Mechanism Of Oxygen Reduction Research Articles

Bimetallic ZnFe–NC prepared using microchannel reactor for oxygen reduction reaction and mechanism research

Bimetallic ZnFe–NC prepared using microchannel reactor for oxygen reduction reaction and mechanism research

Enhanced pulse electrocatalytic reductive-oxidative degradation of chlorinated organic pollutants based on a synergistic effect from Pd single atoms and FeCo2O4 nanowire

Targeting complete dechlorination and decomposition of chlorinated organic pollutants in an environmentally friendly and resource efficient manner. In this investigation, a three-dimensional multi-structured electrode (Pd-NC@Fe/CoCF) comprising Pd monatomic and nitrogen-doped carbon-coated FeCo2O4 nanowire cluster arrays were effectively synthesized. This electrode demonstrated efficient generation of H* and the production of •OH through a (2+1) e- oxygen reduction mechanism under the synergistic action of Pd single atoms and FeCo2O4 nanowire. When integrated with a square-wave pulsed electrocatalytic system, the chlorinated organic pollutants could be fully degraded within 45 min under the most favorable process parameters, which include a pulse voltage of −0.7 V, a duty cycle of 50 %, and a pulse frequency of 0.1 Hz. This results in a removal rate of 92.3 % for TOC and an energy consumption of 1.27 kWh·kg−1. This study presents a sustainable and environmentally friendly approach to the electrochemical degradation of chlorinated organic pollutants.

Identifying the two-electron oxygen reduction mechanism on BC3 site in Cl−-containing electrolytes

The electrochemical synthesis of H2O2 has great potential for applications in the treatment of environmental pollution and energy, but the toxic effect of Cl− on the active sites of catalysts has severely limited the application of this technology in these fields. Developing efficient non-metal-doped catalysts represents an effective strategy to address this issue. Although B-doped carbon materials have demonstrated excellent ORR activity, the understanding of the ORR mechanism on B surface sites remains highly controversial, particularly in seawater electrolytes. The influence of Cl− adsorption behavior on the catalytic reaction center mechanism is still unknown. In this paper, catalysts containing the BC3 structure were successfully prepared with an H2O2 yield of 3.55 mol/ (gcat h) in simulated seawater. The DFT results demonstrated that BC3 functions as a 2e− ORR active site, and the presence of Cl− does not poison it. Instead, it promotes the hydrogenation process of *OOH on its surface, further enhancing its ORR performance. The results provide clarity on how the Cl− of the catalytic environment affects the ORR performance and pathway selectivity of non-metallic B-sites. Additionally, the results offer valuable insights for designing electrocatalysts in complex environments.

Concluding remarks: a summary of the Faraday Discussion on rechargeable non-aqueous metal-oxygen batteries.

The Faraday Discussion on rechargeable non-aqueous metal-oxygen batteries is summarised. The remarks paper highlights the specific science contributions made in the vital areas of oxygen reduction and evolution reaction mechanisms in non-aqueous electrolytes; material developments for stable metal-oxygen battery cathodes; achieving stable metal anodes and protected interfaces; and, finally, contributions concerning the progress towards practical metal-oxygen batteries. Key conclusions associated with these papers will be highlighted in an order such that readers can identify papers that they would like to explore in more detail.

Feasibility of achieving two-electron K-O2 batteries.

A deep understanding of the oxygen (O2) reduction and evolution mechanisms is crucial for understanding metal-O2 batteries. It has become evident that the instability of superoxide in the presence of lithium (Li) ions and sodium (Na) ions is the root cause for the poor reversibility and energy efficiency of Li-O2 and Na-O2 batteries. A straightforward yet elegant method is stabilizing superoxide with the larger potassium (K) ions. Superoxide-based K-O2 batteries, invented by our group in 2013, are operated based on one-electron redox of O2/potassium superoxide (KO2) and have high energy efficiencies without any electrocatalysts. Nevertheless, limiting the anionic redox to O2/superoxide affects the capacity output. Therefore, it is attractive to explore the possibility of beyond KO2 in the K-O2 batteries, especially if the use of catalysts can still be avoided. In this research, solid KO2 was used as the condensed O2 source and pre-dissolved in the dimethyl sulfoxide (DMSO)-based electrolyte. It is encouraging to observe two sets of reversible peaks during the three-electrode cyclic voltammetry scan under an argon atmosphere. One pair of peaks is attributed to the KO2/potassium peroxide (K2O2) interconversion. Such redox has superb reversibility and a small overpotential of 239 mV in the absence of explicit electrocatalysts. Notably, it is further revealed that K2O2 reacts with gaseous O2. Therefore, a gas-open system with an O2 supply is unfavorable for realizing the reversible KO2/K2O2 redox, and a closed cell system with a KO2 supply as the starting active material is suggested instead.

