Study On The Modification Of LaNiO₃ Perovskite Oxide As Bi-functional Oxygen Electrodes

In this paper, perovskit oxide LaNiO3 was used as the catalyst in Li-air batteries. LaNiO3 electrocatalyst was synthesized by a sol-gel method. At the same time, nitrogen-doped LaNiO3 (LNON) and g-C3N4-LaNiO3 (CNL) composite material were synthesized to enhance the electrocatalytic performances. The crystalline structure, morphology and surface composition for each as-prepared material were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission scanning electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). Their electrocatalytic activities for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) were performed on a rotating-disk electrode. The charge/discharge curves for each sample’s were performed on the organic electrolyte Li-air batteries.The ORR and OER polarization curves for XC-72 carbon, LNO, LNON catalysts revealed that the catalytic performances were improved in the order of XC-72 carbon, LNO, LNON/2H, LNON/6H, LNON/4H. The Koutecky-Levich plots demonstrated the ORR overall electron transfer numbers were increased in the same order, and the n value of LNON/4H is about 3.91, indicating the ORR was a four-electrons process in alkaline solution. The first discharge capacity in nonaqueous Li-air battery using of LNON/4H, LNO, XC-72 carbon as the cathode catalyst were 5900 mAh/g,4200 mAh/g and 3300 mAh/g, respectively, and the overvoltage of LNON/4H was the smallest.The results of XPS illustrated an increase of absorbed hydroxyl on the surface of LNON/4H, which indicated the more oxygen vacancy on the surface of LNON. At the same time, the Ni3+content was increased with N-doping, which indicated the N-doped LNO can promote the formation of Ni3+. The improved ORR and OER catalytic performances were related to the existence of Ni3+ion and oxygen vacancy.For x wt.% CNL(x=0,5,10,20,30) composite catalysts, the ORR and OER polarization curves revealed that the catalytic performances were improved in the order of XC-72 carbon, g-C3N4, LNO,30 wt.% CNL,5 wt.% CNL,20 wt.% CNL,10 wt.% CNL. The Koutecky-Levich plots demonstrated the ORR overall electron transfer numbers were increased in the same order, and the n value of 10 wt.% CNL was about 3.86, indicating the ORR was a four-electrons process in alkaline solution. The first discharge capacity in nonaqueous Li-air battery using of 10 wt.% CNL, LNO, XC-72 carbon as the cathode catalyst were 5500 mAh/g,4600 mAh/g and 3600 mAh/g, respectively, and the overvoltage of 10 wt.% CNL was the smallest. The results of XPS illustrated that the g-C3N4 compositing LaNiO3 can promote the adsorption of hydroxyl and the formation of Ni3+ on the surface of the composite catalyst. The improved ORR and OER catalytic performances were related to the more content of Ni3+ ion and OH".