scholarly journals Kinetics of Thermal Reduction Step of Thermochemical Two-step Water Splitting Using CeO2 Particles: MASTER-plot Method for Analyzing Non-isothermal Experiments

2014 ◽  
Vol 49 ◽  
pp. 1970-1979 ◽  
Author(s):  
T. Ishida ◽  
N. Gokon ◽  
T. Hatamachi ◽  
T. Kodama
Keyword(s):  
Water Splitting ◽  
Thermal Reduction ◽  
Reduction Step ◽  
Master Plot ◽  
Kinetics Of

Comparison Studies of Reactivity on Nickel-Ferrite and Cerium-Oxide Redox Materials for Two-Step Thermochemical Water Splitting Below 1400°C

2011 ◽  
Author(s):  
Tatsuya Kodama ◽  
Nobuki Imaizumi ◽  
Nobuyuki Gokon ◽  
Tsuyoshi Hatamachi ◽  
Daiki Aoyagi ◽  
...  
Keyword(s):  
Metal Oxide ◽  
Water Splitting ◽  
Cerium Oxide ◽  
Nickel Ferrite ◽  
Thermal Reduction ◽  
Monoclinic Zirconia ◽  
Reduction Step ◽  
Water Decomposition ◽  
Decomposition Step ◽  
Supported Ni

A two-step thermochemical water splitting cycle using a redox system of non-volatile metal oxide is one of the promising processes for converting concentrated solar high-temperature heat into clean hydrogen in sun-belt regions. In the 1st step of the cycle or the thermal reduction step, metal oxide is thermally reduced to release oxygen molecules in an inert gas atmosphere at a higher temperature above 1400°C. In the second step or the water-decomposition step at a lower temperature, the thermally-reduced metal oxide reacts with steam to produce hydrogen. As the reactive redox metal oxide materials to be capable of working below 1400°C, nickel-doped iron oxides or Ni-ferrites supported on zirconia, and non-stoichiometric cerium oxides are the promising working materials. In the present work, a series of the nickel-ferrite redox materials of monoclinic-zirconia-supported, cubic-YSZ(yttrium-stabilized zirconia)-supported, and non-supported Ni-ferries and non-stoichiometric cerium oxide were compared on reactivity for two-step thermochemical water splitting cycle. The monoclinic-zirconia-supported Ni-ferrite produced the most quantity of hydrogen in the repeated cycles when the thermal reduction step was performed for 30 min at 1400°C and the water decomposition step for 60 min at 1000°C.

Comparative Labelling and Biokinetic Studies of 99mTc-EDTA(Sn) and 99mTc-DTPA(Sn)

1977 ◽  
Vol 16 (01) ◽  
pp. 30-35 ◽  
Author(s):  
N. Agha ◽  
R. B. R. Persson
Keyword(s):  
Complex Formation ◽  
Significant Influence ◽  
Room Temperature ◽  
Ph Value ◽  
Maximum Activity ◽  
Reduction Step ◽  
Labelling Yield ◽  
Different Temperatures ◽  
Kinetics Of

SummaryGelchromatography column scanning has been used to study the fractions of 99mTc-pertechnetate, 99mTcchelate and reduced hydrolyzed 99mTc in preparations of 99mTc-EDTA(Sn) and 99mTc-DTPA(Sn). The labelling yield of 99mTc-EDTA(Sn) chelate was as high as 90—95% when 100 μmol EDTA · H4 and 0.5 (Amol SnCl2 was incubated with 10 ml 99mTceluate for 30—60 min at room temperature. The study of the influence of the pH-value on the fraction of 99mTc-EDTA shows that pH 2.8—2.9 gave the best labelling yield. In a comparative study of the labelling kinetics of 99mTc-EDTA(Sn) and 99mTc- DTPA(Sn) at different temperatures (7, 22 and 37°C), no significant influence on the reduction step was found. The rate constant for complex formation, however, increased more rapidly with increased temperature for 99mTc-DTPA(Sn). At room temperature only a few minutes was required to achieve a high labelling yield with 99mTc-DTPA(Sn) whereas about 60 min was required for 99mTc-EDTA(Sn). Comparative biokinetic studies in rabbits showed that the maximum activity in kidneys is achieved after 12 min with 99mTc-EDTA(Sn) but already after 6 min with 99mTc-DTPA(Sn). The long-term disappearance of 99mTc-DTPA(Sn) from the kidneys is about five times faster than that for 99mTc-EDTA(Sn).

Zinc-telluride nanospheres as an efficient water oxidation electrocatalyst displaying a low overpotential for oxygen evolution

2019 ◽  
Vol 7 (46) ◽  
pp. 26410-26420 ◽  
Author(s):  
Maira Sadaqat ◽  
Laraib Nisar ◽  
Noor-Ul-Ain Babar ◽  
Fayyaz Hussain ◽  
Muhammad Naeem Ashiq ◽  
...  
Keyword(s):  
Water Splitting ◽  
Oxygen Evolution ◽  
Oxygen Evolution Reaction ◽  
Water Oxidation ◽  
Zinc Telluride ◽  
Low Overpotential ◽  
Electrochemical Water Splitting ◽  
Kinetics Of

Electrochemical water splitting is economically unviable due to the sluggish kinetics of the anodically uphill oxygen evolution reaction (OER).

scholarly journals Distance dependent charge separation and recombination in semiconductor/molecular catalyst systems for water splitting

2014 ◽  
Vol 50 (84) ◽  
pp. 12768-12771 ◽  
Author(s):  
Anna Reynal ◽  
Janina Willkomm ◽  
Nicoleta M. Muresan ◽  
Fezile Lakadamyali ◽  
Miquel Planells ◽  
...  
Keyword(s):  
Molecular Structure ◽  
Water Splitting ◽  
Charge Separation ◽  
Molecular Catalyst ◽  
Catalyst Systems ◽  
Kinetics Of

