Enhanced Catalytic Performances Of Perovskite Oxides As High Efficient Oxygen Catalysts

Sluggish kinetics of both oxygen reduction reaction?ORR?and oxygen evolution reaction?OER?have been one of bottlenecks to hinder the commercial application of rechargeable metal-air batteries.It is urgent and necessary to develop non-noble bifunctional catalysts for both the ORR and the OER with high catalytic activities and stabilities.As one of important branch for high performance oxygen catalysts,perovskite oxides have been attracting more and more attentions owing to their high intrinsic catalytic activities,abundant varieties,rich resources,and low cost.However,low electrical conductivity?electron conductivity and ionic conductivity?and specific surface area?surface-interface properties?severely limit their actual catalytic activities.Herein,we try to enhance their catalytic activity and stability of perovskite oxides through the following three strategies:1.Non-metallic element P doping.In this chapter,P doped SrCo_0.5Mo_0.5O₃?SCM?perovskite oxide has been prepared by a facile sol-gel method with NH₄H₂PO₄ as phosphate sources.XRD results show that P doping is favorable for structure transformation of perovskite oxide from hexagonal phase to tetragonal phase.Rotating-disk-electrode?RDE?results exhibit that the ORR half-wave potential of the as-prepared Sr(Co_0.5Mo_0.5)_0.9P_0.1O₃?SCMP?positively shifted 36 mV and the OER cut-off current increased by 8.2 mA cm^-2?at 1.75 V vs.RHE?compared with that of SCM,suggesting better ORR/OER bifunctional catalytic activity of SCMP.2.Ni₂P surface modification.In reducing atmosphere,Ni nanoparticle exsolution will occur on the surface of La_0.8Sr_0.2Cr_0.31Ni_0.69O₃?LSCN?persovskite oxides.In this chapter,we have successfully in-situ transferred these Ni nanoparticles to Ni₂P nanoparticles to form novel Ni₂P/LSCN heterostructure hybrids catalysts?r-LSCN-P?through a simple high temperature phosphating process.The RDE results reveal that a significantly improved catalytic activity for both OER and HER has been obtained after Ni₂P surface modification.The OER potential of r-LSCN-P?1.70 V vs.RHE?is close to that of commercial IrO₂catalyst?1.69 V vs.RHE?at a current density of 20 mA cm^-2,the HER potential of r-LSCN-P?-0.21 V vs.RHE?positively shifted by over 80 mV compared with that of LSCN at a current density of-10 mA cm^-2.After fabricating symmetric electrodes to do all water splitting measurements,the r-LSCN-P//r-LSCN-P electrolytic cell has maintained a constant electrolysis potential of 1.75 V for over 14 h without any attenuation at a current density of 10 mA cm^-2,which exhibits better catalytic stability than that of the PtC//IrO₂double electrode.3.Composited with N-doped CNTs.In this chapter,we reported a low cost and simple approach to in-situ prepare La₂O₃-NCNTs hybrids by using La Ni_0.9Fe_0.1O₃?LNFO?perovskite oxides as precursors,sugar as carbon sources and urea as nitrogen sources.Rotating-ring-disk-electrode?RRDE?tests exhibit that the as-prepared La₂O₃-NCNTs hybrids is a novel robust bifunctional oxygen catalyst.The ORR half-wave potential of La₂O₃-NCNTs hybrids is 65 mV lower than that of commercial Pt/C catalyst,the OER onset potential is 40 m V lower than that of RuO₂ catalyst,while the OER cut-off current density increases 8.3 mA cm^-2at 1.86 V?vs.RHE?.XRD,SEM,TEM,XPS,Raman and BET measurements have been carried out to characterize the composition and structure of the as-prepared La₂O₃-NCNTs hybrids.Coupling effects between NCNTs and La₂O₃ is the main reason for the enhancement of both ORR and OER catalytic activities.