophobic protein environment in synthetic models and biosynthetic protein scaffolds. The selectivity, however, is solely determined by the site of protonation of a ferric peroxide (FeIII-OOH) intermediate and can be governed by installing preorganized second sphere residues in the distal pocket. The 4e-/4H+ reduction of O2 entails protonation of the distal oxygen of the FeIII-OOH species, while 2e-/2H+ reduction requires the proximal oxygen to be protonated. Mechanistic investigations of CO2 reduction by iron porphyrins reveal that the rate-determining step is the C-O bond cleavage of a FeII-COOH species analogous to the O-O bond cleavage step of a FeIII-OOH species in O2 reduction. The selectivity, resulting in either CO or HCOOH, is determined by the site of protonation of this species. These similarities suggests that the chemical principles governing the rate and selectivity of reduction of small molecules like O2, CO2, NOx, and SOx may be quite similar in nature.

Electrokinetic and Impedimetric Dynamics of FeCo-Nanoparticles on Glassy Carbon Electrode

The electrochemical dynamics of a film of FeCo nanoparticles were studied on a glassy carbon electrode (GCE). The film was found to be electroactive in 1 M LiClO4 containing 1:1 v/v ethylene carbonate dimethyl carbonate electrolyte system. Cyclic voltammetric experiments revealed a diffusion-controlled electron transfer process on the GCE/FeCo electrode surface. Further interrogation on the electrochemical properties of the FeCo nanoelectrode in an oxygen saturated 1 M LiClO4 containing 1:1 v/v ethylene-carbonate-dimethyl carbonate revealed that the nanoelectrode showed good response towards the electro-catalytic reduction of molecular oxygen with a Tafel slope of about 120 mV which is close to the theoretical 118 mV for a single electron transfer process in the rate limiting step; and a transfer coefficient (α) of 0.49. The heterogeneous rate constant of electron transfer (ket), exchange current density (io) and time constant (τ) were calculated from data obtained from electrochemical impedance spectroscopy and found to have values of 2.3 x 10-5 cm s-1, 1.6 x 10-4 A cm-2 and 2.4 x 10-4 s rad-1, respectively.

Oxygen reduction reaction catalyzed with titanyl phthalocyanines in nonaqueous and aqueous media

Electrochemical and in situ spectroelectrochemical behaviors and electrocatalytic reduction of molecular oxygen with titanyl phthalocyanines (TiPc) bearing 3,4-(methylenedioxy)-phenoxy substituents were performed in aprotic solvents. Multi electrons and metal-based and ring-based redox processes of TiPcs indicate their possible electrocatalytic activity toward many target species. Different numbers and positions of the substituents of the complexes affect the peaks' character and assignment of the processes. The presence of O2 in the electrolyte system influences the electrochemical and spectral responses of TiPcs. Electrochemical and in situ spectroelectrochemical analysis indicates interaction of molecular oxygen with TiPcs and these interaction mechanisms depend on both the substituent environments of the complexes and the electrolyte system. Langmuir-Blodgett films of the complexes also catalyze molecular oxygen in aqueous media, which is a desired property for their practical application.

Electrocatalytic oxygen reduction and hydrogen evolution reactions on phthalocyanine modified electrodes: Electrochemical, in situ spectroelectrochemical, and in situ electrocolorimetric monitoring

This study describes electrochemical, in situ spectroelectrochemical, and in situ electrocolorimetric monitoring of the electrocatalytic reduction of molecular oxygen and hydronium ion on the phthalocyanine-modified electrodes. For this purpose, electrochemical and in situ spectroelectrochemical characterizations of the metallophthalocyanines (MPc) bearing tetrakis-[4-((4′-trifluoromethyl)phenoxy)phenoxy] groups were performed. While CoPc gives both metal-based and ring-based redox processes, H 2Pc, ZnPc and CuPc show only ring-based electron transfer processes. In situ electrocolorimetric method was applied to investigate the color of the electrogenerated anionic and cationic forms of the complexes. The presence of O 2 in the electrolyte system influences both oxygen reduction reaction and the electrochemical and spectral behaviors of the complexes, which indicate electrocatalytic activity of the complexes for the oxygen reduction reaction. Perchloric acid titrations monitored by voltammetry represent possible electrocatalytic activities of the complexes for hydrogen evolution reaction. CoPc and CuPc coated on a glassy carbon electrode decrease the overpotential of the working electrode for H + reduction. The nature of the metal center changes the electrocatalytic activities for hydrogen evolution reaction in aqueous solution. Although CuPc has an inactive metal center, its electrocatalytic activity is recorded more than CoPc for H + reduction in aqueous solution.

