LSM cathodes

Sol-gel technique has been used to deposit solid electrolyte layers within the LSM cathode. The layer deposited near the cathode/electrolyte interface can provide ionic path for oxide ions, spreading reaction sites into the electrode. Deposition of YSZ or samaria-doped ceria (SDC, Smo.2Ceo.8O2) films in the pore surface of the cathode increased the area of TPB, resulting in a decrease of cathode polarization and increase of cell performance [15],... 

FIGURE 3.15 Polarization curves for the 02 reduction on an LSM cathode in the presence of a Fe-Cr alloy interconnect, measured under a cathodic current passage of 200 mA cnr2 at 900°C. 

The consequences of the electrochemical reduction of high valence chromium species would be the precipitation of Cr203 solid phase at the cathode-electrolyte interface boundary. These led to the hypothesis that the degradation mechanism of LSM cathode is dominated by an electrochemical reduction of high valence vapor species of chromium (Cr03 and C OH O to solid phase Cr203 in competition with the 02 reduction reaction, followed by the chemical reaction with LSM to form (Cr,Mn)304 phases at the TPB, blocking the active sites [174-180], The process is written as follows [174] ... 

In addition to the chemical interactions described above, microstructural changes in the electrode can lead to performance degradation after long operation time. For example sintering of the porous structure can degrade electrode performance. In the case of LSM cathodes, the sintering ability is found to be related to the strontium dopant level and stoichiometric composition of (La, Sr)xMn03. In addition, LSM with A-site deficient compositions (x < 1) sinters more readily than their B-site deficient counterparts (x > 1) [198, 199],... 

Figure 46. Performance characteristics of a cathode-supported thin film Ni—YSZ/YSZ/LSM fuel cell at 600 °C in humidified H2 and air with and without a dense protective yttria-doped ceria (YDC) protection layer introduced between the porous LSM cathode and the thin-film electrolyte. (Reprinted with permission from ref 296. Copyright 1997 Elsevier.)...

Figure 17 shows different mechanistic pathways for the oxygen reduction at the LSM cathode on YSZ electrolyte. The adsorbed, partially fully ionized oxygen may move along the surface to the three phase boundary where it is transformed into the electrolyte. (In principle it may also reach this place directly via the gas phase.) The oxygen may also reach the electrolyte by diffusion through the LSM bulk via a counter motion of O2 and 2e . Note that LSM sandwiched between Pt (serving as a reversible electrode) and YSZ... 

The web site of CFCL UK shows the above construction. The cylindrical cells are lOYSZ electrolyte supported, with LSM cathodes and nickel/lOYSZ anodes. Thermal cycling performance is asserted to be good. Tested endurance with zero deterioration is 1000 h. 

Figure 10. Polarization curves (IR-free) for oxygen reduction at LSM cathode without (O) and with ( ) loading Pt catalysts in O2 at 7 ceii = 800 °C. Pt(A) 0.5 ing/cnr A Pt(A) 0.1 mg/em Pt(C) 0.1 mg/cm. Reproduced from Ref. 30, Copyright (1996), by permission from The Electrochemical Society of Japan.

They oat LSM cathodes increased with the oion at 7 oeii = 800 to 1000 °C (Fig. 17C). The dispersion of nm-sized Pt catalysts on LSM particles greatly enhances the performance, the... 

Figure 17. Dependencies of exchange current density jo at various electrodes on the ionic conductivity of various zirconia solid electrolytes (A) SDC (dashed, dash-dotted, and dotted lines) and Ru (0.5 mg/cm )-dispersed SDC anodes in humidified Hi. Reprinted from Ref. 45, Copyright (1997), with permission from The Electrochemical Society, (B) Pt cathodes in Oj, (C) LfCi jsSriu MnO, (LSM, dashed lines) and Pt (0.1 nig/cnr(-dispersed LSM cathodes in Oi. Each jo value was calculated from the polarization resistance (Rp, 2 tm ), since linear relationships were observed between 7 and j for rj < 0.1 V at all the electrodes and 7 ccii between 800 and 1000°C jo = (RT/nF)Rp. Reproduced by Ref. 46, Copyright (1999), by permission from The Electrochemical Society. 

At the mixed conducting LSM cathode, the Oad can be ionized at the LSM surface besides the TPB, i.e., mixed-conducting path and TPB path in parallel. The contributions of the two pathways to the overall reaction might depend on the number of active sites on the LSM or on the microstructure. Mizusaki et al. " reported that die reaction involving Oad occurred dominantly around TPB in porous La(Ca)MnO, (LCM) cathode. This explanation seems to be valid. 

With nano-SDC infiltrated LSM cathode, the single cell performance was obviously improved. Our micro-stack results proved that the gas flow geometry critically affects the stack performance. The performance of linear micro-stacks decreased with increasing cell number, probably due to the uneven gas/temperature distribution. The symmetric star-shaped design exhibited attractive output, making it very promising for portable power sources. 

Figure 3. Structure of the first Ukrainian thin film zirconia ceramic fuel cell transformer. Left part of the picture shows the LSM cathode of around 10 pm thickness and its surface followed by the dense solid YSZ electrolyte of60-70 pm thickness with a few isolated pores the right part shows the highly porous zirconia—Ni anode. Scanning electron microscopy, Superprobe...

In the first case, YSZ electrolyte of thickness 250 - 400 microns is covered with Ni-cermet anode and LSM cathode of thickness 25-50 microns. IPPE has 4 patents for technology of porous catalytic interfaces electrode-solid electrolyte . More than 200 single cells of this type were tested. At 950 C, power density of 700 mW/cm was achieved (Fig. 6). 

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