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Showing papers on "Redox published in 2015"


Journal ArticleDOI
18 Dec 2015-Science
TL;DR: The fundamental relation between the anionic redox process and the evolution of the O-O bonding in layered oxides is established, and the design of safe and long-lasting batteries requires an understanding of the physical and chemical changes that occur during redox processes.
Abstract: Lithium-ion (Li-ion) batteries that rely on cationic redox reactions are the primary energy source for portable electronics. One pathway toward greater energy density is through the use of Li-rich layered oxides. The capacity of this class of materials (>270 milliampere hours per gram) has been shown to be nested in anionic redox reactions, which are thought to form peroxo-like species. However, the oxygen-oxygen (O-O) bonding pattern has not been observed in previous studies, nor has there been a satisfactory explanation for the irreversible changes that occur during first delithiation. By using Li2IrO3 as a model compound, we visualize the O-O dimers via transmission electron microscopy and neutron diffraction. Our findings establish the fundamental relation between the anionic redox process and the evolution of the O-O bonding in layered oxides.

608 citations


Journal ArticleDOI
23 Dec 2015-Synlett
TL;DR: In this paper, the half-peak potentials for over 180 organic substrates obtained via cyclic voltammetry were reported and used in assessing the thermodynamics of an electron-transfer process.
Abstract: Herein, we report half-peak potentials for over 180 organic substrates obtained via cyclic voltammetry. These values are of great use in assessing the thermodynamics of an electron-transfer process. In addition, we disclose a simple computational method to determine redox potentials of organic substrates.

466 citations


Journal ArticleDOI
TL;DR: The redox code is a set of principles that defines the positioning of the nicotinamide adenine dinucleotide and thiol/disulfide and other redox systems as well as the thiol redox proteome in space and time in biological systems.
Abstract: Significance: The redox code is a set of principles that defines the positioning of the nicotinamide adenine dinucleotide (NAD, NADP) and thiol/disulfide and other redox systems as well as the thiol redox proteome in space and time in biological systems. The code is richly elaborated in an oxygen-dependent life, where activation/deactivation cycles involving O2 and H2O2 contribute to spatiotemporal organization for differentiation, development, and adaptation to the environment. Disruption of this organizational structure during oxidative stress represents a fundamental mechanism in system failure and disease. Recent Advances: Methodology in assessing components of the redox code under physiological conditions has progressed, permitting insight into spatiotemporal organization and allowing for identification of redox partners in redox proteomics and redox metabolomics. Critical Issues: Complexity of redox networks and redox regulation is being revealed step by step, yet much still needs to be lea...

435 citations


Journal ArticleDOI
TL;DR: The Cu-catalyzed aerobic oxidation reactions investigated offer advantages over analogous two-electron oxidation reactions mediated by palladium or other noble metals, and show the ability of Cu to participate in traditional organometallic steps commonly associated with precious-metal catalysts, but also demonstrate the accessibility of reaction steps not typically associated with metals, such as single-Electron transfer.
Abstract: Selective oxidation reactions have extraordinary value in organic chemistry, ranging from the conversion of petrochemical feedstocks into industrial chemicals and polymer precursors to the introduction of heteroatom functional groups into pharmaceutical and agrochemical intermediates. Molecular oxygen (O2) would be the ideal oxidant for these transformations. Whereas many commodity-scale oxidations of simple hydrocarbon feedstocks employ O2 as an oxidant, methods for selective oxidation of more complex molecules bearing diverse functional groups are often incompatible with existing aerobic oxidation methods. The latter limitation provides the basis for our interest in the development of new catalytic transformations and the elucidation of mechanistic principles that underlie selective aerobic oxidation reactions. One challenge inherent in such methods is the incommensurate redox stoichiometry associated with the use of O2, a four-electron oxidant, in reactions that achieve two-electron oxidation of organic molecules. This issue is further complicated by the use of first-row transition-metal catalysts, which tend to undergo facile one-electron redox steps. In recent years, we have been investigating Cu-catalyzed aerobic oxidation reactions wherein the complexities just noted are clearly evident. This Account surveys our work in this area, which has emphasized three general classes of reactions: (1) single-electron-transfer reactions for oxidative functionalization of electron-rich substrates, such as arenes and heterocycles; (2) oxidative carbon-heteroatom bond-forming reactions, including C-H oxidations, that proceed via organocopper(III) intermediates; and (3) methods for aerobic oxidation of alcohols and amines that use Cu(II) in combination with an organic redox-active cocatalyst to dehydrogenate the carbon-heteroatom bond. These reaction classes demonstrate three different pathways to achieve two-electron oxidation of organic molecules via the cooperative involvement of two one-electron oxidants, either two Cu(II) species or Cu(II) and a nitroxyl cocatalyst. They show the ability of Cu to participate in traditional organometallic steps commonly associated with precious-metal catalysts, such as C-H activation and reductive elimination, but also demonstrate the accessibility of reaction steps not typically associated with precious-metal catalysts, such as single-electron transfer. Many of the Cu-catalyzed reactions offer advantages over analogous two-electron oxidation reactions mediated by palladium or other noble metals. For example, carbon-heteroatom oxidative coupling reactions in the first two reaction classes noted above are capable of using O2 as the terminal oxidant, while analogous reactions with Pd commonly require less desirable oxidants, such as hypervalent iodine or electrophilic halogen sources. In addition, the alcohol and amine oxidations in the third reaction class are significantly more efficient and show much broader scope and functional group tolerance than related Pd-catalyzed reactions. The mechanistic basis for these differences are described herein.