Elucidating Oxygen Reduction Mechanisms on Organic Mixed Ionic-Electronic Conducting Polymers

Atmospheric oxygen is an attractive oxidant for the generation of electricity from chemical fuels and for the electrochemical production of hydrogen peroxide. Although not universal, it is generally assumed that an electrocatalyst is needed to reduce oxygen. Recently, a variety of organic mixed ionic-electronic conducting polymers (OMIECs) have been reported to exhibit catalytic behavior for both the 4-electron/4-proton and the 2-electron/2-proton oxygen reduction reaction (ORR).This work sets out to identify the oxygen reduction mechanism of OMIECs through a multi-faceted experimental and theoretical approach. We primarily focus our efforts on p(NDI-T2 P75)—a random copolymer comprised of naphthalene diimide (NDI) and bithiophene (T2) units with 75% polar sidechains—and then expand the understanding built on this system to a range of other OMIECs. Using rotating ring disk electrochemistry, we find that the investigated OMIECs exhibit a high selectivity towards the 2-electron ORR product. Using operando UV-Vis and Raman spectroscopy measurements, we identify changes in OMIEC performance when in the presence of O2. To gain further insights about the catalytic reaction path, we construct and test a microkinetic model. Through this model, we show that the performance of the tested OMIECs can be rationalized through an EC’D reaction mechanism. Our results suggest that these materials do not operate as electrocatalysts for the initial reduction of oxygen to superoxide but do function as catalysts for the disproportionation of superoxide.

Growth of surfactant-free Au-Co bimetallic atom-bomb cracker-like microstructures: A highly active morphological dependent hybrid electrocatalyst for dioxygen reduction

This paper reports the formation of atom-bomb fire cracker (ABC) like Au-Co heterostructures by attaching folic acid-capped AuNPs (FA-AuNPs) on a glassy carbon (GC) electrode followed by cobalt electrodeposition. The characteristic absorption band at 516 nm from the UV–visible spectrum confirms the AuNPs formation and their average size was ∼6 nm as evidenced from HR-TEM. The AuNPs were then assembled on a GC electrode via 1,6-hexadiamine linker followed by the electrodeposition of Co at various applied potentials and time. XPS spectra of Au-Co clearly revealed the zero valent nature of Au and Co and Co2+ in the bimetallic assembly. The SEM results exhibited the variations in the morphology of Au-Co with respect to the applied potential and time. It was found that the deposition of Co at -0.50 V for 600 s leads to the formation of ABC-like structure only at FA-AuNPs surface. The specific atom-bomb morphology of Au-Co was not obtained at bare GC and citrate-capped AuNPs surfaces, indicating the influence of FA-AuNPs. The Au-Co showed higher electrocatalytic activity towards dioxygen reduction by shifting the onset potential by 230 and 280 mV towards zero respectively than Co and AuNPs alone. The Koutecky-Levich plot confirms the four-electron transfer mechanism of oxygen reduction at Au-Co fabricated electrode.

Superoxide anion radical generation in photosynthetic electron transport chain

The review analyzes the data available in the literature on the rates, characteristics and mechanisms of oxygen reduction to a superoxide anion radical at the sites of the photosynthetic electron transport chain where this reduction can occur. The existing assumptions about the role of the components of these sites in this process are critically examined, with use of thermodynamic approaches and the results of recent studies. The process of O2 reduction at the acceptor side of PSI, which is considered the main place of this process in the photosynthetic chain, is described in detail. The evolution of the photosynthetic apparatus in the context of controlling the leakage of electrons to O2 is considered. The reasons limiting the application of the results obtained with isolated segments of the photosynthetic chain to estimate the rates of O2 reduction at the corresponding sites in the intact thylakoid membrane are discussed.

