Solid Oxide Cells (SOC) are the kind of electrochemical devices that provide reversible, dual mod... more Solid Oxide Cells (SOC) are the kind of electrochemical devices that provide reversible, dual mode operation, where electricity is generated in a fuel cell mode and fuel is produced in an electrolysis mode. Our current work encompasses the design, fabrication, and performance analysis of a micro-tubular reversible SOC that is prepared through a single dip-coating technique with multiple dips using conventional materials. Electrochemical impedance and current-voltage responses were monitored from 700 to 800 °C. Maximum power densities of the cell achieved at 800, 750, and 700 °C, was 690, 546, and 418 mW cm−2, respectively. The reversible, dual mode operation of the SOC was evaluated by operating the cell using 50% H2O/H2 and ambient air. Accordingly, when the SOC was operated in the electrolysis mode at 1.3 V (the thermo-neutral voltage for steam electrolysis), current densities of −311, −487 and −684 mA cm−2 at 700, 750 and 800 °C, respectively, were observed. Hydrogen production r...
Reversible solid-oxide fuel cells (rSOFC) attract enormous attentions because of their capability... more Reversible solid-oxide fuel cells (rSOFC) attract enormous attentions because of their capability to operate in both fuel cell and electrolysis modes. rSOFC with a tubular cell design has multiple advantages over a planar design for example allowing faster startup and shutdown. Successful fabrication of tubular cells needs to overcome numerous technological challenges, including control of its mechanical stress and high interlayer electrode resistance. The scope of the present work involves fabrication and testing of anode supported rSOFC single cells using both ionic conducting electrolyte and protonic conducting electrolyte. For the ionic conducting cells, the rSOFCs constituted Ni + yttria-stabilized zirconia (YSZ) anode support tube, Ni + scandia-stabilized zirconia (ScSZ) anode functional layer, scandia-stabilized zirconia (ScSZ) electrolyte, samarium doped ceria (SDC) protective layer, La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) + SDC cathode functional layer, and LSCF cathode current colle...
A controllable and gradient porous structure is desirable for many applications including solid o... more A controllable and gradient porous structure is desirable for many applications including solid oxide fuel cells (SOFC) electrodes. A SOFC contains a minimum three basic ceramic thin films with a thin yet dense electrolyte layer separates the adjacent porous anode and cathode layers. In general, the thinner the electrolyte layer, the smaller the ohmic resistance would be. The anode and cathode layers need to be porous so to allow gases (e.g. H2 and O2) to easily penetrate to the triple-phase boundary (TPB). At the same time the anode and cathode layers serve as the paths of removing the electrons generated at the TPBs. Properly design and fabricated porous electrode microstructure could greatly increase the connectedness of gas, electrons and/or protons/oxygen ions, and therefore reduce the gas diffusion and ohmic resistances of the SOFC electrodes and boost the overall fuel cell performance. Although there are electrolyte- and cathode- supported SOFC developers, the most used confi...
Equilibrium phase fields of the Pb-Fe-O ternary system were identified by longterm equilibrations... more Equilibrium phase fields of the Pb-Fe-O ternary system were identified by longterm equilibrations at a temperature range of 998K - 1048K and characterization of phases by XRD. The following phase fields were identified: (1) Pb – Fe – FeO, (2) Pb – FeO – Fe3O4 (3) Pb – Fe3O4 – PbFe4O7, (4) Pb – PbFe4O7 – PbFe2O5, (5) Pb – Pb2Fe2O5 – PbO, (6) Fe3O4 – PbFe4O7 – PbFe12O19, (7) PbFe12O19 - Fe3O4 –Fe2O3. Based on the results of this study, a partial phase diagram of Pb-Fe-O system was established.
The thermodynamic stability of lanthanide cobaltites is also a function of their existing oxygen ... more The thermodynamic stability of lanthanide cobaltites is also a function of their existing oxygen non-stoichiometry.
Calculated energetics provide key insights into the stability of lead-free alkali niobate and tan... more Calculated energetics provide key insights into the stability of lead-free alkali niobate and tantalate perovskites.
