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Aldo Steinfeld - One of the best experts on this subject based on the ideXlab platform.
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syngas production by simultaneous splitting of h2o and co2via ceria Redox Reactions in a high temperature solar reactor
Energy and Environmental Science, 2012Co-Authors: Philipp Furler, Aldo Steinfeld, Jonathan R ScheffeAbstract:Solar syngas production from H2O and CO2 is experimentally investigated using a two-step thermochemical cycle based on cerium oxide Redox Reactions. A solar cavity-receiver containing porous ceria felt is directly exposed to concentrated thermal radiation at a mean solar concentration ratio of 2865 suns. In the first endothermic step at 1800 K, ceria is thermally reduced to an oxygen deficient state. In the second exothermic step at 1100 K, syngas is produced by re-oxidizing ceria with a gas mixture of H2O and CO2. The syngas composition is experimentally determined as a function of the molar co-feeding ratio H2O:CO2 in the range of 0.8 to 7.7, yielding syngas with H2:CO molar ratios from 0.25 to 2.34. Ten consecutive H2O/CO2-splitting cycles performed over an 8 hour solar experimental run are presented.
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solar syngas production from co2 and h2o in a two step thermochemical cycle via zn zno Redox Reactions thermodynamic cycle analysis
International Journal of Hydrogen Energy, 2011Co-Authors: Peter G. Loutzenhiser, Aldo SteinfeldAbstract:Abstract Solar syngas production from CO2 and H2O is considered in a two-step thermochemical cycle via Zn/ZnO Redox Reactions, encompassing: 1) the ZnO thermolysis to Zn and O2 using concentrated solar radiation as the source of process heat, and 2) Zn reacting with mixtures of H2O and CO2 yielding high-quality syngas (mainly H2 and CO) and ZnO; the ZnO is recycled to the first, solar step, resulting in net reaction βCO2 + (1 − β)H2O → βCO + (1 − β)H2. Syngas is further processed to liquid hydrocarbon fuels via Fischer–Tropsch or other catalytic processes. Second-law thermodynamic analysis is applied to determine the cycle efficiencies attainable with and without heat recuperation for varying molar fractions of CO2:H2O and solar reactor temperatures in the range 1900–2300 K. Considered is the energy penalty of using Ar dilution in the solar step below 2235 K for shifting the equilibrium to favor Zn production.
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review of the two step h2o co2 splitting solar thermochemical cycle based on zn zno Redox Reactions
Materials, 2010Co-Authors: Peter G. Loutzenhiser, Anton Meier, Aldo SteinfeldAbstract:This article provides a comprehensive overview of the work to date on the two‑step solar H2O and/or CO2 splitting thermochemical cycles with Zn/ZnO Redox Reactions to produce H2 and/or CO, i.e., synthesis gas—the precursor to renewable liquid hydrocarbon fuels. The two-step cycle encompasses: (1) The endothermic dissociation of ZnO to Zn and O2 using concentrated solar energy as the source for high-temperature process heat; and (2) the non-solar exothermic oxidation of Zn with H2O/CO2 to generate H2/CO, respectively; the resulting ZnO is then recycled to the first step. An outline of the underlying science and the technological advances in solar reactor engineering is provided along with life cycle and economic analyses.
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solar syngas production via h2o co2 splitting thermochemical cycles with zn zno and feo fe3o4 Redox Reactions
Chemistry of Materials, 2010Co-Authors: Anastasia Stamatiou, Peter G. Loutzenhiser, Aldo SteinfeldAbstract:The solar production of syngas from H2O and CO2 is examined via two-step thermochemical cycles based on Zn/ZnO and FeO/Fe3O4 Redox Reactions. The first, endothermic step is the thermal dissociation of the metal oxide using concentrated solar radiation as the energy source of high-temperature process heat. The second, nonsolar, exothermic step is the reaction of the metal or reduced metal oxide with a mixture of H2O and CO2 yielding syngas (H2 and CO), together with the initial form of the metal oxide that is recycled to the first step. Chemical equilibrium compositions for the systems of Zn and FeO with CO2 + H2O were computed as a function of temperature and pressure for different stoichiometries. A series of dynamic thermogravimetric experimental runs in the range 673−1423 K was carried out to evaluate the reaction kinetics and syngas quality of the second step. The molar flow rate fractions of the gaseous products exhibited linear dependencies on the molar flow rate fractions of the gaseous reactants f...
