| The increasing environmental concerns and energy shortages has inspired intense research on alternative energy sources and storage system,such as fuel cells and metal-air batteries.The OER and ORR are considered as two important reaction in rechargeable energy storage,but they are hindered by sluggish kinetics and high over-potential.Hence,synthesizing high-efficiency and cheap bi-functional electrocatalyst for OER and ORR is very important.Recently,many studies have shown that hybrid of transition metal oxides and nitrogen-doped carbonaceous materials have good ORR and OER activity,especially the ORR activity,because of the M-N-C bonding,but the OER activity still can be improved.This work design to synthesize a hybrid of oxygen-defect-abundant Co3O4-x-x nanoparticles and graphene using laser assisted synthesis method and one-step laser irradiation method.Laser assisted synthesis method can tune concentration of oxygen vacancies?x?from 0.005 to 0.13 by changing the laser energy.Through that method,we obtain the Co3O4-x/NG hybrid and characterize the double active sites?oxygen defects and Co-N-C bondings?,successfully.The Co3O4-x/NG-97?x=0.13?shows the highest OER and ORR performance.The specific activities of OER and ORR are greatly improved by 5.2 and 1.3 times higher than Co3O4/NG,respectively.The Co3O4-x/NG-97 shows a lower over-potential for OER than RuO2 and higher diffusion current density for ORR than Pt/C.The DFT calculations indicate that the oxygen vacancy and Co-N-C bonding at the interface show synergistic mechanism.Further more,this hybrid catalyst also shows perfect capability and stability in rechargeable Zn-air battery equipment compared to Pt/C+RuO2 catalyst.We also try to use one-step laser irradiation method to synthesize Co3O4-x/NG,it also shows good OER/ORR bi-functional electrocatalysis ability.This work provide a new way to design and synthesize high efficient bi-functional electrocatalyst for reversible energy shortages,e.g.metal-air battery. |
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