Chemistry (Weinheim an der Bergstrasse, Germany), Jan 23, 2015
Alkali niobates and tantalates are currently important lead-free functional oxides. The formation... more Alkali niobates and tantalates are currently important lead-free functional oxides. The formation and decomposition energetics of potassium tantalum oxide compounds (K2 OTa2 O5 ) were measured by high-temperature oxide melt solution calorimetry. The enthalpies of formation from oxides of KTaO3 perovskite and defect pyrochlores with K/Ta ratio of less than 1 stoichiometry-K0.873 Ta2.226 O6 , K1.128 Ta2.175 O6 , and K1.291 Ta2.142 O6 -were experimentally determined, and the values are (-203.63±2.92) kJ mol(-1) for KTaO3 perovskite, and (-339.54±5.03) kJ mol(-1) , (-369.71±4.84) kJ mol(-1) , and (-364.78±4.24) kJ mol(-1) , respectively, for non-stoichiometric pyrochlores. That of stoichiometric defect K2 Ta2 O6 pyrochlore, by extrapolation, is (-409.87±6.89) kJ mol(-1) . Thus, the enthalpy of the stoichiometric pyrochlore and perovskite at K/Ta=1 stoichiometry are equal in energy within experimental error. By providing data on the thermodynamic stability of each phase, this work suppl...
Nanocrystalline yttria stabilized zirconia (YSZ) solid electrolyte powders of composition ZrO2-5 ... more Nanocrystalline yttria stabilized zirconia (YSZ) solid electrolyte powders of composition ZrO2-5 mol% Y2O3 were prepared through modified Pechini process and were characterized. Sintered compacts of these powders in form of pellets had 96% of the theoretical density and helium leak rate <10-9 S cc /s. Using a pellet of this electrolyte in a galvanic cell with different oxygen partial pressures across it, emf was measured as a function of temperature and thus qualified for sensor application. Towards the fabrication of the oxygen sensor for Pb and LBE loop, a compact design wherein a YSZ pellet, glass soldered to a metallic component had been chosen for the oxygen meter.
ABSTRACT Heat capacities of PbCrO4(s), Pb2CrO5(s), and Pb5CrO8(s) were measured by differential s... more ABSTRACT Heat capacities of PbCrO4(s), Pb2CrO5(s), and Pb5CrO8(s) were measured by differential scanning calorimetry. The measured heat capacities as a function of temperature are expressed as C p J K−1 mol−1 = 150.37 + 27.74 × 10−3 T − 2.80 × 106 T −2 (T = 300–750 K), C p J K−1 mol−1 = 194.55 + 76.09 × 10−3 T − 4.64 × 106 T −2 (T = 300–700 K), and C p J K−1 mol−1 = 323.35 + 184.80 × 10−3 T − 5.48 × 106 T −2 (T = 300–600 K). From the measured heat capacity data, thermodynamic functions such as enthalpy increments, entropies, and Gibbs energy functions were derived. Graphical Abstract .
Solid Oxide Cells (SOC) are the kind of electrochemical devices that provide reversible, dual mod... more Solid Oxide Cells (SOC) are the kind of electrochemical devices that provide reversible, dual mode operation, where electricity is generated in a fuel cell mode and fuel is produced in an electrolysis mode. Our current work encompasses the design, fabrication, and performance analysis of a micro-tubular reversible SOC that is prepared through a single dip-coating technique with multiple dips using conventional materials. Electrochemical impedance and current-voltage responses were monitored from 700 to 800 °C. Maximum power densities of the cell achieved at 800, 750, and 700 °C, was 690, 546, and 418 mW cm−2, respectively. The reversible, dual mode operation of the SOC was evaluated by operating the cell using 50% H2O/H2 and ambient air. Accordingly, when the SOC was operated in the electrolysis mode at 1.3 V (the thermo-neutral voltage for steam electrolysis), current densities of −311, −487 and −684 mA cm−2 at 700, 750 and 800 °C, respectively, were observed. Hydrogen production r...
Reversible solid-oxide fuel cells (rSOFC) attract enormous attentions because of their capability... more Reversible solid-oxide fuel cells (rSOFC) attract enormous attentions because of their capability to operate in both fuel cell and electrolysis modes. rSOFC with a tubular cell design has multiple advantages over a planar design for example allowing faster startup and shutdown. Successful fabrication of tubular cells needs to overcome numerous technological challenges, including control of its mechanical stress and high interlayer electrode resistance. The scope of the present work involves fabrication and testing of anode supported rSOFC single cells using both ionic conducting electrolyte and protonic conducting electrolyte. For the ionic conducting cells, the rSOFCs constituted Ni + yttria-stabilized zirconia (YSZ) anode support tube, Ni + scandia-stabilized zirconia (ScSZ) anode functional layer, scandia-stabilized zirconia (ScSZ) electrolyte, samarium doped ceria (SDC) protective layer, La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) + SDC cathode functional layer, and LSCF cathode current colle...
