Effect of Volatile Boron Species on the Electrocatalytic Activity of Cathodes of Solid Oxide Fuel Cells

Abstract

The effect of volatile boron species on the electrocatalytic activity, microstructure and phase stability of Ba 0.5 Sr 0.5 Co 0.8 Fe 0.2 O 3-δ (BSCF) cathodes has been studied. The cathodes were heat-treated at 800 • C for 7 days in air in the presence of boron species vaporized from borosilicate glass, and were characterized by EIS, SEM, AFM, SIMS, XRD, XPS and ICP-OES. The results have shown that after the heat-treatment in the presence of borosilicate glass, boron deposition occurs mainly on the region near electrode surface, leading to the significant Ba and in particular Sr segregation, microstructure change and phase decomposition. On the other hand, the microstructure of the inner electrode layer is almost intact. Electrode polarization resistance, R E , of an as-prepared BSCF cathode is 0.93 and 0.23 cm 2 at 650 and 800 • C, respectively, and changes to 2.08 and 0.15 cm 2 after heat-treatment at 800 • C for 7 days in the presence of borosilicate glass, respectively. The increase in R E for the O 2 reduction reaction on BSCF is much lower than that observed on La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ (LSCF) cathodes, indicating that BSCF cathodes have a much better tolerance toward boron deposition and poisoning. The limited attack of volatile boron species on BSCF is most likely related to the much slower kinetics of the formation of strontium and barium borates as compared to the formation of lanthanum borates. This study provides a significant insight into design and development of better contaminant-tolerant cathode materials for durable solid oxide fuel cell (SOFC) technologies.) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 169.230.243.252 Downloaded on 2014-12-11 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 169.230.243.252 Downloaded on 2014-12-11 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 169.230.243.252 Downloaded on 2014-12-11 to IP

ChemInform Abstract: Recent Development on Perovskite‐type Cathode Materials Based on SrCoO3‐δ. Parent Oxide for Intermediate‐Temperature Solid Oxide Fuel Cells

“…[127] Research working on the Cr-poisoning has been profoundly reviewed by Jiang et al [128][129][130] Moreover, the ORR kinetics and the microstructure of SC-based perovskite cathodes are also negatively affected by boron that comes from glass sealants. [131][132][133] The boron can deposit onto the cathode surface and lead to significant Ba and Sr surface segregation. However, higher tolerance to boron is observed for cathodes with low content of La 3+ , which is likely due to higher activity La 2 O 3 with boron than SrO and BaO.…”

A Fundamental Study of Boron Deposition and Poisoning of La0.8Sr0.2MnO3Cathode of Solid Oxide Fuel Cells under Accelerated Conditions

“…[18][19][20][21] Boron is chemically incompatible with the cathode materials, and preferentially reacts with the A-site cations in particular lanthanum to form insulating lanthanum borate, LaBO 3 . 22 The reaction between boron and LSM to form LaBO 3 is generally slow under open circuit conditions.…”

“…Boron deposition mainly occurs in the outmost electrode layer of the BSCF cathode, while the inner region close to the electrode/electrolyte interface is relatively intact and still functions electrochemically. 21 This indicates that boron deposition and poisoning is closely related to the composition of the SOFC cathode materials.The deposition and poisoning of boron impurities on SOFC cathodes could also be affected by the operation conditions. Zhou et al polarized LSM-YSZ and LSCF cathodes at a cell voltage of 0.7 V with boron partial pressure of ∼10 −9 atm for 150 h, and reported boron deposition in both the cathodes with a content of ∼500 ppm in LSCF and ∼40 ppm in LSM-YSZ at 750…”

Development of cathode materials for intermediate temperature solid oxide fuel cells

“…229 Moreover, the ORR kinetics and the microstructure of SrCoO3-δ-based perovskite cathodes are also negatively affected by boron which comes from glass sealants. [230][231][232] The boron can deposit onto the cathode surface and lead to significant Ba and Sr surface segregation. However, higher tolerance to boron is observed for cathodes with low content of La 3+ , which is likely due to higher activity La2O3 with boron than SrO and BaO.…”

“…However, higher tolerance to boron is observed for cathodes with low content of La 3+ , which is likely due to higher activity La2O3 with boron than SrO and BaO. 230,232 Since work on cathode instability in the presence of Cr and B have been extensively and profoundly done and reviewed, [233][234][235][236][237] the susceptibility to CO2 attack at intermediate temperature still remains challenging for AE-containing perovskite cathodes. This review therefore attempts to review recent studies on addressing the susceptibility of most alkaline-earth-containing cathodes to even small content of CO2 in air (~ 300 ppm) at intermediate temperature (< 800 °C).…”