- Silver mediation of Fe(VI) charge transfer: Activation of the K2FeO4 super-iron cathode
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An unexpectedly large Ag(II) mediation of Fe(VI) redox chemistry improves alkaline Fe(VI) cathodic charge transfer. Combined with a Zn anode, this results in a cell with 3- to 5-fold higher energy capacity than the conventional high-power Zn/MnO2 alkaline battery, and twice that previously observed for Zn/BaFeO4. Both experimental results and a model of this phenomenon are presented. The Ag(II) salt may be introduced as a simple composite of AgO with the Fe(VI) salt. The Fe(VI) super-iron salt K2FeO4 has a high 3e- intrinsic charge capacity (406 mA/g), and is more environmentally benign than the Fe(VI) salt BaFeO4, but had exhibited comparatively poor charge transfer. Successful AgO cathodic activation of both K2FeO4 and BaFeO4 redox chemistry are presented. Various other K2FeO4 activators are also studied. An observed interaction of Fe(VI) with Mn(VII/VI) can improve charge efficiency of a K2FeO4 composite with KMnO4 or BaMnO4, albeit not to the extent observed in an K2FeO4/AgO composite cathode. The extent of an activation effect of oxides, hydroxides, and titanates salts, as well as KMnO4, BaMnO4, AgMnO4, and fluorinated graphites, on the cathodic discharge of K2FeO4 are probed.
- Licht, Stuart,Naschitz, Vera,Ghosh, Susanta
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- AgCuO2 as a novel bifunctional electrocatalyst for overall water splitting in alkaline media
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Nanostructured transition metal oxides are among the most prevalent catalysts for the water-splitting process. Herein, AgCuO2 nanoparticles (NPs) are introduced as a novel bifunctional electrocatalyst for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline media. The catalyst, AgCuO2 NPs, exhibited excellent electrocatalytic activity together with a low overpotential for the overall water-splitting process. The AgCuO2 exhibits excellent electrocatalytic activity with a low onset overpotential of 29 mV for the HER and the onset overpotential of 360 mV for the OER, with superior long-term stability in 1.0 M KOH. The catalyst delivered 10 and 100 mA cm?2 at extremely low overpotentials of 42 and 47 mV for the HER and 10 mA cm?2 at an overpotential of 388 mV for the OER. This work suggests an important reference toward the use of novel bimetallic oxides as highly active and stable bifunctional electrocatalysts for high-performance water splitting.
- Kamali Moghaddam, Saeideh,Seyed Ahmadian, Seyed Masoud,Haghighi, Behzad
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- Room temperature solid-state transformation from Ag2Cu 2O3 to Ag2Cu2O4 by ozone oxidation
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The mixed silver-copper oxide, Ag2Cu2O4 has been previously synthesized by electrochemical oxidation of suspensions of the precursor Ag2Cu2O3 and also by direct oxidation/coprecipitation of
- Munoz-Rojas,Fraxedas,Gomez-Romero,Casan-Pastor
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- The millimeter wave spectrum of silver monoxide, AgO
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The pure rotational spectra of 107AgO and 109AgO were recorded in the 117-380 GHz spectral region using a dc-sputtering absorption cell. The 107Ag(I=1/2) and 109Ag(I=1/2) magnetic hyperfine parameters are interpreted in terms of plausible electronic configuration contributions to the X 2Πi state. It is shown that the determined unusual sign of the Λ-doubling and Fermi contact parameters implies that the X 2Πi state is dominated by a three open shell configuration. A comparison with isovalent CuO is made.
