Cr poisoning has been regarded as a significant reason for the degradation of La 0.8 Sr 0.2 Co 0.2 Fe 0.8 O 3-δ (LSCF) cathode in practical application. In recent years, protective coating on cathode surface has been recognized as an effective approach to improve the Cr poisoning resistance of cathode. In this work, Ce 0.8 Gd 0.2 O 1.9−δ (GDC) layer is successfully coated on LSCF nanoparticles by sol-gel method, endowing the GDC coated LSCF (LSCF@GDC) composite material with excellent electrochemical properties and Cr poisoning tolerance. The LSCF@GDC0.32 composite cathode exhibits a lower total impedance increase of 0.20 Ω cm 2 per 200 h and 0.31 Ω cm 2 per 200 h for open circuit and constant current test with SUS430 as Cr source, respectively, compared with the bare LSCF cathode (0.90 Ω cm 2 per 200 h and 1.53 Ω cm 2 per 200 h, respectively). In addition, according to energy dispersion spectrum (EDS) and tip enhanced Raman characterization, the enhanced Cr poisoning tolerance of composite cathode can also be verified through the alleviated SrCrO 4 formation and Cr deposition on LSCF cathode.
Zhenwei Wang,Shikai Zhao,Xue Guo,Jiao Li,Qiangqiang Hu,Yurun Feng,Fangyong Yu,Haibin Sun
La 0·6 Sr 0·4 Co 0·2 Fe 0·8 O 3-δ (LSCF), one kind of state-of-art solid oxide fuel cells (SOFCs) cathodes, often suffers from the chromium poisoning in the operating condition with Cr-based stainless steel interconnects, resulting in deteriorating cell performances. A simple electroless silver plating method was used to modify the surface of LSCF cathodes (named LSCF-Ag), and the anti-chromium stability of LSCF cathodes was studied. After the Cr treatment for 40 h, the polarization resistance ( R p ) of LSCF cathodes changes from 0.26 Ω cm 2 to 0.62 Ω cm 2 at 700 °C, while that of LSCF-Ag cathodes shows nearly no change (from 0.24 Ω cm 2 to 0.26 Ω cm 2 at 700 °C). In LSCF-Ag cathodes, the formation of AgCrO 2 instead of SrCrO 4 avoids the lack of excessive Sr in the A site of LSCF, and AgCrO 2 has an electronic conductivity two orders of magnitude greater than SrCrO 4 , thereby exhibiting significant survivability to Cr. The single cell with LSCF-Ag cathodes after Cr treatment shows a stable peak powder density of 288 mW cm −2 at 700 °C while taking wet hydrogen and air as fuel and oxidizer . As a comparison, the peak power density of single cells with blank LSCF cathodes drops by 12%. It is suggested that the simple electroless silver plating on LSCF cathodes is an effective method to suppress cathode chromium poisoning.
Cr-poisoning effect on pure double-perovskite PrBa 0.5 Sr 0.5 Co 1.5 Fe 0.5 O 5+δ (PBSCF) cathode and La 2 NiO 4+δ (LN)-coated PBSCF cathode is investigated. During the Cr poisoning test at 750 °C in the presence of SUS430 interconnect, the electrochemical performance of pure PBSCF cathode shows severe degradation, and the significant increase in R P is mainly contributed by the increased R L . The BaCrO 4 deposits are identified on the PBSCF cathode surface. LN-coated PBSCF cathode, by contrast, shows remarkable tolerance towards chromium. The reaction between volatile Cr species and PBSCF cathode can be prevented by a dense LN coating. Thus, a more stable electrochemical performance is achieved by LN-coated cathode during the Cr poisoning test. The results indicate that the introduction of LN coating not only improves the cathode electrochemical performance, but also prevents the cathode from being poisoned by chromium.
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