Efficient Oxygen Reduction Reaction Using Ruthenium Tetrakis(diaquaplatinum)Octacarboxyphthalocyanine Catalyst Supported on MWCNT Platform

AbstractElectrocatalytic reduction of molecular oxygen in alkaline solution using a novel ruthenium tetrakis(diaquaplatinum)octacarboxyphthalocyanine (RuOCPcPt) electrocatalyst supported on multi‐walled carbon nanotube electrode has been described. We show that the oxygen reduction activity follows a direct 4‐electron transfer process at high kinetic rate constant, 3.57×10−2 cm s−1.

Platinum and Non‐Platinum Nanomaterials for the Molecular Oxygen Reduction Reaction

Herein, some chemical approaches to the tailoring of nanodivided materials are highlighted. Transition-metal materials in nanodivided form are essentially devoted to study the electrocatalytic reduction of molecular oxygen (ORR) in acid medium. This Minireview focuses on the physical and chemical structures of platinum-based and non-platinum-based materials. Due to the research dynamism in this field, the discussion is limited to a comprehensive review of ORR cathode materials investigated in the author's laboratory as well as to some relevant work obtained in other laboratories concerning the electrochemical ORR pathway and substrate effects.

Tailor-Designed Platinum Nanoparticles Electrodeposited onto Gold Electrode: Catalytic Activity for Oxygen Reduction

This work examines the electrocatalytic reduction of molecular oxygen at Pt nanoparticles (nano-Pt) electrodeposited onto polycrystalline gold (poly-Au) electrode in -saturated . Cyclic and hydrodynamic voltammetry techniques were used for the evaluation of the electrocatalytic activity of the nano-Pt modified poly-Au electrodes. The nano-Pt was electrodeposited onto unmodified poly-Au electrode and poly-Au electrode modified with a submonolayer of a thiol compound (typically cysteine) . In the latter case, Pt nanoparticles were electrodeposited, preferentially, at the bare fraction of the poly-Au electrode free from cysteine [i.e., the domains of the poly-Au] while the other facets (i.e., and ) were under the protection of cysteine. The nano-Pt electrodeposited onto the is characterized by small average particle size (ca. ) compared to that electrodeposited onto the unmodified Au electrode (ca. ). The nano- electrode offers a high electrocatalytic activity toward the oxygen reduction reaction (ORR) as compared with the nano- and bare polycrystalline Pt electrodes. A positive shift of the onset potential of the ORR was obtained at the nano- electrode as compared to the bare Pt electrode. A proper design of the nano- binary catalyst is the key point which controls the catalytic activity of the proposed electrocatalyst.

Electrocatalytic Reduction of Molecular Oxygen at Poly(1,8-diaminonaphthalene) and Poly(Co(II)-(1,8-diaminonaphthalene)) Coated Electrodes

The application of poly(Co(II)-(1,8-diaminonaphthalene))(poly(Co-DAN)) and poly(1,8-diaminonaphthalene) (Poly(1,8-DAN)) to the electrocatalytic reduction of molecular oxygen was investigated, which were electrochemically grown by the potential cycling method on the glassy carbon electrodes. The reduction of oxygen at the polymer and its metal complex polymer coated electrodes were irreversible and diffusion controlled. The Poly(1,8-DAN) and Poly(Co-DAN) films revealed the potential shifts for the oxygen reduction to 30 mV and 110 mV, respectively, in an aqueous solution, compared with that of the bare electrode. Hydrodynamic voltammetry with a rotating ring-disk electrode showed that Poly(1,8-DAN) and Poly(Co-DAN) coated electrodes converted respectively 84% and 22% of to via a four electron reduction pathway.

Oxygen reduction at Au nanoparticles electrodeposited on different carbon substrates

The electrocatalytic reduction of molecular oxygen (O 2) has been performed in O 2-saturated 0.5 M KOH solution at Au nanoparticles electrodeposited onto two different carbon substrates, namely glassy carbon (GC) and highly oriented pyrolytic graphite (HOPG). Cyclic voltammetry (CV) technique has been used in this investigation. The electrocatalytic activity of the Au nanoparticle-based electrodes is inherently related to its electrodeposition conditions (i.e., the absence or presence of some additives) as well as the nature of the substrate. For instance, Au nanoparticles electrodeposited onto GC (nano-Au/GC) from K[AuBr 4] in the presence of 25 μM cysteine showed a high electrocatalytic activity towards the oxygen reduction reaction (ORR) as demonstrated by the largest positive shift of the cathodic peak potential (at ca. −0.165 V versus Ag/AgCl/KCl (sat)). On the other hand, two well-separated successive reduction peaks corresponding to the 2-step 4-electron reduction of oxygen were observed at the different nano-Au/HOPG electrodes. The relative ratio of the two peak current heights changed significantly depending on the electrodeposition conditions of the Au nanoparticles. The morphology of the different Au nanoparticles electrodeposited onto the different substrates was depicted by scanning electron microscope (SEM) technique.

