Lanthanum strontium vanadate in solid oxide fuel cells.

Solid oxide fuel cells (SOFCs) are high temperature energy conversion devices with the advantages of fuel flexibility and high efficiency. Limitations of SOFC cermet anodes have been stimulating oxide anodes. Lanthanum strontium vanadate, La1-xSrxVO3 (LSV, 0 ≤ x ≤ 1), have been synthesized and examined as potential SOFC anode materials. LSV appear to be chemically compatible with yttria-stabilized zirconia (YSZ) at least up to 1300°C. Electrode performance is evaluated by impedance spectroscopy and dc polarization between 800 to 1000°C. Good electrode performance is achieved with LSV(x = 0.2, 0.3, 0.4, 0.5)–YSZ composite anodes, in both pure H2 and 3% H2O humidified CH4. For half-cells with La0.6Sr0.4VO3–YSZ anode, polarization resistance is 0.85 Ω cm2 and 1.38 Ω cm2 at 900°C in pure H2 and wet CH4, respectively. When drawing a current of 0.2 A/cm2 at 900°C, the overpotential is 0.13 V in pure H2, and slightly higher in wet CH4, 0.20 V. Further optimization of electrode microstructures is needed to maximize the performance of LSV for potential SOFC application. LSV synthesized by soft chemistry methods show higher catalytic activity than those via solid state reactions. To elucidate the interfacial reaction behaviours, impedance responses of LSV8020 (50 wt. %)–YSZ anodes are recorded and interpreted in H2–H2O–He atmosphere. The typical impedance pattern corresponds to three types of physical phenomena, viz. reaction impedance, gas concentration impedance, and inductive loops that only emerge at highly biased conditions. The gas concentration impedance is significantly inhibited in wet atmosphere. A detrimental water effect is observed for up to 15 vol. % H2O. The double layer structure of solid oxide fuel cell anode/electrolyte interfaces is simulated by Markov Chain Monte Carlo methods. A case study is carried out on lanthanum strontium vanadate (LSV)/yttria-stabilized zirconia (YSZ). The density of oxygen vacancies directly adjacent to the LSV/YSZ interface is one order of magnitude higher than the bulk value of YSZ. The spatial variation of oxygen vacancies in the double layer region exhibits exponential decay behaviour. The double layer undergoes pronounced relaxations when the interfaces are under anodic biases in the range from 0 to 150 mV. The results indicate that 70–80% of the oxygen vacancies are immobilized in the Helmholtz–Perrin layer. The rationale has wide applications on elucidating anodic reaction mechanisms and potential distributions across anode/electrolyte interfaces. The double layer of electrode/electrolyte interfaces plays a fundamental role in determining the performance of solid state electrochemical cells.DOCTOR OF PHILOSOPHY (MAE