Fabrication and Electrochemical Testing of Silver Pattern Cathodes for Proton Conducting It-SOFC

Dense silver (Ag) cathodes with different triple phase boundary (TPB; the interface of gas, electrolyte and electrode) length (LTPB) and electrode area (AELT) were fabricated by photolithography and E-beam evaporation over different proton-conducting electrolytes such as BaZr0.4Ce0.4Y0.1Yb0.1O3– δ (BZCYYb4411). A bi-layer lift-off resist method appears more versatile than single layer for successful pattern cathode fabrication. The electrochemical behaviors of Ag pattern cathodes over the BZCYYb4411 electrolyte were tested with counter electrode such as Ba0.5Sr0.5Co0.8Fe0.2O3-δ and correlated against geometric features such as LTPB and AELT to understand the oxygen reduction kinetics and mechanism for proton conducting solid oxide fuel cells. Figure 1

Superoxide Anion Radical Generation in Photosynthetic Electron Transport Chain.

This review analyzes data available in the literature on the rates, characteristics, and mechanisms of oxygen reduction to a superoxide anion radical at the sites of photosynthetic electron transport chain where this reduction has been established. The existing assumptions about the role of the components of these sites in this process are critically examined using thermodynamic approaches and results of the recent studies. The process of O2 reduction at the acceptor side of PSI, which is considered the main site of this process taking place in the photosynthetic chain, is described in detail. Evolution of photosynthetic apparatus in the context of controlling the leakage of electrons to O2 is explored. The reasons limiting application of the results obtained with the isolated segments of the photosynthetic chain to estimate the rates of O2 reduction at the corresponding sites in the intact thylakoid membrane are discussed.

Inhibition of superoxide radical diffusion by Van der Waals forces for boosting photocatalytic H2O2 production

The conversion of superoxide radical (·O2−) to hydrogen peroxide (H2O2) is critical in the photocatalytic formation of H2O2 via the sequential two-step single-electron oxygen reduction mechanism. Providing a high concentration of ·O2− is an effective approach to promoting this process in terms of chemical kinetics. It is, however, extremely challenging to implement this idea in the photocatalytic solution due to the limited lifespan of ·O2−. To this end, a concept about local ·O2− enrichment catalyst surface was proposed in this study and achieved in an innovative PSI/C3N4 photocatalyst. The results of theoretical calculations and temperature-dependent photocatalytic studies indicate that PSI on the C3N4surface can serve as a diffusion buffer for ·O2−, capturing them through Van der Waals interactions and separating them by energy perturbations. As a result, a local enrichment of ·O2− was established on the PSI/C3N4 surface during photocatalysis, strengthening the photocatalytic conversion of ·O2− to H2O2, thus allowing the PSI/C3N4-4 photocatalyst to produce H2O2 at a rate of approximately 2.4 and 2.65 times greater than pure C3N4 under visible light and LED irradiation, respectively. This study presents a promising strategy for enhancing photocatalytic H2O2 production efficiency by selectively enriching ·O2− on the catalyst surface.

Electrochemical Crosslinking of Alginate-Towards Doped Carbons for Oxygen Reduction.

