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Electrochemical study of the composite electrolyte based on samaria-doped ceria and containing yttria as a second phase
KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
KTH, School of Information and Communication Technology (ICT), Material Physics, Functional Materials, FNM.
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2011 (English)In: Solid State Ionics, ISSN 0167-2738, E-ISSN 1872-7689, Vol. 188, no 1, 58-63 p.Article in journal (Refereed) Published
Abstract [en]

The purpose of this study is to develop new oxide ionic conductors based on nanocomposite materials for an advanced fuel cell (NANOCOFC) approach. The novel two phase nanocomposite oxide ionic conductors, Ce0.8Sm0.2O2-delta (SDC)-Y2O3 were synthesized by a co-precipitation method. The structure and morphology of the prepared electrolyte were investigated by means of X-ray diffraction (XRD) and high resolution scanning electron microscopy (HRSEM). XRD results showed a two phase composite consisting of yttrium oxide and samaria doped ceria and SEM results exhibited a nanostructure form of the sample. The yttrium oxide was used on the SDC as a second phase. The interface between two constituent phases and the ionic conductivities were studied with electrochemical impedance spectroscopy (EIS). An electrochemical study showed high oxide ion mobility and conductivity of the Y2O3-SDC two phase nanocomposite electrolytes at a low temperature (300-600 degrees C). Maximum conductivity (about 1.0 S cm(-1)) was obtained for the optimized Y2O3-SDC composite electrolyte at 600 degrees C. It is found that the nanocomposite electrolytes show higher conductivities with the increased concentration of yttrium oxides but decreases after reaching a certain level. A high fuel cell performance, 0.75 W cm(-2), was achieved at 580 degrees C.

Place, publisher, year, edition, pages
2011. Vol. 188, no 1, 58-63 p.
Keyword [en]
Interfaces, Electrochemical impedance spectroscopy (EIS), Oxides, Doped ceria
National Category
Physical Chemistry
URN: urn:nbn:se:kth:diva-35109DOI: 10.1016/j.ssi.2010.11.002ISI: 000291116700012ScopusID: 2-s2.0-79954989972OAI: diva2:428608
QC 20110630Available from: 2011-06-30 Created: 2011-06-20 Last updated: 2011-12-13Bibliographically approved
In thesis
1. Functional nanocomposites for advanced fuel cell technology and polygeneration
Open this publication in new window or tab >>Functional nanocomposites for advanced fuel cell technology and polygeneration
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

In recent decades, the use of fossil fuels has increased exponentially with a corresponding sharp increase in the pollution of the environment. The need for clean and sustainable technologies for the generation of power with reduced or zero environment impact has become critical. A number of attempts have been made to address this problem; one of the most promising attempts is polygeneration. Polygeneration technology is highly efficient and produces lower emissions than conventional methods of power generation because of the simultaneous generation of useable heat and electrical power from a single source of fuel. The overall efficiency of such systems can be as high as 90%, compared to 30-35% for conventional single-product power plants.

A number of different technologies are available for polygeneration, such as micro gas turbines, sterling engines, solar systems, and fuel cells. Of these, fuel cell systems offer the most promising technology for polygeneration because of their ability to produce electricity and heat at a high efficiency (about 80%) with either low or zero emissions. Various fuel-cell technologies can be used in polygeneration systems. Of these, solid oxide fuel cells (SOFCs) are the most suitable because they offer high system efficiency for the production of electricity and heat (about 90%) coupled with low or zero emissions. Compared to other types of fuel cells, SOFCs have fuel flexibility (direct operation on hydrocarbon fuels, such as biogas, bio-ethanol, bio-methanol, etc.) and produce high-quality heat energy. The development of polygeneration systems using SOFCs has generally followed one of two approaches. The first approach involves the design of a SOFC system that operates at a temperature of 850 oC and uses natural gas as a fuel. The second approach uses low-temperature (generally 400-600 oC) SOFC (LTSOFC) systems with biomass, e.g., syngas or liquid fuels, such as bio-methanol and bio-ethanol. The latter systems have strong potential for use in polygeneration.

