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Application of Rare-Earth Doped Ceria and Natural Minerals for Solid Oxide Fuel Cells
KTH, School of Industrial Engineering and Management (ITM), Energy Technology. (Solid Oxide Fuel Cells)ORCID iD: 0000-0003-1479-0464
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Although solid oxide fuel cell (SOFC) technology exhibits considerable advantages as compared to other energy conversion devices, e.g. high efficiency, low emission and fuel flexibility, its high operating temperature leads to rapid component degradation and has thus hampered commercialization. In recent years, intensive research interests have been devoted to lowering the operating temperature from the elevated temperature region (800-1,000 ℃) to intermediate or low-temperature range (<800 ℃). To achieve this goal, material selection plays a dominant role, involving improving the conductivity of existing electrolytes and developing new exploitable materials. This dissertation is focused on enhancing the ionic conductivity of rare-earth oxides (principally doped ceria) and exploring new candidate materials (e.g. natural minerals) for low temperature (LT) SOFCs.

In this work, the scientific contributions can be divided into four aspects:

i)                To develop desirable superionic conductors, Sm3+/Pr3+/Nd3+ triple-doped ceria is designed to realize the desired doping for Sm3+ in bulk and Pr3+/Nd3+ at surface domains via a two-step wet chemical co-precipitation method. It exhibits high ionic conductivity, 0.125 S cm-1 at 600 ℃. The SOFC device using this material as electrolyte displays a high output power density of 710 mW cm-2 at 550 ℃.

ii)              To further clarify the individual effect of Pr3+ in the doped ceria, a single-element (Pr3+) doped ceria is studied, exhibiting a mixed electronic/ionic conduction property, capable of being employed as the core component of electrolyte-layer free solid oxide fuel cells (EFFCs).

iii)             To investigate various rare-earth doped-ceria materials in double- and triple-element doping solutions for LT-SOFCs, Sm3+/Ca2+ co-doped ceria and La3+/Pr3+/Nd3+ triple-doped ceria are synthesized and then further incorporated with semiconductors, e.g. La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) or Ni0.8Co0.15Al0.05Li-oxide (NCAL), to serve as a semiconducting-ionic conducting membrane in EFFCs.

iv)             To exploit the feasibility of natural mineral cuprospinel (CuFe2O4) as an alternative material for LT-SOFCs, three different types of fuel cell devices are fabricated and tested. The device using CuFe2O4 as cathode exhibits a maximum power density of 180 mW cm-2 with an open circuit voltage of 1.07 V at 550 °C, while the device using a homogeneous mixture membrane of CuFe2O4, Li2O-ZnO-Sm0.2Ce0.8O2 (LZSDC), and LiNi0.8Co0.15Al0.05O2 (NCAL) demonstrates an improved power output, 587 mW cm-2 under the same measurement conditions.  

Based on this work, a new triple-doping strategy is exploited to improve the ionic conductivity of doped ceria materials by surface- and bulk-doping methodology. Furthermore, the material developments of single-phase mixed electronic/ionic conducting doped ceria and doped ceria/semiconductor composites are realized and verify the feasibility of EFFC technology. Investigations on CuFe2O4 indicate the utility of natural minerals in developing cost-effective materials for LT-SOFCs.    

Abstract [sv]

Även om fastoxid bränslecellers (SOFC) uppvisar signifikanta fördelar jämfört med andra energiomvandlingstekniker, t.ex. hög verkningsgrad, låga emissioner och bränsleflexibilitet, leder dess höga driftstemperatur till snabb komponentdegradering, vilken har hindrat kommersialiseringen. Under de senaste åren har intensiv forskning ägnats åt att sänka driftstemperaturerna från de höga temperaturregionerna (800-1,000 °C) till mellanliggande eller låga temperaturintervaller (<800 ℃). För att uppnå detta mål spelar materialvalet en dominerande roll, vilket bland annat innebär att man förbättrar ledningsförmågan hos befintliga elektrolyter och utvecklar nya material. Denna avhandling fokuserar på att förbättra den jonledande förmågan hos oxider av sällsynta jordartsmetaller, huvudsakligen dopad ceriumoxid, samt forskning på nya kandidatmaterial, t.ex. naturliga mineraler.

