Highly porous Co3O4 and Ni-deposited Co3O4 nanoflowers as bifunctional catalysts for oxygen reduction and evolution reactions

Co3O4 nanoflowers (NFs) were obtained from cobalt hydroxide coated on silica, Co(OH)(2)@SiO2, prepared from a homogenous mixture of urea and cobalt nitrate in an aqueous solution. The Co3O4@SiO2 was obtained by calcining Co(OH)(2)@SiO2 under atmospheric air for 3 h and then immersing in sodium hydroxide to yield Co(3)O(4)NFs. The Ni-deposited Co3O4 NFs (Ni@Co3O4-NFs) were synthesized by chemical deposition of nickel nanoparticles onto Co3O4-NF by a reducing agent, NaBH 4 . The physical characterization of Co3O4-NFs and Ni@Co3O4-NFs was performed by Brunauer-Emmett-Teller analysis, scanning electron microscopy and X-ray diffraction. The electrochemical properties of Co3O4-NFs and Ni@Co3O4-NFs for the oxygen reduction and evolution reaction were determined in an 8 M KOH solution. Ni@Co3O4-NF showed a better cell performance than that of Co3O4-NF. Moreover, Ni@Co3O4-NF exhibited a higher stability and longer life cycles at 20 mA cm(-2) at a 2 h charging and discharging rate as compared to Co3O4-NF. Therefore, Co3O4-NF and Ni@Co3O4-NF could be used as a cathode material for Zn-air rechargeable batteries.