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Superionic Conductivity of Sm3+, Pr3+, and Nd3+ Triple-Doped Ceria through Bulk and Surface Two-Step Doping Approach
KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
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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. Vol. 9, no 28, p. 23614-23623
Keywords [en]
LT-SOFCs, doped ceria, bulk and surface doping, oxygen ion conductivity, redox
National Category
Ceramics
Identifiers
URN: urn:nbn:se:kth:diva-212346DOI: 10.1021/acsami.7b02224ISI: 000406172700035Scopus ID: 2-s2.0-85024920908OAI: oai:DiVA.org:kth-212346DiVA, id: diva2:1134814
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
In thesis
1. Application of Rare-Earth Doped Ceria and Natural Minerals for Solid Oxide Fuel Cells
Open this publication in new window or tab >>Application of Rare-Earth Doped Ceria and Natural Minerals for Solid Oxide Fuel Cells
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
Low-temperature solid oxide fuel cells; Doped ceria; Material characterizations; Electrochemical performances; Natural minerals, 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:nbn:se:kth:diva-257718 (URN)978-91-7873-277-7 (ISBN)
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

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