Monolithic flat tubular types of solid oxide fuel cells with integrated electrode and gas channels

Park, Sungtae,Sammes, Nigel Mark,Song, Ki-Hun,Kim, Taewook,Chung, Jong-Shik Elsevier 2017 INTERNATIONAL JOURNAL OF HYDROGEN ENERGY - Vol.42 No.2

<P><B>Abstract</B></P> <P>A new monolithic solid oxide fuel cell (SOFC) design stacked with flatten tubes of unit cells without using metallic interconnector plate is introduced and evaluated in this study. The anode support is manufactured in a flat tubular shape with fuel channel inside and air gas channel on the cathode surface. This design allows all-ceramic stack to provide flow channels and electrical connection between unit cells without needing metal plates. This structure not only greatly reduces the production cost of SOFC stack, but also fundamentally avoids chromium poisoning originated from a metal plate, thereby improving stack stability. The fuel channel was created in the extrusion process by using the outlet shape of mold. The air channel was created by grinding the surface of pre-sintered support. The anode functional layer and electrolyte were dip-coated on the support. The cathode layer and ceramic interconnector were then spray coated. The maximum power density and total resistance of unit cell with an active area of 30 cm<SUP>2</SUP> at 800 °C were 498 mW/cm<SUP>2</SUP> and 0.67 Ωcm<SUP>2</SUP>, respectively. A 5-cell stack was assembled with ceramic components only without metal plates. Its maximum power output at 750 °C was 46 W with degradation rate of 0.69%/kh during severe operation condition for more than 1000 h, proving that such all-ceramic stack is a strong candidate as novel SOFC stack design.</P> <P><B>Highlights</B></P> <P> <UL> <LI> New design of all ceramic monolithic SOFC stack is proposed with flat-tubular cell. </LI> <LI> Two layers of thin ceramic interconnectors are developed and applied. </LI> <LI> The 5-cell stack exhibits a degradation rate of 0.69%/kh at 750 °C. </LI> </UL> </P>

Ru-doped lanthanum strontium titanates for the anode of solid oxide fuel cells

Yoon, Heechul,Zou, Jing,Sammes, Nigel Mark,Chung, Jongshik Elsevier 2015 International journal of hydrogen energy Vol.40 No.34

<P><B>Abstract</B></P> <P>Lanthanum strontium titanate perovskite (LST) was doped with Ru (La<SUB>0.4</SUB>Sr<SUB>0.6</SUB>Ti<SUB>1−x</SUB>Ru<SUB>x</SUB>O<SUB>3−δ</SUB> (LSTR), x = 0.02, 0.05), and its properties were characterized by various methods for possible use as the anode material in solid oxide fuel cells (SOFCs). The thermal expansion coefficients of Ru-doped samples (10.2–10.3 × 10<SUP>−6</SUP> K<SUP>−1</SUP>) are about the same as LST (10.4 × 10<SUP>−6</SUP> K<SUP>−1</SUP>), which is similar to that of YSZ. It has been found that under a reducing atmosphere, doped Ru is precipitated from the structure. This decreases the total electrical conductivity and increases the ionic conductivity because of the increased number of B-site deficiencies created by the Ru precipitation. Impedance spectra measured with the buttons cells of the LSTRs-YSZ/YSZ/LSM-YSZ/LSM configuration reveal that the polarization resistance with the LST–YSZ anode increases with time (from 4.95 Ω cm<SUP>2</SUP> to 5.78 Ω cm<SUP>2</SUP> in 24 h of H<SUB>2</SUB> fuel atmosphere), whereas the resistance with Ru-doped LST–YSZ anodes decreases with time (from 4.87 Ω cm<SUP>2</SUP> and 4.17 Ω cm<SUP>2</SUP> to 4.06 Ω cm<SUP>2</SUP> and 2.74 Ω cm<SUP>2</SUP> for the LSTR0.02-YSZ and LSTR0.05-YSZ anodes, respectively). Accordingly, the final maximum power density at 850 °C also increases from 52 mW/cm<SUP>2</SUP> for LST–YSZ to 74 mW/cm<SUP>2</SUP> and 115 mW/cm<SUP>2</SUP> for the LSTR0.02-YSZ and LSTR0.05-YSZ anodes, respectively.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The Ru doped LST perovskites are synthesized by EDTA-citrate method. </LI> <LI> The doped Ru affects the conduction behavior of LST in a reducing atmosphere. </LI> <LI> The overall performance is improved with Ru doping to LST anode. </LI> </UL> </P>

