Oxygen Transfer Process Research Articles

Towards Production of a Highly Catalytic and Stable Graphene-Wrapped Graphite Felt Electrode for Vanadium Redox Flow Batteries

Despite the appealing features of vanadium redox flow batteries as a promising energy storage solution, the polarization losses, among other factors, prevent widespread applications. The dominant contribution to these polarization losses is the sluggish (even irreversible) electron-transfer towards reactions, leading to large over-potentials (poor rate capability). In particular, the positive half-cell reaction suffers from a complex mechanism since electron- and oxygen-transfer processes are key steps towards efficient kinetics. Thus, the positive reaction calls for electrodes with a large number of active sites, faster electron transfer, and excellent electrical properties. To face this issue, a graphene-wrapped graphite felt (GO-GF) electrode was synthesized by an electrospray process as a cost-effective and straightforward way, leading to a firm control of the GO-deposited layer-by-layer. The voltage value was optimized to produce a homogeneous deposition over a GF electrode after achieving a stable Taylor cone-jet. The GO-GF electrode was investigated by cyclic voltammetry and electrochemical impedance spectroscopy in order to elucidate the electrocatalytic properties. Both analyses reflect this excellent improvement by reducing the over-potentials, improving reversibility, and enhancing collected current density. These findings confirm that the GO-GF is a promising electrode for high-performance VRFB, overcoming the performance-limiting issues in a positive half-reaction.

Comparative study on ferrate oxidation of BPS and BPAF: Kinetics, reaction mechanism, and the improvement on their biodegradability

Bisphenol S (BPS) and bisphenol AF (BPAF) were increasingly consumed and these compounds are resistant to environmental degradation. Herein, ferrate oxidation of BPS and BPAF was investigated, and biodegradability of the oxidation products was examined. The second-order reaction rate constants of ferrate with BPS and BPAF were 1.3 × 103 M−1s−1 and 3 × 102 M−1s−1, respectively, at pH 7.0, 25 °C. In the oxidation process, some BPS molecules dimerized, while other BPS molecules were oxidized through oxygen-transfer process, leading to the formation of hydroxylation products and benzene-ring cleavage products. The dominant reaction of BPAF with ferrate was oxygen-transfer process, and BPAF was degraded into lower molecular weight products. The variation of assimilable organic carbon (AOC) suggested that the biodegradability of BPAF and BPS was largely improved after ferrate oxidation. Compared with the BPS oxidation products, the BPAF oxidation products were easier to be bio-consumed. Pure culture test showed that BPAF inhibited the growth of Escherichia coli, while ferrate oxidation completely eliminated this toxic effect. Co-existing humic acid (HA, 1 mg C/L to 5 mg C/L) decreased the removal of BPS and BPAF with ferrate. Compared with BPAF, more oxidation intermediates formed in the ferrate oxidation of BPS may be reduced by HA to the parent molecular. Thus, the inhibition effect of HA on the ferrate oxidation of BPS was more obvious than that on BPAF.

Understanding the Coexistence of Two Bipolar Resistive Switching Modes with Opposite Polarity in Pt/TiO2/Ti/Pt Nanosized ReRAM Devices

Redox-type resistive random access memories based on transition-metal oxides are studied as adjustable two-terminal devices for integrated network applications beyond von Neumann computing. The prevailing, so-called, counter-eight-wise (c8w) polarity of the switching hysteresis in filamentary-type valence change mechanism devices originates from a temperature- and field-controlled drift-diffusion process of mobile ions, predominantly oxygen vacancies in the switching oxide. Recently, a bipolar resistive switching (BRS) process with opposite polarity, so-called, eight-wise (8w) switching, has been reported that, especially for TiO2 cells, is still not completely understood. Here, we report on nanosized (<0.01 μm2) asymmetric memristive cells from 3 to 6 nm thick TiO2 films by atomic layer deposition, which reveal a coexistence of c8w and 8w switching in the same cell. As important characteristics for the studied Pt/TiO2/Ti/Pt devices, the resistance states of both modes are nonvolatile and share one common state; i.e., the high-resistance state of the c8w mode equals the low-resistance state of the 8w-mode. A transition between the opposite hysteresis loops is possible by voltage control. Specifically, 8w BRS in the TiO2 cells is a self-limited low-energy nonvolatile switching process. Additionally, the 8w reset process enables the programming of multilevel high-resistance states. Combining the experimental results with data from simulation studies allows to propose a model, which explains 8w BRS by an oxygen transfer process across the Pt/TiO2 Schottky interface at the position of the c8w filament. Therefore, the coexistence of c8w and 8w BRS in the nanoscale asymmetric Pt/TiO2/Ti/Pt cells is understood from a competition between drift/diffusion of oxygen vacancies in the oxide layer and an oxygen exchange reaction across the Pt/TiO2 interface.