Electrochemical crosslinking of alginate strands by in situ iron oxidation was explored using a potentiostatic regime. Carbon-based materials co-doped with iron, nitrogen, and/or sulfur were prepared via electrolyte composition variation with a nitrogen-rich compound (rivanol) or through post-treatments with sodium sulfide. Nanometer-sized iron particles were confirmed by transmission and field emission scanning electron microscopy in all samples as a consequence of the homogeneous dispersion of iron in the alginate scaffold and its concomitant growth-limiting effect of alginate chains. Raman spectra confirmed a rise in structural disorder with rivanol/Na2S treatment, which points to more defect sites and edges known to be active sites for oxygen reduction. Fourier transform infrared (FTIR) spectra confirmed the presence of different iron, nitrogen, and sulfur species, with a marked difference between Na2S treated/untreated samples. The most positive onset potential (-0.26 V vs. saturated calomel electrode, SCE) was evidenced for the sample co-doped with N, S, and Fe, surpassing the activity of those with single and/or double doping. The mechanism of oxygen reduction in 0.1 M KOH was dominated by the 2e- reduction pathway at low overpotentials and shifted towards complete 4e- reduction at the most negative explored values. The presented results put forward electrochemically formed alginate gels functionalized by homogeneously dispersed multivalent cations as an excellent starting point in nanomaterial design and engineering.

Photocatalytic Synthesis of Hydrogen Peroxide from Molecular Oxygen and Water

Hydrogen peroxide is a powerful and green oxidant that allows for the oxidation of a wide span of organic and inorganic substrates in liquid media under mild reaction conditions, and forms only molecular water and oxygen as end products. Hydrogen peroxide is therefore used in a wide range of applications, for which the well-documented and established anthraquinone autoxidation process is by far the dominating production method at the industrial scale. As this method is highly energy consuming and environmentally costly, the search for more sustainable synthesis methods is of high interest. To this end, the article reviews the basis and the recent development of the photocatalytic synthesis of hydrogen peroxide. Different oxygen reduction and water oxidation mechanisms are discussed, as well as several kinetic models, and the influence of the main key reaction parameters is itemized. A large range of photocatalytic materials is reviewed, with emphasis on titania-based photocatalysts and on high-prospect graphitic carbon nitride-based systems that take advantage of advanced bulk and surface synthetic approaches. Strategies for enhancing the performances of solar-driven photocatalysts are reported, and the search for new, alternative, photocatalytic materials is detailed. Finally, the promise of insitu photocatalytic synthesis of hydrogen peroxide for water treatment and organic synthesis is described, as well as its coupling with enzymes and the direct insitu synthesis of other technical peroxides.

Quantum Mechanical Study of Oxygen Ligands Protonation for the Stable States of the Laccase Active Site.

Laccases are enzymes catalyzing the oxidation of a wide range of organic and inorganic substrates accompanied by molecular oxygen reduction to water. Recently, oxygen reduction by laccases has been studied by single-crystal serial X-ray crystallography with increasing absorption doses at subatomic resolution. There were two determined structures corresponding to the reduced and oxidized stable states of the laccase active site. However, the protonation of the oxygen ligands involved cannot be determined even at subatomic resolution. In the present work, the protonation of oxygen ligands in the active site of laccase for the two stable states determined in the X-ray study was explored using quantum mechanical and continuum-electrostatics calculations. This is important for understanding the reaction of the oxygen reduction mechanism in laccases. The high precision of X-ray data at subatomic resolutions allowed us to optimize the quantum mechanical calculations.

Some aspects of hydrogen oxidation in solid oxide fuel cell: A brief historical overview

Environmentally friendly and resource-efficient ways to generate, convert, store and transport electricity are important areas of scientific and technological development. Fuel cells are direct converters of chemical energy into electricity with low emissions of harmful components. One of the most promising types of fuel cells is the solid oxide fuel cell (SOFC). The electrical power generated by the SOFC is mainly limited by the ohmic resistance of the electrolyte and the polarization of the electrodes. The ohmic resistance can be reduced by reducing the thickness of the electrolyte. To reduce the polarization resistance, other approaches are needed, namely a detailed study of the mechanisms of electrode reactions and the determination of the nature of rate-determining stages. Until now, fuel oxidation at the anode of the SOFC, as opposed to oxygen reduction at the cathode, has not been well understood. Even for conventional nickel-ceramic anodes, there is no clear understanding of the nature of the rate-determining steps of hydrogen oxidation. This review provides a brief historical background on the development of SOFCs, some insights into the oxygen reduction mechanisms, and a more detailed review of the kinetics of hydrogen oxidation at SOFC anodes.

