The aim of experiment is to synthesize mesoporous NiCo2O4@Ni. All the reagents used in this experiment were analytical grade and were used without further purification. In a typical synthetic procedure, a piece of nickel foam was thoroughly cleaned with 3 M HCl solution in an ultrasound bath for 30 minutes in order to remove the NiO layer on the surface and then washed by deionized water and absolute ethanol. Put it into watch glasses for drying. C4H6NiO4 • 4H2O (0.3 g), Co(NO3)2 • 6H2O (0.6 g) and hexamethylenetetramine (HMT, 0.8 g) were dissolved into a mixed solution of deionized water (30 mL) and ethanol (20 mL) under vigorous magnetic stirring. After stirring for 30 min, the as-obtained solution was transferred into a 60 mL polytetra-fluoroethylene (PTFE) (Teflon)-lined autoclave, and then use the cleaned nickel foam which has been worked to immerse into the reaction solution. The autoclave was sealed and maintained at 95 °C for 8 hours in an electric oven. After cooling to room temperature, the products on the nickel foam were washed with deionized water and absolute ethanol for several times respectively and then dried the nickel foam at 60°C overnight. Afterward, the samples were annealed at 250° C, 350° C and 450° C for 1h at a ramping rate of 1°C min-1 to transform into NiCo2O4@Ni-250, NiCo2O4@Ni-350 and NiCo2O4@Ni-450.
NiCo2O4@Ni-350 is a new air electrode material which has been synthesized via a hydrothermal method. This nanomaterial displays good bifunctional ORR/OER activity, cyclic stability, low cost and high energy density in the discharge and charge process. Further studies are ongoing to improve the Zn-Air batteries performance by manipulating the structure.
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