375 citations


Journal ArticleDOI
TL;DR: In this paper, the results of a variety of catalyst characterization and reaction kinetics measurements were presented, including surface area/pore volume measurements, temperature programmed reduction by H2 (H2-TPR), NH3 temperature programmed desorption (NH3-TPD), and DRIFTS and solid-state nuclear magnetic resonance (NMR) spectroscopies.

319 citations


Journal ArticleDOI
TL;DR: X-ray absorption and emission spectroscopy, FTIR and DFT unravel the major Cu species in the activated Cu-SSZ-13 catalyst for NH3-SCR.
Abstract: Cu-SSZ-13 is a highly active NH3-SCR catalyst for the abatement of harmful nitrogen oxides (NOx, x = 1, 2) from the exhausts of lean-burn engines. The study of Cu-speciation occurring upon thermal dehydration is a key step for the understanding of the enhanced catalytic properties of this material and for identifying the SCR active sites and their redox capability. Herein, we combined FTIR, X-ray absorption (XAS) and emission (XES) spectroscopies with DFT computational analysis to elucidate the nature and location of the most abundant Cu sites in the activated catalyst. Different Cu species have been found to be dominant as a function of the dehydration temperature and conditions. Data analysis revealed that the dehydration process of Cu cations is essentially completed at 250 °C, with the formation of dehydrated [CuOH]+ species hosted in close proximity to 1-Al sites in both d6r and 8r units of the SSZ-13 matrix. These species persist at higher temperatures only if a certain amount of O2 is present in the gas feed, while under inert conditions they undergo virtually total “self-reduction” as a consequence of an OH extra-ligand loss, resulting in bi-coordinated bare Cu+ cations. Synchrotron characterization supported by computational analysis allowed an unprecedented quantitative refinement of the local environment and structural parameters of these Cu(II) and Cu(I) species.

303 citations


Journal ArticleDOI
TL;DR: In this paper, the performance of several electrode materials such as carbon-felt, carbon-fiber, carbongraphite, platinum, lead dioxide, dimensionally stable anode (DSA), (Ti/RuO 2 -IrO 2 ), and BDD (Boron-Doped Diamond) were tested for the destruction of the antibiotic amoxicillin (AMX) in aqueous medium.

293 citations


Journal ArticleDOI
TL;DR: Characteristics of several redox electrolytes are reported to illustrate operational/self-discharge mechanisms and the design rules for high performance in electrochemical double-layer capacitors.
Abstract: Electrochemical double-layer capacitors exhibit high power and long cycle life but have low specific energy compared with batteries, limiting applications. Redox-enhanced capacitors increase specific energy by using redox-active electrolytes that are oxidized at the positive electrode and reduced at the negative electrode during charging. Here we report characteristics of several redox electrolytes to illustrate operational/self-discharge mechanisms and the design rules for high performance. We discover a methyl viologen (MV)/bromide electrolyte that delivers a high specific energy of ∼14 Wh kg(-1) based on the mass of electrodes and electrolyte, without the use of an ion-selective membrane separator. Substituting heptyl viologen for MV increases stability, with no degradation over 20,000 cycles. Self-discharge is low, due to adsorption of the redox couples in the charged state to the activated carbon, and comparable to cells with inert electrolyte. An electrochemical model reproduces experiments and predicts that 30-50 Wh kg(-1) is possible with optimization.