- Steimle,Tanimoto,Namiki,Saito
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- Stabilized alkaline Fe(VI) charge transfer
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Superiron cathodes, consisting of unusual Fe(VI) particles, are substantially stabilized with a low-level zirconia coating, which improves the experimental energy storage capacity of alkaline superiron batteries. Fe(VI) cathodes sustain three-electron alkaline reduction at a single, energetic [0.60 V vs standard hydrogen electrode (SHE)] potential. Superiron cathode salts such as K2 FeO4 and Cs2 FeO4 are stable in the solid state but tend to be passivated in alkaline electrolyte due to the formation of an Fe(III) overlayer. A zirconia coating is derived from ZrCl4 through an organic medium by the conversion of ZrCl4 to ZrO2. The zirconia coating shuttles hydroxide through to the interior cathode material, sustains a high rate of alkaline cathode charge transfer in the redox reduction of Fe(VI) to Fe(III) redox reduction, and inhibits Fe(III) passivation. The zirconia coating effectively enhances the stability of these superiron cathodes. However, for an Fe(VI) salt, which is not stable in the solid state, such as BaFeO2, an applied zirconia coating is not observed to stabilize alkaline cathodic charge transfer. Small particle and solid KOH and AgO additives each are observed to improve Fe(VI) cathodic charge transfer and enhance accessible Fe(VI) gravimetric capacity.
- Licht, Stuart,Yu, Xingwen,Wang, Yufei
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- Thermal decomposition of metal nitrates in air and hydrogen environments
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The decomposition of metal nitrates in air has been systematically studied by thermogravimetry. Observed temperature of decomposition (Td) have been inversely correlated to the charge densities (CD) of the metal cations. Due to a back-donation of electronic cloud from the nitrate to an unfilled d-orbital of transition and noble metals, their nitrates generally exhibited lower TdS ( 850 K). The thermal stability/reducibility of metal nitrates in an hydrogen atmosphere has also been studied by temperature-programmed reduction (TPR). Observed reduction temperatures (Tr) for nitrates of the base metals and the noble metals are lower than their Td, i.e., Tr d. The lowering of Tr might be attributed to a spillover of hydrogen to a nitrate moiety through heterolytic (ionic) and homolytic (atomic) dissociation of hydrogen on the respective base and noble metals. The stoichiometry of hydrogen consumption, quantitatively measured from TPR, varied with the group of metal cations. According to the stoichiometry, the end product in the TPR reduction was NH3 (NH2/NNO3-a??4.4) and N2 (NH2/NNO3-a??2.4) for nitrates of the noble and base metals, respectively. The Trs for nitrates of the transition metals are often a??20 K higher than their Tds, and the ratio NH(2)/NNO3- varies widely between 0.7 and 3.2. Their reduction may be triggered by thermal decomposition.
- Yuvaraj, Shanmugam,Lin, Fan-Yuan,Chang, Tsong-Huei,Yeh, Chuin-Tih
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- The super-iron boride battery
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A high-capacity alkaline redox storage chemistry is explored based on an environmentally benign zirconia-stabilized Fe6+ B2- chemistry. This super-iron boride battery sustains an electrochemical potential matched to the pervasive, conventional MnO2 -Zn battery chemistry, but with a much higher electrochemical storage capacity. Whereas a conventional alkaline battery pairs the 2 e- zinc anode with a 1 e- MnO2 cathode, the new alkaline cell couples an 11 e- boride anode, such as VB2, with a 3 e- storage hexavalent iron cathode. The cell has an open circuit and discharge potential comparable to the conventional, commercial alkaline battery. Based on VB2 (72.6 g mol-1) and the Fe(VI) salt K2 FeO4 (198.0 g mol-1), the super-iron boride cell has an 11 Faraday theoretical capacity of 369 mAh g-1. Added AgO mediates and further facilitates the 3 e- K2 FeO4 reductive charge transfer, and we demonstrate for super-iron boride that over 300 mAh g-1 is approached experimentally, which is substantially higher than the conventional Zn MnO2 alkaline battery with an experimental capacity (to 0.8 V) of 160 mAh g-1 and a theoretical capacity of 224 mAh g-1.
- Licht, Stuart,Yu, Xingwen,Wang, Yufei,Wu, Huiming
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- Differences in thermal decomposition of Ag(I), Mn(II), Fe(II) and Fe(III) complexes of cyclic dithiocarbamates
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The thermal decomposition of pyrrolidinedithiocarbamate (Pyr) and piperidinedithiocarbamate (Pip) complexes of Ag(I), Mn(II), Fe(II) and Fe(III) have been investigated by thermogravimetry and differential scanning calorimetry. The decomposition intermedia
- Bernal, Cláudia,Neves, Eduardo Almeida,Cavalheiro, éder T.G.
