No abstract

No abstract

No abstract

Although many benefits are expected by reducing the operating temperature of solid oxide fuel cells ͑SOFCs͒ with alloy interconnectors, it should be of concern that chromium oxyhydroxide vapor generated from an oxide scale (Cr 2 O 3 ), which is formed on the surface of most high temperature oxidation-resistant alloys, degrades the performance of the cathode under polarization. We have investigated a relationship between resistance against the Cr poisoning and compositions of electrode and electrolyte to show the possibility of a mitigating the Cr poisoning without reducing the chromium oxyhydroxide vapor pressure. Sr-doped LaMnO 3 ͑LSM͒ electrode on yttria-stabilized zirconia electrolyte with a current collector made of a Cr-containing alloy showed fast degradation under a polarization, which was due to the precipitation of Cr 2 O 3 at the electrode/electrolyte interface as a result of the reduction of the chromium oxyhydroxide vapor. In the present study, the degradation by the Cr poisoning has been investigated for the LSM electrode on four types of electrolytes. The degree of the degradation was found to depend on the composition of the electrolyte on which the electrode was prepared. This suggests that the electrochemical properties of the electrode/electrolyte interface influence the reduction of the chromium oxyhydroxide vapor. We have found that when La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 and Ce 0.8 Sm 0.2 O 1.9 were used as the electrode and the electrolyte, respectively, the significant Cr poisoning is not caused even in the presence of the chromium oxyhydroxide vapor at the temperature range from 923 to 1173 K.

No abstract

No abstract

The electrochemical oxidation of H2 and CO in a H2‐H2O‐CO‐CO2 system at the interface of a porous Ni‐yttria stabilized zirconia (YSZ) cermet electrode and YSZ electrolyte has been studied using complex‐impedance spectroscopy and direct‐current polarization measurements of 1023 and 1273 K under a constant oxygen partial pressure. The polarization resistance increased when the CO concentration ratio. pCO/false[pH2+pCOfalse] , exceeded 0.2 and 0.5 at 1023 and 1273 K, respectively. The electrochemical oxidation rate of H2 was 1.9–2.3 times and 2.3–3.1 times higher than that of CO at 1023 and 1273 K, respectively, and the water‐gas shift reaction was found to be much faster than the electrode reaction at both temperatures. An equivalent‐circuit analysis of the complex‐impedance spectra suggested that the lower electrochemical oxidation rate of CO (compared to H2 ) was caused mainly by the larger diffusion resistance of CO than H2 on the electrode surface at 1023 K, and by both the larger surface diffusion resistance and charge‐transfer resistance at 1273 K. © 2000 The Electrochemical Society. All rights reserved.

No abstract