I det här arbetet kan det vetenskapliga bidraget delas in i fyra aspekter:

i)                Att utveckla en trippel-dopingmetodik för att syntetisera önskvärda superjoniska ledningsförmågor i Sm3+/Pr3+/Nd3+ dopad ceriumoxid. Detta material konstruerades med hjälp av en tvåstegs våtkemisk samutfällningsmetod för att åstadkomma en önskad dopning för Sm3+ i bulk och Pr3+/Nd3+ vid ytdomäner. Materialet uppvisar en hög jonisk ledningsförmåga, 0.125 S cm-1 vid 600 ℃. En SOFC-enhet som använder denna trippeldopade ceriumoxid som elektrolyt har uppvisat en hög effekttäthet på 710 mW cm-2 vid 550 ℃;

ii)              För att ytterligare klargöra den individuella effekten av Pr3+ i det dopade ceriummaterialet studerades enfas Pr-dopade ceria, vilken uppvisade en blandad elektronisk/jonisk ledningsegenskap som skulle användas som kärnkomponent i avancerad elektrolytskiktsfri fastoxid bränsleceller (EFFC).

iii)             Att undersöka olika sällsynta jordartade dopade ceriummaterial i lösningar med dubbel- och trippelelement (Sm3+/Ca2+ och La3+/Pr3+/Nd3+) applicerade för SOFC-teknik med låg temperatur. De dubbel- och tripeldopade ceriummaterialen var sammansatta med halvledare, dvs Ni0.8Co0.15Al0.05Li-oxid (NCAL) och La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) för att fungera som en halvledande jonisk ledande membran i EFFCs.

iv)             Att utnyttja naturligt kopparspinell (CuFe2O4) som ett alternativt material för SOFC. För första gången tillverkades tre olika typer av anordningar för att undersöka den optimala appliceringen av CuFe2O4 i SOFC. Enheten med CuFe2O4 som katodkatalysator uppvisade en maximal effekttäthet av 180 mW cm-2 med en öppen kretsspänning 1.07 V vid 550 ℃. En effekttäthet på 587 mW cm-2 emellertid uppnådes från anordningen bestående av ett homogentblandat membran med CuFe2O4, Li2O-ZnO-Sm0.2Ce0.8O2 och LiNi0.8Co0.15Al0.05O2.

Baserat på detta arbete utnyttjades en ny strategi för att förbättra jonledningsförmågan hos dopade ceriummaterial genom yt- och bulkdopningsmetodik. Vidare verifierades utvecklingen av EFFC-teknikens tillförlitlighet av enfasad, blandad elektronisk/jonledande dopade ceriumoxid samt jonledande multidopade ceria-och halvledarkompositer. Dessa resultat visar att naturliga mineraler kan spela en viktig roll för att utveckla kostnadseffektiva material för bränsleceller.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2019. , p. 109
Series
TRITA-ITM-AVL ; 2019:24
Keywords [en]
Low-temperature solid oxide fuel cells; Doped ceria; Material characterizations; Electrochemical performances; Natural minerals
Keywords [sv]
Lågtemperatur fastoxidbränsleceller; Dopade ceriumoxid; Materialkarakteriseringar; Elektrokemiska prestanda; Naturliga mineraler.
National Category
Engineering and Technology Energy Engineering
Research subject
Energy Technology; Materials Science and Engineering; Chemical Engineering
Identifiers
URN: urn:nbn:se:kth:diva-257718ISBN: 978-91-7873-277-7 (print)OAI: oai:DiVA.org:kth-257718DiVA, id: diva2:1347923
Public defence
2019-09-27, K1, Teknikringen 56, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2019-09-03 Created: 2019-09-02 Last updated: 2019-09-03Bibliographically approved
List of papers
1. Superionic Conductivity of Sm3+, Pr3+, and Nd3+ Triple-Doped Ceria through Bulk and Surface Two-Step Doping Approach
Open this publication in new window or tab >>Superionic Conductivity of Sm3+, Pr3+, and Nd3+ Triple-Doped Ceria through Bulk and Surface Two-Step Doping Approach
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2017 (English)In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 9, no 28, p. 23614-23623Article in journal (Refereed) Published
Abstract [en]

