Molecular Oxygen Reduction Reaction Research Articles

Interfacial and ion-pairing catalysis for oxygen-tolerant large-scale ATRP in ab initio emulsion

A cooperative interfacial and ion-pairing catalysis, coupled with a molecular oxygen reduction reaction (ORR), to scale up an Atom Transfer Radical Polymerization of n-butyl acrylate (BA) from 20 mL to 10 L (scale-up factor = 500) in ab initio emulsion conditions is introduced. The polymerization is driven by the regeneration of [CuIL]+ through CuII/Cu0 comproportionation. [CuIL]+ simultaneously converts O2 to H2O2 (which is then degraded by sodium pyruvate) and drives the polymerization of butyl acrylate. The anionic surfactant sodium dodecyl sulfate (SDS) facilitates catalyst transport inside and outside the micelles by ion-pairing catalysis. n-Butyl acrylate polymerizations are investigated on a small scale with Cu0 wire and on a larger scale with Cu0 powder. On a 10 L scale, the polymerization yielded controlled PBA-Br (Mn = 32.3 × 103; Ð = 1.39, ∼1.64 kg) after 9 h. Chain extension of PBA-Br macroinitiators proved their livingness. An on-line electrochemical monitoring was also introduced to determine the instantaneous CuI and CuII concentrations at the Cu0 wire surface during the polymerization.

Identification of a Durability Descriptor for Molecular Oxygen Reduction Reaction Catalysts.

The development of durable platinum-group-metal-free oxygen reduction reaction (ORR) catalysts is a key research direction for enabling the wide use of fuel cells. Here, we use a combination of experimental measurements and density functional theory calculations to study the activity and durability of seven iron-based metallophthalocyanine (MPc) ORR catalysts that differ only in the identity of the substituent groups on the MPcs. While the MPcs show similar ORR activity, their durabilities as measured by the current decay half-life differ greatly. We find that the energy difference between the hydrogenated intermediate structure and the final demetalated structure (ΔEdemetalation) of the MPcs is linearly related to the degradation reaction barrier energy. Comparison to the degradation data for the previously studied metallocorrole systems suggested that ΔEdemetalation also serves as a descriptor for the corrole systems and that the high availability of protons at the active site due to the COOH group of the o-corrole decreases the durability.

One-Pot Graphene Supported Pt3Cu Nanoparticles—From Theory towards an Effective Molecular Oxygen Reduction Reaction Catalyst

In this work, recent research progresses in the formation of Pt3Cu nanoparticles onto the surface of graphene are described, and the obtained results are contrasted with previously published theoretical studies. To form these nanoparticles, tetrabutylammonium hexachloroplatinate, and copper acetylacetonate are used as platinum and copper precursors, respectively. Oleylamine is used as a reductor and a solvent. The obtained catalyst is characterized via X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and energy dispersive spectroscopy X-ray (EDS). To assess the catalytic activity, the graphene-supported Pt3Cu material is tested with cyclic voltammetry, “CO stripping”, and oxygen reduction reaction potentiodynamic curves to find the nature and the intrinsic electrochemical activity of the material. It can be observed that the tetrabutylammonium cation plays a critical role in anchoring and supporting nanoparticles over graphene, from which a broad discussion about the true nature of the anchoring mechanism was derived. The growth mechanism of the nanoparticles on the surface of graphene was observed, supporting the conducted theoretical models. With this study, a reliable, versatile, and efficient synthesis of nanocatalysts is presented, demonstrating the potentiality of Pt3Cu/graphene as an effective cathode catalyst. This study demonstrates the importance of reliable ab inito theoretical results as a useful source of information for the synthesis of the Pt3Cu alloy system.