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- Low-activation solid-state syntheses by reducing transport lengths to atomic scales as demonstrated by case studies on AgNO3 and AgO
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We have studied solid-state reactions of educt mixtures of elements in an atomic dispersion. The reduced transport distances allow for extremely low activated reactions. This has been demonstrated by case studies on AgNO3 and AgO, which form an
- Fischer, Dieter,Jansen, Martin
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- Evidence for an Ag4O3 Phase of Silver Oxide
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The structure of chemically and electrochemically prepared AgO materials was investigated by extended X-ray absorption fine structure (EXAFS) spectroscopy.It was found that chemically prepared (CP) AgO is composed of Ag(+) and Ag(3+) ions coordinated with two oxygens at 2.13 Angstroem and four oxygens at 1.99 Angstroem, respectively.For electrochemically prepared (EP) AgO, the Ag(+) ions are also coordinated with two oxygens at a distance of 2.13 Angstroem.However, the coordination number for the Ag(3+) ions varies from 2.8 to 3.5 oxygens without any significant change in the coordination distance of 1.99 Angstroem.That is, EP AgO is really AgO1-δ, where δ is the degree of oxygen deficiency near the Ag(3+) ions.The magnitude of δ can be as large as 0.29 +/- 0.05 and is a strong function of preparation procedures.The EXAFS results reveal that a phase of silver oxide, Ag4O3, is formed electrochemically.The EXAFS results also suggest that the electrochemical oxidation of Ag or Ag2O to AgO proceeds via the formation of Ag4O3 as an intermediate step.
- Mansour, A. N.
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- Surface characterization study of the thermal decomposition of Ag2CO3
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The changes in chemical states and composition of the surface region of a Ag2CO3 powder at various stages during thermal decomposition have been examined using X-ray photoelectron spectroscopy (XPS) and ion scattering spectroscopy (ISS). The near-surface region of the as-received powder consists primarily of Ag2CO3 although some hydrocarbon and alcohol contaminants also are present. A 155°C anneal results in partial decomposition of Ag2CO3 to Ag metal and oxides and reduces the amounts of the C contaminants. An anneal at 170°C causes further decomposition of the Ag2CO3 to Ag metal, Ag2O, and AgO. ISS data indicate that at 205°C oxygen migrates more rapidly to the outermost atomic layer than it desorbs, resulting in an increased oxygen concentration. The AgO species undergoes further decomposition to Ag2O during a 340°C anneal treatment. Between 340 and 430°C the Ag2O decomposes, leaving only Ag metal and subsurface oxygen in the near-surface region of the sample. These results are consistent with temperature-programmed reaction (TPR) data which exhibit a CO2 peak at 260°C and an O2 peak at 420°C. Both the XPS and TPR data indicate that the thermal decomposition of these species are activated since their decompositions occur at temperatures much higher than predicted by equilibrium thermodynamic calculations.
- Epling, William S.,Hoflund, Gar B.,Salaita, Ghaleb N.
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- New Method of Describing Monoclinic Silver(I,III)Oxide (AgO), Single Crystal Growing and X-ray Structural Analysis.
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A new route for the synthesis of monoclinic AgO has been developed, yielding, for the first time, coarse crystalline samples which apparently do not show deviations from the ideal composition. On electrolysis of aqueous AgF solutions, AgO forms at the anode as crystals of 1. 0 multiplied by 0. 2 multiplied by 0. 05 mm in size. The crystal structure has been refined using single-crystal diffractometer data. The thermal stability recorded by differential thermal and thermogravimetric analysis techniques is improved over samples prepared previously by chemical oxidation.
- Jansen, M.,Fischer, P.