289 citations


Journal ArticleDOI
TL;DR: It is proposed that a narrow electronic state of significant oxygen 2p character near the Fermi level exchanges electrons with the oxygen adsorbates, highlighting the importance of surface anion-redox chemistry in oxygen-deficient transition-metal oxides.
Abstract: Surface redox centres in metal oxides play a key role in catalytic performance, and the conventional view is that the transition-metal cations dominate this behaviour. Here, the authors perform an in operando spectroscopic study, and find that oxygen anions are a significant redox partner to molecular oxygen.

283 citations


Journal ArticleDOI
TL;DR: The reversible Cu2+/Cu3+ redox couple in P2 phase oxides is proved for the first time and the attractive long cycling stability is demonstrated.
Abstract: An air-stable copper-based P2-Na7/9Cu2/9Fe1/9Mn2/3O2 is designed and synthesized by a simple solid-state method and investigated as a positive electrode material for sodium-ion batteries. The attractive long cycling stability is demonstrated by the capacity retention of 85% after 150 cycles at 1 C rate without phase transformation. The reversible Cu2+/Cu3+ redox couple in P2 phase oxides is proved for the first time.

281 citations


Journal ArticleDOI
TL;DR: In this article, a new framework model of catalysis in an amorphous, hydrated and volume-active oxide is proposed: within the oxide film, cobalt ions at the margins of Co-oxo fragments undergo CoII↔ CoIII ↔ CoIV oxidation-state changes coupled to structural modification and deprotonation of Cooxo bridges, and an active site is formed at which the O-O bond-formation step can take place.
Abstract: Water oxidation by amorphous oxides is of high interest in artificial photosynthesis and other routes towards non-fossil fuels, but the mode of catalysis in these materials is insufficiently understood. We tracked mechanistically relevant oxidation-state and structural changes of an amorphous Co-based catalyst film by in situ experiments combining directly synchrotron-based X-ray absorption spectroscopy (XAS) with electrocatalysis. Unlike a classical solid-state material, the bulk material is found to undergo chemical changes. Two redox transitions at midpoint potentials of about 1.0 V (CoII0.4CoIII0.6 ↔ all-CoIII) and 1.2 V (all-CoIII ↔ CoIII0.8CoIV0.2) vs. NHE at pH 7 are coupled to structural changes. These redox transitions can be induced by variation of either electric potential or pH; they are broader than predicted by a simple Nernstian model, suggesting interacting bridged cobalt ions. Tracking reaction kinetics by UV-Vis-absorption and time-resolved mass spectroscopy reveals that accumulated oxidizing equivalents facilitate dioxygen formation. On these grounds, a new framework model of catalysis in an amorphous, hydrated and volume-active oxide is proposed: Within the oxide film, cobalt ions at the margins of Co-oxo fragments undergo CoII ↔ CoIII ↔ CoIV oxidation-state changes coupled to structural modification and deprotonation of Co-oxo bridges. By the encounter of two (or more) CoIV ions, an active site is formed at which the O–O bond-formation step can take place. The Tafel slope is determined by both the interaction between cobalt ions (width of the redox transition) and their encounter probability. Our results represent a first step toward the development of new concepts that address the solid-molecular Janus nature of the amorphous oxide. Insights and concepts described herein for the Co-based catalyst film may be of general relevance also for other amorphous oxides with water-oxidation activity.

Journal ArticleDOI
TL;DR: A mechanistic electron spin resonance study reveals that the choice of supporting electrolytes greatly affects the chemical stability of the charged radical species especially the negative side radical anion, which dominates the cycling stability of these flow cells.
Abstract: Nonaqueous redox flow batteries hold the promise of achieving higher energy density because of the broader voltage window than aqueous systems, but their current performance is limited by low redox material concentration, cell efficiency, cycling stability, and current density. We report a new nonaqueous all-organic flow battery based on high concentrations of redox materials, which shows significant, comprehensive improvement in flow battery performance. A mechanistic electron spin resonance study reveals that the choice of supporting electrolytes greatly affects the chemical stability of the charged radical species especially the negative side radical anion, which dominates the cycling stability of these flow cells. This finding not only increases our fundamental understanding of performance degradation in flow batteries using radical-based redox species, but also offers insights toward rational electrolyte optimization for improving the cycling stability of these flow batteries.

