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Fabrication of novel electrolyte-layer free fuel cell with semi-ionic conductor (Ba0.5Sr0.5Co0.8Fe0.2O3-delta- Sm0.2Ce0.8O1.9) and Schottky barrier
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics.ORCID iD: 0000-0001-5380-975X
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.ORCID iD: 0000-0002-3133-7031
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2016 (English)In: Journal of Power Sources, ISSN 0378-7753, E-ISSN 1873-2755, Vol. 328, p. 136-142Article in journal (Refereed) Published
Abstract [en]

Perovskite Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF) is synthesized via a chemical co-precipitation technique for a low temperature solid oxide fuel cell (LTSOFC) (300-600 degrees C) and electrolyte-layer free fuel cell (EFFC) in a comprehensive study. The EFFC with a homogeneous mixture of samarium doped ceria (SDC): BSCF (60%:40% by weight) which is rather similar to the cathode (SDC: BSCF in 50%:50% by weight) used for a three layer SOFC demonstrates peak power densities up to 655 mW/cm(2), while a three layer (anode/ electrolyte/cathode) SOFC has reached only 425 mW/cm(2) at 550 degrees C. Chemical phase, crystal structure and morphology of the as-prepared sample are characterized by X-ray diffraction and field emission scanning electron microscopy coupled with energy dispersive spectroscopy. The electrochemical performances of 3-layer SOFC and EFFC are studied by electrochemical impedance spectroscopy (EIS). As-prepared BSCF has exhibited a maximum conductivity above 300 S/cm at 550 degrees C. High performance of the EFFC device corresponds to a balanced combination between ionic and electronic (holes) conduction characteristic. The Schottky barrier prevents the EFFC from the electronic short circuiting problem which also enhances power output. The results provide a new way to produce highly effective cathode materials for LTSOFC and semiconductor designs for EFFC functions using a semiconducting-ionic material.

Place, publisher, year, edition, pages
Elsevier, 2016. Vol. 328, p. 136-142
Keywords [en]
Co-precipitation, Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF), LTSOFC, Electrolyte-layer free fuel cell (EFFC), Perovskite oxide, Semi-ionic conductor
National Category
Materials Chemistry Inorganic Chemistry Ceramics
Identifiers
URN: urn:nbn:se:kth:diva-193795DOI: 10.1016/j.jpowsour.2016.07.093ISI: 000383293400015Scopus ID: 2-s2.0-84984850892OAI: oai:DiVA.org:kth-193795DiVA, id: diva2:1039532
Funder
EU, FP7, Seventh Framework Programme, TRISOFC_03042012Swedish Research Council, 621-2011-4983ÅForsk (Ångpanneföreningen's Foundation for Research and Development)
Note

QC 20161024

Available from: 2016-10-24 Created: 2016-10-11 Last updated: 2019-03-06Bibliographically approved
In thesis
1. Semiconductor-ionic Materials for Low Temperature Solid Oxide Fuel Cells
Open this publication in new window or tab >>Semiconductor-ionic Materials for Low Temperature Solid Oxide Fuel Cells
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Solid oxide fuel cell (SOFC) is considered as an attractive candidate for energy conversion within the fuel cell (FC) family due to several advantages including environment friendly, use of non-noble materials and fuel flexibility. However, due to high working temperatures, conventional SOFC faces many challenges relating to high operational and capital costs besides the limited selection of the FC materials and their compatibility issues. Recent SOFC research is focused on how to reduce its operational temperature to 700 ºC or lower. Investigation of new electrolytes and electrode materials, which can perform well at low temperatures, is a comprehensive route to lowering the working temperature of SOFC. Meanwhile, semiconductor-ionic materials based on semiconductors (perovskite/composite) and ionic materials (e.g. ceria based ion conductors) have been identified as potential candidates to operate in low temperature range with adequate SOFC power outputs.

This investigation focuses on the development of semiconductor-ionic materials for low temperature solid oxide fuel cell (SOFC) and electrolyte-layer free fuel cell (EFFC). The content of this work is divided into four parts:

First part of the thesis consists of the work on conventional SOFC to build knowledge and bridge from conventional SOFC to the new EFFC. Novel composite electrode (semiconductor) materials are synthesized and studied using established electrochemical and analytical methods such as x-ray diffraction (XRD), scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). The phase structure, morphology and microstructure of the composite electrodes are studied using XRD and SEM, and the weight loss is determined using TGA. An electrical conductivity of up to 143 S/cm of as-prepared material is measured using DC 4 probe method at 550 ºC. An electrolyte, samarium doped ceria (SDC) is synthesized to fabricate a conventional three component SOFC device. The maximum power density of 325 mW/cm2 achieved from the conventional device at 550 ºC.

In the second part of the thesis, semiconductor-ionic materials based on perovskite and composite materials are prepared for low temperature SOFC and EFFC devices. Semiconductor-ionic materials are prepared via nanocomposite approach based on two-phase semiconductor electrode and ionic electrolyte. This semiconductor-ionic functional component was shown to integrate all fuel cell components anode, electrolyte and cathode functions into a single component, i.e. “three in one”, resulting in enhanced catalytic activity and improved SOFC performance.

The third part of the thesis addresses the development and optimization of the EFFC technologies by studying the Schottky junction mechanism in such semiconductor-ionic type devices. Perovskite and functional nanocomposites (semiconductor-ionic materials) are developed for EFFC devices. Materials characterizations are performed using a number of standard experimental and analytical techniques. Maximum power densities from 600 mW/cm2 up to 800 mW/cm2 have been achieved at 600 ºC.