Carbon spheres modified titanium air diffusion cathode for boosting H2O2 and application in disinfection

In situ electrochemical disinfection via H2O2 through two-electron molecular oxygen reduction reaction (2e-ORR) represents a promising strategy for sustainable disinfection. However, its disinfection performance is largely confined by its low selectivity/reactivity towards two-electron oxygen reduction reaction (2e-ORR) for H2O2 production. To tackle this, carbon spheres modified tubular titanium air diffusion cathode (CS@TTC) was developed. It intended to improve interfacial structures for high H2O2 production through a facile hydrothermal carbonation approach. Evolution of morphology and chemical nature of carbon spheres have been systemically investigated under diverse hydrothermal temperature, hydrothermal time and pyrolysis temperature·H2O2 accumulation has improved 6.59-fold at CS@TTC compared to the raw base TTC. Both chemical nature of carbon sphere and a superior oxygen mass transfer (0.0284 s−1) were responsible for this enhancement. Besides, CS@TTC cathode was used in the electrochemical system for disinfection performance, in which 6.42 log of E. coli was deactivated after 120 min. Hence, this study gives an insight into that the H2O2-based electrochemical disinfection is promising to be a next-generation process.

An anode fabricated by Co electrodeposition on ZIF-8/CNTs/CF for peroxymonosulfate (PMS) activation

A Co@ZIF-8/CNTs-CF anode for PMS activation was prepared by Co electrodeposition on carbon felt (CF) modified with ZIF-8 and carbon nanotubes (CNTs). The results showed that the fabricated Co@ZIF-8/CNTs-CF anode was an effective peroxymonosulfate (PMS) activator toward tetracycline (TC) removal. Compared with that in reaction system of bare CF anode + PMS, the reaction system of Co@ZIF-8/CNTs-CF anode + PMS exhibited 3.08 times decrease in the activation energy demanded and 4.21 times increase in the reaction rate constant (k), resulting in a kinetic favorable process of PMS activation by the Co@ZIF-8/CNTs-CF anode. The enhanced activation performance of the fabricated anode was ascribed to the high contents of the pyrrolic N and low valence state of Co in the Co@ZIF-8/CNTs-CF anode. Furthermore, the influence factors on the characteristics of transformation among the generated reactive species during the anodic PMS activation process were comprehensively investigated by the quenching experiments and the electron paramagnetic resonance (EPR) tests. The results showed that the SO4•- and reactive oxygen-containing reactive species (O2•- and 1O2) were generated during the activation of PMS by anode and became the major contributors toward TC removal. The production of 1O2 was through the dismutation of O2•-. In addition, the EPR experiments demonstrated that O2•- was generated mainly through the anodic PMS activation but the electrochemically driven molecular oxygen reduction reaction (ORR) process. The fabricated Co@ZIF-8/CNTs-CF anode for PMS activation provided a reference for the wastewater treatment based on the electrochemical advanced oxidation processes (EAOPs).

Insights into highly efficient piezocatalytic molecule oxygen activation over Bi2Fe4O9: Active sites and mechanism

Piezocatalytic molecular oxygen activation has been regarded as a promising and low energy-cost strategy for environment remediation, yet the piezocatalytic activity is still far from satisfactory and little is known on its activation mechanism, which greatly hinders its further development. Herein, the piezocatalyst Bi2Fe4O9 nanosheets (BFO NSs) are synthesized via a facile hydrothermal method, which exhibit excellent piezocatalytic performance for sulfamethoxazole degradation. O2∙- generated via the molecular oxygen reduction reaction by piezo-electrons and the piezo-holes were confirmed as major active species for organic pollutants degradation. Further theoretical calculations and XPS analyses confirm the Fe2+ sites as active centers activate molecular oxygen into O2∙- via donating the electrons to molecular oxygen and the piezo-electrons reduce Fe3+ to Fe2+. This work provides atomic-scale insights into the active sites of piezocatalytic molecular oxygen activation, which can inspire the development of more efficient piezocatalysts for environment application.

Electrocatalysis of molecular oxygen reduction reaction at liquid-liquid interface and DFT computational study of proton transfer from the conjugate acid of 2,2'-dipyridylamineto oxygen.