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solar hydrogen production via a two step thermochemical process based on mgo mg Redox Reactions thermodynamic and kinetic analyses
International Journal of Hydrogen Energy, 2008Co-Authors: Maria Elena Galvez, Aldo Steinfeld, A Frei, G Albisetti, G LunardiAbstract:Abstract Solar hydrogen production via a two-step water-splitting thermochemical cyclic process is considered via MgO/Mg Redox Reactions. The first endothermic step is the production of Mg by carbothermal or methanothermal reduction of MgO, using concentrated solar energy as the source of high-temperature process heat. The second exothermic step is the steam-hydrolysis of Mg for the production of H 2 and MgO; the latter is recycled to the first step. Both reaction steps have been thermodynamically examined and experimentally investigated by means of thermogravimetric analysis. The carbothermal reduction of MgO was performed in the temperature range 1450–1550 °C using wood charcoal and petroleum coke as reducing agents. The steam-hydrolysis of Mg was studied in the temperature range 350–550 °C using various water vapor concentrations. Solid products were characterized via BET, XRD, and SEM. The rate laws of both reaction steps were determined by applying either a solid–solid diffusion kinetic model or the gas–solid shrinking core kinetic model.
Peter G. Loutzenhiser - One of the best experts on this subject based on the ideXlab platform.
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solar electricity via an air brayton cycle with an integrated two step thermochemical cycle for heat storage based on co 3 o 4 coo Redox Reactions iii solar thermochemical reactor design and modeling
Solar Energy, 2017Co-Authors: Andrew J Schrader, Gretchen L Schieber, Gianmarco De Dominicis, Peter G. LoutzenhiserAbstract:Abstract A two-step solar thermochemical cycle based on Co3O4/CoO Redox Reactions integrated into an Air Brayton cycle is considered for thermochemical heat storage. The two-step cycle encompasses (1) the thermal reduction of Co3O4 to CoO and O2 driven by concentrated solar irradiation and (2) the re-oxidation of CoO with O2 to Co3O4, releasing heat and completing the cycle. An evacuated horizontal solar thermochemical reactor is proposed with an inclined slope and quartz window for promoting direct irradiation of dense, granular Co3O4/CoO flows. Mechanical analysis of flat and spherical quartz window designs for a 5 kWth scale prototype was performed to ensure window stability. Detailed mass and heat transfer analysis for a 5 kWth scale prototype was performed coupling Monte Carlo ray tracing for radiative heat exchange to the energy balances for the bed and the reactor. A parametric study of the reactor design was performed with varying cavity depth, particle inlet temperature, and solar concentration ratio. The optimal solar reactor design maximized conversion of Co3O4 to CoO and particle outlet temperature while preventing particle overheating and achieved a Co3O4 to CoO conversion of 0.91, particle outlet temperature of 1385 K, maximum flow temperature of 1572 K, and absorption efficiency of 0.76.