Journal ArticleDOI
TL;DR: In this article, a coaxial dielectric barrier discharge (DBD) reactor was used for plasma-catalytic removal of low concentration formaldehyde over a series of Cu-Ce oxide catalysts prepared by the citric acid sol-gel method.
Abstract: In this study, a coaxial dielectric barrier discharge (DBD) reactor has been used for plasma-catalytic removal of low concentration formaldehyde over a series of Cu–Ce oxide catalysts prepared by the citric acid sol–gel method. The effect of the Cu/Ce molar ratio on the removal of formaldehyde and CO 2 selectivity has been investigated as a function of specific energy density (SED). In comparison to the plasma-only process, the combination of plasma with the Cu–Ce binary oxide catalysts significantly enhances the reaction performance, while the presence of CuO or CeO 2 in the DBD reactor has a negative effect on the removal of HCHO. This suggests that the interactions between Cu and Ce species change the properties of the catalysts and consequently affect the performance of the plasma-catalytic process. The highest removal efficiency of 94.7% and CO 2 selectivity of 97.3% were achieved when the Cu1Ce1 catalyst (Cu/Ce = 1:1) was placed in the DBD reactor at the SED of 486 J L −1 . The interaction between Cu and Ce species results in a larger specific surface area and pore volume, along with a greater formation of surface adsorbed oxygen (O ads ), which favors the oxidation of formaldehyde in the plasma process. In addition, the redox cycles between Cu and Ce species facilitate the formation of additional active oxygen atoms and contribute to the plasma-catalytic oxidation reactions. Plausible reaction mechanisms involved in the plasma-catalytic oxidation of HCHO have been proposed.

Journal ArticleDOI
TL;DR: In this article, the authors report cobalt oxide nanochains as multifunctional catalysts for the electrochemical oxygen evolution reaction (OER) at both alkaline and neutral pH, oxidant-driven, photochemical water oxidation in various pH, and the Electrochemical oxygen reduction reaction (ORR) in alkaline medium.
Abstract: Future advances in renewable and sustainable energy require advanced materials based on earth-abundant elements with multifunctional properties. The design and the development of cost-effective, robust, and high-performance catalysts that can convert oxygen to water, and vice versa, is a major challenge in energy conversion and storage technology. Here we report cobalt oxide nanochains as multifunctional catalysts for the electrochemical oxygen evolution reaction (OER) at both alkaline and neutral pH, oxidant-driven, photochemical water oxidation in various pH, and the electrochemical oxygen reduction reaction (ORR) in alkaline medium. The cobalt oxide nanochains are easily accessible on a multigram scale by low-temperature degradation of a cobalt oxalate precursor. What sets this study apart from earlier ones is its synoptical perspective of reversible oxygen redox catalysis in different chemical and electrochemical environments.

Journal ArticleDOI
TL;DR: A complete catalytic cycle is proposed that uncovers an unprecedented pathway in which crucial O-O bond formation occurs in a two-step, one-electron process where the peroxo intermediate generated has no formal M-O Bond but is strongly hydrogen bonded to the auxiliary ligand.
Abstract: A new family of tetra-anionic tetradentate amidate ligands, N1,N1′-(1,2-phenylene)bis(N2-methyloxalamide) (H4L1), and its derivatives containing electron-donating groups at the aromatic ring have been prepared and characterized, together with their corresponding anionic Cu(II) complexes, [(LY)Cu]2–. At pH 11.5, the latter undergoes a reversible metal-based III/II oxidation process at 0.56 V and a ligand-based pH-dependent electron-transfer process at 1.25 V, associated with a large electrocatalytic water oxidation wave (overpotential of 700 mV). Foot-of-the-wave analysis gives a catalytic rate constant of 3.6 s–1 at pH 11.5 and 12 s–1 at pH 12.5. As the electron-donating capacity at the aromatic ring increases, the overpotential is drastically reduced down to a record low of 170 mV. In addition, DFT calculations allow us to propose a complete catalytic cycle that uncovers an unprecedented pathway in which crucial O–O bond formation occurs in a two-step, one-electron process where the peroxo intermediate g...

