Investigation Of Hydrogen Peroxide Reduction Reaction On Perovskite Oxides:Descriptor And Substitution Effects

The current energy crisis and environmental problem are severe challenges to the society.In order to resolve the issues,new renewable energy sources are urgent to be developed,among which the fuel cells have attracted much attention due to their superiorities.At present,the common cathode reaction in the fuel cell system is oxygen reduction reaction?ORR?,which severely restricts the performance of the cell due to the low solubility of O₂ and high energy barrier of ORR.Recently,H₂O₂ shows great promise in replacing O₂ as cathode oxidant,since H₂O₂ is highly soluble,easy to be reduced,convenient and safe to store and transfer.Among the catalysts for hydrogen peroxide reduction reaction?HPRR?,the perovskite oxides are great potential catalysts with the advantages of easy preparation,low cost,easy modification and high activity/stability.Nevertheless,the contemporary research of perovskite oxides for HPRR is still at its starting stage.There is little study in HPRR on perovskite and the principle for designing highly active perovskite oxide catalysts.Therefore,it is urgent to investigate the descriptor of HPRR on perovskite oxides and substitution effects in HPRR on perovskite oxides,which are the main focuses of this work.?.The descriptor of HPRR on perovskite oxidesA series of perovskite oxides with different B site eg electron occupancies were synthesized via the co-precipitation method.After analyzing their HPRR activity,we established a "volcano" correlation between eg occupancy and HPRR activity.According to this correlation,we found that the perovskite oxide with a near-unity eg occupancy possessed the highest activity.Further study showed that the eg occupancy actually affected the rate determining step?RDS?in HPRR on active B site,which led to the discrepancy in activity.By analyzing the possible RDS with the fitted Tafel slopes,the possible HPRR mechanisms were proposed.?.Substitution effects in HPRR on perovskite oxidesTwo series of perovskite oxides?i.e.,LaxSr1-xCoO3?LSCO?and LaCoxMn1-xO3?LCMO??based on LaCoO3?LCO?were prepared by sol-gel approach.Through studying the HPRR activity of substituted samples,we found that the Sr substituted samples showed the surface Sr segregation which led to the coverage of surface active Co site by inert surface Sr-O species.Thus,the Sr substituted LSCO samples exhibited lower HPRR activity compared with LCO.Contrarily,the 20%Mn substituted LMCO sample showed the highest HPRR activity.With further analysis,it revealed that the Mn substitution enhanced the distortion of BO6 structure in LCO,which changed the B site's electronic structure.What's more,the ratio of highly active M3+ species also increased.These factors all contributed to its high HPRR activity.The above work methodologically studied the "structure-property" correlation between the intrinsic electronic structure of perovskite oxide and its HPRR activity,which provided the principle for designing highly active perovskite oxide catalysts for HPRR.