Express-method for Estimation of Electrocatalytic Activity of Oxide Films toward Oxygen Transfer Reactions

Oxidation catalysis of organic substances has attracted special attention in recent years due to of their high industrial significance in green and energy chemistry. The implementation of a transition metal-based catalyst in combination with oxygen is an alternative to the traditional procedures. This study justifies the application of amperometric response 'in situ' for estimation of the electrocatalytic activity of metal oxide films, which are known to be promising for oxygen transfer processes. The reaction of electrooxidation of Mn2+ ions may be termed as a 'marker' for oxygen transfer reactions due to its kinetic features, such as proportionality between the current density and the surface concentration of •OH-radicals. The relative parameter, kox, has been offered for estimation of the oxidizing capacity of an anode material toward oxygen transfer reaction in reference to platinum oxidizing capacity. kox value is automatically calculated exactly during electroplating of MnOx as a ratio of the current density of Mn2+ + 2H2O – 2e→MnO2+4H+ reaction on the tested surface to the current density of this reaction on Pt surface. The developed method was tested during the investigation of catalytic activity of MnOx films for electrooxidation of glucose. The parameter kox was calculated for other anode materials and was analyzed. The application of the new method allows estimating and comparing the catalytic performance toward oxygen transfer reactions of anode materials or of the same material in different modifications, such as nano particles, composites, different compositions etc. The pre-test reduces manifold the time spent for determination of oxidizing capacity of oxides.

High-power positive electrode based on synergistic effect of N- and WO3 -decorated carbon felt for vanadium redox flow batteries

Although Vanadium Redox Flow Batteries (VRFB) are suitable for grid-scale applications, their power-related cost must be reduced in order to boost the use of this technology in the market, allowing their widespread commercialization. One effective way to make the VRFB a competitive and viable solution could be through new strategies for improving the electrocatalytic activity of the electrodes with enhanced electrolyte/electrode interface characteristics. Herein, we report the synergistic effect demonstrated by N- and WO3- decorated carbon-based positive electrode, named HTNW electrode, which demonstrates the feasibility of achieving: i) enhanced electrocatalytic activity, achieving large current density and high reversibility towards VO2+/VO2+ couple (promotion of oxygen and electron transfer processes), ii) decrement of the electron-transfer resistance from 76.18 Ω to 13.00 Ω for the pristine electrode and HTNW electrodes, respectively; iii) 51% of the electrolyte utilization ratio at high rates (i.e. 200 mA cm−2) with 70% of energy efficiency; iv) increment of more than 50% of the power–peak in comparison with pristine electrode.

Graphene functionalization: Mechanism of carboxyl group formation

Carboxyl groups are ubiquitous in graphene-based materials. Decades ago, they were important in conferring cation-exchange properties to coal and coal-derived chars; today they are instrumental in converting graphite to graphene as well as in a wide variety of surface functionalization processes. And yet the essential mechanistic details of their formation have not received the attention they deserve. Here we perform quantum chemical calculations based on the density functional theory to reveal the elementary oxygen-transfer processes that are consistent with the abundant experimental literature on the oxidation of sp2-hybridized carbon materials. Prototypical graphene clusters decompose nitric acid to nitrogen oxides and the reactive hydroxyls. Carboxyl groups are thus formed by virtue of sequential hydroxyl attack at the carbon active sites (Cf) which weakens and cleaves the contiguous aromatic C-C bonds. A comparison with the other common oxidants (X, e.g., chlorate or permanganate) is carried out by distinguishing the 1O-down and 2O-down oxygen-transfer pathways. This constitutes an essential step toward the unification of a wide variety of oxidation processes involving semiquinone or dioxirane surface intermediates: Cf + XO3- = C(O) + NO2− (or ClO2−) vs. Cf + XO3- = C(O2−) + NO (or ClO) vs. Cf + XO4- = C(O2) + XO2-.

