Uncovering The Impact Of Strain And Oxygen Defect On The Oxygen Evolution Reaction Activity Of Perovskite Oxide

The sluggish kinetics of the oxygen evolution reactions severely limit the performance of many electrochemical energy conversion and storage systems,such as metal air batteries and water electrolysis.In order to break the dilemma caused by applying noble metal catalysts as oxygen evolution catalysts,researchers have conducted extensive explorations in developing alternative catalysts and optimizing catalysts.Cost-effective perovskite oxides have been widely studied as promising alternative materials.There is in need of improvement before the perovskite is widely commercialized.In the optimization of the catalytic performance of perovskite catalysts,stress and oxygen deficiency regulation have been extensively studied as effective control methods.The effects on the catalytic activity of perovskites,oxygen deficiency and strain are not well defined,and the mechanism of effects is not clear.Firstly,the experiments carried on the single crystal model prepared by pulsed laser deposition system verified that the higher activity of La_0.7Sr_0.3CoO₃?LSC?thin film under compressive strain which is derived from the strain and oxygen defects coupling impacts.The electrochemistry experimental results showed that the compressive strain film?LSC/LAO?exhibited higher catalytic activity than the tensile strain film?LSC/LAO?.Cobalt valence analysis and lattice analysis both showed LSC/LAO was introduced less oxygen vacancies after heat treatment because its lower oxygen vacancy formation energy and thus it is less likely to form oxygen defects.It is means that LSC/LAO exhibited higher catalytic activity originated from its less oxygen defects.The second part of this study further explored the application of the strain engineering for improving the OER performance actual perovskite catalyst LSC nanofibers with diameters of 30nm and100nm were synthesized electrospinning method.The lattice structure,surface composition and OER activity of the nanofibers were compared with the micron-sized LSC powder.XRD analysis confirmed that the lattice parameters of 30nm nanofibers were significantly smaller than that of the LSC powder and the 100nm fibers.The lattice changes suggested that,due to the size effect,the compressive strain was introduced by surface stress in the 30nm nanofibers,which greatly enhanced its intrinsic activity and achieved general activity that was 4 to 5 times the activity of the bulk material,which was consistent with the higher catalytic activity of the LSC film under the compressive strain state in the previous study.Finally,we investigated the effects of oxygen defects on OER performance of actual perovskite catalyst.Different concentrations of oxygen defects were introduced into 100nm LSC nanofibers prepared through series heat treatment.Electrochemical experiments found that,as the oxygen defects increased,the activity of the material decreased.Theoretical calculations have also confirmed that an increase in oxygen defects causes more electrons to fill in the high energy orbit and an increase in the band gap.In addition,the analysis of surface elements was found that the increase of oxygen defect caused the decrease of surface oxygen specis and modified OH adsorption.These changes in nanofiber may be responsible for the reduced OER activity of LSC nanofibers observed in electrochemical tests.