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solar electricity via an air brayton cycle with an integrated two step thermochemical cycle for heat storage based on co3o4 coo Redox Reactions ii kinetic analyses
Solar Energy, 2015Co-Authors: Alexander P Muroyama, Andrew J Schrader, Peter G. LoutzenhiserAbstract:Abstract A two-step solar thermochemical cycle based on Co3O4/CoO Redox Reactions integrated into an Air Brayton cycle is considered for thermochemical heat storage. The two-step cycle encompasses (1) the thermolysis of Co3O4 to CoO and O2 driven by concentrated solar irradiation and (2) the re-oxidation of CoO with O2 to Co3O4, releasing heat and completing the cycle. The cycle steps can be decoupled, allowing for thermochemical heat storage and integration into an Air Brayton cycle for continuous electricity production. Kinetic analyses to identify the rate limiting mechanisms and determine kinetic parameters for both the thermolysis of Co3O4 and the re-oxidation of CoO with O2 were performed using a combination of isothermal and non-isothermal thermogravimetry. The Co3O4 thermolysis between 1113 and 1213 K followed an Avrami–Erofeyev nucleation model with an Avrami constant of 1.968 and apparent activation energy of 247.21 kJ mol−1. The O2 partial pressure dependence between 0% and 20% O2–Ar was determined with a power rate law, resulting in a reaction order of 1.506. Ionic diffusion was the rate limiting step for CoO oxidation between 450 and 750 K with an apparent activation energy of 58.07 kJ mol−1 and no evident dependence on O2 concentration between 5% and 100% O2–Ar. Solid characterization was performed using scanning electron microscopy and X-ray powder diffraction.
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solar syngas production from co2 and h2o in a two step thermochemical cycle via zn zno Redox Reactions thermodynamic cycle analysis
International Journal of Hydrogen Energy, 2011Co-Authors: Peter G. Loutzenhiser, Aldo SteinfeldAbstract:Abstract Solar syngas production from CO2 and H2O is considered in a two-step thermochemical cycle via Zn/ZnO Redox Reactions, encompassing: 1) the ZnO thermolysis to Zn and O2 using concentrated solar radiation as the source of process heat, and 2) Zn reacting with mixtures of H2O and CO2 yielding high-quality syngas (mainly H2 and CO) and ZnO; the ZnO is recycled to the first, solar step, resulting in net reaction βCO2 + (1 − β)H2O → βCO + (1 − β)H2. Syngas is further processed to liquid hydrocarbon fuels via Fischer–Tropsch or other catalytic processes. Second-law thermodynamic analysis is applied to determine the cycle efficiencies attainable with and without heat recuperation for varying molar fractions of CO2:H2O and solar reactor temperatures in the range 1900–2300 K. Considered is the energy penalty of using Ar dilution in the solar step below 2235 K for shifting the equilibrium to favor Zn production.
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review of the two step h2o co2 splitting solar thermochemical cycle based on zn zno Redox Reactions
Materials, 2010Co-Authors: Peter G. Loutzenhiser, Anton Meier, Aldo SteinfeldAbstract:This article provides a comprehensive overview of the work to date on the two‑step solar H2O and/or CO2 splitting thermochemical cycles with Zn/ZnO Redox Reactions to produce H2 and/or CO, i.e., synthesis gas—the precursor to renewable liquid hydrocarbon fuels. The two-step cycle encompasses: (1) The endothermic dissociation of ZnO to Zn and O2 using concentrated solar energy as the source for high-temperature process heat; and (2) the non-solar exothermic oxidation of Zn with H2O/CO2 to generate H2/CO, respectively; the resulting ZnO is then recycled to the first step. An outline of the underlying science and the technological advances in solar reactor engineering is provided along with life cycle and economic analyses.
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solar syngas production via h2o co2 splitting thermochemical cycles with zn zno and feo fe3o4 Redox Reactions
Chemistry of Materials, 2010Co-Authors: Anastasia Stamatiou, Peter G. Loutzenhiser, Aldo SteinfeldAbstract:The solar production of syngas from H2O and CO2 is examined via two-step thermochemical cycles based on Zn/ZnO and FeO/Fe3O4 Redox Reactions. The first, endothermic step is the thermal dissociation of the metal oxide using concentrated solar radiation as the energy source of high-temperature process heat. The second, nonsolar, exothermic step is the reaction of the metal or reduced metal oxide with a mixture of H2O and CO2 yielding syngas (H2 and CO), together with the initial form of the metal oxide that is recycled to the first step. Chemical equilibrium compositions for the systems of Zn and FeO with CO2 + H2O were computed as a function of temperature and pressure for different stoichiometries. A series of dynamic thermogravimetric experimental runs in the range 673−1423 K was carried out to evaluate the reaction kinetics and syngas quality of the second step. The molar flow rate fractions of the gaseous products exhibited linear dependencies on the molar flow rate fractions of the gaseous reactants f...