Understanding the Regioselectivity of Aromatic Hydroxylation over Divanadium-Substituted γ-Keggin Polyoxotungstate

The aromatic hydroxylation of pseudocumene (PC) with aqueous hydrogen peroxide catalyzed by the divanadium-substituted γ-Keggin polyoxotungstate TBA4[γ-PW10O38V2(μ-O)(μ-OH)] (TBA-1H, TBA = tetrabutylammonium) has been studied using kinetic modeling and DFT calculations. This reaction features high chemoselectivity and unusual regioselectivity, affording 2,4,5-trimethylphenol (TMP) as the main product. Then the computational study was extended to the analysis of the regioselectivity for other alkoxy- and alkylarene substrates. The protonation/deprotonation of TBA-1H in MeCN/tBuOH (1:1) was investigated by 31P NMR spectroscopy. Forms with different protonation states, [γ-PV2W10O40]5– (1), [γ-HPV2W10O40]4– (1H), and [γ-H2PV2W10O40]3– (1H2), have been identified, and the protonation equilibrium constants were estimated on the basis of the 31P NMR data. DFT calculations were used to investigate the oxygen transfer process from hydroperoxo species, [γ-PW10O38V2(μ-O)(μ-OOH)]4– (2) and [γ-PW10O38V2(μ-OH)(μ-OOH)]3...

A new method to measure and model dynamic oxygen microdistributions in moving biofilms

Biofilms in natural environments offer a superior solution to mitigate water pollution. Artificially intensified biofilm reactors represented by rotating biological contactors (RBCs) are widely applied and studied. Understanding the oxygen transfer process in biofilms is an important aspect of these studies, and describing this process in moving biofilms (such as biofilms in RBCs) is a particular challenge. Oxygen transfer in RBCs behaves differently than in other biological reactors due to the special oxygen supply mode that results from alternate exposure of the biofilm to wastewater and air. The study of oxygen transfer in biofilms is indispensable for understanding biodegradation in RBCs. However, the mechanisms are still not well known due to a lack of effective tools to dynamically analyze oxygen diffusion, reaction, and microdistribution in biofilms. A new experimental device, the Oxygen Transfer Modeling Device (OTMD), was designed and manufactured for this purpose, and a mathematical model was developed to model oxygen transfer in biofilm produced by an RBC. This device allowed the simulation of the local environment around the biofilm during normal RBC operation, and oxygen concentrations varying with time and depth in biofilm were measured using an oxygen microelectrode. The experimental data conformed well to the model description, indicating that the OTMD and the model were stable and reliable. Moreover, the OTMD offered a flexible approach to study the impact of a single-factor on oxygen transfer in moving biofilms.In situ environment of biofilm in an RBC was simulated, and dynamic oxygen microdistributions in the biofilm were measured and well fitted to the built model description.

Application of mathematical modelling for investigating oxygen transfer energy requirement and process design of an aerobic continuous stirred tank fermenter

Fermentation kinetic and oxygen transfer modelling coupled with energy analysis was applied to investigate how key input design variables influenced fermenter size, feed substrate requirement, wasted substrate and aeration system electrical energy requirement. The study showed that trade-offs and compromises are required to select the values of key input variables that can produce superior process designs in terms of the output variables. For example, reducing steady-state oxygen concentration reduced aeration system energy requirements and associated carbon footprint but increased fermenter size and associated cost. Mathematical modelling can assist in more precisely zoning in quantitatively on the selection of design input variable values that can produce a best compromise between conflicting design output variables. Mathematical modelling can also highlight design sensitivities. For example, if the steady-state sugar concentration is reduced below a certain value, then this can lead to an exponential increase in fermenter volume and associated cost, thus it is prudent to operate on the conservative side of this value.

