Preparation Of Metal@carbon Core-shell Structure Catalysts Derived From Metal Organic Frameworks And Their Catalytic Research For Hydrogen Evolution Reaction

Metal-organic frameworks(MOFs) possess of diverse compositions, high surface area, controllable and uniform porosity, have shown great application potential in oxygen reduction reaction(ORR), supercapacitors and Li-ion batteries. However, only a few literatures have been reported in the literature where MOFs were used as electrocatalysts for hydrogen evolution reaction(HER). Recent research demonstrate that MOFs can converted to metal@carbon hybrid composite directly by simple pyrolysis of MOFs under inert atmosphere or phosphatization process as well as sulfuration process. Materials like this structure not only can prevent metal from dissolving in acid electrolyte, but also enhance the HER catalytic activity through effective electron transfer from metal to carbon. Thus, MOFs may be viable alternative catalysts of Pt for HER. In this thesis, ZIF-67 and Zn-Fe-MOFs were used as precursor for the preparation of CoSe2@DC and Au@Zn-Fe-C and studied their performance and mechanism as HERcatalysts. The details are listed below:1. ZIF-67 were used as precursor for the preparation of CoSe2 nanoparticles embedded defective carbon nanotubes(CoSe2@DC), the calcined process including three steps: carbonization, oxidation and selenylation. The results shown that CoSe2@DC are effective HER catalyst in 0.5 M H2SO4, with a low onset potential of-40 m V vs. RHE and small Tafel slope of 82 mV dec-1, such a HER performance was better or at least comparable to those of leading carbon and metals-based HER catalysts. A series of structure characterization and electrochemical tests were applied to study the mechanism of CoSe2@DC for HER. And it turns out that the bigger electrochemical area and more active sites brought by multilevel structure formed after pyrolysis as well as introduction of more defects of carbon nanotubes by oxidation process were account for the high HER catalytic activity of Co Se2@DC.2. Besides, we also synthesized core-shell nanocomposites based on gold nanoparticle@zinc-iron embedded porous carbons(Au@Zn-Fe-C) by calcination of mixture of Zn-Fe-MOFs and gold nanoparticles. In fact, Au@Zn-Fe-C exhibits high catalytic activity in both HER in acid electrolyte and ORR in basic electrolyte. The results indicate that there are synergistic effects of electron transfer between Au nanoparticles core and porous carbons shell, and it likely enhance the adsorption of protons in HER and oxygen intermediates in ORR thus enhance the overall performance.