Theoretical Study on the Regulation of Oxygen Reduction Mechanism by Modulating the Spatial Structure of Active Sites on Platinum★

Theoretical Study on the Regulation of Oxygen Reduction Mechanism by Modulating the Spatial Structure of Active Sites on Platinum^★

Solid-phase preparation of defective carbon supported PtNi alloy electrocatalyst and analysis of its oxygen reduction mechanism

In the present work, PtNi-loaded defective carbon (Pt/ZnPPC) was prepared by solid-phase method. Carbon support with specific defect types, such as Zn metal nitrogen carbon (ZnPPC850), N-doped carbon (ZnPPC950) and defective carbon (ZnPPC1050), were selectively obtained by optimizing the pyrolysis temperature to explore the effect of defect types on oxygen reduction reactions (ORR). Electrochemical measurements showed that the half-wave potential of the PtNi metal nanoparticle-loaded ZnPPC1050 catalyst (PtNi-ZnPPC1050) outperformed the commercial JM-Pt/C by 35 mV, and by 45 mV compared to the PtNi-loaded ZnPPC950 catalyst (PtNi-ZnPPC950), suggesting that the defects in the ZnPPC1050 support resulting from the evaporation of N by pyrolysis can interact well with Pt metal electrically, allowing the PtNi nanoparticles to be uniformly distributed. Meanwhile, the defects lead to the carrier containing a large number of active sites making its catalytic performance even much better than the pyridine nitrogen sites in ZnPPC950. The carbon defect structure is loosened and porous with high specific surface area, which can effectively load PtNi nanoparticles and enhance the mass transfer. We obtained a new bimetallic oxygen reduction catalyst loaded with PtNi on defective carbon and elucidated the effect of five-membered ring carbon defect structure and N-doped structure on metal-carrier interaction.

(Digital Presentation) Intercalated Layered TaSi2N4 Electrodes of Zn–Air Battery

Metal–air batteries have attracted significant attention due to their excellent advantage of high-energy-density metal anodes with air cathodes. The development of structurally stable materials has been a great challenge for Zn-air batteries. Layered 2D materials provide unique opportunities due to their facial synthesis and structural stability. In this presentation, we demonstrate intercalated architecture TaSi2N4 layered material for cathode and anode of Zn–air batteries. The mechanistic aspects of Zn storage will be shown. These van der Waals materials undergo a phase during Zn loading. Interestingly, TaSi2N4 surface shows the two-electron mechanism of oxygen reduction. These layered materials will create new possibilities for the development of unique electrodes of Zn–air batteries.

OH-···Au Hydrogen Bond and Its Effect on the Oxygen Reduction Reaction on Au(100) in Alkaline Media.

Using ab initio molecular dynamics simulations with fully solvated ions, we demonstrate that solvated OH- forms a stable hydrogen bond with Au(100). Unlike the hydrogen bond between H2O and Au reported previously, which is more favorable for negatively charged Au, the OH-···Au interaction is stabilized when a small positive charge is added to the metal slab. For electro-catalysis, this means that while OH2···Au plays a significant role in the hydrogen evolution reaction, OH-···Au could be a significant factor in the oxygen reduction reaction in alkaline media. It also points to a fundamental difference in the mechanism of oxygen reduction between gold and platinum electrodes.

Influence of Nano-Sized SiC on the Laser Powder Bed Fusion of Molybdenum

Consolidation of pure molybdenum through laser powder bed fusion and other additive manufacturing techniques is complicated by a high melting temperature, thermal conductivity and ductile-to-brittle transition temperature. Nano-sized SiC particles (0.1 wt%) were homogeneously mixed with molybdenum powder and the printing characteristics, chemical composition, microstructure, mechanical properties were compared to pure molybdenum for scan speeds of 100, 200, 400, and 800 mm/s. The addition of SiC improved the optically determined density and flexural strength at 400 mm/s by 92% and 80%, respectively. The oxygen content was reduced by an average of 52% over the four scan speeds analyzed. Two mechanisms of oxygen reduction were identified as responsible for the improvements: oxidation of free carbon and the creation of secondary phase nanoparticles. This study illustrates the promising influence of nanoparticle additions to refractory metals in laser powder bed fusion.