Железо в неживой и живой природе

The paper considers crystal structure and chemical properties of iron, its oxidation numbers and participation of iron in redox processes in animate and inanimate nature. Depending on temperature and pressure, iron can have five crystal structures: a, b, g, d and e. Sketches of unit crystal cells are drawn. Interstices that may be occupied by impurity atoms are shown. Iron may have oxidation numbers from zero (pure iron) to +8. The most important are oxidation numbers of 0, +2 and +3. Iron oxide +2 (FeO) has black colour, while iron oxide +3 (Fe2O3) is bright red. Iron is the key participant in the process of oxygen transfer in steelmaking processes. The transfer processes consists of acquisition of oxygen by iron at the cost of its oxidation to FeO (Fe+2) and Fe2O3 (Fe+3), oxygen being transferred to the metal melt [O]. Redox processes and oxygen transfer processes are bound with the change of iron oxidation number. A doubt is expressed on oxygen attachment to hemoglobin in molecular form,, and a writing of reactions involving hemoglobin in the blood based on redox reactions is proposed. Reactions of oxygen transfer by the blood are proposed. In the lungs, where partial oxygen pressure is high, a part of Fe+2 of the hemoglobin gives electrons and oxidates to Fe+3, which results in the change of the blood colour: (Hb·4Fe+2) + O2 ↔ (Hb·4Fe+3·2O–2). In the capillars, Fe+3 attaches electrons, gives oxygen participating in oxidation, and reduces to Fe+2: (Hb·4Fe+3·2O–2) + Cсреды = (Hb·4Fe+2) + CO2. In this writing of reactions there is no place for molecular oxygen. In accordance with the present scheme, redox reactions in the lungs and capillars occur at a high rate with participation and transfer of electrons.

Oxygen profile and clogging in vertical flow sand filters for on-site wastewater treatment

13 million people (about 20% of the population) use on-site wastewater treatment in France. Buried vertical sand filters are often built, especially when the soil permeability is not sufficient for septic tank effluent infiltration in undisturbed soil. Clogging is one of the main problems deteriorating the operation of vertical flow filters for wastewater treatment. The extent of clogging is not easily assessed, especially in buried vertical flow sand filters. We suggest examining two possible ways of detecting early clogging: (1) NH4–N/NO3–N outlet concentration ratio, and (2) oxygen measurement within the porous media. Two pilot-scale filters were equipped with probes for oxygen concentration measurements and samples were taken at different depths for pollutant characterization. Influent and effluent grab-samples were taken three times a week. The systems were operated using batch-feeding of septic tank effluent. Qualitative description of oxygen transfer processes under unclogged and clogged conditions is presented. NH4–N outlet concentration appears to be useless for early clogging detection. However, NO3–N outlet concentration and oxygen content allows us to diagnose the early clogging of the system.

Characterization of tissue scaffolds for time-dependent biotransport criteria – a novel computational procedure

This study aims to establish a new computational framework that allows modeling transient oxygen diffusion in tissue scaffolds more efficiently. It has been well known that the survival of cells strongly relies on continuous oxygen/nutrient supply and metabolite removal. With optimal design in scaffold architecture, its ability to sustain long distance oxygen supply could be improved considerably. In this study, finite element based homogenization procedure is first used to characterize the initial effective biotransport properties in silico. These initial properties are proper indicators to prediction of the on-going performance of tissue scaffolds over time. The transient model by adopting an edge-based smoothed finite element method with combination of mass-redistributed method is then established to more efficiently simulate the transient oxygen transfer process in tissue scaffolds. The proposed new method allows large time steps to model the oxygen diffusion process without losing numerical accuracy, thereby enhancing the computational efficiency significantly, in particular for the design optimization problems which typically require numerous analysis iterations. A number of different scaffold designs are examined either under net diffusion without cell seeding, or under cellular oxygen/nutrient uptake with or without considering cell viability. The association between the homogenized effective diffusivity of net scaffold microstructures and corresponding transient diffusion and time-dependent cellular activities is divulged. This study provides some insights into scaffold design.

