LSM Composite Cathodes

At anodes, the electrochemical oxidation of fuels such as hydrogen (H2) and natural gas occurs. Anodes must fulfill the following requirements. 

Basically, Ni-YSZ cermet materials are the most commonly used anode materials. The following sections describe the main types of anode materials, their advantages, and disadvantages. 

Though Ni is an excellent electrocatalyst for the electrochemical oxidation of hydrogen, if the fuel cell is using natural gas as the fuel, then no external fuel cell reformer is required because the reforming reactions can take place inside the Ni/YSZ cermet anode as follows. 

If H2O content is small, then reaction (3.24) will happen as follows 

This carbon will be deposited on the anode surface due to methane cracking. This carbon will cover the active sites on the anode surface hence leading to performance degradation of the cell. High steam/carbon ratios are used to suppress the carbon formation anyhow the steam addition leads to a reduction in anode electrical potential due to the presence of oxygenation in the fuel. The carbon deposition can be controlled by carefully choosing the fuel composition and operating temperature. 

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Figure 4.1.24. Effect of inductance error on the impedance spectrum of a symmetrical cell. Open symbols raw data closed symbols data corrected for stray inductance of 36 x 10" H. The sample is a YSZ tape of area 0.21 cm with an LSM composite cathode on both sides, measured in air, 850°C.

Song HS, Kim WH, Hyun SH, and Moon J. Influences of starting particulate materials on micro structural evolution and electrochemical activity of LSM-YSZ composite cathode for SOFC. J. Electroceram. 2006 17 759-764. 

Xia C, Zhang Y, and Liu M. LSM-GDC composite cathodes derived from a sol-gel process. Electrochem. Solid State Lett. 2003 6 A290-A292. 

Figure 51. Zero-bias impedance of a 60%/40% LSM/YSZ composite cathode, measured at 950 °C as a function of The magnitude of the lowest-frequency arc ( 1 Hz) was quantified using equivalent circuit analysis and found to scale inversely with P02 and only weakly with temperature. (Reprinted with permission from ref 346. Copyright 2001 Elsevier.)...

Jorgensen M.J., Mogensen M. (2001) Impedance of solid oxide fuel cell LSM/YSZ composite cathodes. Journal of the Electrochemical Society 148(5), A433-A442. 

As an example of a cathode film the (Lag gSrg 2)o.9Mn03 (LSM) per-ovskite will be used for electrode preparation and evaluation. Composite symmetrical and asymmetrical (Lag gSr 2) MnOj-YSZ (LSM-YSZ) structures were prepared on dense YSZ substrate (0.4 mm thick) [21]. The symmetrical cell was used for composite LSM-YSZ and composite LSM-YSZAfSZ electrode overpotential evaluation, while asymmetrical for fuel cell performance and electrode overpotential measurement. The composite cathode was prepared similarly to the composite anode (Figure 3-18). The procedure follows ... 

Regarding the development of LSM based composite cathodes, several works have reported the preparation of LSM-SDC cathodes from the powders obtained by different synthesis methods (Ye et al., 2007 Chen et al., 2007 Xu et al., 2009). However, no reports on the... 

A SEM micrograph of the cathode/electrolyte interface and preliminary results on the electrochemical activity of YSZ electrolyte-supported SOFCs containing Ni-YSZ anode and a LSCF-SDC composite cathode are shown in Fig. 14. As it can be seen in Fig. 14(a), the composite film not only has good adhesion to the electrolyte, but also possesses a porous microstructure which is required for the oxidant electrochemical reduction. It indicates that such a composite film can have a good performance as SOFC cathode. By the LSV technique, qualitative information about electrochemical activity of this SOFC was acquired. The power density curves (Fig. 14b) revealed that maximum power densities were 19, 26, 36 and 46 mW/cm2 at 800, 850, 900 and 950 °C. It is possible to compare these first results with literature data and safely state that the LSCF-SDC cathode composite is qualitatively better than other plain standard materials or cathode composites already reported. It should also be mentioned that the result obtained at 800 °C is similar to that reported by Mucdllo et al (Mucdllo et al., 2006) for a SOFC single cell with LSM-YSZ cathode, Ni-YSZ anode and 70 pm... 

The electronic conductors commonly used for SOFCs are lanthanum strontium manganite (LSM) for cathodes and nickel metal for anodes. The anodes are prepared in situ by reduction of a nickel oxide/ electrolyte composite. 

This section presents two examples of composite cathodes for SOFC. For these systems, the most commonly used cathode material and solid electrolyte are LSM and YSZ, respectively. Electrode impedances appear over a small space scale, characteristic of atomic dimensions, and as a result their spectra differ from those of bulk materials in several ways listed below. 

M. J. J0rgensen and M. Mogensen [2001] Impedance of Solid Oxide Fuel Cell LSM/YSZ Composite Cathodes,... 

Song, H.S., Lee, S., Hyun, S.H., Kim, J. Moon, X Compositional influence of LSM-YSZ composite cathodes on improved performance and disability of solid oxide fuel-cells. J. Power Sources 187 (2009), pp. 25-31. 

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