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- Electrodeposition of silver(II) oxide films
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Continuous films of silver(II) oxide (AgO) have been electrodeposited directly from aqueous solutions of 50 mM silver acetate/25 mM sodium acetate onto 430 stainless steel, polycrystalline platinum, and indium-tin oxide-coated glass. Current efficiencies for the electrodeposition process ranged from 62 to 95% and were a function of the applied current density. X-ray diffraction of the electrodeposited films reveals a [010] texture when the thickness is greater than 1 μm. Freshly ground films or powders exhibit only reflections consistent with the monoclinic AgO structure. Rietveld analysis confirms the ground films are single-phase AgO with a P 21/c space group. The films were imaged and film thickness was measured by atomic force microscopy. Thermogravimetric analysis shows that the films begin to decompose in air above 13O°C, with an abrupt weight loss between 180 and 20O°C. The total weight loss of 6.4 to 6.5% corresponds to thermal decomposition of AgO to Ag2O with loss of oxygen. A direct optical bandgap of 1.1 eV was measured. The black AgO films absorb strongly in the near infrared and throughout the visible region. The four-point resistivity of the AgO films was 12 ± 1 Ω cm.
- Breyfogle, Bryan E.,Hung, Chen-Jen,Shumsky, Mark G.,Switzer, Jay A.
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- Asymmetric Total Synthesis and Biosynthetic Implications of Perovskones, Hydrangenone, and Hydrangenone B
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Perovskones and hydrangenones are a family of structurally complex triterpenoids that were mainly isolated from the genus Salvia medicinal plants. These isoprenoids exhibit a broad range of biological activities, such as antitumor and antiplasmodial activities. Here, we report the collective total synthesis of perovskone, perovskones C, D, F, hydrangenone, and hydrangenone B. The key strategies in this work include the following: (1) an asymmetric photoenolization/Diels-Alder reaction was developed to construct a tricyclic ring bearing three contiguous quaternary centers, which was used to build the core icetexane skeleton; (2) a bioinspired Diels-Alder reaction of perovskatone D with trans-α-ocimene was applied to stereospecifically generate perovskones; (3) late-stage oxidations and ring forming steps were developed to synthesize perovskones and hydrangenones. Our synthetic work suggests that (1) perovskatone D may serve as the precursor of the biosynthesis of perovskones and (2) the formation of hydrangenone and hydrangenone B, containing a five-membered D ring, may involve an oxidative ring cleavage and ring regeneration process.
- Gao, Shuanhu,He, Haibing,Hou, Min,Wen, Guoen,Yang, Baochao,Zhang, Quan
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- Coordination chemistry of Cu(II), Co(II), Zn(II) and Ag(I) complexes of isomeric pyridine 2- and 4-carboxamides and their biological activity evaluation
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Eight complexes of Cu(II), Co(II), Zn(II) and Ag(I) with rarely studied ligands, N,N-diisopropyl/butylpicolinamide (L1/L2), and N,N-diisopropyl/butylisonicotinamide (L3/L4), have been synthesized and characterized spectroscopically, and their molecular and crystal structures have been reported. Diverse coordination modes of these positional isomers have been discovered, discussed and compared with the limited available literature in light of their respective convergent and divergent nature. All the complexes show stable and extended 1D, 2D or 3D coordination/H-bonded networks owing to a large number of weak C–H?O/X and other intermolecular interactions. Further, the ligands as well as the metal complexes have been evaluated for their antimicrobial activity and have turned out to be potent antimicrobial agents.
- Lumb, Isha,Sran, Balkaran Singh,Sood, Henna,Arora, Daljit Singh,Hundal, Geeta
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p. 153 - 166
(2017/03/09)
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- AgO investigated by photoelectron spectroscopy: Evidence for mixed valence
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We present photoelectron spectroscopy investigations of in-situ prepared AgO. The sample was prepared by room temperature oxidation of Ag in an electron cyclotron resonance O2 plasma. In contrast to other measurements based on ex situ prepared AgO powder samples, our investigations show a distinct double peak structure of the O 1s signal with a remarkable chemical shift of 2.9 eV between the two O 1s components. These two components can not be motivated from a crystallographic point of view as the oxygen sites are all equivalent in the unit cell. We interpret this double peak structure as a characteristic feature of AgO and discuss it in terms of mixed valences.
- Bielmann, M.,Schwaller, P.,Ruffieux, P.,Groening, O.,Schlapbach, L.,Groening, P.