In this study, the catalytic effect of 2,2'-dipyridylamine (DPA) on the reduction of oxygen (O2) at the polarized water/1,2-dichloroethane (DCE) interface was investigated. Ferrocene (Fc) and tetrathiafulvalene (TTF) were weak electron donors used in this study. Slow reduction of O2 at the interface containing Fc and TTF was significantly accelerated upon the addition of DPA. Voltammetry and biphasic shake flask experiments revealed that DPA acts as a proton ionophore to transfer protons between the aqueous and organic phases. The PA, GB, and pKa values of all possible conjugate acids of DPA were calculated. Then, a mechanism was suggested to explain the interaction between protonated DPA and oxygen molecular. The mechanism was computationally analyzed by using density functional theory (DFT). Furthermore, DFT calculations at the B3LYP/6-31G** level of theory showed that the conjugate acid species of DPA transfer proton to O2 at the interface. The results show that DPA-H2+ and DPA-H1+ are the best species to transfer proton to molecular oxygen.

Enhancement of the oxygen reduction reaction electrocatalytic activity of metallo-corroles using contracted cobalt(iii) CF3-corrole incorporated in a high surface area carbon support.

Molecular oxygen reduction reaction catalysts based on metallo-corrole with the smallest meso-substituent reported to-date, Co(iii)CF3-corrole, was synthesized and compared to the well-studied Co(iii)tpfcorrole when adsorbed on a high surface area carbon support. This study shows the improved electrocatalytic performance with the new corrole, attributed to its unique compact structure, which enables surface interactions in favor of lowering the reaction overpotential by 70 mV.

Electrocatalytic properties of a dinuclear cobalt(III) coordination compound in molecular oxygen reduction reaction

A new dinuclear cobalt(III) coordination compound, [Co2L(μ‐N3)(N3)2]·CH3OH (1), was synthesized and characterized by elemental analysis, spectroscopic methods, and single‐crystal X‐ray analysis in which H3L is a heptadentate ligand obtained by the condensation of triethylenetetramine with 5‐bromo‐2‐hydroxybenzaldehyde. X‐ray analysis revealed that two cobalt(III) ions have distorted octahedral geometry and are connected together by a phenoxy and an azide bridging ligand. The catalytic activity of compound 1 for oxygen (O2) reduction reaction was investigated. Compound 1 can efficiently catalyze the reduction of O2 by a weak electron donor, ferrocene (Fc), at the polarized water–1,2‐dichloroethane interface. It was found that compound 1 can catalyze O2 reduction to H2O2, whereas in the presence of Fc, it can catalyze the reduction of O2 to water.

Doping of Carbon Quantum Dots (CDs) in Calcium Phosphate Nanorods for Inducing Ectopic Chondrogenesis via Activation of the HIF-α/SOX-9 Pathway

Calcium phosphate (CaPs)-based nanostructures are mostly known to induce osteogenic differentiation of mesenchymal stem cells (MSCs). However, in the current study, doping of carbon quantum dots into calcium phosphate nanorods (C-CaPs) has been observed to affect the differentiation pathway and enhanced the expression of chondrogenic genes instead of osteogenic ones. Here, we report a microwave-assisted single-step synthesis and doping of carbon dot into calcium phosphate nanorods and their ectopic chondrogenicity in a rodent subcutaneous model. High-resolution transmission electron microscopy, X-ray powder diffraction, and X-ray photoelectron spectroscopy studies show that the doping of carbon dots results in p-type semiconductor-like structure formation at the phosphate site of the bioceramic nanostructure, whereas UV–vis absorption shows a drastic drop in band-gap energy, which enhances the molecular oxygen reduction reaction. The cytocompatibility, free radical scavenging property, and fluorescence mi...

