Preparation And Electro-catalytic Performance Of Perovskite Bifunctional Catalysts For Anode Reactions Of Lithium-oxygen Battery

The perovskite-type transition-metal oxides exhibits good electrocatalytic activity for oxygen reduction reaction?ORR?and oxygen evolution reaction?OER?in alkaline solutions,and their physical and chemical properties can be flexibly adjusted by changing the type of transition metal elements.Therefore,the common perovskite oxides containing lanthanum were chosen as research objects.Element doping and special morphological design were used to improve their catalytic activities for ORR and OER.Finally,we obtained the perovskite-type catalyst with excellent catalytic performance towards oxygen reactions.In addition,the electrochemistry performance of the hybrid lithium oxygen batteries with perovskite-type catalyst prepared in this work was tested.The main achievements are listed as below:1.Preparation and characterization of perovskite-type transition-metal oxides containing lanthanum.We prepared four nano-level perovskite-type catalysts LaBO₃?B=Mn,Fe,Co,Ni?by a standard sol-gel method.And citric acid,metal nitrates were used as complexing agent and raw materials,respectively.The catalytic performance of these catalysts was tested in alkaline electrolyte.The results show that LaMnO₃ exhibits an outstanding catalytic activity for ORR,but a poor catalytic activity towards OER,while LaCoO₃ presents good catalytic performance for OER but common performance towards ORR.These oxides were used as catalysts in anode of hybrid Li-O₂ batteries,respectively.According to testing results of these batteries,the same conclusion as above can be obtained.2.In order to improve the OER electroactivity of LaMnO₃,the Co element was doped into crystal lattice of LaMnO₃.We prepared a series of nano-level perovskite oxides LaMn_1-xCo_xO₃ by a standard sol-gel method.And citric acid,metal nitrates were used as complexing agent and raw materials,respectively.The bifunctional electrocatalytic performance of LaMn_1-xCo_xO₃ was characterized in alkaline media.According to the testing results,the OER activities of LaMn_1-xCo_xO₃ displays a trend from rising to decline,which the LaMn_0.7Co_0.3O₃ obtained when x=0.3 shows the highest OER catalytic activity.Namely,the LaMn_0.7Co_0.3O₃ possesses the best ORR and OER catalytic performance among the series of LaMn_1-xCo_xO₃ samples.Meanwhile,the hybrid Li-O₂ battery with LaMn_0.7Co_0.3O₃ shows lower charge voltage than that of LaMnO₃ and superior cycling stability in alkaline electrolyte.3.The special morphology structure was designed for perovskite composite LaMn_0.7Co_0.3O₃ to alleviate agglomeration and increase its specific surface area.We prepared nano-level perovskite composite LaMn_0.7Co_0.3O₃/C nanofiber with special morphology via electrostatic spinning,and studied the effects of morphology change on catalytic activity.DMF acted as solvent,the mixture of PVP and PAN,lanthanum nitrate,cobalt nitrate and manganese acetate were used as raw materials.Results indicate that LaMn_0.7Co_0.3O₃/C nanofiber has similar ORR performance with LaMn_0.7Co_0.3O₃prepared using sol-gel method;and its OER activity is improved further,which its OER potential shows a negative shift of 50 mV compared with that of LaMn_0.7Co_0.3O₃.In addition,the LaMn_0.7Co_0.3O₃/C nanofiber exhibits superior charge voltage and excellent cycling stability in alkaline electrolyte according to the results of cycling discharge-charge testing.Thus,morphology change indeed improves catalytic properties of catalyst by increasing specific surface area.