The molecular structure of the catalyst strongly influences the kinetics of charge separation and recombination.

scholarly journals Solar Thermochemical Hydrogen Production via Terbium Oxide Based Redox Reactions

2016 ◽  
Vol 2016 ◽  
pp. 1-9 ◽  
Author(s):  
Rahul Bhosale ◽  
Anand Kumar ◽  
Fares AlMomani
Keyword(s):  
Oxygen Partial Pressure ◽  
Partial Pressure ◽  
Water Splitting ◽  
Thermal Reduction ◽  
Terbium Oxide ◽  
Heat Recuperation ◽  
Solar Thermochemical ◽  
Oxidation By Water ◽  
Heat Released ◽  
Reaction Equilibrium

The computational thermodynamic modeling of the terbium oxide based two-step solar thermochemical water splitting (Tb-WS) cycle is reported. The 1st step of the Tb-WS cycle involves thermal reduction of TbO2into Tb and O2, whereas the 2nd step corresponds to the production of H2through Tb oxidation by water splitting reaction. Equilibrium compositions associated with the thermal reduction and water splitting steps were determined via HSC simulations. Influence of oxygen partial pressure in the inert gas on thermal reduction of TbO2and effect of water splitting temperature (TL) on Gibbs free energy related to the H2production step were examined in detail. The cycle (ηcycle) and solar-to-fuel energy conversion (ηsolar-to-fuel) efficiency of the Tb-WS cycle were determined by performing the second-law thermodynamic analysis. Results obtained indicate thatηcycleandηsolar-to-fuelincrease with the decrease in oxygen partial pressure in the inert flushing gas and thermal reduction temperature (TH). It was also realized that the recuperation of the heat released by the water splitting reactor and quench unit further enhances the solar reactor efficiency. AtTH=2280 K, by applying 60% heat recuperation, maximumηcycleof 39.0% andηsolar-to-fuelof 47.1% for the Tb-WS cycle can be attained.

Considerations for the Design of Solar-Thermal Chemical Processes

2010 ◽  
Vol 132 (3) ◽  
Author(s):  
Janna Martinek ◽  
Melinda Channel ◽  
Allan Lewandowski ◽  
Alan W. Weimer
Keyword(s):  
Solar Energy ◽  
Water Splitting ◽  
Thermal Reduction ◽  
Absorption Efficiency ◽  
Chemical Processes ◽  
Solar Thermal ◽  
System Efficiency ◽  
Field Efficiency ◽  
Definition Of ◽  
Solar Field

A methodology is presented for the design of solar thermal chemical processes. The solar receiver efficiency for the high temperature step, defined herein as the ratio of the enthalpy change resulting from the process occurring in the receiver to the solar energy input, is limited by the solar energy absorption efficiency. When using this definition of receiver efficiency, both the optimal reactor temperature for a given solar concentration ratio and the solar concentration required to achieve a given temperature and efficiency shift to lower values than those dictated by the Carnot limitation on the system efficiency for the conversion of heat to work. Process and solar field design considerations were investigated for ZnO and NiFe2O4 “ferrite” spinel water splitting cycles with concentration ratios of roughly 2000, 4000, and 8000 suns to assess the implications of using reduced solar concentration. Solar field design and determination of field efficiency were accomplished using ray trace modeling of the optical components. Annual solar efficiency increased while heliostat area decreased with increasing concentration due to shading and blocking effects. The heliostat fields designed using system efficiency for the conversion of heat to work were found to be overdesigned by up to 21% compared with those designed using the receiver efficiency alone. Overall efficiencies of 13–20% were determined for a “ferrite” based water splitting process with thermal reduction conversions in the range of 35–100%.

Internally Circulating Fluidized Bed Reactor Using m-ZrO2 Supported NiFe2O4 Particles for Thermochemical Two-Step Water Splitting

2010 ◽  
Vol 132 (2) ◽  
Author(s):  
Nobuyuki Gokon ◽  
Hiroki Yamamoto ◽  
Nobuyuki Kondo ◽  
Tatsuya Kodama
Keyword(s):  
Fluidized Bed ◽  
Water Splitting ◽  
Gas Flow ◽  
Circulating Fluidized Bed ◽  
Fluidized Bed Reactor ◽  
Thermal Reduction ◽  
Input Power ◽  
Light Irradiation ◽  
Bed Temperature ◽  
N2 Flow Rate

A windowed internally circulating fluidized bed reactor was tested using m-ZrO2-supported NiFe2O4(NiFe2O4/m-ZrO2) particles as redox material for thermochemical two-step water splitting to produce hydrogen from water. The internally circulating fluidized bed of NiFe2O4/m-ZrO2 particles is directly heated by solar-simulated Xe light irradiation through a transparent quartz window mounted on top of the reactor. A sun simulator with three Xe lamps at laboratory scale has been newly installed in our laboratory for testing the fluidized bed reactor. The input power of incident Xe light can be scaled up to 2.6 kWth. Temperature distributions within the fluidized bed are measured under concentrated Xe light irradiation with an input power of 2.6 kWth. Hydrogen productivity and reactivity for the fluidized bed of NiFe2O4/m-ZrO2 particles are examined using two different reactors under the N2 flow rate and flow ratio, which yield a higher bed temperature. The feasibility of successive two-step water splitting using the fluidized bed reactor is examined by switching from N2 gas flow in the thermal reduction step to a steam/N2 gas mixture in the water decomposition step. It is confirmed that hydrogen production takes place in the single fluidized bed reactor by successive two-step water splitting.

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