Structural and electrical properties of Sr(Ti, Fe)O3-δ materials for SOFC cathodes

Abstract

Doped strontium titanates are very versatile materials. Iron doped SrTiO 3 can be used, for example, as a material for resistive gas sensors and fuel cell electrodes. In this paper, two compositions based on Fe doped SrTiO 3 were studied as possible candidates for cathode application in SOFCs. Namely, SrTi 0.65 Fe 0.35 O 3 and SrTi 0.50 Fe 0.50 O 3 were examined. A chemical reactivity between electrode and YSZ electrolyte material was investigated, since Sr containing cathode materials in contact with YSZ electrolyte are prone to form insulating phases. Electrical conductivity of bulk samples showed relatively low total conductivities of 0.4 S cm −1 and~2 S cm −1 for STF35 and STF50 respectively. Suitability for cathode application was studied by Electrochemical Impedance Spectroscopy in a symmetrical electrode configuration. Area specific resistance (ASR) was determined in the temperature range from 600°C to 800°C. At 790°C samples show polarization ASR of approximately 0.1Ω cm 2 . It can be expected that further reduction of electrode ASR can be obtained by introduction of ceria barrier layer and tailoring of the electrode microstructure.

Microstructural and electrical properties of Y0.07Sr0.93-x TiO3-δ perovskite ceramics

“…One of the most widely used representatives of perovskite materials is strontium titanate (SrTiO 3 ). It has been reported in the literature that it is one of the most promising candidates for anode and cathode materials for Solid Oxide Fuel Cells, because of catalytic and conductivity performance [3,20]. However, in a pure form strontium titanate is a dielectric material, so it requires some modifications.…”

Investigation of thin perovskite layers between cathode and doped ceria used as buffer layer in solid oxide fuel cells

“…Such an increase indicates change in oxygen reduction reaction due to formation of a new, poorly catalytic, or nonconducting phase in the cathode/CGO interface or lower than LNF electronic conductivity of STF. Such a strong negative influence of STF itself is unlikely since it was shown to exhibit ASR values comparable to other cathode material like LSM or LNF [20] when deposited on YSZ electrolyte. Possibility of reaction between STF and LNF was subsequently confirmed by XRD analysis [36].…”

“…LSCF is a state-of-the-art mixed ionic-electronic conductor [4,5]. STF is a much weaker electronic conductor but exhibits higher ionic conductivity and the order of magnitude higher surface exchange coefficient [20]. Table 1 lists ionic and electronic conductivities of these perovskites at 800°C.…”

Development of stable oxygen transport membranes

“…Oxygen ions diffuse -either via an oxygen vacancy or interstitial diffusion mechanism -to the opposite side of the membrane, which is counterbalanced by transport of electronic charge carriers. Upon arrival at the membrane surface at the low pO 2 side, the reverse exchange reactions occur [25] .…”

“…pO 2 ′ and pO 2 ′′ are the oxygen partial pressures maintained at the high and low pO 2 side of the membrane, respectively. A changeover in rate-limiting step occurs, from bulk diffusion to surface-exchange, upon decreasing the membrane thickness below a characteristic thickness, L c , [25]. L c is given by…”