The effect of Co and Zn addition on densification and electrical properties of ceria-based nanopowders

CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIORIn this work, cobalt and zinc-doped Ce0.8Gd0.2O1.9 samples were prepared starting from a commercial nanopowder and compared to the undoped material. The powder samples were pressed and afterwards sintered by a two-step procedure, before characterization by X-Ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Impedance Spectroscopy (IS) in air. Cobalt or zinc additions are effective as sintering aid, allowing peak sintering temperatures around 1000 degrees C to reach densifications above of 93% of theoretical density, showing no evidence for the presence of secondary phases. The total conductivity at 800 degrees C of pressed Zn-doped samples (6.7x10(-2) S/cm) and Co-doped samples (7.5x10(-2) S/cm) is similar for undoped samples (7.2x10(-2) S/cm) showing that Zn and Co has a positive effect on densification without compromising the electrical conductivity.In this work, cobalt and zinc-doped Ce0.8Gd0.2O1.9 samples were prepared starting from a commercial nanopowder and compared to the undoped material. The powder samples were pressed and afterwards sintered by a two-step procedure, before characterization by X-Ray Diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Impedance Spectroscopy (IS) in air. Cobalt or zinc additions are effective as sintering aid, allowing peak sintering temperatures around 1000 degrees C to reach densifications above of 93% of theoretical density, showing no evidence for the presence of secondary phases. The total conductivity at 800 degrees C of pressed Zn-doped samples (6.7x10(-2) S/cm) and Co-doped samples (7.5x10(-2) S/cm) is similar for undoped samples (7.2x10(-2) S/cm) showing that Zn and Co has a positive effect on densification without compromising the electrical conductivity.19510571063CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIORCNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOCAPES - COORDENAÇÃO DE APERFEIÇOAMENTO DE PESSOAL DE NÍVEL SUPERIORSem informaçãoSem informaçãoFinancial supports from CAPES and CNPq are greatly appreciated. We would like to thank Rita C. G. Vinhas (State University of Campinas, Campinas Campus, Brazil), for helping with the XPS measurements

Mixed Ionic-Electronic Conducting Membranes (MIEC) for Their Application in Membrane Reactors: A Review

Mixed ionic-electronic conducting membranes have seen significant progress over the last 25 years as efficient ways to obtain oxygen separation from air and for their integration in chemical production systems where pure oxygen in small amounts is needed. Perovskite materials are the most employed materials for membrane preparation. However, they have poor phase stability and are prone to poisoning when subjected to CO2 and SO2, which limits their industrial application. To solve this, the so-called dual-phase membranes are attracting greater attention. In this review, recent advances on self-supported and supported oxygen membranes and factors that affect the oxygen permeation and membrane stability are presented. Possible ways for further improvements that can be pursued to increase the oxygen permeation rate are also indicated. Lastly, an overview of the most relevant examples of membrane reactors in which oxygen membranes have been integrated are provided.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 679933. The present publication reflects only the author’s views and the European Union is not liable for any use that may be made of the information contained therein

Challenges in Fabricating Solid Oxide Fuel Cell Stacks for Portable Applications: A Short Review

Despite being the most efficient and quiet operation type of fuel cells, solid oxide fuel cells (SOFCs) deal with several constraints in terms of fabrication cost, material selection and durability issues due to their high operating temperature. The high operating temperature of SOFCs limits their stationary and large-scale applications. Moreover, these constraints restrict the commercialization of portable SOFCs. Therefore, the operation temperature of SOFCs must be reduced to overcome the aforementioned problems. However, this task is challenging because the operation temperature mainly affects the material preparation and the stack design to produce the electrical power needed for small-scale applications. This paper provides an overview of the challenges faced by each component such as the materials, the design of stack, fabrication cost and related research in fabricating high power SOFC stacks

Development of dual-layer hollow fiber with modified electrolyte for micro-tubular solid oxide fuel cell