(Europe Section Heinz Gerischer Award Address) TiO2-Based Visible Light Photocatalysts Based on Interfacial Charge Transfer Process

TiO2 is known as an efficient photocatalyst and is well studied aiming for environmental and energy application. However, TiO2 absorbs only UV light and thus its application had been limited. We recently demonstrated that the surface modification of TiO2 with Cu(II) or Fe(III) nanoclusters produced a new optical absorption in the visible light region. We also found that those surface modified TiO2s show an efficient visible-light-sensitivity in photocatalysis under ambient conditions. Its reaction mechanism can be explained as follows. In the case of Cu(II) nanocluster-grafted TiO2 (Cu(II)-TiO2) for example, electrons in the valence band (VB) of TiO2 are excited to the Cu(II) nanoclusters under visible-light irradiation through an interfacial charge transfer (IFCT) process. The introduction of excited electrons into the Cu(II) nanoclusters leads to the formation of Cu(I) species, which efficiently reduce oxygen molecule through two-electron process. In other words, Cu(II) nanocluster serves as a multi-electron catalyst for molecular oxygen reduction reaction. In addition, during the IFCT process, holes are generated in the deep VB of TiO2 and are used for the decomposition of organic compounds. Thus, these nanocluster-modified TiO2s show very strong oxidation power even under visible light excitation and are promising materials for visible-light-sensitive photocatalytic applications under ambient conditions. In this lecture, I will review our studies on these IFCT-based TiO2 visible light sensitive photocatalysts, and also show the results of their demonstration tests obtained in some public spaces such as airports and hospitals towards anti-bacterial and anti-virus building material application..

Electrochemical behavior of a number of bispyridyl-substituted porphyrins and their electrocatalytic activity in molecular oxygen reduction reaction

The investigation of electrochemical properties of active layers containing 5,15-bis(pyrid-3-yl)-3,7,13,17-tetramethyl-2,8,12,18-tetraethylporphine, [5,15-bis(pyrid-3-yl)-3,7,13,17-tetramethyl-2,8,12, 18-tetraethylporphinato]cobalt(II), bispyridine[5,15-bis(pyrid-3-yl)-3,7,13,17-tetramethyl-2,8,12,18-tetraethylporphinato]cobalt(III), [5,15-bis(pyrid-4-yl)-3,7,13,17-tetramethyl-2,8,12,18-tetraethylporphinato]cobalt(II) and bispyridine[5,15-bis(pyrid-4-yl)-3,7,13,17-tetramethyl-2,8,12,18-tetraethylporphinato]cobalt(III) in 0.1 M KOH aqueous solution has been carried out by cyclic voltammetry. The potential ranges of redox processes related to the transformation of the porphyrin macrocycle, pyridyl substituents and central metal have been established. The electrochemical parameters of oxygen electroreduction reaction (the half-wave potential — E[Formula: see text](O[Formula: see text]), the maximum potential — E[Formula: see text](O[Formula: see text]), the current density — j, the activation energy — Eact) have been determined. It was shown that all porphyrins exhibit the catalytic activity. The electroreduction process of oxygen on electrode with the porphyrin-ligand occurs via 2-electron mechanism to give hydrogen peroxide ion HO2-, and on ones with the cobalt porphyrins — via parallel-sequential pathway including 2-electron and 4-electron processes to give HO2-, OH-. The presence of pyridine axial ligands in Co-complexes leads to a significant increase of the electrocatalytic activity in molecular oxygen reduction reaction.

Examing Proton Coupled Electron Transfer, Oxygen Reduction, and Anion Diffusion Using a Hybrid Bilayer Membrane

In this talk, we report on our work synthesizing and characterizing Cu-based catalysts for the oxygen reduction reaction. In particular we prepared the first synthetic Cu O2 reduction catalyst that forms a self-assembled monolayer (SAM) on Au surfaces. We embeded this Cu catalyst inside a hybrid bilayer membrane (HBM) by depositing a monolayer of lipid on the SAM. By incorporating an alkyl phosphate in the lipid layer, we develop the first HBM containing a reversible switch that gates proton transport to a molecular oxygen reduction reaction (ORR) catalyst. We envision that this strategy can give unique mechanistic insight not only to the ORR, but to all proton-coupled electron transfer (PCET) reactions. We also use the hybrid bilayer membrane as an electrochemical platform to study anion diffusion through a lipid monolayer. We first append lipid on a self-assembled monolayer that contains a covalently-bound Cu(I)/(II) redox center. We then perform cyclic voltammetry using different anions in the bulk solution and extract thermodynamic and kinetic information about anion transport. We analyze the results using linear combinations of fundamental chemical trends, and determine that anion transport quantitatively correlates to polarity and basicity, a relationship we formalize as the lipid permeability parameter. In addition, we discuss how our findings can be interpreted according to the two leading mechanisms describing ion permeability through lipids. Our results demonstrate that anion transport in a HBM is best described by the solubility-diffusion mechanism, not the pore mechanism.