Fourth part of the thesis describes the theoretical simulation of EFFCs. In this work, an updated numerical model is applied in order to study the EFFC device, which introduces some modifications to the existing relations for traditional fuel cell models. The simulated V-I and P-I curves have been compared with experimental curves, and both types of curves show a good consistency.

Abstract [sv]

Bränsleceller av typen fastoxid (SOFC) anses vara en attraktiv kandidat för energiomvandling bland bränsleceller (FC) beroende på flera fördelar som bl.a. miljövänlighet, användning av icke-ädla material och deras bränsleflexibilitet. På grund av hög driftstemperatur står dock konventionella SOFC inför många utmaningar. Bland dessa finns höga drifts- och kapitalkostnader samt det begränsade urvalet av FC-material och relaterade kompatibilitetsproblem. En trend inom SOFC-forskning är inriktning på hur man sänker driftstemperaturen åtminstone till 700 ºC eller lägre. Undersökning av nya elektrolyt- och elektrodmaterial som kan fungera bra vid låga temperaturer är en mödosam väg för att sänka SOFCs arbetstemperatur. Som alternativ finns halvledande-jonledande material som är baserade på perovskit/komposit- och jonledande material. Dessa är potentiella kandidater att arbeta i ett lågt temperaturområde med tillräckliga SOFC-prestanda.

Denna forskning fokuserar på utveckling av halvledar-joniska material för lågtemperatur-solid oxid bränsleceller och elektrolytskikt-fria bränsleceller (EFFC). Detta arbete är indelat i fyra delar:

Den första delen av avhandlingen handlar om arbetet med konventionell SOFC för att bygga kunskap och att överbrygga från konventionell SOFC till det nya EFFC. Nya halvledande kompositelektrodmaterial syntetiseras och studeras med hjälp av etablerade elektrokemiska och analytiska metoder, såsom röntgendiffraktion (XRD), scanning-elektronmikroskopi (SEM) och termogravimetrisk analys (TGA). Fasstrukturen, morfologin och mikrostrukturen hos kompositelektroderna studeras med användning av XRD och SEM, och viktminskningen bestäms med användning av TGA. En elektrisk ledningsförmåga på 143 S/cm av sådant framställt material har uppmätts med användning av DC 4-sond-metoden vid 550 ºC. En elektrolyt, Samarium-dopad Ceriumoxid (SDC) syntetiseras för att tillverka en konventionell SOFC-enhet baserad på tre komponenter. En maximal effekttäthet på 325 mW/cm2 har uppnåtts från den konventionella enheten vid 550 ºC.

I andra delen av avhandlingen är halvledarjoniska material baserade på perovskit och kompositmaterial förberedda för SOFC- och EFFC-enheter med låg temperatur. Halvledar-joniska material har konstruerats genom att skapa en komposit av nano-partiklar (nanokomposit) baserat på halvledarelektrod och elektrolyt i olika kristallina faser som kombineras i en tvåfas-struktur. Denna halvledar-joniska funktionella komponent har visats integrera alla anod-, elektrolyt- och katodfunktioner i bränslecellkomponenterna i en enda komponent, dvs "tre i en", vilket resulterade i förbättrad katalytisk aktivitet och förbättrad SOFC-prestanda.

Tredje delen av avhandlingen tar upp utvecklingen och optimeringen av EFFC-tekniken genom att studera Schottky-kopplingsmekanismen i sådana anordningar av halvledar-jonisk typ. Perovskit och funktionella nanokompositer (halvledar-joniska material) har utvecklats för EFFC-enheter. Materialkarakteriseringar utförs med användning av ett antal standardiserade experimentella och analytiska metoder. En maximal effekttäthet från 600 mW/cm2 upp till och 800 mW/cm2 har uppnåtts vid 600 ºC.

Den fjärde delen av avhandlingen beskriver den teoretiska simuleringen av EFFCs. I detta arbete tillämpas en uppdaterad numerisk modell för att studera EFFC-enheten som introducerar vissa modifieringar av de rådande sambanden i traditionella bränslecellsmodeller. De simulerade V-I- och P-I-kurvorna har jämförts med experimentella kurvor, och båda typerna av kurvor visar god samstämmighet.

Place, publisher, year, edition, pages
Stockholm, Sweden: KTH Royal Institute of Technology, 2019. p. 92
Series
TRITA-ITM-AVL ; 2019:7
Keywords
Semiconductor-ionic materials; electrolyte-layer free fuel cell; low temperature solid oxide fuel cell; fuel to electricity conversion; Schottky junction; theoretical and experimental curves, Halvledar-joniska material; elektrolytskikt-fri bränslecell; lågtemperatur fastoxidbränslecell; bränsle till elomvandling; Schottky junction; teoretiska och experimentella kurvor
National Category
Engineering and Technology
Research subject
Energy Technology
Identifiers
urn:nbn:se:kth:diva-245185 (URN)978-91-7873-132-9 (ISBN)
Public defence
2019-03-29, Kollegiesalen, Brinellvägen 8, Stockholm, 10:00 (English)
Opponent
Supervisors
Available from: 2019-03-06 Created: 2019-03-06 Last updated: 2019-03-06Bibliographically approved

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