| In this paper LaNiO3 electrocatalyst was synthesized by a sol-gel method using ethylene glycol as thickening agent and citric acid as complex agent. At the same time, LaNiO3 was doped by Co or Mn or Fe cation at B site to enhance the electrocatalytic performances. The crystalline structure, morphology and surface composition of the as-prepared materials were characterized by XRD, SEM and XPS. The intrinsic catalytic properties of oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) were studied in 0.1 M alkaline potassium hydroxide solution using the rotating disk electrode technique.The ORR and OER polarization curves revealed that the bifunctional catalytic performances were improved in the order of Glass carbon, XC-72 Carbon and LaNiO3. For LaNi1-xCoxO3 (x=0.1,0.2,0.3,0.4,0.5,0.6,1.0) perovskite oxides, LaNio.8Coo.2O3 performanced the best bifunctional catalytic performances, the ORR onset potential, limiting current density and overall electron transfer number of which were-0.077 V, 5.2 mA/cm2 and 4, respectively. LaNio.8Coo.2O3 showed the highest OER limitimg current density (68 mA/cm2) and the most negative OER onset potential (0.35 V). LaNio.6Coo.4O3 had the similary OER limitimg current density with LaNio.8Coo.2O3, but with a more positive OER onset potential. From XPS spectrum, the perovskite oxides had a higher Ni3+/Ni2+ratio with a minor replacement of Ni cation with Co cation. However, when the doping content was too high (x> 0.2), the Ni3+/Ni2+ratio decreased with increasing the doping content. For LaNi1-xCoxO3 (x=0.1,0.2,0.3,0.4,0.5,0.6,1.0) catalysts, increasing the doping content could induce an increase of absorbed hydroxyl on the surface of the catalyst, a stronger covalency of B-O2 bond, and a higher Ni3+/Ni2+ ratio.For LaNii-yMny03 (y=0.1,0.2,0.3,0.4,0.5,0.6) perovskite oxides, LaNi0.8Mno.2O3 performanced the best bifunctional catalytic performances, the ORR onset potential, limiting current density and overall electron transfer number of which were-0.107 V,5.5 mA/cm2 and 4, respectively. LaNio.8Mno.2O3 showed the highest OER limitimg current density (70 mA/cm2) and the most negative OER onset potential (0.31 V). LaNio.6Mno.4O3 had the similary OER limitimg current density with LaNio.8Mno.2O3, but with a more positive OER onset potential. From XPS spectrum, the perovskite oxides had a higher Ni3+/Ni2+ratio with a minor replacement of Ni cation with Mn cation. However, when the doping content was too high (y> 0.2), the Ni3+/Ni2+ ratio decreased with increasing the doping content. For LaNi1-yMny03 (y=0.1,0.2,0.3, 0.4,0.5,0.6) catalysts, increasing the doping content could induce an increase of absorbed hydroxyl on the surface of the catalyst, a stronger covalency of B-O2 bond, and a higher Ni3+/Ni2+ratio.For LaNi1-yFeyO3 (y=0,0.1,0.2,0.6) catalysts, LaNio.8Feo.2O3 performanced the best bifunctional catalytic performance. Then Li-air batteries using LaNi0.8Feo.2O3 as composite catalyst were assembled to analyze its electrochemical charge/diacharge performance. The results showed that the discharge capacity of the assembled battery was about 500 mAh/g. The round trip efficiencies (ORR/OER) were 76% and 72% for LaNio.8Feo.2O3 and LaNiO3 respectively at first cycle, close to the other high efficient perovskite materials (e. g.73% of Sro.95Ceo.o5Co03-δ) and non-precious metal catalysts (e. g.79% of Fe/N/C). The overpotentials of LaNio.8Feo.2O3 is lower than that of LaNiO3 by 0.215 V and 0.312 V measured at the middle of discharge/charge of the 1st and 10th cycles respectively, indicating an obviously improved catalytic activity and cell durability after Fe doping on LaNiO3. |
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