Reasearch Of La_0.75Sr_0.25Cr_0.5Mn_0.5O_3-δ-Based Composite Cathode Of Solid Oxide Electrolysis Cell Used For Electrolysis Of CO₂

High-temperature electrolysis of H2 O, CO₂ and co-electrolysis of H2O-CO₂ can be performed in solid oxide electrolysis cell（SOEC）. Using excess electricity and heat, solid oxide electrolysis cells（SOECs） can not only electrochemical convert steam to clean and renewable hydrogen, but also can convert greenhouse gas CO₂ to CO, which is significant fuel and chemical raw materials. Less electricity energy is needed in SOECs since they are operated at high temperature, it makes SOEC a promising new energy technology. In this paper, the preparation of La_0.75Sr_0.25Cr_0.5Mn_0.5O_3-δ-based cathode materials and test methods were modified and investigated systematically. In order to enhance the chemical adsorption of reaction gas for electrolysis, composite cathode was prepared by adding a small amount of Ca O into LSCM, which could enhance the electrochemical performance of SOEC significantly when cathode was exposed to low concentration of reactants.At first, direct electrolysis of CO₂ was performed in a symmetric cell with LSCM electrode, and higher electrolysis current density was obtained. At the same time, we found that current density in long term and at high applied voltage degrades with time, and the degradation mainly comes from LSCM cathode. Furthermore, the electrochemical performance of LSCM and LSM was almost the same when they were used as anode of SOEC in the process of the electrolysis of CO₂. In order to avoid the leakage of oxygen in air to the cathode space of SOEC, inert gas Ar was employed to purge the anode of SOEC, which was benefited to the enhancement of current efficienc y.Sencondly, the electrochemical performance of SOEC with a configuration of LSCM|YSZ|LSM was investigated with different CO₂ concentrations. A platform was found in Voltage-Current density curve when the cathode was operated under low CO₂ concentration. The lower CO₂ concentration at the cathode, the higher working temperature of SOEC and the slower voltage scan rate, the platform of Voltage-Current density curve became more obvious. When the platform appears, the AC impedance spectra show obvious feature attributed to gas diffusion, the adsorption and dissociation processes on electrode. In order to enhance the LSCM cathode’s adsorption ability of CO₂, a small amount of Ca O was added to LSCM to form a composite cathode and the electrolysis of CO₂ was performed under different CO₂ concentration at the cathode. Although both the resistivity of the cathode and charge transfer resistance increased by the Ca O addition, the current density of SOEC was still enhanced significantly under low CO₂ concentration of CO₂, at the same time, the platform of current density disappeared. LSCM-Ca O composite cathode possessed higher electrochemical performance under low concentration of CO₂ higher operating temperature.Finally, high-temperature electrolysis of steam and co-electrolysis of steam/CO₂ were demonstrated in a SOEC with a configuration of LSCM|YSZ|LSM. Results indicated that the more concentration of electrolytic reaction gas, the better electrochemical performance of SOEC. High-temperature electrolysis of H2 O and co-electrolysis of H2O/CO₂ were also performed in a SOEC with LSCM-Ca O composite cathode. The result showed that the electrochemical performance enhanced substantially and the low frequency resistance decreased obviously. After introducing Ca O to LSCM cathode, current density at 850℃ and an applied voltage of 2.0 Vincreased by 12.1%, 67.6% and 71.2% when cathode were exposed to reaction gases of 5%CO₂/95%Ar、3%H2O/97%Ar and 10%H2O/30%CO₂/97%Ar, respectively.