Design Of Cobalt-based MOF-derived Carbon-based Compounds For Zinc-air Batteries

Zinc-air batteries（ZABs）can be used as one of the most viable power sources for driving future electric power grids and electric vehicles due to their high theoretical energy density,low cost and environmental friendliness.However,the oxygen reduction reaction（ORR）and oxygen evolution reaction（OER）with slow kinetics and high over-potentials were the main factors leading to low energy conversion efficiency of ZABs.Therefore,designing and preparing of bifunctional ORR and OER catalysts with low cost,high activity and stability were highly demanded to achieve excellent ZABs performance.Carbon-based compounds derived from metal-organic framework（MOFs）had many advantages,such as suitable nitrogen doping,controllable composition and high porosity,etc.,and could be used as alternative materials for noble metal electrocatalysts.Therefore,in this thesis,two carbon-based composites with multiple catalytic active centers were designed and synthesized with cobalt-based MOFs as the precursors by adjusting the components of the precursors and post treatment processes.The main works were as follows:（1）Co₂P/Co-N-C was successfully prepared via high-temperature pyrolysis of ZIF-67 and low-temperature phosphating post treatment.The high content of pyridine nitrogen and graphite nitrogen in the carbon lattice,and the carbon-coated metal Co had high ORR catalytic activity.The synergy between the metal Co and Co₂P enhanced the OER activity.Therefore,the Co₂P/Co-N-C composite exhibited good bifunctional catalytic performance.When used as a cathode catalyst for ZABs,Co₂P/Co-N-C achieved a peak power density(168 m W cm^-2)superior to the noble metal Pt/C+Ru O₂ and a long cycle life（over 200 h）（2）A series of uniformly dispersed nitrogen-doped carbon-coated Mn O and metallic Co（Mn O/Co@N-C）were synthesized by adjusting the Co and Mn components in the cobalt-manganese bimetal MOF and high-temperature pyrolysis.Benefiting from the synergy and electronic interaction between Mn O and metallic Co,as well as the high content of pyridine nitrogen and graphitic nitrogen,the optimal Mn O/Co@N-C-0.3 performed good bifunctional catalytic activity.ZABs based on Mn O/Co@NC-0.3 catalysts achieved the large peak power density(153 m W cm^-2),the large larspecific capacity(776 m Ah g^-1)and the good rate performance as well as the long cycle life（over 300 h）In summary,this thesis designed carbon-based transition metal compounds derived from MOF as efficient oxygen catalysts for ZABs.It will provide a method and idea of designing efficient,economical,and durable oxygen catalysts.