Journal ArticleDOI
TL;DR: The results unveil an unexpectedly rich network of coupled chemical reactions between NO and H2S/sulfide, suggesting that the bioactivity of either transmitter is governed by concomitant formation of polysulfides and anionic S/N-hybrid species.
Abstract: Experimental evidence suggests that nitric oxide (NO) and hydrogen sulfide (H2S) signaling pathways are intimately intertwined, with mutual attenuation or potentiation of biological responses in the cardiovascular system and elsewhere. The chemical basis of this interaction is elusive. Moreover, polysulfides recently emerged as potential mediators of H2S/sulfide signaling, but their biosynthesis and relationship to NO remain enigmatic. We sought to characterize the nature, chemical biology, and bioactivity of key reaction products formed in the NO/sulfide system. At physiological pH, we find that NO and sulfide form a network of cascading chemical reactions that generate radical intermediates as well as anionic and uncharged solutes, with accumulation of three major products: nitrosopersulfide (SSNO−), polysulfides, and dinitrososulfite [N-nitrosohydroxylamine-N-sulfonate (SULFI/NO)], each with a distinct chemical biology and in vitro and in vivo bioactivity. SSNO− is resistant to thiols and cyanolysis, efficiently donates both sulfane sulfur and NO, and potently lowers blood pressure. Polysulfides are both intermediates and products of SSNO− synthesis/decomposition, and they also decrease blood pressure and enhance arterial compliance. SULFI/NO is a weak combined NO/nitroxyl donor that releases mainly N2O on decomposition; although it affects blood pressure only mildly, it markedly increases cardiac contractility, and formation of its precursor sulfite likely contributes to NO scavenging. Our results unveil an unexpectedly rich network of coupled chemical reactions between NO and H2S/sulfide, suggesting that the bioactivity of either transmitter is governed by concomitant formation of polysulfides and anionic S/N-hybrid species. This conceptual framework would seem to offer ample opportunities for the modulation of fundamental biological processes governed by redox switching and sulfur trafficking.

Journal ArticleDOI
01 Nov 2015-Carbon
TL;DR: In this article, a new cathode for electro-Fenton process was set up by electrochemical deposition of reduced graphene oxide (rGO) on the surface of carbon felt (CF).

Journal ArticleDOI
Peng Yang1, Shanshan Yang1, Zhinan Shi1, Zhonghua Meng1, Renxian Zhou1 
TL;DR: In this paper, a coprecipitation method was used to obtain mesoporous structures with larger specific surface area and pore volume, and metal ions can go into the lattice of fluorite, which contributes to improving the stability of active components.
Abstract: Cerium-transition metal mixed oxides (4Ce1M, M = V, Cr, Mn, Fe, Co, Ni and Cu) were prepared by coprecipitation method and investigated for deep oxidation of four chlorinated VOCs with quite different molecule structures. 4Ce1M catalysts show mesoporous structures with larger specific surface area and pore volume, and some metal ions can go into the lattice of fluorite, which contributes to improving the stability of the active components. The redox properties of 4Ce1M catalysts are significantly promoted due to the strong interaction between CeO 2 and MO x , which facilitates the destruction of the reactants and byproducts at lower temperature in the process of CVOCs oxidation. Especially, 4Ce1Cr catalyst exhibits the best catalytic activity and selectivity, mainly due to the formation of Cr 6+ species with strong oxidizing ability. 4Ce1Cr also represents good durability for DCE destruction during the 100 h continuous test, and the chemical adsorbed Cl species on the surface can be removed above 325 °C. Moreover, the presence of water or non-chlorinated VOCs can slightly decrease the conversion of chlorinated VOCs at lower temperature due to the competitive adsorption for active sites, while promote at higher temperature (above 300 °C) because of the contribution to removing Cl species away from the surface.

Journal ArticleDOI
TL;DR: An electrochemical filter for sequential electro-Fenton reactions to optimize the treatment process and was compared to individual electrochemical and Fenton process using oxalate, a persistent organic, as a target molecule.
Abstract: Electro-Fenton is a promising advanced oxidation process for water treatment consisting a series redox reactions. Here, we design and examine an electrochemical filter for sequential electro-Fenton reactions to optimize the treatment process. The carbon nanotube (CNT) membrane stack (thickness ∼ 200 μm) used here consisted of 1) a CNT network cathode for O2 reduction to H2O2, 2) a CNT-COOFe(2+) cathode to chemical reduction H2O2 to (•)OH and HO(-) and to regenerate Fe(2+) in situ, 3) a porous PVDF or PTFE insulating separator, and 4) a CNT filter anode for remaining intermediate oxidation intermediates. The sequential electro-Fenton was compared to individual electrochemical and Fenton process using oxalate, a persistent organic, as a target molecule. Synergism is observed during the sequential electro-Fenton process. For example, when [DO]in = 38 ± 1 mg L(-1), J = 1.6 mL min(-1), neutral pH, and Ecell = 2.89 V, the sequential electro-Fenton oxidation rate was 206.8 ± 6.3 mgC m(-2) h(-1), which is 4-fold greater than the sum of the individual electrochemistry (16.4 ± 3.2 mgC m(-2) h(-1)) and Fenton (33.3 ± 1.3 mgC m(-2) h(-1)) reaction fluxes, and the energy consumption was 45.8 kWh kgTOC(-1). The sequential electro-Fenton was also challenged with the refractory trifluoroacetic acid (TFA) and trichloroacetic acid (TCA), and they can be transferred at a removal rate of 11.3 ± 1.2 and 21.8 ± 1.9 mmol m(-2) h(-1), respectively, with different transformation mechanisms.

