Solid oxide electrolysis cells (SOECs) are devices that convert electrical energy into chemical energy and are widely used for hydrogen production from steam or CO generation from CO2. Spinel-type oxides are commonly used as a coating on metal interconnects because of their high electrical conductivity (σ) in the air and matching thermal expansion with that of the electrolyte. They have been used as oxygen electrodes in solid oxide cells in recent years, but their application in fuel electrodes was less studied. In this research, MnFeCr1–xCoxO4 (x = 0, 0.05, 0.2) spinel oxides with a σ around 0.1 S cm–1 were used as the fuel electrode of an SOEC. The MnFeCr0.95Co0.05O4 (MFCC5) and MnFeCr0.8Co0.2O4 (MFCC20) with Co doping on the Cr site decomposed partially during the water electrolysis, producing CoFe alloy and MnO particles on the parent spinels, forming a metal/oxide interface that further enhanced the electrocatalytic performance and durability of the cell. MFCC5 was able to achieve a current density of 1550 mA cm–2 at 1.6 V and maintained a current density of about 600 mA cm–2 after the 150 h durability test at 1.3 V at 800 °C. The Faraday efficiency was close to unity. The in situ exsolution process driven by the cathodic current significantly changed the performance of the cell, but a high performance was still maintained. In situ exsolution of the metals from the reducible cations was a feasible way of designing the spinel-type cathode for SOECs.
Wanbin Lin,Weibin Su,Yanpu Li,Te-Wei Chiu,Manish Singh,Zehua Pan,Liangdong Fan
Solid oxide electrolysis cells (SOECs) hold enormous potential for efficient conversion of CO 2 to CO at low cost and high reaction kinetics. The identification of active cathodes is highly desirable to promote the SOEC's performance. This study explores a lithium-doped perovskite La 0.6- x Li x Sr 0.4 Co 0.7 Mn 0.3 O 3- δ ( x = 0, 0.025 0.05, and 0.10) material with in situ generated A-site deficiency and surface carbonate as SOEC cathodes for CO 2 reduction. The experimental results indicate that the SOEC with the La 0.55 Li 0.05 Sr 0.4 Co 0.7 Mn 0.3 O 3- δ cathode exhibits a current density of 0.991 A cm −2 at 1.5 V/800 °C, which is an improvement of ≈30% over the pristine sample. Furthermore, SOECs based on the proposed cathode demonstrate excellent stability over 300 h for pure CO 2 electrolysis. The addition of lithium with high basicity, low valance, and small radius, coupled with A-site deficiency, promotes the formation of oxygen vacancy and modifies the electronic structure of active sites, thus enhancing CO 2 adsorption, dissociation process, and CO desorption steps as corroborated by the experimental analysis and the density functional theory calculation. It is further confirmed that Li-ion migration to the cathode surface forms carbonate and consequently provides the perovskite cathode with an impressive anti-carbon deposition capability, as well as electrolysis activity.
Guangdong Li,Yunjie Gou,Rongzheng Ren,Chunming Xu,Jinshuo Qiao,Wang Sun,Zhenhua Wang,Kening Sun
Solid oxide electrolysis cells (SOECs) have emerged as one of the most potent techniques for hydrogen production. As the restricted step for SOEC, as well as the most predominant obstacle to the scaled application, oxygen evolution reaction (OER) should be urgently accelerated by developing potent electrocatalysts. Despite inferior electrochemical activity to cobalt-based materials, perovskite ferrites exhibit great potential in the future with regard to good intrinsic stability and durability, abundant reserves, and good compatibility with other SOEC components. In this work, fluorination is introduced to the typical perovskite ferrite to further intensify the OER process. Ab initio calculations combined with physical–chemical characterizations are performed to reveal the mechanism. The doped F− leads to debilitating the strength of the metal–oxygen bond and then reduces the energy for oxygen vacancy formation and ion migration, which renders improvements to sub-processes of OER on the anode. The well-verified material, PrBaFe2O5+δF0.1 (PBFOF), exhibited a low polarization resistance of 0.058 Ω cm−2. Single cells based on PBFOF showed a high current density of 2.28 A cm−2 at 750 °C under 1.3 V. This work provides a clear insight into the mechanism of fluorination on perovskites and high-activity anode material for SOEC.
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