Self-Assembly of Peptide Nanostructures onto an Electrode Surface for Nonenzymatic Oxygen Sensing

We report here the fabrication of a biomimetic sensor for direct oxygen reduction; the sensor consists of multicopper oxidases derived from cyclic-tetrameric copper(II) species containing the ligand (4-imidazolyl)ethylene-2-amino-1-ethylpyridine (apyhist) that are self-assembled with l-diphenylalanine micro/nanostructures (FF-MNTs). The [Cu4(apyhist)4]4+/FF-MNT complex was immobilized onto the surface of a glassy carbon (GC) electrode by poly ion complex formation with a Nafion film. This hybrid membrane allows regular proton transport to a Cu-based molecular oxygen reduction reaction catalyst, and the imidazole group in the imine ligand (apyhist) acts as a local buffer in the vicinity of the O2 reducing center, thus aiding the catalyst in retaining its selectivity for 4e–/4H+ oxygen reduction reaction. This nanocomposite provided improved sensing characteristics in the electrode interface with respect to the electroactive surface area, the diffusion coefficient, and the electron transfer kinetics. In addition, the hybrid film [Cu4(apyhist)4]4+/FF-MNT-coated GC electrode was successfully used as an enzymeless electrochemical sensor for the detection of dissolved oxygen in aqueous media at two concentration intervals, viz., 0.2–3.0 mg L–1 and greater than 3.0 mg L–1, with sensitivities of 25.0 and 80.2 μA L mg–1 cm–2, respectively, and a detection limit of 0.1 mg L–1. Evaluated in terms of relative standard deviation, the repeatability of the proposed sensor was less than 9.0% for ten measurements of a solution of 6.5 mg L–1 oxygen. Experimental efforts were conducted to use this proposed platform for O2 determination with real samples. Results from theoretical investigations using density functional theory support the hypothesis that the [Cu4(apyhist)4]4+ complex can act as the sole source of protons and electrons in the O2 reduction reaction.

Proton switch for modulating oxygen reduction by a copper electrocatalyst embedded in a hybrid bilayer membrane.

Molecular switches gate many fundamental processes in natural and artificial systems. Here, we report the development of an electrochemical platform in which a proton carrier switches the activity of a catalyst. By incorporating an alkyl phosphate in the lipid layer of a hybrid bilayer membrane, we regulate proton transport to a Cu-based molecular oxygen reduction reaction catalyst. To construct this hybrid bilayer membrane system, we prepare an example of a synthetic Cu oxygen reduction reaction catalyst that forms a self-assembled monolayer on Au surfaces. We then embed this Cu catalyst inside a hybrid bilayer membrane by depositing a monolayer of lipid on the self-assembled monolayer. We envisage that this electrochemical system can give a unique mechanistic insight not only into the oxygen reduction reaction, but into proton-coupled electron transfer in general.

Tailoring of metal cluster-like materials for the molecular oxygen reduction reaction

Abstract Research of nanometer scale range catalysts based on cluster-like mono-, bi-metallic, and chalcogenides for oxygen reduction reaction (ORR) as cathodes, a major challenge for polymer electrolyte membrane fuel cells (PEMFCs) nowadays, for facilitating efficient electron transfer using the carbonyl chemical route is reviewed. A strategy aimed at reducing the amount of expensive catalyst materials, giving the accessibility of non-noble materials and taking into account the activity and selectivity of cathodes for the ORR is devised as well.