Electrochemical performance of (La,Sr)(Co,Fe)O3–(Ce,Gd)O3 composite cathodes

The present study reports thermal and electrical properties of Sr 1-x Y x CoO 2.5+δ (x = 0-0.40) as a promising cathode for intermediatetemperature solid oxide fuel cells. The results show that x = 0.10 is the best composition possessing a single primitive cubic perovskite structure, stable conductivity and the lowest polarization resistance. Thermogravimetric analysis indicates an oxygen intake from RT to ∼375 • C, above which oxygen loss occurs. The oxygen gain-loss behavior corresponds well with the conductivity increase-decrease trending, reflecting that oxygen-nonstoichiometry controls the hole-concentration (or oxidation-state of Co-ions). Electrochemical impedance spectroscopy analysis further reveals that the overall ORR polarization consists of a faster charge-transfer and a slower surface oxygen exchange.

mentioning

confidence: 99%

Thermal and Electrical Stability of Sr_0.9Y_0.1CoO_2.5+δas a Promising Cathode for Intermediate-Temperature Solid Oxide Fuel Cells

Jiang

Wang

Xiong

et al. 2016

“…[8][9][10] However, cobalt containing oxides are known to induce thermomechanical failure due to their large thermal expansion coefficients (TECs), which cause a mismatch between the cathode and electrolyte. The large TEC mismatch negatively affects the durability under thermal cycling in SOFC systems.…”

mentioning

confidence: 99%

Scale-Down and Sr-Doping Effects on La₄Ni₃O_10-δ–YSZ Nanocomposite Cathodes for IT-SOFCs

Kim

Choi

Jun

et al. 2014

Among the Ruddlesden-Popper series, La n+1 Ni n O 3n+1 (n = 1, 2, and 3) has attracted tremendous attention as an intermediate temperature solid oxide fuel cell (IT-SOFC) cathode because of its favorable properties for realizing high performance. Inter alia, La 4 Ni 3 O 10-δ (n = 3) has in particular gained recognition as a promising cathode material owing to its high electrical conductivity and cell performance in IT-SOFC applications. The fabrication of nano-sized La 4 Ni 3 O 10-δ composites requires a low sintering temperature process because high sintering temperature gives rise to solid state reactions between the constituents, which leads to the formation of an undesired electrical insulator and the formation of a low surface area thin-film on the surface. The infiltration method is therefore chosen to fabricate nano-sized La 4 Ni 3 O 10-δ composites because it can provide reduced particle size of La 4 Ni 3 O 10-δ by separating the sintering process of the cathode from the high temperature sintering process of the electrolyte. In this work, we investigated the electrochemical properties of La 4 Ni 3 O 10-δ composites prepared by an infiltration method in terms of application as an IT-SOFC cathode material as well as the effect of strontium doping at La sites. A fuel cell converts chemical energy to electrical energy by using hydrogen or hydrocarbon as fuel. Inter alia, a solid oxide fuel cell (SOFC) is a promising power generation device with high efficiency, excellent performance, low emissions, and attractive fuel flexibility at high operating temperature. Nevertheless, high operating temperature gives rise to some drawbacks such as interface reactions between cell components, electrode phase transitions, restrictions on choice of materials, and so on. The key to solving those problems lies in developing intermediate-temperature SOFCs (IT-SOFCs) (500-700• C). 1,2However, the low operating temperature gives rise to poor activity for the oxygen reduction reaction (ORR) at the cathode. Accordingly, the development of cathode materials with high electro-catalytic activity and excellent durability is necessary for commercialization of IT-SOFCs. [3][4][5] In this respect, mixed ionic electronic conductors (MIECs) based on transition metal (e.g. Mn, Fe, Co, and Ni) oxides have received remarkable attention. 3,4,6 MIECs have the capability to conduct oxygen ions and electrons simultaneously, which leads to an increase of electrochemical reactive sites. It is generally accepted that the entire surface of MIECs may work as reactive sites for the ORR, because the ORR can occur at not only the triple phase boundary (TPB) but also the two phase boundary (2PB).6,7 Specifically, the TPB is a reaction site where the gas phase meets the electronic and ionic conducting phases at the electrode-electrolyte interface. In the case of MIECs, the ORR also occurred at the 2PB, which corresponds with the interface boundaries between MIECs and oxygen gas.Among various MIECs, cobalt containing oxides such as LaCoO 3 , PrCoO 3 , and...

“…37 The high R P of the pristine cathode.-It should be noted that the R P value of the commercial pristine LSCF+GDC cathode employed in this study is noticeably higher than those reported in the literature. 9 One possible source of discrepancy could arise from how the current collector is treated during the electrochemical testing. We have recently argued that silver metal commonly used as a current collector in electrochemical tests become highly mobile and ORRactive at t > 650 • C. 33 The volatile silver species then transport to the porous backbones of the cathode and promote the ORR kinetics as a catalyst.…”

Section: R O Reduction By Mc-mentioning

confidence: 99%

“…[6][7][8] To search for highly active IT-cathodes with low activation energy, current research has been primarily focused on the areas of materials development, catalysts nanostructuring and microstructural optimization, which includes, but not limited to (1) exploration of mixed ionic and electronic conducting (MIEC) oxygen-deficient perovskitestructured oxides, e.g. La x Sr 1-x Co 1-y Fe y O 3-δ (LSCF), 9 Sm x Sr 1-x CoO 3-δ (SSCo), 10 Ba x Sr 1-x Co 1-y Fe y O 3-δ (BSCF) 3 and LnBaCo 2 O 6-δ (Ln = Pr, Nd, Sm and Gd); 11 (2) introduction of nanostructured ORR-active noble-metal and oxide catalysts into cathode backbones; [12][13][14][15] (3) optimization of cathode microstructure to maximize the ORR-active sites. [16][17][18][19] However, so far none of the above developments has been successfully employed in commercial SOFCs, and new IT-cathode materials are still in great demand.…”

mentioning

confidence: 99%

Molten Carbonates as an Effective Oxygen Reduction Catalyst for 550–650°C Solid Oxide Fuel Cells

Gong¹,

Li²,

Zhang³

et al. 2013

We report the first study that investigates the use of molten carbonates as an effective catalyst to promote electrochemical oxygen reduction reaction (ORR) at the cathode of intermediate temperature solid oxide fuel cells (IT-SOFCs). A series of binary Li-K carbonate compositions were incorporated into the porous backbones of a commercial cathode assembled in symmetrical impedance cells for electrochemical characterization. Within the temperature range of 550-650 • C, we observed that the polarization and ohmic area-specific resistances of the original sample can be significantly reduced by the introduction of molten carbonates. A new ORR charge-transfer model involving two intermediate species CO 5 2− and CO 4 2− as the fast oxygen absorber and transporter, respectively, was presented as the mechanism for the facile ORR kinetics promoted by molten carbonates.