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- Surface characterization study of the thermal decomposition of Ag2CO3 using X-ray photoelectron spectroscopy and electron energy loss spectroscopy
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X-ray photoelectron spectroscopy (XPS) and electron energy loss spectroscopy (ELS) have been used to examine Ag2CO3 powder before and after annealing in vacuum at 350 and 500°C. The data indicate that the Ag2CO3 decomposes in a stagewise manner to Ag2O and then Ag metal. ELS reference spectra have also been obtained from Ag-containing standards including Ag metal, Ag2O and AgO; and these spectra have been used as the basis for understanding the ELS data obtained from Ag2CO3 before and after decomposition.
- Salaita, Ghaleb N.,Hazos, Zoltan F.,Hoflund, Gar B.
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- Electronic structure of silver oxides investigated by AgL XANES spectroscopy
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The chemistry of binary and multinary silver oxides spans from subvalent species (with a mean oxidation number for Ag smaller than + 1) to compounds with Ag in high oxidation states as + 2 and + 3. We have investigated a range of silver oxides, including the binary compounds Ag2O, AgO, Ag3O4 and Ag2O3 as well as subvalent ternary oxides, by AgL3 and AgL1 XANES spectroscopy. The different valence states of silver are clearly reflected in AgL3 and AgL1 XANES spectra. The method thus allows the determination of average oxidation numbers. In addition, the degree of electronic interaction (localized or delocalized electronic states) in silver-oxygen compounds can be estimated on the basis of AgL3 XANES spectra.
- Behrens, Peter,A?mann, Stefanie,Bilow, Uta,Linke, Christoph,Jansen, Martin
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p. 111 - 116
(2008/10/08)
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- Use of ozone to prepare silver oxides
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The possible use of ozone to produce higher oxides was analyzed thermodynamically. Because the activity of oxygen in ozone is approx. 1018 at room temperature and approx. 108 at 773 K, ozone may react with metals to yield higher-oxidation-state products than does an ambient pressure of pure oxygen. In agreement with this thermodynamic prediction, silver oxides (AgO and Ag2O) were synthesized experimentally by blowing a gas mixture of 6 vol% ozone and oxygen through a water-cooled lance. Neither Ag3O4 nor Ag2O3 was detected. Slow oxygen diffusion into a metal and/or reaction products and decomposition of unstable oxides that are formed successively are obstacles to practical applications of syntheses via ozone oxidation.
- Suzuki, Ryosuke O.,Ogawa, Takamichi,Ono, Katsutoshi
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p. 2033 - 2038
(2008/10/09)
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- Surface-embedded oxygen: Electronic structure of Ag(111) and Cu(poly) oxidized at atmospheric pressure
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We investigated the surface electronic structure of an oxidized Ag(111) single crystal and a polycrystalline Cu foil prepared under conditions of pressure and temperature (1000 mbar and 900 K) far beyond those used in usual UHV studies. It has recently been shown that a strongly bound oxygen species (Oγ) apart from oxygen atoms chemisorbed on the surface (Oα) or oxygen atoms dissolved in the bulk (Oβ) can be prepared on silver surfaces. Using core-level photoemission we show these three atomic oxygen species, Oα, Oβ and Oγ, exhibit characteristic spectral properties. X-ray absorption spectroscopy at the O K-edge indicates that the formation of the strongly bound Oγ species is accompanied by a strong hybridization between O2p and Ag4d states and that also the Ag5sp states are important for the metal-to-oxygen covalent interaction. The reaction with methanol was used to selectively remove the surface-embedded atomic species and to study the effect of the strongly bound oxygen Oγ species on the valence electronic structure of silver. This separation of the oxygen species did not work for the more reactive copper-oxygen system. The chemical bonding interaction of the novel Oγ species with silver is discussed in terms of the ligand-field theory emphasizing the covalent character of the interaction. For copper, the spectroscopic analysis is complicated by the existence of a stable oxide Cu2O with similar bonding properties of the oxygen than postulated for the surface-embedded species in silver. VCH Verlagsgesellschaft mbH, 1997.
- Schedel-Niedrig,Bao,Muhler,Schloegl
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p. 994 - 1006
(2007/10/03)
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