High-temperature SOFCs have obvious disadvantages, and challenges remain for lowering the cost to meet commercial interest. The SOFC systems need lower operating temperatures to reduce their overall costs.

This thesis focuses on the development of nanocomposites for advanced fuel-cell technology (NANOCOFC), i.e., the next generation SOFCs, which are low-temperature (400-600 oC), marketable, and affordable SOFCs. In addition, new concepts that pertain to fuel-cell science and technology—NANOCOFC (—are explored and developed. The content of this thesis is divided into five parts:

In the first part of this thesis (Papers 1-5), the two-phase nanocomposite electrolytes, viz. ceria-salt and ceria-oxide, were prepared and studied using different electrochemical techniques. The microstructure and morphology of the composite electrolytes were characterised using XRD, SEM and TEM, and the thermal analysis was conducted using DSC. An ionic conductivity of 0.1 S/cm was obtained at 300 ºC, which is comparable to that of conventional YSZ operating at 1000 ºC. The maximum output power density was 1000 mW/cm2 at 550 oC. A co-doped ceria-carbonate was also developed to improve the ionic conductivity, morphology, and performance of the electrolyte.

In the second part of this thesis (Papers 7-9), composite electrodes that contained less or no nickel (Ni) were developed for a low-temperature SOFC. All of the elements were highly homogenously distributed in the composite electrode, which resulted in high catalytic activity and good ASOFC performance. The substitution of Ni by Zn in these electrodes could reduce their cost by a factor of approximately 25.

In the third part of this thesis (Papers 10), an advanced multi-fuelled solid-oxide fuel cell (ASOFC) with functional nanocomposites (electrolytes and electrodes) was developed. Several different types of fuel, such as gaseous (hydrogen and biogas) and liquid fuels (bio-ethanol and bio-methanol), were tested. Maximum power densities of 1000, 300, 600, and 550 mW/cm2 were achieved with hydrogen, bio-gas, bio-methanol, and bio-ethanol, respectively, in the ASOFC. Electrical and total efficiencies of 54% and 80%, respectively, were achieved when the single cell was used with hydrogen.

The fourth part of this thesis (Papers 11) concerns the design of a 5 kW ASOFC system based on the demonstrated advanced SOFC technology. A polygeneration system based on a low-temperature planar SOFC was then designed and simulated. The efficiency of the overall system was approximately 80%.

The fifth part of this thesis (Paper 12) describes a single-layer multi-fuelled electrolyte-free fuel cell that is a revolutionary innovation in renewable-energy sources. Conventional fuel cells generate electricity by ion transport through the electrolyte. However, this new device works without an electrolyte, and all of the processes occur at particle surfaces in the material. Based on a theoretical calculation, an additional 18% enhancement of the fuel cell’s efficiency will be achieved using this new technology compared to the conventional technologies.

Our developed ASOFC systems with functional nanocomposites offer significant advantages in reducing the operational and capital costs for the production of power and heat by using different fuels based on the fuel-cell technology. ASOFC systems can be used for polygeneration with renewable fuels (i.e., biomass fuels) at high efficiency as a sustainable solution to energy generation in our society. The results have been achieved for this thesis work has demonstrated an advanced fuel cell technology.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. xx, 83 p.
Trita-KRV, 12:10
Polygeneration, advanced fuel cell, functional materials, ceria-carbonate nanocomposites, multi-fuelled, electrolyte free fuel cell
National Category
Energy Engineering
Research subject
SRA - Energy
urn:nbn:se:kth:diva-51476 (URN)978-91-7501- 191-2 (ISBN)
Public defence
2011-12-19, Sal (M2), Brinellvägen 64 Entreplan, KTH, Stockholm, 10:00 (English)
QC 20111213Available from: 2011-12-13 Created: 2011-12-12 Last updated: 2012-03-29Bibliographically approved

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