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Electrochemical properties of LaCePr-oxide/K2WO4 composite electrolyte for low-temperature SOFCs
KTH, School of Industrial Engineering and Management (ITM), Energy Technology.ORCID iD: 0000-0002-3133-7031
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2017 (English)In: Electrochemistry communications, ISSN 1388-2481, E-ISSN 1873-1902, Vol. 77, p. 44-48Article in journal (Refereed) Published
Abstract [en]

In this study, we introduced tungstate into solid oxide fuel cells (SOFCs) for the first time by using a La/Pr-doped CeO2 (LCP)/K2WO4 composite as the electrolyte, which exhibited remarkably enhanced grain boundary conduction compared to that of single-phase LCP. The composition dependence of the electrical conductivity was investigated. As a result, the composite with 10 wt% K2WO4 was proven to be the optimum ratio, revealing a significantly higher ionic conductivity than LCP, along with a negligible electronic conductivity. The fuel cell using the LCP/K2WO4 electrolyte displayed an encouraging performance of 500 mW cm(-2) at 550 degrees C. These findings indicate that the LCP/K2WO4 composite is a promising electrolyte for low-temperature SOFCs.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE INC , 2017. Vol. 77, p. 44-48
Keywords [en]
Composite electrolyte, Solid oxide fuel cells, Electrical property, LaCePr-oxide, K2WO4
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-206690DOI: 10.1016/j.elecom.2016.12.013ISI: 000399510400011Scopus ID: 2-s2.0-85013435367OAI: oai:DiVA.org:kth-206690DiVA, id: diva2:1094068
Note

QC 20170509

Available from: 2017-05-09 Created: 2017-05-09 Last updated: 2018-09-14Bibliographically approved
In thesis
1. Development of Natural Mineral Composites for Low-Temperature Solid Oxide Fuel Cells
Open this publication in new window or tab >>Development of Natural Mineral Composites for Low-Temperature Solid Oxide Fuel Cells
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Solid oxide fuel cells (SOFCs) have attracted growing attention worldwide because of their high conversion efficiency and low emissions when paired with clean fuel sources. Currently, reducing the temperature of SOFC to a low-temperature (LT) range is a mainstream trend of SOFC research. One effective way to reach this target is to explore alternative electrolytes that can maintain a desirable ionic conductivity at low temperatures. Meanwhile, it has been found that natural minerals hold great potential as functional materials for energy conversion technologies, especially ion-conducting hematite and rare-earth oxides. This thesis presents an experimental investigation of novel composite electrolytes based on two common natural minerals: hematite (LW) (α-Fe2O3) and La0.33Ce0.62Pr0.05O2-δ (LCP) for LT-SOFCs application. Initially, hematite (LW) and LCP are characterized and demonstrated as electrolytes in SOFCs. It is found the hematite ore is a mixture of α-Fe2O3, silica, and calcite, while the LCP mineral is a La/Pr co-doped CeO2. Both hematite (LW) and LCP cells exhibit encouraging performance with power densities of 150-225 and 295-401 mW cm-2 at 500-600 ℃, respectively.

Following above findings, two mineral based nanocomposites – hematite-LCP and LCP/K2WO4 – are developed. Electrochemical and electrical studies reveal that the hematite-LCP gains a significantly enhanced conductivity (0.116 S cm-1 at 600 ℃) compared to individual hematite (LW) and LCP. The hematite-LCP based SOFC exhibits attractive power densities of 386-625 mW cm-2 at 450-600 ℃. Further investigation indicates that heterophasic interfacial conduction plays a crucial role in resulting in the good performance. Another composite LCP/K2WO4 is synthesized from LCP and tungstate through a wet-chemical route. The obtained composites exhibit enhanced grain boundary conduction compared to that of LCP. The composition dependence of the electrical conductivity has been studied, indicating that 90 wt% LCP/10 wt% K2WO4 is the optimum proportion with highest ionic conductivity and negligible electronic conductivity. The corresponding SOFC displays the highest power density of 500 mW cm-2 at 550 ℃. 

Furthermore, by incorporating a semiconductor La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) into LCP and hematite-LCP, respectively, two semiconducting-ionic composites LCP-LSCF and hematite/LCP-LSCF are designed. Crystallographic and morphological characterizations are carried out to gain insight into the material features, and the two composites are applied as the intermediate membrane layer in LT electrolyte-layer free fuel cells (EFFCs). Investigations in terms of conductivity and fuel cell performance reveal that the two composites obtain improved ionic conductivities and cell power outputs compared with those of LCP and hematite-LCP. It is also found the two composites possess mixed ionic and electronic conductivities, which are balanced in the optimal composites. Additionally, stability and Schottky junction of the best-performance EFFC are studied to verify its reliability. 

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2018. p. 114
Series
TRITA-ITM-AVL ; 2018:44
Keywords
Natural hematite; Natural rare-earth; LT-SOFCs; composite electrolytes; material characterization; conductivity; electrochemical performance.
National Category
Chemical Engineering Composite Science and Engineering
Research subject
Chemical Engineering; Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-235055 (URN)978-91-7729-942-4 (ISBN)
Public defence
2018-10-11, Kollegiesalen, Brinellvägen 8, Stockholm, 10:00 (English)
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Supervisors
Note

QC 20180917

Available from: 2018-09-17 Created: 2018-09-14 Last updated: 2018-09-17Bibliographically approved

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