Sufficiently high oxygen ion conductivity of electrolyte is critical for good performance of low-temperature solid oxide fuel cells (LT-SOFCs). Notably, material conductivity, reliability, and manufacturing cost are the major barriers hindering LT-SOFC commercialization. Generally, surface properties control the physical and chemical functionalities of materials. Hereby, we report a Sm3+, Pr3+, and Nd3+ triple-doped ceria, exhibiting the highest ionic conductivity among reported doped-ceria oxides, 0.125 S cm(-1) at 600 degrees C. It was designed using a two-step wet-chemical coprecipitation method to realize a desired doping for Sm3+ at the bulk and Pr3+/Nd3+ at surface domains (abbreviated as PNSDC). The redox couple Pr3+ Pr4+ contributes to the extraordinary ionic conductivity. Moreover, the mechanism for ionic conductivity enhancement is demonstrated. The above findings reveal that a joint bulk and surface doping methodology for ceria is a feasible approach to develop new oxide-ion conductors with high impacts on advanced LT-SOFCs.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2017
Keywords
LT-SOFCs, doped ceria, bulk and surface doping, oxygen ion conductivity, redox
National Category
Ceramics
Identifiers
urn:nbn:se:kth:diva-212346 (URN)10.1021/acsami.7b02224 (DOI)000406172700035 ()2-s2.0-85024920908 (Scopus ID)
Funder
Swedish Research Council, 621-2011-4983EU, FP7, Seventh Framework Programme, 303454
Note

QC 20170821

Available from: 2017-08-21 Created: 2017-08-21 Last updated: 2019-09-03Bibliographically approved
2. A Single-Phase Mixed-Conductive Pr-Doped CeO2 Membrane for Advanced Fuel-to-Electricity Technology
Open this publication in new window or tab >>A Single-Phase Mixed-Conductive Pr-Doped CeO2 Membrane for Advanced Fuel-to-Electricity Technology
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Pr-doped CeO2 has exhibited many interesting properties relying on the flexible valence of praseodymium. The tailorable doping contents of praseodymium determine the ionic or mixed electronic-ionic conductivity properties of the Pr-doped CeO2. Interestingly, the characteristic feature that praseodymium element preferably attributes on the surface of ceria particles facilitates the surface exchange kinetics for oxygen transport relying on oxygen vacancies and resulting in high ionic conduction. Hereby, we investigated a 10 mol.% Pr-doped CeO2 (Pr-CeO2) synthesized by hydrothermal method focusing on its surface conductive properties. The as-prepared Pr-CeO2 exhibited a high electrical conductivity of 0.36 S cm-1 at 600 ℃. Using this mixed conductive Pr-CeO2, we fabricated a solid oxide fuel cell (SOFC) device in a ‘sandwich’ configuration while p-type semiconductor Ni0.8Co0.15Al0.05Li-oxide was pasted on both sides of Pr-CeO2 membrane layer. This device exhibited a comparable peak power density of 776 mW cm-2 at 600 ℃ to the conventional ionic conducting electrolyte-based SOFCs. Furthermore, the mechanism for surface conductivity enhancement has been discussed. These findings reveal an alternative methodology to prepare materials with significant impacts on advanced R&D SOFC technology.

National Category
Engineering and Technology Materials Engineering
Identifiers
urn:nbn:se:kth:diva-256523 (URN)
Note

QC 20190903

Available from: 2019-08-27 Created: 2019-08-27 Last updated: 2019-09-03Bibliographically approved
3. Industrial grade rare-earth triple-doped ceria applied for advanced low-temperature electrolyte layer-free fuel cells
Open this publication in new window or tab >>Industrial grade rare-earth triple-doped ceria applied for advanced low-temperature electrolyte layer-free fuel cells
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2017 (English)In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 42, no 34, p. 22273-22279Article in journal (Refereed) Published
Abstract [en]