Atsushi Ueda - One of the best experts on this subject based on the ideXlab platform.
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solid state Redox Reactions of licoo2 r3m for 4 volt secondary lithium cells
Journal of The Electrochemical Society, 1994Co-Authors: Tsutomu Ohzuku, Atsushi UedaAbstract:LiCoO[sub 2] (R[bar 3]m; a = 2.82 [angstrom], c = 14.1 [angstrom] in hexagonal setting) was prepared and examined in nonaqueous lithium cells using 1M LiClO[sub 4] propylene carbonate solution at 30 C. The oxidation of LiCoO[sub 2] and the reduction of Li[sub 1[minus]x]CoO[sub 2] proceeded reversibly in the voltage region above 3.9 V. X-ray diffraction (XRD) examinations indicated the reaction proceeded in a topotactic manner, i.e., two-phase Reactions (0 < x < 1/4 and 3/4 < x < 1 in Li[sub 1[minus]x]CoO[sub 2]) and a single-phase reaction (1/4 < x < 3/4). A monoclinic phase was observed in 3/4 < x < 1 in addition to that at about x = 0.45. Detailed open-circuit voltage measurements were carried out. The open-circuit voltage are invariable at 3.92 V for 0 < x < 1/4 and at 4.50 V for 3/4 < x < 1. The two straight lines are connected smoothly by a composition-dependent curve for 1/4 < x < 3/4, which was consistent with the XRD observations. The differences and similarities between the solid-state Redox Reactions of LiCoO[sub 2] and LiNiO[sub 2] were discussed by comparing the structural and electrochemical data. Possible lithium ordering at x = 1/4 andmore » 3/4 for this type of material is described in terms of a [2 x 2] superlattice in a triangular lattice of sites.« less
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solid state Redox Reactions of lini1 2co1 2 o 2 r 3m for 4 volt secondary lithium cells
Journal of The Electrochemical Society, 1994Co-Authors: Atsushi Ueda, Tsutomu OhzukuAbstract:LiNi[sub 1/2]Co[sub 1/2]O[sub 2] (R[bar 3]m; a = 2.84 [angstrom], c = 14.1 [angstrom] in hexagonal setting) whose parent structure was a solid solution of LiNiO[sub 2] and LiCoO[sub 2] was prepared and examined in a nonaqueous lithium cell. The oxidation of LiNi[sub 1/2]Co[sub 1/2]O[sub 2] and reduction of [open square]Ni[sub 1/2]Co[sub 1/2]O[sub 2] proceeded reversibly in the voltage range above 3.5 V. X-ray diffractional examinations indicated the reaction proceeded in a topotactic manner. During the oxidation of LiNi[sub 1/2]Co[sub 1/2]O[sub 2], the c-axis dimension elongated from 14.1 to 14.5 [angstrom] and the a-axis shortened from 2.84 to 2.80 [angstrom] almost linearly as a function of x in Li[sub 1[minus]x]Ni[sub 1/2]Co[sub 1/2]O[sub 2] until x reached about 0.5. Consequently, the lattice volume remained almost invariable at 98.5 A[sup 3]. Further oxidation resulted in the shrinkage of the c-axis dimension and the elongation of the a-axis. Detained open-circuit voltage measurements also were carried out. The open-circuit voltages varied as a function of x in Li[sub 1[minus]x]Ni[sub 1/2]Co[sub 1/2]O[sub 2] following a hyperbolic tangent curve, not an S-shaped Nernstian curve. The composition-dependent open-circuit voltage curve together with the XRD observations indicated that the reaction proceeded in a homogeneous phase. Differences and similaritiesmore » of the solid-state Redox Reactions among LiNiO[sub 2], LiNi[sub 1/2]Co[sub 1/2]O[sub 2], and LiCoO[sub 2] were discussed.« less
Tsutomu Ohzuku - One of the best experts on this subject based on the ideXlab platform.
