A distributed charge transfer model for IT-SOFCs based on ceria electrolytes

A distributed charge transfer model for IT-SOFCs with MIEC electrolyte and composite electrodes is developed. A physically-based description of the electronic leakage current in the electrolyte is included, together with mass and charge conservation equations. The model is applied to simulate experimental polarization curves and impedance spectra collected on IT-SOFCs consisting of SDC electrolytes, Cu-Pd-CZ80 infiltrated anodes and LSCF/GDC composite cathodes. Hydrogen electro-oxidation experiments are examined (H2/N2humidified mixtures, 700â\u97¦C, 30â\u80\u93100% H2molar fraction). A significant increase of the ohmic resistance measured in the impedance spectra is revealed at decreasing the H2partial pressure or increasing the voltage (from 0.71 cm2at 100% H2to 0.81 cm2at 30% H2). Good agreement between the calculated and experimental polarization and EIS curves is achieved by fitting the exchange current density and the capacitance of each electrode. Model and theoretical analyses allow to rationalize the observed shift of the ohmic resistance, highlighting the key-role played by the electronic leakage current. Overall, the model is able to capture significant kinetic features of IT-SOFCs, and allows to gain insight into relevant parameters for the optimal design of the cell (electrochemically active thickness, current and potential distribution, mass diffusion gradients)

New insights into the dynamics that control the activity of ceria-zirconia solid solutions in thermochemical water splitting cycles

The reactivity of a ceria-rich Ce0.85Zr0.15O2 solid solution toward the thermochemical water splitting process (TWS) was studied over repeated H2/H2O redox cycles. The structural and surface modifications after treatment at high temperature under air or N2 atmospheres were characterized by high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and positron annihilation lifetime spectroscopy (PALS). Samples treated under nitrogen resulted more active due to phase segregation with formation of a zirconyl oxynitride phase in catalytic amount. Insertion of N3- into the structure contributes to an increase in the numbers of oxygen vacancies that preferably arrange in large clusters, and to the stabilization of Ce3+ centers on the surface. In comparison, treatment under air resulted in a different arrangement of defects with less Ce3+ and smaller and more numerous vacancy clusters. This affects charge transfer and H-coupling processes, which play an important role in boosting the rate of H2 production. The behavior is found to be only slightly dependent on the starting ceria-zirconia composition, and it is related to the development of a similar surface heterostructure configuration, characterized by the presence of at least a ceria-rich solid solution and a (cerium-doped) zirconyl oxynitride phase, which is supposed to act as a promoter for TWS reaction. The above findings confirm the importance of a multiphase structure in the design of ceria-zirconia oxides for water splitting reaction and allow a step forward to find an optimal composition. Moreover, the results indicate that doping with nitrogen might be a novel approach for the design of robust, thermally resistant, and redox active materials.Postprint (author's final draft

The Role of Neodymium in the Optimization of a Ni/CeO2 and Ni/CeZrO2 Methane Dry Reforming Catalyst

The development of a sustainable economy based on the use of renewable resources and the reduction of greenhouse gases emissions is an important mandate in modern societies to minimize the global warming. The CO2-reforming of methane through a conversion of CO2 and CH4 to syngas is a suitable process for this purpose and there is growing interest in the development of new catalysts for this process’ application at an industrial scale. This study is the first to investigate methane dry reforming activity of nickel supported on CeO2 and CeO2–ZrO2 solid solutions doped with neodymium. The supports were synthesized using a surfactant-assisted co-precipitation method and characterized through several analytical techniques to understand the role of synthesis parameters in the distribution of the dopant as well as in the properties of the supports. Co-doping with Zr and Nd resulted in an enhancement of dry reforming activity of ceria due to a higher dispersion of Ni and changes in the strength of basic sites. It was also shown that the addition of Nd helped to mitigate coking issues by increasing the mobility of surface oxygen in ceria and ceria–zirconia oxides and, accordingly, the rate of oxidation of carbonaceous deposits

Ceria Based Materials with Enhanced OSC Properties for H₂ Production by Water Splitting Reaction

