Preparation Of Chromate Cathode And Evaluation Of Electrochemical Process For High Temperature Electrolysis

Using a high temperature solid oxide electrolyzer, CO2 and steam can be electrolyzed into CO and H2 as well as oxygen. The traditional Ni-based composite cathode of solid oxide electrolyzer is easy to be oxidized. This paper mainly studies the preparation of perovskite chromate cathode and high temperature electrolytic electrochemical process. Firstly, the working principle and structure of a solid oxide electrolyzer as well as its key materials are presented in detail in this paper. The polarization loss and thermodynamic analysis of a solid oxide electrolyzer is also described briefly. Finally, with respect to the development of solid oxide electrolyzer, the research progress of steam electrolysis, CO2 reduction and H2O/CO2 co-electrolysis in recent years is also presented in detail.Firstly, this paper mainly studies the electrochemical process of the La0.75Sr0.25Cr0.sMn0.5O3-δ/Sm0.2Ce0.8O2-δ (LSCM/SDC) composite electrode symmetrical electrolyzer for direct electrolysis of CO2. High temperature electrolysis of pure CO2 is tested at 800℃ and under the voltage of 0.5,1.0,1.5 and 2.0 V, respectively. It has the highest current efficiency of about 69% while the voltage is 1.0 V. However, the current density and current efficiency are decreased with the increased voltages. Then, this paper using the impregnation method, mixes LSCM with the Fe metal catalysts to study the catalytic performance for the current efficiency. Direct high temperature steam electrolysis is performed both in the atmosphere of 3% H2O/5% H2/Ar and 3% H2O/Ar. It is obviously that the current efficiency is significantly increased with the Fe catalysts doped electrode for steam electrolysis. According to the microstructure images of cathode after 11 h electrolysis test, Fe catalysts aggregation phenomenon is observed on the cathode surface.Finally, this paper mainly prepares the A-site deficient and B-site excess perovskite electrode materials (La0.75Sr0.25)0.95(Cr0.8Ni0.2)0.95Ni0.05O3-δ (LSCNNi) and study the electrochemical process of steam electrolysis. X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and X-ray photoelectron spectrometer (XPS) are used to characterize the property of LSCNNi. Steam electrolysis is performed at 800℃ and in the atmosphere of both 3% H2O/5% H2/Ar and 3% H2O/Ar. The current efficiency of the electrolyzer with La0.75Sr0.25Cr0.8Ni0.2(LSCN) cathode is approximately 79% and 74% at 2.0 V, respectively. However, the current efficiency of the elctrolyzer with LSCNNi cathode reaches approximately 87% and 81%, respectively. Ultimately, the performance of the long term test suggests that the novel electrode is useful to improve the stability of steam electrolysis. This paper finally summarizes the experimental results, and the future development of solid oxide electrolyzer is also discussed.