First-Principles Study of Oxygen Transfer and Hydrogen Oxidation Processes at the Ni-YSZ-Gas Triple Phase Boundaries in a Solid Oxide Fuel Cell Anode

A model of Ni-yttria stabilized zirconia (YSZ)-gas triple phase boundary (TPB) is built to simulate the oxygen transfer and hydrogen oxidation processes in solid oxide fuel cell anodes by using density functional theory. The highest barrier in the anodic processes is found in the step of oxygen transfer from the YSZ surface to the TPB site, where the oxygen is connected with nickel and yttrium/zirconium atoms. Three TPB sites and associated reaction paths, near Y or Zr atoms, and one nickel site on the Ni terrace are compared for the hydrogen oxidation reaction. Depending on the local structures of TPB sites, the reaction barrier of the (O + H)* → OH* reaction varies from 0.46 to 0.57 eV, and the reaction barrier of (OH + H)* → H2O* varies from 0.83 to 1.05 eV. When O or OH is on the Ni site, which is only 3 Å from the Y at TPB site, the reaction barriers of the above reactions are 1.15 and 1.02 eV, respectively.

Enhanced iron(III) corrole-catalyzed oxidations with iodobenzene diacetate: Synthetic and mechanistic investigations

The electron-deficient iron(III) corrole complex catalyzes the efficient oxidation of hydrocarbons using PhI(OAc)2 as an mild oxygen source. The catalyst stability against degradation was much enhanced owing to the mild oxidizing ability of PhI(OAc)2. Excellent selectivity and high catalytic efficiency (with up to 1400 TON) have been achieved in alkene epoxidations. This promising oxygen transfer process is mechanistically rationalized in terms of a putative high-valent iron(V)-oxo species as the active oxidant.

Bioprocess Engineering Aspects of the Cultivation of a Lovastatin Producer Aspergillus terreus.

The aim of this work is to review bioprocess engineering aspects of lovastatin (antihypercholesterolemia drug) production by Aspergillus terreus in the submerged culture in the bioreactors of various scale presented in the scientific literature since the nineties of the twentieth century. The key factor influencing the cultivation of any filamentous species is fungal morphology and that is why this aspect was treated as the starting point for further considerations. Fungal morphology is known to have an impact on the following issues connected with the cultivation of A. terreus reviewed in this article. These are broth viscosity in conjunction with non-Newtonian behaviour of the cultivation broths, and multistage oxygen transfer processes: from gas phase (air) to liquid phase (broth) and diffusion in the fungal agglomerates. The latest achievements concerning the controlling A. terreus morphology during lovastatin biosynthesis with the use of morphological engineering techniques were also reviewed. Last but not least, some attention was paid to the type of a bioreactor, its operational mode and kinetic modelling of lovastatin production by A. terreus.

Numerical Simulation of Dissolved Oxygen Transfer in an Aerated Pond

Dissolved oxygen transfer in an aeration pond was studied by numerical method in this paper. 2d water pond current induced by water-wheel aerators and oxygen transfer process was simulated by finite volume method. In order to verify the relationships between current and dissolved oxygen transfer, we set 4 layout styles with 4 aerators in a water pond. It is proved that different layout styles induce different flow structures and dissolved oxygen distribution. Traditional layout (style a) is not the best way for oxygen transfer, and other styles (style b, c &amp;d) are all superior to the traditional layout. But water flow structures are not the same results. Water circulation performance is style a, c, b, d in sequence. Style c (flow to corners along pond wall) is the best way by comprehensive consideration of both water circulation performances and dissolved oxygen distribution.