A novel surfactant-assisted synthesis method was developed in our laboratory to enhance the oxygen storage capacity (OSC) and the thermo stability of a TWC catalyst based on zirconia and rare earth oxides. The same procedure was used to prepare ceria-zirconia compositions with different amounts of ceria, both doped and undoped with La and Nd. The potential use of these materials in a two-step solar thermochemical water splitting cycle for the production of H2 was investigated. For this purpose the O2 release of the materials was measured through thermogravimetric analysis in N2 at 1573K. Then all prepared compositions were subjected to an aging treatment at temperature above 1573K in air or in N2 flow and their activity in producing H2 via water splitting at 1073K was evaluated with respect to their structural evolution. The results obtained highlight that the reactivity depends on the temperature and atmosphere of the treatments and on the composition. The best result was obtained for the ceria rich composition treated at 1573K in N2 and for the corresponding doped composition treated in air

Water splitting reaction on ceria-zirconia solid solution driven by surface heterogeneity

Ce0.15Zr0.85O2 was investigated in the two-step water splitting reaction. High-temperature treatment in N-2 induced compositional and structural heterogeneities which contributed to a six-fold increase of H-2 yield after the first cycle. Ceria surface enrichment and the formation of a ceria-zirconia oxynitride phase positively affected the reduction and oxidation steps.Peer ReviewedPostprint (author's final draft

Water splitting reaction on Ce0.15Zr0.85O2 driven by surface heterogeneity

5siCe0.15Zr0.85O2 was investigated in the two-step water splitting reaction. High-temperature treatment in N-2 induced compositional and structural heterogeneities which contributed to a six-fold increase of H-2 yield after the first cycle. Ceria surface enrichment and the formation of a ceria-zirconia oxynitride phase positively affected the reduction and oxidation steps.nonenonePappacena, Alfonsina; Boaro, Marta; Armelao, Lidia; Llorca, Jordi; Trovarelli, AlessandroPappacena, Alfonsina; Boaro, Marta; Armelao, Lidia; Llorca, Jordi; Trovarelli, Alessandr

A modified coprecipitation synthesis of ceria based materials for fuel cell applications

Abstract: Ceria-samaria and ceria-zirconia mixed oxides have been prepared by a modified coprecipitation method (CP-H2O2) adding H2O2 to the water solution of the corresponding nitrates in order to obtain a material with improved catalytic properties versus the oxidation of light hydrocarbons. In fact, adding H2O2 during the coprecipitation of the oxides is an effective way to improve the reducibility at low temperature, the oxygen storage capacity (OSC) and the thermal resistance of these mixed oxide compositions. Several parameters of the synthesis such as the amount of H2O2 , pH, temperature and aging of the precipitate has been investigated and correlated with the structural and morphological characteristics of the oxides obtained. The materials have been also characterized in terms of its sintering capability and conductivity. Moreover the characteristics of the ceria-samaria oxides so prepared have been compared with those ones synthesized by other approaches and with one purchased. Ceria- samaria prepared by CP-H2O2 shown a higher surface area (SA) and OSC while the conductivity could be improved by an appropriate processing of powders. The aim of the work was to realize a material with enhanced catalytic properties, to be used as catalytic promoter in the intermediate temperature solid oxide fuel cell (ITSOFC) anode and cathode

The Role of Neodymium in the Optimization of a Ni/CeO2 and Ni/CeZrO2 Methane Dry Reforming Catalyst

The development of a sustainable economy based on the use of renewable resources and the reduction of greenhouse gases emissions is an important mandate in modern societies to minimize the global warming. The CO2-reforming of methane through a conversion of CO2 and CH4 to syngas is a suitable process for this purpose and there is growing interest in the development of new catalysts for this process\u2019 application at an industrial scale. This study is the first to investigate methane dry reforming activity of nickel supported on CeO2 and CeO2\u2013ZrO2 solid solutions doped with neodymium. The supports were synthesized using a surfactant-assisted co-precipitation method and characterized through several analytical techniques to understand the role of synthesis parameters in the distribution of the dopant as well as in the properties of the supports. Co-doping with Zr and Nd resulted in an enhancement of dry reforming activity of ceria due to a higher dispersion of Ni and changes in the strength of basic sites. It was also shown that the addition of Nd helped to mitigate coking issues by increasing the mobility of surface oxygen in ceria and ceria\u2013zirconia oxides and, accordingly, the rate of oxidation of carbonaceous deposits