Carbon-Based Materials Co-Doped With N,F And Transition Metals For Electrocatalysis

Zinc air battery has the advantages of high theoretical energy density,environmental protection,safety and reliability,and has gradually developed into an important device for electrochemical conversion and energy storage.However,the oxygen evolution reaction（OER）and oxygen reduction reaction（ORR）kinetics that occur on the ZAB air cathode are relatively slow,which severely limits its charge and discharge efficiency.Although noble metals can be used as catalysts to accelerate the OER/ORR reaction process,noble metal catalysts have poor stability and high cost,which severely restricts the practical application of ZAB devices.Therefore,it is a significant research to find stable,efficient and low-cost non-noble metal catalysts to replace precious metal catalysts.Among many non-precious metal catalysts,functionalized carbon nanomaterials have the advantages of high stability and environmental friendliness,and are regarded as one kind of the promising electrocatalysts.There are many ways to prepare carbon nanomaterials.Among them,pyrolysis of metal organic framework materials（MOFs）to obtain carbon materials is a simple and effective method.Based on this,this paper designs a functional carbon nanomaterial with MOFs as the precursor and doped with hetero-elements,and uses it as an electrocatalyst in ZAB.The main contents are as follows:（1）Synthesize a MOF material（Fe-NH₂-MIL-88B）,take Fe-NH₂-MIL-88B as the precursor,react with trifluoroacetic anhydride,and successfully introduce fluorine-containing groups into the precursor.Then,the modified precursor was used as a template,mixed with melamine in different proportions,and then cracked at different temperatures to directly obtain a series of Fe,N,and F co-doped carbon-based functional nanomaterials.Among them,Fe NFC-800 has the best ORR catalytic performance.In 0.1 M KOH solution,its onset potential(E_onset)and half-wave potential(E_1/2)reach 0.93 V and 0.83 V,respectively,which is comparable to commercial Pt/C(E_onset=0.97 V,E_1/2=0.84 V).Fe NFC-800 is used as the cathode catalyst to assemble a zinc-air battery.Its open circuit voltage（OCV）reaches1.57 V,and its maximum power density（Pmax）reaches 196 m W cm^-2,which is much higher than the commercial Pt/C(1.42 V,140 m W cm^-2).In general,this chapter synthesizes an effective ORR catalyst and shows a good application prospect in ZAB.（2）We prepared Fe,Co,N and F co-doped carbon-based materials（Fe Co NFC）.In Fe Co NFC,the synergistic effect of Fe and Co metallic elements and N and F hetero elements makes Fe Co NFC have better OER catalytic performance,and its overpotential is342 m V.Fe Co NFC also has relatively good ORR activity.The half-wave potential(E_1/2)in ORR is 0.82 V.Therefore,Fe Co NFC has excellent ORR/OER bifunctional catalytic activity.Fe Co NFC was used as the cathode catalyst to assemble a liquid zinc-air battery,and its open circuit voltage and maximum power density were 1.46 V and 160 m W cm^-2,respectively;and then assembled into a flexible zinc-air battery（FZAB）,the open circuit potential and maximum power density were respectively 1.702 V and 118 m W cm^-2,higher than FZAB(1.4 V,22 m W cm^-2)with Pt/C+Ru O₂ as the cathode catalyst.This is enough to show that multi-element doped carbon-based materials have excellent OER/ORR dual-functional catalytic activity,which can provide a reference for the design of air cathode electrocatalysts for zinc-air batteries.