Doped La_0.5Ba_0.5MnO_3-δ Electrode For Solid Oxide Electrolysis Cells

As a clean and efficient energy conversion device,solid oxide electrolysis cell（SOEC）can produce chemicals using electrical energy.Its electrodes play key roles in catalyzing electrochemical redox reactions,which have an important influence on the performance of the electrolysis cell.A-site ordered double perovskite La_0.5Ba_0.5Mn O_3-δhas attracted much attentions due to its excellent catalytic activity and stability for the electrochemical oxidation of CH₄ and H₂.In this work,Co and Ni are doped in the B site of La_0.5Ba_0.5Mn O_3-δ,which is used to catalyze the electrochemical reduction of H₂O and CO₂ and the electrochemical oxidation of CH₄.The exsolution of the transition metals on electrode surface during reduction and its influence on the catalytic activity of the electrode are investigated.In this work,La_0.5Ba_0.5Mn_1-xCo_xO_3-δ（0≤x≤0.4）cathode is synthesized via penchini method for H₂O/CO₂-SOEC.The doping of Co increases the content of oxygen vacancy in La_0.5Ba_0.5Mn O_3-δ,and improves the conductivity in a reducing atmosphere.The structure of La_0.5Ba_0.5Mn O_3-δchanges from mixed cubic and hexagonal perovskite phases to a tetragonal phase after reduction,and Co nanoparticles are exsolved on the surface of the cathode in the meantime.The exsolution of metallic Co promotes the adsorption and surface reaction of CO₂,thus improving the electrochemical catalytic activity of the material.Supported by a 300μm-thick La_0.8Sr_0.2Ga_0.8Mg_0.2O_3-δelectrolyte layer,a H₂O-SOEC with La_0.5Ba_0.5Mn_0.7Co_0.3O_3-δas the cathode and Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δas the anode obtains electrolysis current densities of 0.46 and 1.01 A cm^-2 with an applied voltage of 1.3 V at 700 and 800 ^oC,respectively.An electrolysis current density of 0.88 A cm^-2 is also obtained at 1.2 V and 850 ^oC by a CO₂-SOEC with the same structure.The cathode exhibits a high stability in both H₂O and CO₂ atmospheres.For the H₂O-CO₂ co-electrolysis,the ratio of CO to H₂ in the product is 2.3-2.6,and the Faradaic efficiency exceeds 95%.La_0.5Ba_0.5Mn_1-xNi_xO_3-δelectrode is also prepared by penchini method in this work.The exsolution of metallic Ni in the reduction atmosphere significantly increases the catalytic activity of the electrode for CH₄ electrochemical oxidation and CO₂electrochemical reduction.With La_0.5Ba_0.5Mn_0.95Ni_0.05O_3-δas the electrode,a symmetric electrolysis cell supported by the electrolyte layer is fabricated for the electrochemical CO₂ reforming of CH₄.A current density of 0.55 A cm^-2 is achieved at850 ^oC and 1.2 V.The conversion of CH₄ is 30%,and the Faradaic efficiency is above80%.The products of CH₄ electrochemical oxidation mainly include H₂,CO,C₂H₄ and C₂H₆,and the product selectivity is affected by the catalytic activity of the electrode and the electrolysis current density.