Effects of transition metal ion dopants on the performance of Ca_2.9Bi_0.1Co₄O_9-δ cathode

Zou, J.,Park, J.,Yoon, H.,Mark Sammes, N.,Chung, J. Elsevier Sequoia 2013 Journal of alloys and compounds Vol.558 No.-

A systematic study of 10 transition metal ions (M=Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu and Zn) doping in Ca<SUB>2.9</SUB>Bi<SUB>0.1</SUB>Co<SUB>4</SUB>O<SUB>9-δ</SUB> cathode for solid oxide fuel cells is performed by measuring their crystal structures, electrical conductivities and electrochemical performances. The presence of metal ion dopants in the Ca<SUB>2.9</SUB>Bi<SUB>0.1</SUB>Co<SUB>4</SUB>O<SUB>9-δ</SUB> matrix significantly influences its crystal structure and electrochemical performances. The electrochemical performances of metal ion-doped Ca<SUB>2.9</SUB>Bi<SUB>0.1</SUB>Co<SUB>4</SUB>O<SUB>9-δ</SUB> cathodes are quantified in terms of the electrical conductivity, impedance and power density of button cells. Doping with small amounts of ions for cobalt has negligible effect on the structure of powder samples as all of them form single-phase solid solutions with monoclinic misfit layered structure. However, the bar type samples of doping with Ti, Cr, Mn, Fe, Co, Ni, Cu and Zn keep the structure intact while those of doping with Sc and V slightly decompose after sintering. It is proposed that the metal dopants are located at different sites of double layered Ca<SUB>2.9</SUB>Bi<SUB>0.1</SUB>Co<SUB>4</SUB>O<SUB>9-δ</SUB> matrix due to their different ion radii, which mainly accounts for the difference of conductivity of doped samples. Among them, the Cu doped Ca<SUB>2.9</SUB>Bi<SUB>0.1</SUB>Co<SUB>4</SUB>O<SUB>9-δ</SUB> sample (Ca<SUB>2.9</SUB>Bi<SUB>0.1</SUB>Co<SUB>3.9</SUB>Cu<SUB>0.1</SUB>O<SUB>9-δ</SUB>) shows the highest electrical conductivity in the whole temperature range and has the lowest area specific resistance at 750 and 800<SUP>o</SUP>C. The Ca<SUB>2.9</SUB>Bi<SUB>0.1</SUB>Co<SUB>3.9</SUB>Cu<SUB>0.1</SUB>O<SUB>9-δ</SUB>|Ce<SUB>0.8</SUB>Sm<SUB>0.2</SUB>O<SUB>2+γ</SUB>|NiO+Ce<SUB>0.8</SUB>Sm<SUB>0.2</SUB>O<SUB>2+γ</SUB> button cell shows obvious improvement than Ca<SUB>2.9</SUB>Bi<SUB>0.1</SUB>Co<SUB>4</SUB>O<SUB>9-δ</SUB>|Ce<SUB>0.8</SUB>Sm<SUB>0.2</SUB>O<SUB>2+γ</SUB>|NiO+Ce<SUB>0.8</SUB>Sm<SUB>0.2</SUB>O<SUB>2+γ</SUB> button cell. The maximal power densities of the Ca<SUB>2.9</SUB>Bi<SUB>0.1</SUB>Co<SUB>3.9</SUB>Cu<SUB>0.1</SUB>O<SUB>9-δ</SUB> cathode-cell were 689, 465 and 331mWcm<SUP>-2</SUP> at 800, 750 and 700<SUP>o</SUP>C respectively.