In this study, the mixed electron-ion conductive nanocomposite of the industrial-grade rare-earth material (Le(3+), Pr3+ and Nd3+ triple-doped ceria oxide, noted as LCPN) and commercial p-type semiconductor Ni0.8Co0.15Al0.05Li-oxide (hereafter referred to as NCAL) were studied and evaluated as a functional semiconductor-ionic conductor layer for the advanced low temperature solid oxide fuel cells (LT-SOFCs) in an electrolyte layer-free fuel cells (EFFCs) configuration. The enhanced electrochemical performance of the EFFCs were analyzed based on the different semiconductor-ionic compositions with various weight ratios of LCPN and NCAL. The morphology and microstructure of the raw material, as prepared LCPN as well the commercial NCAL were investigated and characterized by Xray diffraction (XRD), scanning electron microscope (SEM), and energy-dispersive X-ray spectrometer (EDS), respectively. The EFFC performances and electrochemical properties using the LCPN-NCAL layer with different weight ratios were systematically investigated. The optimal composition for the EFFC performance with 70 wt% LCPN and 30 wt% NCAL displayed a maximum power density of 1187 mW cm(-2) at 550 degrees C with an open circuit voltage (OCV) of 1.07 V. It has been found that the well-balanced electron and ion conductive phases contributed to the good fuel cell performances. This work further promotes the development of the industrial-grade rare-earth materials applying for the LTSOFC technology. It also provides an approach to utilize the natural source into the energy field.

Place, publisher, year, edition, pages
PERGAMON-ELSEVIER SCIENCE LTD, 2017
Keywords
Industrial-grade rare-earth doped, ceria, Electrolyte layer-free fuel cells, Ionic conductor, Electronic conductor, Electrochemical performance
National Category
Mechanical Engineering
Identifiers
urn:nbn:se:kth:diva-215836 (URN)10.1016/j.ijhydene.2017.04.075 (DOI)000411545300073 ()2-s2.0-85020065957 (Scopus ID)
Conference
5th Global Conference on Materials Science and Engineering (CMSE), NOV 08-11, 2016, Tunghai Univ, Taichung, TAIWAN
Note

QC 20171017

Available from: 2017-10-17 Created: 2017-10-17 Last updated: 2019-09-03Bibliographically approved
4. Natural CuFe2O4 mineral for solid oxide fuel cells
Open this publication in new window or tab >>Natural CuFe2O4 mineral for solid oxide fuel cells
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2017 (English)In: International journal of hydrogen energy, ISSN 0360-3199, E-ISSN 1879-3487, Vol. 42, no 27, p. 17514-17521Article in journal (Refereed) Published
Abstract [en]

Natural mineral, cuprospinel (CuFe2O4) originated from natural chalcopyrite ore (CuFeS2), has been used for the first time in low temperature solid oxide fuel cells. Three different types of devices are fabricated to explore the optimum application of CuFe2O4 in fuel cells. Device with CuFe2O4 as a cathode catalyst exhibits a maximum power density of 180 mW/cm(2) with an open circuit voltage 1.07 V at 550 degrees C. And a power output of 587 mW/cm(2) is achieved from the device using a homogeneous mixture membrane of CuFe2O4, Li2O-ZnO-Sm0.2Ce0.8O2 and LiNi0.8Co0.15Al0.05O2. Electrochemical impedance spectrum analysis reveals different mechanisms for the devices. The results demonstrate that natural mineral, chalcopyrite, can provide a new implementation to utilize the natural resources for next generation fuel cells being cost-effective and make great contributions to the environmentally friendly sustainable energy.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
Natural mineral, Cuprospinel, Chalcopyrite, Cathodic catalyst, Low temperature solid oxide fuel cells
National Category
Energy Engineering
Identifiers
urn:nbn:se:kth:diva-212942 (URN)10.1016/j.ijhydene.2017.01.039 (DOI)000406725500059 ()2-s2.0-85011585976 (Scopus ID)
Conference
2nd International Symposium on Catalytic Science and Technology in Sustainable, China
Funder
Swedish Research Council, 621-2011-4983
Note

QC 20170825

Available from: 2017-08-25 Created: 2017-08-25 Last updated: 2019-09-03Bibliographically approved
5. Preparation and characterization of Sm and Ca co-doped ceria-La0.6Sr0.4Co0.2Fe0.8O3-delta semiconductor-ionic composites for electrolyte-layer-free fuel cells
Open this publication in new window or tab >>Preparation and characterization of Sm and Ca co-doped ceria-La0.6Sr0.4Co0.2Fe0.8O3-delta semiconductor-ionic composites for electrolyte-layer-free fuel cells
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2016 (English)In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 4, no 40, p. 15426-15436Article in journal (Refereed) Published
Abstract [en]

