Preparation Of Oxygen Electrode Based On Metal Organic Framework-derived Compound For Zinc-air Battery

Owning to its high energy densities,abundant storage of raw materials,and green environmental protection,rechargeable zinc-air battery has been targeted as a promising technology to meet the energy requirements for future electric vehicles and other energy-demanding devices.However,it is a challenge that the slow kinetics reactions of oxygen reduction and oxygen evolution on the air electrode of zinc-air battery,which should be overcame by high efficiency catalysts.At present,the industrialization of noble-metal based catalysts with the best catalytic activity is limited by the high cost and scarce resources.Therefore,it is very of that importance to explore highly efficient oxygen electrocatalyst of nonprecious metal-based material with low cost and abundant resources.As researches show that,the carbon-based transition metal atoms,transition metal nitrides and transition metal oxides,derived by high temperature carbonization for precursor of metal-organic-framework compounds,have great catalytic activity of oxygen electrcatalyst.Based on the above research results,the specific research work of this paper is as followed,?1?Mn doped Co-NC bifunctional catalyst was successfully synthesized with ZIF67 as template via facile solution immersion method and pyrolysis treatment.The supported catalyst was systematically optimized with respect to Mn/Co component ratios and carbonation temperatures and the experimental results indicated that the catalyst with 0.02 of component ratio and 800 of carbonization temperature shows the best performance.Such as the Mn/Co-NC-0.02-800 catalyst exhibits outstanding ORR?half-wave potential of 0.80 V?as well as comparatively superior OER activity?potential@10 mA cm^-22 of 1.66 V?,outperforming a commercial Pt/C+RuO₂electrocatalyst.When the catalyst was applied to the air electrode of a zinc-air battery,the liquid batteries exhibit a high peak power density of 136 mW cm^-22 and a stable cycle performance of 250 h at current density of 5 mA cm^-2.The all-state-solid Zinc-air batteries also display a cycle stability of 10 h at current density of 2 mA cm^-2.This is attributed to the fact that the electronic effects between Mn and Co can enrich the active center and enhance the conductivity.?2?Carbon nanotube composites supported on graphene?Co-NC/G?were derived by pyrolysis of three-dimensional petal-shaped ZIF67 on graphene substrate in the nitrogen atmosphere,Co-NC/G was used as oxygen electrode bifunctional catalyst.The electrochemical test results show that the Co-NC/G bifunctional catalyst exhibits the obvious improvement of ORR?half-wave potential of 0.81 V?and OER?potential@10 mA cm^-22 of 1.68 V?activity in comparing to bare Co-NC and graphene compound.In aqueous Zn-air battery tests,primary batteries demonstrate a high maximum power density of 855.3 mAh g^-11 and rechargeable batteries are able to be operated smoothly for 125 cycles at current density of 5 mA cm^-2.The all-state-solid batteries also exhibit excellent cycle performance of 12 h at current density of 2 mA cm^-2.It is attributed to the graphene substrate and carbon nanotubes,which increase the degree of graphitization of the catalyst and expose more active sites,thus improving the performance of catalyst.