Study of degradation intermediates formed during electrochemical oxidation of pesticide residue 2,6-dichlorobenzamide (BAM) at boron doped diamond (BDD) and platinum–iridium anodes

Electrochemical oxidation is a promising technique for degradation of otherwise recalcitrant organic micropollutants in waters. In this study, the applicability of electrochemical oxidation was investigated concerning the degradation of the groundwater pollutant 2,6-dichlorobenzamide (BAM) through the electrochemical oxygen transfer process with two anode materials: Ti/Pt90–Ir10 and boron doped diamond (Si/BDD). Besides the efficiency of the degradation of the main pollutant, it is also of outmost importance to control the formation and fate of stable degradation intermediates. These were investigated quantitatively with HPLC–MS and TOC measurements and qualitatively with a combined HPLC–UV and HPLC–MS protocol. 2,6-Dichlorobenzamide was found to be degraded most efficiently by the BDD cell, which also resulted in significantly lower amounts of intermediates formed during the process. The anodic degradation pathway was found to occur via substitution of hydroxyl groups until ring cleavage leading to carboxylic acids. For the BDD cell, there was a parallel cathodic degradation pathway that occurred via dechlorination. The combination of TOC with the combined HPLC–UV/MS was found to be a powerful method for determining the amount and nature of degradation intermediates.

Visible light-promoted selective oxidation of sulfides to sulfoxides catalyzed by ruthenium porphyrins with iodobenzene diacetate

Under visible light irradiation, the carbonyl ruthenium(II) porphyrin complexes efficiently catalyze the selective oxidation of sulfides to sulfoxides with iodobenzene diacetate [PhI(OAc)2] as the oxygen source. Various thioanisoles and allylic sulfides were oxidized to the corresponding sulfoxides without overoxidation to sulfones. The high selectivity of this unprecedented oxygen-transfer process is mechanistically rationalized by a low-reactivity ruthenium(IV)-oxo species which can be detected in the reaction of carbonyl ruthenium(II) porphyrin with iodobenzene diacetate. To the best of our knowledge, this is the first demonstration of a mild and high-yield method for the highly selective sulfoxidations by ruthenium porphyrins and PhI(OAc)2.

Preparation of Nd2Fe14B/C magnetic powder and its application in proton exchange membrane fuel cells

Nd2Fe14B and Nd2Fe14B/C magnetic powders are prepared by the ball-milling and high-temperature baking methods, respectively. The effect of the magnetic powder in the oxygen transfer process is studied using the three-electrode electrochemical system, rotating disk glassy carbon electrode, and proton exchange membrane fuel cells (PEMFCs). Results show that the magnetic electrode has higher electric double-layer capacitance and lower charge-transfer resistance than the nonmagnetic electrode at different Nd2Fe14B/C load densities. In addition, the oxygen diffusion coefficient and transfer coefficient for the magnetic electrode are both larger than the nonmagnetic electrode. At 0.40 mg cm−2 Nd2Fe14B/C load density in the PEMFC cathode, the magnetic PEMFC discharge current increases by 39.874% compared with the nonmagnetic PEMFC at 0.20 V discharge voltage. The magnetic PEMFC discharge performance at 0.80 mg cm−2 Nd2Fe14B/C load density is lower than the magnetic PEMFC at 0.40 mg cm−2 load density. These factors result in the decline of magnetic PEMFC discharge performance at higher Nd2Fe14B/C load density, including decreased Pt/C actual catalyst area and increased magnetic interactions among different magnetic particles.

Strategies for enhancing electrochemical activity of carbon-based electrodes for all-vanadium redox flow batteries

Two strategies for improving the electroactivity towards VO2+/VO2+ redox pair, the limiting process in all-vanadium redox flow batteries (VFBs), were presented. CuPt3 nanoparticles supported onto graphene substrate and nitrogen and oxygen polyacrylonitrile (PAN)-functionalized electrodes materials have been evaluated. The morphology, composition, electrochemical properties of all electrodes prepared was characterized with field emission-scanning electrode microscopy, X-ray photoelectron spectroscopy, cyclic voltammetry, electrochemical impedance spectroscopy and cell charge–discharge test. The presence of the CuPt3 nanocubes and nitrogen and oxygen functionalities enhance the electrocatalytic activity of the electrodes materials accelerating the oxygen and electron transfer processes. The battery performance was also evaluated using PAN-functionalized electrodes exhibiting a high of energy efficiency of 84% (at current density 20mAcm−2) up to 30th cycle, indicating a promising alternative for improving the VFB.