A series of Sm and Ca co-doped ceria, i.e. Ca0.04Ce0.96-xSmxO2-delta (x = 0, 0.09, 0.16, and 0.24) (SCDC), were synthesized by a co-precipitation method. Detailed morphology, composition, crystal structure and electrochemical properties of the prepared materials were characterized. The results revealed that Sm and Ca co-doping could enhance the ionic conductivity in comparison with that of single Ca-doped samples. The composition as Ca0.04Ce0.80Sm0.16O2-delta exhibited a highest ionic conductivity of 0.039 S cm(-1) at 600 degrees C in comparison with the rest of the series, and the optimal ionic conductivity can be interpreted by the coupling effect of oxygen vacancies and mismatch between the dopant ionic radius and critical radius. Composite formation between the semiconductor La0.6Sr0.4Co0.2Fe0.8O3-delta (LSCF) and the as-prepared SCDC contributed to a remarkable improvement in the ionic conductivity, an unexpectedly high ionic conductivity of 0.188 S cm(-1) was obtained for LSCF-SCDC composites at 600 degrees C, which was four times higher than that of pure SCDC. Using transmission electron microscopy and spectroscopy approaches, we detected an enrichment of oxygen in the LSCF-SCDC interface region and a depletion of oxygen vacancies in LSCF-SCDC and LSCF-LSCF grain boundaries was significantly mitigated, which resulted in the enhancement of ionic conductivity of semiconductor-ionic LSCF-SCDC composites. The electrolyte-layer-free fuel cell (EFFC) fabricated from the LSCF-SCDC semiconductor-ionic membrane demonstrated excellent performances, e.g. 814 mW cm(-2) at 550 degrees C for using the LSCF-Ca0.04Ce0.80Sm0.16O2-delta (SCDC2).

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2016
Keywords
Calcium, Crystal structure, Doping (additives), Electrolytes, Fuel cells, Grain boundaries, High resolution transmission electron microscopy, Ionic conductivity, Oxygen, Precipitation (chemical), Semiconductor doping, Semiconductor insulator boundaries, Transmission electron microscopy
National Category
Materials Chemistry
Identifiers
urn:nbn:se:kth:diva-196653 (URN)10.1039/c6ta05763b (DOI)000386310600020 ()2-s2.0-84991677516 (Scopus ID)
Funder
Swedish Research Council, 621-2011-4983EU, FP7, Seventh Framework Programme, 303454
Note

QC 20161122

Available from: 2016-11-22 Created: 2016-11-17 Last updated: 2019-09-03Bibliographically approved
6. CoFeZrAl-oxide based composite for advanced solid oxide fuel cells
Open this publication in new window or tab >>CoFeZrAl-oxide based composite for advanced solid oxide fuel cells
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2016 (English)In: Electrochemistry communications, ISSN 1388-2481, E-ISSN 1873-1902, Vol. 73, p. 15-19Article in journal (Refereed) Published
Abstract [en]

A novel CoFeZrAl-oxide (CFZA) consisted of FeAl2O4, Co3O4 and ZrO2 was prepared by an auto ignition process, displaying a typical morphology of nanorods. The corresponding fuel cell was constructed by using CFZA as the ion-conducting membrane, incorporated between two layers of Ni0.8Co0.15Al0.05Li-oxide pasted on nickel foam (Ni-NCAL), which was used as both electrodes and current collectors. The fuel cell presented an open circuit voltage of 1.07 V and maximum power density of 631 mW/cm(2) at 600 degrees C. The reduction of FeAl2O4 to oxygen-deficient FeAl2O4 (delta) under H-2 condition contributed to the ionic conduction, then the ionic conductor FeAl2O4 (-) (delta) composited with insulator ZrO2 to further enhance the ionic conductivity due to composite effect.

Keywords
CoFeZrAl-oxide, Solid oxide fuel cell, Ionic conduction, Nanocomposite
National Category
Chemical Engineering
Identifiers
urn:nbn:se:kth:diva-199519 (URN)10.1016/j.elecom.2016.10.005 (DOI)000389203100004 ()2-s2.0-84992090856 (Scopus ID)
Note

QC 20170117

Available from: 2017-01-17 Created: 2017-01-09 Last updated: 2019-09-02Bibliographically approved

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