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solid state Redox Reactions of licoo2 r3m for 4 volt secondary lithium cells
Journal of The Electrochemical Society, 1994Co-Authors: Tsutomu Ohzuku, Atsushi UedaAbstract:LiCoO[sub 2] (R[bar 3]m; a = 2.82 [angstrom], c = 14.1 [angstrom] in hexagonal setting) was prepared and examined in nonaqueous lithium cells using 1M LiClO[sub 4] propylene carbonate solution at 30 C. The oxidation of LiCoO[sub 2] and the reduction of Li[sub 1[minus]x]CoO[sub 2] proceeded reversibly in the voltage region above 3.9 V. X-ray diffraction (XRD) examinations indicated the reaction proceeded in a topotactic manner, i.e., two-phase Reactions (0 < x < 1/4 and 3/4 < x < 1 in Li[sub 1[minus]x]CoO[sub 2]) and a single-phase reaction (1/4 < x < 3/4). A monoclinic phase was observed in 3/4 < x < 1 in addition to that at about x = 0.45. Detailed open-circuit voltage measurements were carried out. The open-circuit voltage are invariable at 3.92 V for 0 < x < 1/4 and at 4.50 V for 3/4 < x < 1. The two straight lines are connected smoothly by a composition-dependent curve for 1/4 < x < 3/4, which was consistent with the XRD observations. The differences and similarities between the solid-state Redox Reactions of LiCoO[sub 2] and LiNiO[sub 2] were discussed by comparing the structural and electrochemical data. Possible lithium ordering at x = 1/4 andmore » 3/4 for this type of material is described in terms of a [2 x 2] superlattice in a triangular lattice of sites.« less
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solid state Redox Reactions of lini1 2co1 2 o 2 r 3m for 4 volt secondary lithium cells
Journal of The Electrochemical Society, 1994Co-Authors: Atsushi Ueda, Tsutomu OhzukuAbstract:LiNi[sub 1/2]Co[sub 1/2]O[sub 2] (R[bar 3]m; a = 2.84 [angstrom], c = 14.1 [angstrom] in hexagonal setting) whose parent structure was a solid solution of LiNiO[sub 2] and LiCoO[sub 2] was prepared and examined in a nonaqueous lithium cell. The oxidation of LiNi[sub 1/2]Co[sub 1/2]O[sub 2] and reduction of [open square]Ni[sub 1/2]Co[sub 1/2]O[sub 2] proceeded reversibly in the voltage range above 3.5 V. X-ray diffractional examinations indicated the reaction proceeded in a topotactic manner. During the oxidation of LiNi[sub 1/2]Co[sub 1/2]O[sub 2], the c-axis dimension elongated from 14.1 to 14.5 [angstrom] and the a-axis shortened from 2.84 to 2.80 [angstrom] almost linearly as a function of x in Li[sub 1[minus]x]Ni[sub 1/2]Co[sub 1/2]O[sub 2] until x reached about 0.5. Consequently, the lattice volume remained almost invariable at 98.5 A[sup 3]. Further oxidation resulted in the shrinkage of the c-axis dimension and the elongation of the a-axis. Detained open-circuit voltage measurements also were carried out. The open-circuit voltages varied as a function of x in Li[sub 1[minus]x]Ni[sub 1/2]Co[sub 1/2]O[sub 2] following a hyperbolic tangent curve, not an S-shaped Nernstian curve. The composition-dependent open-circuit voltage curve together with the XRD observations indicated that the reaction proceeded in a homogeneous phase. Differences and similaritiesmore » of the solid-state Redox Reactions among LiNiO[sub 2], LiNi[sub 1/2]Co[sub 1/2]O[sub 2], and LiCoO[sub 2] were discussed.« less
Matthew F. Chisholm - One of the best experts on this subject based on the ideXlab platform.
