MOFs-Derived Carbon-Based Materials: Synthesis And Applications In Electrocatalytic Field

The development of new energy storage and conversion devices using electrochemical energy technology,including metal-air batteries and water splitting devices,is one of the main directions to establish new sustainable energy and conversion systems.However,the electrochemical reaction processes in these devices are complex and often require efficient catalysts to work properly.Although noble metal(e.g.,Pt、Ru O2、Ir O2)-based catalysts have high electrocatalytic activity,their high cost,scarce resources,and lack of multifunctional electrocatalytic performance greatly limit their promotion and commercialization in the field of electrocatalysis.Therefore,the development of highly active,cost-effective and durable non-noble metal-based electrocatalysts is of great significance for commercial applications of metal-air batteries and water splitting devices.As precursors of nanomaterials,metal-organic frameworks(MOFs)can provide the favorable conditions for the preparation of catalysts,such as composition,specific surface area,and porosity,which have attracted much attention in recent years.In view of this,the paper mainly through the design of a series of MOFs as precursors to prepare a series of MOFs-derived carbon-based materials that can be used in zinc-air batteries or water splitting devices,and through various characterization means to study the correlation between their composition,structure,properties and structure-activity relationship.The specific research contents and results are as follows:1.A series of adenine-functionalized ZIF-7 precursors were synthesized by mixed ligand strategy.Nitrogen doped porous nanocarbon-based materials were prepared by pyrolysis in argon and strong acid oxidation etching.Studies have shown that the introduction of adenine can significantly affect the nitrogen content and porosity of carbon materials.When the adenine doping amount is 50 %(NC-50)and 30 %(NC-30),the samples exhibit excellent multifunctional catalytic activity.And the Zn-air battery assembled with NC-50 as air electrodes also showed good charge-discharge performance.In addition,based on the characterization and electrochemical test results,the role of micropores and their surface functional groups is further emphasized,which provides a new strategy for designing the structure and composition of new materials.2.Using different Co2+ sources,a series of Co2+ doped anionic Metal-Organic Frameworks were synthesized and used as precursors to prepare a series of cobalt and nitrogen co-doped porous carbon-based materials.After pyrolysis of the precursor prepared with Co2+ chelate as cobalt source,as-obtained Co T@NC material has unique morphology,high specific surface area,and uniform distribution of multiple active sites(Co/CoNx/Co Ox).Co T@NC exhibits excellent trifunctional catalytic activity in alkaline solutions.For ORR,the half-wave potential of Co T@NC is 0.86 V,which is superior to commercial Pt/C catalysts.For HER and OER,the overpotential of OER and HER are 350 m V and 209 m V,respectively.In addition,both of the assembled Zn-air battery and the water splitting device using Co T@NC catalyst show excellent performance and good stability.Moreover,the relationship between precursors and pyrolysis products was preliminary studied,which provided some experimental and theoretical basis for the design and synthesis of highefficiency electrocatalysts.3.According to the previous chapter,Fe3+ doped anionic metal-organic frameworks were prepared by using Fe3+complex as iron source.By adjusting the pyrolysis temperature,porous nitrogen-doped CNTs wrapped Fe/Fe5C2 nanoparticle material was obtained.Due to 1D CNTs,high surface area,and synergistic effects of iron nanoparticles,Fe5C2 nanoparticles,and Fe-Nx active sites,Fe-Fe5C2@CNTs-900 showed excellent ORR and OER bifunctional performance.The half-wave potential of Fe-Fe5C2@CNTs-900 for ORR was better than that of commercial Pt/C catalysts in alkaline solution.The overpotential of Fe-Fe5C2@CNTs-900 was 330 m V at current density of 10 m A cm-2 for OER.More importantly,Fe-Fe5C2@CNTs-900 also could be used as an air cathode to assemble the Znair battery,which possesses a higher power density(137 m W cm-2)and cycle stability than commercial Pt/C catalysts.In addition,the results show that the pyrolysis temperature plays a decisive role in the composition and morphology of the material,thus affecting its catalytic performance.4.Fe0.1-STU/GO-x composites were prepared by “one-pot” method using Fe3+ doped bimidazole Metal-Organic Framework combined with graphene oxide and directly used for OER.The results show that Fe0.1-STU/GO-x not only retain the porosity of the original MOFs,but also improve the OER activity of Fe0.1-STU/GO-x through the synergistic effect of MOFs and graphene oxide.When the GO doping amount was 6 wt %,Fe0.1-STU/GO-6 showed the optimal OER catalytic activity.The overpotential of Fe0.1-STU/GO-6 is 374 m V for OER in alkaline solution when the current density is 10 m A cm-2.The work provides a new way to design and prepare original MOFs directly for catalytic OER.