| Rechargeable lithium-air(Li-air)battery has been considered as a more promising energy storage technology over the traditional lithium-ion battery because of the ultrahigh energy density.A lot of researchers are devoted to developing the effective cathode catalysts,and transition metal oxides have been widely studied due to low cost,abundance and good catalytic activity.In this article,nitrogen doped LaNiO3(LNON)and a-MnO2/Co3O4 were prepared and selected as typical transition metal oxides electrocatalysts for Li-air battery.And the X-ray diffraction(XRD),the X-ray photoelectron spectroscopy(XPS)and the scanning electron microscopy(SEM)were applied to the material characterizations for LNON and α-MnO2/Co3O4.Furthermore,the catalytical activities in aqueous alkaline electrolyte and electrochemical performances based on Li-air battery were also investigated.In the first section of this article,LNON was prepared and studied,for the first time,as a bifunctional electrocatalyst for oxygen cathode in a rechargeable Li-air battery.The introduction of N into the perovskite lattice introduces additional oxygen vacancies to facilitate the formation/decomposition of Li2O2 and enables the N-doped catalyst with improved ORR/OER catalytic activity over the nondoped one.Spcifically,in the alkaline electrolyte,LNON/4h were able to deliver the highest limiting diffusion current density of the ORR and OER,and the n value of LNON/4h is about 3.91,which is the most close to a four-electron process of the ORR.Furthermore,compared to pure LaNiO3(LNO),the Li-air battery based on LNON/4h catalyst showed an improved electrochemical performance.The LNON/4h-supported cathode delivered an initial discharge-specific capacity of 5910 mA h g-1 under a current density of 50 mA g-1.And When tested under the current density of 250 mA g-1 and the cutoff capacity of 500 mAh g-1,the LNON/4h-supported cathode can maintain a stable cycling for 50 cycles within a voltage window of 2.5-4.7 V.The current density and specific capacity of cathode were calculated based on the mass of cathode catalyst.In another section,the α-MnO2/Co3O4 hybrid catalyst was prepared by a two-step hydrothermal method followed by calcination.The improved catalytic activities are not only attributed to the synergistic effect,but the interfacial effect between α-MnO2 and Co3O4 nanopaticles.In the alkaline electrolyte,α-MnO2/Co3O4 were able to deliver the highest limiting diffusion current density and the optimal on-set potential of the ORR and OER.When applied to the Li-air battery,the α-MnO2/Co3O4 hybrid catalyst also showed an improved battery performance.The α-MnO2/Co3O4-supported cathode delivered an initial discharge-specific capacity of 5699 mA h g-1 with a lower overpotential of 1.22 V under a current density of 100 mA g-1.And When tested under the current density of 500 mA g-1 and the cutoff capacity of 1000 mA h g-1,the α-MnO2/Co3O4-supported cathode can maintain a stable cycling for 40 cycles within a voltage window of 2.2-4.7 V.The current density and specific capacity of cathode were calculated based on the mass of KB. |