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reversible Redox Reactions in an epitaxially stabilized srcoox oxygen sponge
arXiv: Materials Science, 2013Co-Authors: Hyoungjeen Jeen, I. Cheng Tung, C. M. Folkman, Woo-seok Choi, Dillon D. Fong, Michael D Biegalski, Hiromichi Ohta, John W. Freeland, Dongwon Shin, Matthew F. ChisholmAbstract:Fast, reversible Redox Reactions in solids at low temperatures without thermomechanical degradation are a promising strategy for enhancing the overall performance and lifetime of many energy materials and devices. However, the robust nature of the cation's oxidation state and the high thermodynamic barrier have hindered the realization of fast catalysis and bulk diffusion at low temperatures. Here, we report a significant lowering of the Redox temperature by epitaxial stabilization of strontium cobaltites (SrCoOx) grown directly as one of two distinct crystalline phases, either the perovskite SrCoO3-{\delta} or the brownmillerite SrCoO2.5. Importantly, these two phases can be reversibly switched at a remarkably reduced temperature (200~300 °C) in a considerably short time (< 1 min) without destroying the parent framework. The fast, low temperature Redox activity in SrCoO3-{\delta} is attributed to a small Gibbs free energy difference between two topotatic phases. Our findings thus provide useful information for developing highly sensitive electrochemical sensors and low temperature cathode materials.
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reversible Redox Reactions in an epitaxially stabilized srcoox oxygen sponge
arXiv: Materials Science, 2013Co-Authors: Hyoungjeen Jeen, I. Cheng Tung, C. M. Folkman, Woo-seok Choi, Dillon D. Fong, Michael D Biegalski, Hiromichi Ohta, John W. Freeland, Dongwon Shin, Matthew F. ChisholmAbstract:Fast, reversible Redox Reactions in solids at low temperatures without thermomechanical degradation are a promising strategy for enhancing the overall performance and lifetime of many energy materials and devices. However, the robust nature of the cation's oxidation state and the high thermodynamic barrier have hindered the realization of fast catalysis and bulk diffusion at low temperatures. Here, we report a significant lowering of the Redox temperature by epitaxial stabilization of strontium cobaltites (SrCoOx) grown directly as one of two distinct crystalline phases, either the perovskite SrCoO3-{\delta} or the brownmillerite SrCoO2.5. Importantly, these two phases can be reversibly switched at a remarkably reduced temperature (200~300 {\deg}C) in a considerably short time (< 1 min) without destroying the parent framework. The fast, low temperature Redox activity in SrCoO3-{\delta} is attributed to a small Gibbs free energy difference between two topotatic phases. Our findings thus provide useful information for developing highly sensitive electrochemical sensors and low temperature cathode materials.
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Reversible Redox Reactions in an epitaxially stabilized SrCoO x oxygen sponge
Nature Materials, 2013Co-Authors: Hyoungjeen Jeen, I. Cheng Tung, C. M. Folkman, Woo-seok Choi, Dillon D. Fong, Michael D Biegalski, Hiromichi Ohta, John W. Freeland, Dongwon Shin, Matthew F. ChisholmAbstract:Fast, reversible Redox Reactions in solids at low temperatures without thermomechanical degradation are a promising strategy for enhancing the overall performance and lifetime of many energy materials and devices. However, the robust nature of the cation's oxidation state and the high thermodynamic barrier have hindered the realization of fast catalysis and bulk diffusion at low temperatures. Here, we report a significant lowering of the Redox temperature by epitaxial stabilization of strontium cobaltites (SrCoO(x)) grown directly as one of two distinct crystalline phases, either the perovskite SrCoO(3-δ) or the brownmillerite SrCoO(2.5). Importantly, these two phases can be reversibly switched at a remarkably reduced temperature (200-300 °C) in a considerably short time (< 1 min) without destroying the parent framework. The fast, low-temperature Redox activity in SrCoO(3-δ) is attributed to a small Gibbs free-energy difference between two topotatic phases. Our findings thus provide useful information for developing highly sensitive electrochemical sensors and low-temperature cathode materials.
