Preparation And Electrocatalytic Properties Of Cobalt-Doped Lanthanum Nickelate Single Crystal Films

In the face of a series of challenges such as energy shortage and environmental deterioration caused by human social activities,developing and promoting sustainable clean energy is a major problem to be solved urgently.Electrolyzed water technology is considered to be one of the effective ways to solve energy and environment problems.However,this process is limited by its own slow Oxygen Evolution Reaction（OER）kinetics,so electrocatalysts are needed to reduce the overpotential and increase the activity of the reaction.The ABO₃ perovskite oxide is an ideal alternative electrocatalyst for precious metal materials（Ir and Ru based）due to its low price,easy mining,long-term stability and high OER catalytic activity under alkaline conditions.In this study,the Pulsed Laser Deposition（PLD）technique was used to synthesize a series of LaNi_xCo_1-xO₃（x=0,0.1,0.3,0.5,0.7,0.9 or 1）films and their OER properties are systematically investigated.The main research contents are as follows:First,by tuning the growth condition variables of the film,including the substrate,laser energy density,deposition time,annealing oxygen pressure,the film growth conditions suitable for measuring OER properties that can improve the crystallinity and reduce the resistance of the film are determined.A series of LaNi_xCo_1-xO₃（x=0,0.1,0.3,0.5,0.7,0.9 or 1）epitaxial single crystal films,as the model system of OER electrocatalyst,were grown on LaAlO₃（LAO）<001>under the best growth conditions.The structural and electrical characterization of the films showed that the films prepared in this study have high crystallinity,good film quality,low resistance and smooth surface morphology,suggesting that they are suitable for OER electrocatalyst.Second,the electrochemical properties of a series of thin films were characterized to explore the effect of B-site doping on their OER activities.The results show that the current density of the films doped with Co increases,the over-potential decreases,the electrochemical active surface area increases,and the charge transfer resistance decreases,as compared with the cases of ideal LaNi O₃,indicating that B-site doping can effectively improve the OER catalytic activity of LaNi O₃perovskite oxides.Among them,LaNi_0.7Co_0.3O₃ shows the best OER catalytic performance in alkaline solution.At1.65 V vs RHE voltage,the current densities of La Co O₃ and LaNi O₃ thin film are 44.25μA/cm²and 214.91μA/cm²,respectively,and the current density of LaNi_0.7Co_0.3O₃ thin film is as high as 442.09μA/cm².The influence of substitution of Co for Ni in LaNi O₃on its electronic structure was investigated by means of electronic structure characterization and theoretical calculations.The results show that as the Ni content increases,the ratio of Ni/Co gradually increases,the content of Ni³⁺gradually increases,the content of Co³⁺gradually decreases,the ratio of Ni³⁺/Ni²⁺continuously increases,and the ratio of Co³⁺/Co²⁺gradually decreases.In addition,Co doping reduces the potential barrier of OER reaction,reduces the required free energy,reduces the overpotential of OER reaction,and improves the charge transfer ability.This study thus provides a new way to improve the catalytic activity of OER for LaNi O₃.