Oxygen pumping based on <i>c</i>-axis-oriented lanthanum silicate ceramics: challenge toward low operating temperature

Abstract

A new electrochemical oxygen separation pump was developed by using c-axis-oriented La 9.66 Si 5.3 B 0.7 O 26.14 (c-LSBO), which has high oxide-ionic conductivity (>10 ¹3 S cm ¹1) up to 300°C. Interfacial resistance between the electrode and c-LSBO was investigated to realize the full potential of LSBO as an oxygen separation material. The formation of a Sm-doped CeO 2 (SDC) thin film (thickness: 300 nm) between the electrode and c-LSBO was effective for suppressing the interfacial resistance. Furthermore, a mixed conductive La 0.6 Sr 0.4 Co 0.78 Ni 0.02 Fe 0.2 O 3¹¤ (LSCFN) was applied to the electrode for enhancing the oxygen reduction/evolution activity on the electrode. The LSCFN/SDC/c-LSBO symmetric cell showed an oxygen permeation flux of 3.5 mL cm ¹2 min ¹1 (1.0 A cm ¹2) at 600°C under an applied DC voltage of 1.5 V; this value was 67 times that of Pt/c-LSBO. This oxygen pump based on the LSCFN/SDC/c-LSBO symmetric cell would find promising application in oxygen separation at intermediate temperatures. Further reduction of the interfacial resistance and polarization resistance of the electrode may decrease the operating temperatures to below 400°C.

Effect of Boron Substitution on Oxide-Ion Conduction in c-Axis-Oriented Apatite-Type Lanthanum Silicate

“…The O4 sites exist along a linear path along the c -axis, so oxide ions at the O4 site are the primary conduction path in apatite-structured materials. Because of the high oxide-ion conductivity, when apatite-type LSO is applied to the solid electrolyte in electrochemical devices such as intermediate-temperature SOFCs, oxygen-separation membranes, and gas sensors, , the operating temperature can be expected to be lowered to values below 873 K. There are two strategies to improve the oxide-ion conductivity of this material. One is elemental substitution into the La and Si sites.…”

DC-Voltage-Induced High Oxygen Permeation through a Lanthanum Silicate Electrolyte with a Cerium Oxide Thin Film

“…38,39 Therefore, it can be inferred that the n-type MIEC formed in situ causes a drastic increase in the oxygen permeation flux at high applied voltages. We previously reported that the formation of an SDC interlayer with an isotropic oxide-ion conduction pathway enhanced the oxygen incorporation into c-LSBO from the triple phase boundary (TPB), 32) as shown in Fig. 5.…”

“…30,31 Additionally, by employing c-LSBO in a novel oxygen separation device and gas sensor, our group demonstrated lowto-intermediate temperature operability. 32,33 In terms of the oxygen pumping properties, cell resistance decreased by more than 80% at a DC voltage of 2.0 V upon the inclusion of an intermediate Sm0.2Ce0.8O2 (SDC) thin film layer between the c-LSBO electrolyte and the Pt electrode, compared with that of the cell without the SDC. Furthermore, using a p-type oxide-based MIEC, La0.6Sr0.4Co0.78Ni0.02Fe0.2O3 electrode, a high oxygen permeation flux of 3.5 mL cm −2 min −1 was achieved at 600 °C and a DC voltage of 1.5 V. 32 Further improvements in the oxygen pumping properties at low temperatures will significantly contribute to the realization of on-site oxygen supply and electrolysis technology.…”

Study of oxygen diffusion in dense lanthanum oxide ceramics

“…18) On the basis of reaction Eqs. (8) and (9), we speculate that small amounts of SrO and GeO 2 have a small effect on the oxygen vacancies in La 2 O 3 . The second pathway to the introduction of oxygen vacancies is the formation of nonstoichiometric La 2 O 3 during sintering.…”