Journal ArticleDOI
TL;DR: The fundamentals of electron transfer reactions in mitochondria and emerging knowledge on the 11 potential sources of mitochondrial O2−•/H2O2 in tandem with their significance in contributing to overall O2 −•/ H2 O2 emission in health and disease are discussed.
Abstract: Mitochondria fulfill a number of biological functions which inherently depend on ATP and O2−•/H2O2 production. Both ATP and O2−•/H2O2 are generated by electron transfer reactions. ATP is the product of oxidative phosphorylation whereas O2−• is generated by singlet electron reduction of di-oxygen (O2). O2−• is then rapidly dismutated by superoxide dismutase (SOD) producing H2O2. O2−•/H2O2 were once viewed as unfortunately by-products of aerobic respiration. This characterization is fitting considering over production of O2−•/H2O2 by mitochondria is associated with range of pathological conditions and aging. However, O2−•/H2O2 are only dangerous in large quantities. If produced in a controlled fashion and maintained at a low concentration, cells can benefit greatly from the redox properties of O2−•/H2O2. Indeed, low rates of O2−•/H2O2 production are required for intrinsic mitochondrial signaling (e.g. modulation of mitochondrial processes) and communication with the rest of the cell. O2−•/H2O2 levels are kept in check by anti-oxidant defense systems that sequester O2−•/H2O2 with extreme efficiency. Given the importance of O2−•/H2O2 in cellular function, it is imperative to consider how mitochondria produce O2−•/H2O2 and how O2−•/H2O2 genesis is regulated in conjunction with fluctuations in nutritional and redox states. Here, I discuss the fundamentals of electron transfer reactions in mitochondria and emerging knowledge on the 11 potential sources of mitochondrial O2−•/H2O2 in tandem with their significance in contributing to overall O2−•/H2O2 emission in health and disease. The potential for classifying these different sites in isopotential groups, which is essentially defined by the redox properties of electron donator involved in O2−•/H2O2 production, as originally suggested by Brand and colleagues is also surveyed in detail. In addition, redox signaling mechanisms that control O2−•/H2O2 genesis from these sites are discussed. Finally, the current methodologies utilized for measuring O2−•/H2O2 in isolated mitochondria, cell culture and in vivo are reviewed.

Journal ArticleDOI
TL;DR: In this paper, the effect of acid treatment in mixed MnOx-CeO2 samples has been investigated in the catalytic total oxidation of formaldehyde, and the acid treatment has no effect on the textural and redox properties of the materials.
Abstract: The effect of acid treatment in mixed MnOx–CeO2 samples has been investigated in the catalytic total oxidation of formaldehyde. The acid treatment has no effect on the textural and redox properties of the materials when Mn is stabilized in a MnOx–CeO2 solid solution (Mn content below 50%). However, these properties were found to be highly altered by acid treatment when the solubility limit of Mn in the ceria was exceeded (Mn content above 50%). This enabled access to the primary porosity and oxidized the manganese species to a higher oxidation state via a Mn dismutation reaction. As a result, the catalytic activity of pure manganese oxide, after chemical activation, in the oxidation of formaldehyde is greatly improved—at 100 °C, the conversion of formaldehyde is increased by a factor of 5 and the corresponding intrinsic reaction rate by 1.4. Combined in situ surface analysis unambiguously identified formate species as a result of formaldehyde oxidation at room temperature on the chemically activated pure ...

Journal ArticleDOI
TL;DR: In this paper, an all-vanadium redox flow battery (VRFB) was constructed with modified carbon paper electrodes in the high-performance no-gap design, and the roundtrip energy efficiency was improved from 63% to 76% at a current density of 200mV.

Journal ArticleDOI
TL;DR: In this article, a novel design lithium-organic non-aqueous redox flow battery based on a modified ferrocene catholyte was presented, which produced desired electrochemical performance exceeding most of the currently reported nonaqueous RFB systems.
Abstract: We will present a novel design lithium-organic non-aqueous redox flow battery based on a modified ferrocene catholyte. This RFB produced desired electrochemical performance exceeding most of the currently reported nonaqueous RFB systems.