Preliminary Studies about Synthesis and Electrical Properties of Ruthenium Doped Lanthanum Strontium Titanate as a Potential Anode of Solid Oxide Fuel Cells

Yoon, Heechul,Zou, Jing,Park, Sungtae,Sammes, Nigel Mark,Chung, Jong Shik The Electrochemical Society 2013 ECS Transactions Vol.57 No.1

<P>The lanthanum strontium titanate (LST) is one of the most representative alternative anode materials. Although it shows low catalytic properties, the disadvatage could be improved by doping of ruthenium which is widely used as catalyst under steam reforming reaction or oxidation reaction. The ruthenium doped lanthanum strontium titanates (LSTRs) powders were synthesized by complex EDTA-citrate method showing well crystallinity. Additionally, the prepared samples were evaluated through various experimental tests. For example, the stability in the reducing atmosphere and chemical compativity with YSZ electrolyte such as reactivity test in high temperature were confirmed by XRD (X-ray diffraction). And electrical conductivity in wet H<SUB>2</SUB> atmosphere at 900ºC is about 350.6 S/cm, 342.4 S/cm and 179.1 S/cm with sintered bar of LST, LSTR0.02 and LSTR0.05, respectively.</P>

Performance of an Anode Supported Solid Oxide Fuel Cell with Indirect Internal Reforming

Park, Sungtae,Zou, Jing,Yoon, Heechul,Sammes, Nigel Mark,Chung, Jong Shik The Electrochemical Society 2013 ECS Transactions Vol.57 No.1

<P>The conversion of fuel into hydrogen-rich gas is necessary for fuel cells. This can be achieved either indirectly in fuel processing systems, in which the hydrocarbon feed is converted in an external catalytic steam reformer, or directly in the fuel cell. In this paper, the unit module of solid oxide fuel cell was assembled by one reformer and four cells. The reformer was fabricated by extruded dummy cell and combined with two cells on each side respectively. The reforming catalyst was coated on internal channel of the dummy cell. The unit module has successfully tested with wet CH<SUB>4</SUB> as fuel and air as oxidant and its maximum power density exceeded 150 mW/cm<SUP>2</SUP> at 750 ºC.</P>

Preliminary Studies about Carbon Deposition Behavior of Ni-Metal/YSZ Bimetallic Cermet Anode of SOFC

Chung, Yong Sik,Kim, Hwan,Yoon, Heechul,Chung, Jong Shik,Sammes, Nigel Mark The Electrochemical Society 2013 ECS Transactions Vol.57 No.1

<P>Nickel/Yttrium-stabilized zirconia (Ni/YSZ) composite is the standard anode material with high stability and catalytic activity in both oxidation of H<SUB>2</SUB> and reforming hydrocarbons. However, carbon is deposited on the surface of Ni catalyst in hydrocarbon atmosphere which is called coking. It leads to decrease in percolation, power density, and eventually crack. In this paper, 5 mol% of titanium Oxide (TiO<SUB>2</SUB>) and manganese oxide (MnO) are added to NiO/YSZ powder. Prepared mixed anode powder is applied on Ni/YSZ support button cell as functional anode. Hydrogen oxidation catalytic activities of sample anodes were measured by IV curve, and polarization resistances were measured by impedance spectroscopy analysis at 800 C in dry H2 atmosphere. Ni/YSZ, 5 mol% MnO Ni/YSZ and 5mol% TiO<SUB>2</SUB> Ni/YSZ cells showed power density of 628mW/cm<SUP>2</SUP>, 458mW/cm<SUP>2</SUP> and 382mW/cm<SUP>2 </SUP>at 0.6V respectively. Cells survived in dry CH4 atmosphere for 16, 27 and 32 minutes without performance drop.</P>

Design and Fabrication of Electrolyte-Supported Tubular SOFC Combined with Supercritical Water Oxidation on Biomass Gas

Kim, Hwan,Parfitt, Andrew,Park, Sung Tae,Chung, Yong Sik,Chung, Jong Shik,Sammes, Nigel Mark The Electrochemical Society 2013 ECS Transactions Vol.57 No.1

<P>Solid oxide fuel cells (SOFCs) are relatively simple and environmental friendly devices for the production of electricity from hydrocarbons. The use of a high pressure supercritical water (SCW) reactor containing a SOFC has the potential for using a multitude of logistical liquid fuels that would otherwise not be possible in a regular SOFC system. A SOFC-SCW system was designed to allow the anode to be exposed to the pressure and chemical milieu of the supercritical water oxidation reactor. The effects of the amount of water/fuel and oxygen fed into the reactor under SCW conditions at 400°C were studied. The effects on electrochemical performance as well as preliminary results on a number of feed stocks, for example pectin, are also described.</P>