Electrocatalytic Reduction of Oxygen at Au Nanoparticles–Manganese Oxide Nanoparticle Binary Catalysts

The electrocatalytic reduction of molecular oxygen has been performed in -saturated solution at binary catalysts of Au nanoparticles and manganese oxide nanoparticles electrodeposited onto glassy carbon (GC) electrodes. Cyclic voltammetric (CV) and rotating ring-disk electrode (RRDE) techniques have been utilized in this study. CV measurements showed that the electrochemically deposited nanoparticles have a good catalytic activity toward the disproportionation of hydrogen peroxide ( in alkaline media) to water and . A significant positive shift of the peak potential of the oxygen reduction reaction (ORR) was observed upon loading Au nanoparticles onto the GC substrate. The combined use of and Au nanoparticles resulted in the occurrence of the ORR at a potential close to that obtained at Pt electrodes, supporting an apparent four-electron reduction pathway as revealed from the RRDE voltammetric results. The current study proposed a novel binary catalyst system (composed of metal/metal oxide nanoparticles) as a very promising candidate to replace the costly Pt-based electrocatalysts in alkaline air electrodes.

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.

Electrochemical properties of porphyrin-doped polypyrrole films

Meso-tetra-(4-sulfonatophenyl)-porphin (TPPS 4) has been incorporated into polypyrrole (PPy) films as a dopant-anion during electropolymerisation from aqueous solutions. The addition of TPPS 4 to the polymerisation solution increases the rate of electropolymerisation substantially, changes the morphology markedly, and increases the redox-activity of the PPy films formed. This catalytic effect of the TPPS 4 on the rate of electropolymerisation was established in the case of non-metallized porphyrin; it means that the effect is not caused by the influence of redox-active metal-ions inserted into the porphin centre. Insertion of the Co 2+ ions into the porphin centres was carried out from acetate solutions with high efficiency (70%) even in the case of thick (3–10 μm) TPPS 4 doped PPy films. Well-developed waves connected with the Co 2+/3+ transition taking place in meso-tetra-(4-sulfonatophenyl)-porphyrinato cobalt (II) (CoTPPS 4) were established. The voltammograms measured in an air atmosphere show that the electrocatalytic reduction of molecular oxygen starts at the same potential as the wave of Co redox-transition. The PPy films have been characterised by cyclic voltammetry, SEM, AFM, and X-ray microanalysis.

Electrocatalytic Reduction of Molecular Oxygen Using a Poly(terthiophene carboxylic acid) Appended by 1,5-Diaminonaphthalene Copper Complex

The conducting polymer electrochemically obtained from a newly synthesized -terthiophene--carboxylic acid monomer was modified with 1,5-diaminonaphthalene by covalent bonding, and the modified electrode was complexed with copper ions. All modifications were characterized by Fourier transform infrared spectroscopy (FTIR), electron spectroscopy for chemical analysis (ESCA), and cyclic voltammetry (CV) techniques. The electrode modified with copper ions caused a positive shift in the peak potential for oxygen reduction to 0.30 V when compared to the absence of copper in the modified electrode. An ESCA study indicates the participation of Cu(I) species in the process of catalytic reduction of oxygen. The kinetics for oxygen reduction was studied by rotating ring-disk voltammetry. The results reveal 3.6 electrons participating in the reduction of oxygen with about 75% conversion to water in an aqueous medium of 0.1 M The kinetic study also indicates the presence of an inner sphere mechanism between copper and oxygen during the latter’s reduction. The calculated rate constant from the kinetic study on the electrocatalytic reduction of oxygen was found to be higher when compared to other copper complexes adsorbed on the carbon electrode surface. This modified electrode was also tested for the estimation of oxygen content in an aqueous solution. © 2002 The Electrochemical Society. All rights reserved.

