| Zinc-air battery has the advantages of high specific energy,large capacity and low cost,and has good application prospect in energy storage and electric vehicle.The core material of zinc-air battery is a bifunctional catalyst with both oxygen reduction(ORR)and oxygen evolution(OER)reaction.Although precious metals such as Pt,RuO2 and IrO2 have been used as bifunctional catalysts,their high cost and low stability have hindered the commercialization of zinc-air batteries.Therefore,research and development of highly efficient non-precious metal bifunctional catalyst is of great significance.In this paper,nitrogen-doped hierarchical porous carbon(NHPC)was prepared by pre-carbonization high temperature carbonization activation method using KOH as activator.On the basis,the Co3O4/NHPC bifunctional catalyst was prepared by carrying out the Co3O4 nanoparticles on NHPC by oil bath hydrothermal method.The effects of preparation conditions and composition of Co3O4/NHPC catalyst on the electrocatalytic performance of ORR and OER were studied.Firstly,NHPC was prepared by pre-carbonization high temperature carbonization activation using KOH as the activator.When the mass ratio of KOH to the pre-carbonized product was 0.4,the specific surface area of NHPC was 2047 m2 g-1,nitrogen content of 3.85%.On the basis,the Co3O4/NHPC catalyst was prepared by oil bath-hydrothermal method.The ultrahigh specific surface area and surface nitrogen doping of NHPC are favorable to promote the high dispersion of Co3O4 nanoparticles.When the oil bath temperature is 80 ℃ and the amount of ammonia is 1 mL,Co3O4 nanoparticles are uniformly dispersed on the NHPC with an average particle size of 7.2 nm,which is significantly smaller than that of commercial Vulcan XC-72 and BP2000 carbon supported on the catalyst.The catalyst has a three-dimensional pore structure with NHPC,with a specific surface area of 1070 m2 g-1 and a nitrogen content of 4.93 wt.%.Secondly,Co3O4/NHPC was prepared as ORR and OER bifunctional catalyst,and the mechanism of electrocatalytic performance was revealed.The results show that the half-wave potential of Co3O4/NHPC catalyst is 0.835 V,12 mV higher than commercial Pt/C,kinetic current density is 15.85 mA cm-2(jk 0.8 V vs.RHE),3.76 times for commercial Pt/C.The reaction current was only 9.3%lower than that of commercial Pt/C(32%),and the methanol resistance was better than commercial Pt/C in the constant current time test of 10000 s.The OER results show that the potential of the catalyst at the current density of 10 mA cm-2 is 1.65 V,10 mV higher than commercial RuO2.The reaction current decreased by only 8.2%and the stability was higher than that of commercial RuO2(66%)in the constant current time test of 10000 s,showing better catalytic activity and stability than the commercial RuO2.The excellent bifunctional catalytic activity of ORR and OER is mainly due to the high dispersion of Co3O4 nanoparticles,the three-dimensional connected pore structure,the high surface area and the surface-doped nitrogen with synergistic catalysis.Finally,the Co3O4/NHPC catalyst was used as the air electrode,the zinc plate as the anode,and the zinc-air battery was constructed.The results show that the open potential of the battery is as high as 1.39 V,the peak power density was 80 mW cm-2,which is higher than the commercial Pt/C,the specific capacitance of the battery at a current density of 20 mA cm-2 is 674 mAh gzn-1(energy density of～768 Wh kg-1(Zn),156 mAh gZn-higher than commercial Pt/C,and stable operation for 38 h after mechanical recharging. |
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