Journal ArticleDOI
TL;DR: In this article, the authors examined LiI as an electrolyte and additive in Li oxygen cells with ethereal electrolyte solutions and found that at high concentrations of LiI, the presence of the salt promotes a side reaction that forms LiOH as a major product.
Abstract: Mankind has been in an unending search for efficient sources of energy. The coupling of lithium and oxygen in aprotic solvents would seem to be a most promising direction for electrochemistry. Indeed, if successful, this system could compete with technologies such as the internal combustion engine and provide an energy density that would accommodate the demands of electric vehicles. All this promise has not yet reached fruition because of a plethora of practical barriers and challenges. These include solvent and electrode stability, pronounced overvoltage for oxygen evolution reactions, limited cycle life and rate capability. One of the approaches suggested to facilitate the oxygen evolution reactions and improve rate capability is the use of redox mediators such as iodine for the fast oxidation of lithium peroxide. In this paper we have examined LiI as an electrolyte and additive in Li oxygen cells with ethereal electrolyte solutions. At high concentrations of LiI, the presence of the salt promotes a side reaction that forms LiOH as a major product. In turn, the presence of oxygen facilitates the reduction of I3− to 3I− in these systems. At very low concentrations of LiI, oxygen is reduced to Li2O2. The iodine formed in the anodic reaction serves as a redox mediator for Li2O2 oxidation.

Journal ArticleDOI
TL;DR: CeO2 works as the most effective heterogeneous catalyst for imine formation from benzyl alcohol and aniline at 303 K among various metal oxides and showed more than 38-fold higher activity than other simpleMetal oxides.
Abstract: We disclosed the redox properties of CeO2 in organic reactions at low temperature of 303 K. CeO2 works as the most effective heterogeneous catalyst for imine formation from benzyl alcohol and aniline at 303 K among various metal oxides and showed more than 38-fold higher activity than other simple metal oxides. CeO2 is applicable to the reaction of various alcohols and amines and gives high yields (80–98 %) and high selectivities (89–>99 %). Kinetic measurements, MS, and FTIR analyses demonstrated that the high activity of CeO2 is a result of reactive oxygen species at the redox sites on CeO2. This discovery can help to create a new field in metal oxide catalysis.

Journal ArticleDOI
TL;DR: Using time-resolved resonant X-ray emission spectroscopy, it is demonstrated that active Ce(3+) species in a ceria-supported platinum catalyst during CO oxidation are short-lived and therefore cannot be observed under steady-state conditions and ceria reduction is a kinetically relevant step in CO oxidation.
Abstract: Identification of active species and the rate-determining reaction steps are crucial for optimizing the performance of oxygen-storage materials, which play an important role in catalysts lowering automotive emissions, as electrode materials for fuel cells, and as antioxidants in biomedicine. We demonstrated that active Ce(3+) species in a ceria-supported platinum catalyst during CO oxidation are short-lived and therefore cannot be observed under steady-state conditions. Using time-resolved resonant X-ray emission spectroscopy, we quantitatively correlated the initial rate of Ce(3+) formation under transient conditions to the overall rate of CO oxidation under steady-state conditions and showed that ceria reduction is a kinetically relevant step in CO oxidation, whereas a fraction of Ce(3+) was present as spectators. This approach can be applied to various catalytic processes involving oxygen-storage materials and reducible oxides to distinguish between redox and nonredox catalytic mechanisms.

Journal ArticleDOI
TL;DR: The addition of water or methanol to the electrolyte allows a shift of oxidation potentials in a specific range, creating suitable systems for selective anodic cross-coupling reactions, and this driving force for selectivity in oxidative coupling might also explain previous findings using HFIP and hypervalent iodine reagents.
Abstract: Solvents such as 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) with a high capacity for donating hydrogen bonds generate solvates that enter into selective cross-coupling reactions of aryls upon oxidation. When electric current is employed for oxidation, reagent effects can be excluded and a decoupling of nucleophilicity from oxidation potential can be achieved. The addition of water or methanol to the electrolyte allows a shift of oxidation potentials in a specific range, creating suitable systems for selective anodic cross-coupling reactions. The shift in the redox potentials depends on the substitution pattern of the substrate employed. The concept has been expanded from arene-phenol to phenol-phenol as well as phenol-aniline cross-coupling. This driving force for selectivity in oxidative coupling might also explain previous findings using HFIP and hypervalent iodine reagents.