Electrocatalytic reduction of molecular oxygen on a sodium montmorillonite-methyl viologen carbon paste chemically modified electrode

A carbon paste electrode (CPE) modified with sodium montmorillonite (SWy-2)-methyl viologen (MV) is developed. The intermolecular complex of SWy-2 and MV has an electrocatalytic effect on oxygen reduction. The cyclic voltammograms of the electroreduction of molecular oxygen show an enhanced current peak in an air-saturated phosphate buffer solution. In this study, the experimental parameters are optimized and the mechanism of the catalytic process is discussed. This chemically modified electrode will offer a possibility of developing a sensitive method for the determination of dissolved oxygen.

Synthesis and studies on the electrocatalytic reduction of molecular oxygen by non-planar cobalt(II) tetrakis-( N-methyl pyridyl)-β-octabromoporphyrin

Synthesis and studies on the electrocatalytic reduction of molecular oxygen by non-planar cobalt(II) tetrakis-( N-methyl pyridyl)-β-octabromoporphyrin

Kinetics studies of oxygen reduction in acid medium on novel semiconducting transition metal chalcogenides

The aim of this work was to investigate a Ru-cluster material with a low molybdenum concentration. This latter is considered to act as an adsorption site for molecular oxygen. Transition metal chalcogenide materials based on Mo-Ru-Se for electrocatalytic reduction of molecular oxygen in acid medium were chemically prepared by reacting the transition metal carbonyl compounds and selenium powder in xylene solvent (140 °C). The stoichiometry of the semiconducting electrocatalyst corresponds to (Ru 1 − x Mo x ) y SeO z where 0.02 < x < 0.04; 1 < y < 3 and z ≈ 2 y. Kinetics parameters were obtained using steady state measurements with the rotating ring disk electrode ( rrde) with electrocatalyst deposited on glassy carbon disks or with the powder incorporated in a disk of carbon paste matrix. Oxygen reduction proceeds mostly via a four-electron transfer reaction (96%) to water as determined by the rotating ring disk electrode technique. The heterogeneous rate constants, k 1 (water formation from oxygen), k 2 (hydrogen peroxide formation) and k 3 (water production from generated H 2O 2) were evaluated over the potential range of 0.70 to 0V/ nhe. Temperature dependence (296 K to 338 K) and kinetic parameters were evaluated. It is concluded that minimising the molybdenum content leads to improved electrocatalysis.

Electrochemical investigation of dioxygen interaction with two cobalt chelates in solution and at the electrode surface

The interaction between molecular oxygen and the metal atom in two Co(II) complexes with bis(diacetylmonoxime-imino)propane-1,3 ( A) and with the related ligand obtained from cobaloxime by substitution of both the O-H ⋯ O bridges with the -BF 2-group ( B) is investigated using electrochemical and spectroelectrochemical techniques. Notwithstanding the stability of the Co(II) complex B in air, the results suggest the formation of a dioxygen adduct as an unstable intermediate in the electrocatalytic reduction of molecular oxygen in the presence of either A or B. Furthermore, the oxygenation ratio at a given pO 2 appears to be quite different for the homogeneous reaction of A in the Co(II) oxidation state in bulk as compared with either the electrogenerated Co(II) (from complex A) on the electrode surface or the Co(II) complex B.

Electrocatalytic reduction of molecular oxygen by mononuclear and binuclear cobalt phthalocyanines

Investigations of the electrocatalytic activity of mononuclear and binuclear cobalt phthalocyanines for the reduction of molecular oxygen established that the latter compounds are more effective catalysts than the corresponding mononuclear species. A correlation between the half-band widths for the Q band of these species and their catalytic efficiency, expressed as a kinetically-limited current, suggests that the increase in activity may be attributed to electronic coupling between the phthalocyanine rings.

Electrochemical simulation of function of cytochrome oxidase using synthetic porphyrins.

In order to mimic the function of cytochrome oxidase and inversely to get insight into its function and structure and furthermore their correlation, electrocatalytic reduction of molecular oxygen was examined using water-soluble and immobilized iron and cobalt porphyrins and phthalocyanines. In the presence of iron porphyrins, oxygen was reduced via hydrogen peroxide to water quantitatively by an electrogenerated penta-coordinated high-spin iron (II) form of the porphyrins at potentials closely correlated with iron (III) to iron (II) reduction potentials. The rate constant of oxygen reduction in natural enzyme system was attained only by the use of porphyrins containing a lot of amino groups, suggesting inversely one of the causes of high composition ratio of basic amino acids in this enzyme. By the use of iron phthalocyanines also, oxygen was reduced via hydrogen peroxide to water at potentials correlated with iron (II) to iron (I) reduction potentials. Howerver when mononuclear cobalt complexes were employed, hydrogen peroxide was produced almost quantitatively as the final product.