A controllable and gradient porous structure is desirable for many applications including solid o... more A controllable and gradient porous structure is desirable for many applications including solid oxide fuel cells (SOFC) electrodes. A SOFC contains a minimum three basic ceramic thin films with a thin yet dense electrolyte layer separates the adjacent porous anode and cathode layers. In general, the thinner the electrolyte layer, the smaller the ohmic resistance would be. The anode and cathode layers need to be porous so to allow gases (e.g. H2 and O2) to easily penetrate to the triple-phase boundary (TPB). At the same time the anode and cathode layers serve as the paths of removing the electrons generated at the TPBs. Properly design and fabricated porous electrode microstructure could greatly increase the connectedness of gas, electrons and/or protons/oxygen ions, and therefore reduce the gas diffusion and ohmic resistances of the SOFC electrodes and boost the overall fuel cell performance. Although there are electrolyte- and cathode- supported SOFC developers, the most used confi...
Equilibrium phase fields of the Pb-Fe-O ternary system were identified by longterm equilibrations... more Equilibrium phase fields of the Pb-Fe-O ternary system were identified by longterm equilibrations at a temperature range of 998K - 1048K and characterization of phases by XRD. The following phase fields were identified: (1) Pb – Fe – FeO, (2) Pb – FeO – Fe3O4 (3) Pb – Fe3O4 – PbFe4O7, (4) Pb – PbFe4O7 – PbFe2O5, (5) Pb – Pb2Fe2O5 – PbO, (6) Fe3O4 – PbFe4O7 – PbFe12O19, (7) PbFe12O19 - Fe3O4 –Fe2O3. Based on the results of this study, a partial phase diagram of Pb-Fe-O system was established.
The thermodynamic stability of lanthanide cobaltites is also a function of their existing oxygen ... more The thermodynamic stability of lanthanide cobaltites is also a function of their existing oxygen non-stoichiometry.
Calculated energetics provide key insights into the stability of lead-free alkali niobate and tan... more Calculated energetics provide key insights into the stability of lead-free alkali niobate and tantalate perovskites.
Chemistry (Weinheim an der Bergstrasse, Germany), Jan 23, 2015
Alkali niobates and tantalates are currently important lead-free functional oxides. The formation... more Alkali niobates and tantalates are currently important lead-free functional oxides. The formation and decomposition energetics of potassium tantalum oxide compounds (K2 OTa2 O5 ) were measured by high-temperature oxide melt solution calorimetry. The enthalpies of formation from oxides of KTaO3 perovskite and defect pyrochlores with K/Ta ratio of less than 1 stoichiometry-K0.873 Ta2.226 O6 , K1.128 Ta2.175 O6 , and K1.291 Ta2.142 O6 -were experimentally determined, and the values are (-203.63±2.92) kJ mol(-1) for KTaO3 perovskite, and (-339.54±5.03) kJ mol(-1) , (-369.71±4.84) kJ mol(-1) , and (-364.78±4.24) kJ mol(-1) , respectively, for non-stoichiometric pyrochlores. That of stoichiometric defect K2 Ta2 O6 pyrochlore, by extrapolation, is (-409.87±6.89) kJ mol(-1) . Thus, the enthalpy of the stoichiometric pyrochlore and perovskite at K/Ta=1 stoichiometry are equal in energy within experimental error. By providing data on the thermodynamic stability of each phase, this work suppl...
Nanocrystalline yttria stabilized zirconia (YSZ) solid electrolyte powders of composition ZrO2-5 ... more Nanocrystalline yttria stabilized zirconia (YSZ) solid electrolyte powders of composition ZrO2-5 mol% Y2O3 were prepared through modified Pechini process and were characterized. Sintered compacts of these powders in form of pellets had 96% of the theoretical density and helium leak rate <10-9 S cc /s. Using a pellet of this electrolyte in a galvanic cell with different oxygen partial pressures across it, emf was measured as a function of temperature and thus qualified for sensor application. Towards the fabrication of the oxygen sensor for Pb and LBE loop, a compact design wherein a YSZ pellet, glass soldered to a metallic component had been chosen for the oxygen meter.
ABSTRACT Heat capacities of PbCrO4(s), Pb2CrO5(s), and Pb5CrO8(s) were measured by differential s... more ABSTRACT Heat capacities of PbCrO4(s), Pb2CrO5(s), and Pb5CrO8(s) were measured by differential scanning calorimetry. The measured heat capacities as a function of temperature are expressed as C p J K−1 mol−1 = 150.37 + 27.74 × 10−3 T − 2.80 × 106 T −2 (T = 300–750 K), C p J K−1 mol−1 = 194.55 + 76.09 × 10−3 T − 4.64 × 106 T −2 (T = 300–700 K), and C p J K−1 mol−1 = 323.35 + 184.80 × 10−3 T − 5.48 × 106 T −2 (T = 300–600 K). From the measured heat capacity data, thermodynamic functions such as enthalpy increments, entropies, and Gibbs energy functions were derived. Graphical Abstract .
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