The excellent ionic conductivity at temperature ranges from 400-700 °C has made cerium gadolinium oxide (CGO) as one of promising alternative solid electrolyte materials for intermediate temperature solid oxide fuel cell (IT-SOFC) application. However, the requirement of high sintering temperature up to 1550 °C for densification of CGO electrolyte complicates the cell fabrication process as it reduces the porosity in the electrode layers, particularly in the co-sintering step of anode/electrolyte dual-layer hollow fiber (DLHF). Hence, the fabrication of the DLHF is challenging due to the different sintering behaviors of the each layer. The main objective of this study is to develop anode/electrolyte DLHFs with improved electrolyte properties with reduced co-sintering temperature for IT-SOFCs via a single-step phase inversion-based co-extrusion/co-sintering technique. The sintering properties of electrolyte flat sheet was studied by comparing two approaches, (i) using mix particle size electrolyte and (ii) addition of lithium oxide as sintering additive in the electrolyte. The DLHF with modified electrolyte was later fabricated by phase inversion based co-extrusion and co-sintered at temperature ranging from 1400 to 1500 °C. The DLHF was evaluated in term of the morphology, mechanical strength and gas-tightness as well as electrical conductivity, porosity and permeability of the anode layer. This study showed that a dense CGO flat sheet layer sintered at 1450 °C with the addition of 30% nano size CGO particles were obtained. Meanwhile, the doping of 2 mol% of lithium nitrate into CGO was found to reduce the sintering temperature to 1400 °C. When the co-sintering temperature increased, the mechanical strength, gas-tightness and electrical conductivity were increased, whereas the porosity and permeability of the anode layer were decreased. The DLHF that was co-sintered at 1450 °C showed sufficient properties and therefore, it was chosen for the construction of micro-tubular SOFC (MT-SOFC). When comparing the maximum power density of MT-SOFC namely nickel (Ni)-CGO/CGO (unmodified), Ni-CGO/30%nano-70%micron CGO (first approach) and Ni- CGO/lithium (Li)-CGO (second approach); it was found that the Ni-CGO/30%nano- 70%micron CGO cell performed the best. At 500 °C, the cell produced the highest maximum power density, which was 275 Wm-2 as compared to Ni-CGO/Li-CGO cell (60 Wm-2) and Ni-CGO/CGO cell (200 Wm-2). Porous anode in Ni- CGO/30%nano-70%micron CGO DLHF provided active reaction site, while dense electrolyte layer resulted from pore filling caused by the introduction of 30% nano sized CGO particles improved the gas-tightness of the electrolyte. Meanwhile, the closed pore caused by the migration of Li ions in anode sponge–like region of Ni- CGO/Li-CGO hindered the triple phase boundary region that impaired the cell performance. This limited the inclusion of Li in DLHF design. Nevertheless, the results from this study has proven the feasibilities to accelerate the densification of electrolyte as well as presented an advanced electrolyte material for MT-SOFC

Au/CeO2 Catalysts: Structure and CO Oxidation Activity

In this comprehensive review, the main aspects of using Au/CeO2 catalysts in oxidation reactions are considered. The influence of the preparation methods and synthetic parameters, as well as the characteristics of the ceria support (presence of doping cations, oxygen vacancies concentration, surface area, redox properties, etc.) in the dispersion and chemical state of gold are revised. The proposed review provides a detailed analysis of the literature data concerning the state of the art and the applications of gold–ceria systems in oxidation reactionsPeer reviewe

Au/CeO2 catalysts: structure and CO oxidation activity

In this comprehensive review, the main aspects of using Au/CeO2 catalysts in oxidation reactions are considered. The influence of the preparation methods and synthetic parameters, as well as the characteristics of the ceria support (presence of doping cations, oxygen vacancies concentration, surface area, redox properties, etc.) in the dispersion and chemical state of gold are revised. The proposed review provides a detailed analysis of the literature data concerning the state of the art and the applications of gold–ceria systems in oxidation reaction