Journal ArticleDOI
TL;DR: A new approach to constructing supramolecular systems for the photocatalytic generation of hydrogen from water by encapsulating an organic dye molecule into the pocket of a redox-active metal-organic polyhedron, which exhibits TON values comparable to the highest values reported for related cobalt/fluorescein systems.
Abstract: The design of artificial systems that mimic highly evolved and finely tuned natural photosynthetic systems is a subject of intensive research. We report herein a new approach to constructing supramolecular systems for the photocatalytic generation of hydrogen from water by encapsulating an organic dye molecule into the pocket of a redox-active metal-organic polyhedron. The assembled neutral Co4L4 tetrahedron consists of four ligands and four cobalt ions that connect together in alternating fashion. The cobalt ions are coordinated by three thiosemicarbazone NS chelators and exhibit a redox potential suitable for electrochemical proton reduction. The close proximity between the redox site and the photosensitizer encapsulated in the pocket enables photoinduced electron transfer from the excited state of the photosensitizer to the cobalt-based catalytic sites via a powerful pseudo-intramolecular pathway. The modified supramolecular system exhibits TON values comparable to the highest values reported for related cobalt/fluorescein systems. Control experiments based on a smaller tetrahedral analogue of the vehicle with a filled pocket and a mononuclear compound resembling the cobalt corner of the tetrahedron suggest an enzymatic dynamics behavior. The new, well-elucidated reaction pathways and the increased molarity of the reaction within the confined space render these supramolecular systems superior to other relevant systems.

Journal ArticleDOI
TL;DR: The lactate dehydrogenase (LDH) is purified from the strictly anaerobic, acetogenic bacterium Acetobacterium woodii, which uses flavin-based electron confurcation to drive endergonic lactate oxidation with NAD(+) as oxidant.
Abstract: Lactate is a common substrate for major groups of strictly anaerobic bacteria, but the biochemistry and bioenergetics of lactate oxidation is obscure. The high redox potential of the pyruvate/lactate pair of E0 ' = -190 mV excludes direct NAD(+) reduction (E0 ' = -320 mV). To identify the hitherto unknown electron acceptor, we have purified the lactate dehydrogenase (LDH) from the strictly anaerobic, acetogenic bacterium Acetobacterium woodii. The LDH forms a stable complex with an electron-transferring flavoprotein (Etf) that exhibited NAD(+) reduction only when reduced ferredoxin (Fd(2-) ) was present. Biochemical analyses revealed that the LDH/Etf complex of A. woodii uses flavin-based electron confurcation to drive endergonic lactate oxidation with NAD(+) as oxidant at the expense of simultaneous exergonic electron flow from reduced ferredoxin (E0 ' ≈ -500 mV) to NAD(+) according to: lactate + Fd(2-) + 2 NAD(+) → pyruvate + Fd + 2 NADH. The reduced Fd(2-) is regenerated from NADH by a sequence of events that involves conversion of chemical (ATP) to electrochemical ( Δ μ ˜ Na + ) and finally redox energy (Fd(2-) from NADH) via reversed electron transport catalysed by the Rnf complex. Inspection of genomes revealed that this metabolic scenario for lactate oxidation may also apply to many other anaerobes.

Journal ArticleDOI
TL;DR: A new redox mediator tris[4-(diethylamino)phenyl]amine (TDPA) is reported here on, that—at 3.1 V—exhibits the lowest and closest potential redox couple compared to the equilibrium voltage of the Li-oxygen cell of those reported to date, with a second couple also at a low potential.
Abstract: Owing to its high theoretical specific energy, the Li-oxygen battery is one of the fundamentally most promising energy storage systems, but also one of the most challenging. Poor rechargeability, involving the oxidation of insoluble and insulating lithium peroxide (Li2O2), has remained the “Achilles’ heel” of this electrochemical energy storage system. We report here on a new redox mediator tris[4-(diethylamino)phenyl]amine (TDPA), that—at 3.1 V—exhibits the lowest and closest potential redox couple compared to the equilibrium voltage of the Li-oxygen cell of those reported to date, with a second couple also at a low potential of 3.5 V. We show it is a soluble “catalyst” capable of lowering the Li2O2 charging potential by >0.8 V without requiring direct electrical contact of the peroxide and that it also facilitates high discharge capacities. Its chemical and electrochemical stability, fast diffusion kinetics, and two dynamic redox potentials represent a significant advance in oxygen-evolution catalysis. ...