Metal-organic Framewoks Derived Materials For Energy Applications

Metal-organic frameworks(MOFs),a novel type of porous crystalline materials,have attracted increasing attention for various applications due to their high surface area,permanent porosity,and controllable structures.MOFs are excellent precursors for the design and fabrication of nanostructured porous carbons and metal oxides,especially for hierarchical nanostructures.MOFs can be prepared with endless combinations of organic and inorganic constituents by simple coordination chemistry,and it is possible to control their porous architectures,pore volumes,surface areas,and tailorable chemical components.These unique properties of MOFs-derived materials make them highly attractive for energy applications,such as in hydrogen(H2)and oxygen(O2)evolution,catalysis of oxygen(O2),supercapacitors and so on.Supercapacitors depend on the development of novel carbon materials with optimized porous structures,high surface area,high conductivity,and high electrochemical stability.Many MOFs-derived porous carbon composites have been reported for supercapacitors.However,there are still some problems to be solved in the preparation of suitable porous structures as well as high-nitrogen-doped and graphitized composites.Nowadays,Pt,IrO2 and other noble metal catalysts are considered as state of the art catalyst for electrocatalytic hydrogen production,oxygen production and oxygen reduction.Therefore,the synthesis of highly efficient non-noble metal electrocatalysts is an alternative to precious metal catalysts.Recently,significant efforts have been devoted to the applications of MOFs derived materials owing to their outstanding properties such as high surface area,excellent accessibility to active sites,and enhanced mass transport and diffusion.Nevertheless,there is still a gap between electrocatalysis with precious metals and that with MOFs derivatives in the catalytic activity,and general synthetic approaches are highly desirable but still limited.In order to solve the above-mentioned problems,the synthesis of highly efficient supercapacitor electrode materials and electrocatalytic materials,ZIFs,one kind of metal-organic framework material,was used as templates for the preparation of high-performance electrochemical materials.The main contents of this thesis are as follows:1.In this chapter,three kinds of cobalt-containing porous carbon composites(C-S-Co@ CN,H-Co @ CN and Co @ CN)were synthesized from three kinds of cobalt-based MOFs(core-shell ZIF-67 @ ZIF-8,hollow ZIF-67 @ ZIF-8,BMZIF),and their morphological characteristics,pore structure and supercapacitor properties were investigated.Among them,Co @ CN electrode material has excellent electrochemical properties and the highest specific capacitance(251.5 F/g).2.Cobalt phosphate nanosheets composite(CoP-NS/C)was prepared by a novel one-step phosphation of MOFs nanosheets method and used as a bifunctional efficient and durable catalyst for HER and OER.It showed excellent electrocatalytic performances for both HER and OER in acidic and alkaline media,respectively.Especially,OER performance under alkaline conditions exceeds commercial noble metal oxide(IrO2).3.In the same way,B-CoP nanoparticles with a special banded morphology were synthesized by two-step low temperature phosphation method used MOFs nanosheets as template.In HER(acidic conditions)and OER(alkaline conditions)electrocatalytic reactions,the catalyst has excellent catalytic activity.The overpotential of B-CoP is 122mV(HER)and 273mV(OER)with a current density of 10 mA/cm2.4.In this chapter,a cobalt-porous carbon composite with uniform size and carbon nanotubes-grafted by a simple one-step calcination with MOFs material(ZIF-67 @ZIF-8),denoted Co @ C-CNT,as a catalyst for the electrocatalytic reduction of oxygen,showed comparable catalytic activity to the commercial Pt/C electrode.