Synthesis Of MOFs-derived Carbon Micro/Nanomaterials And Their Applications In Electrocatalytic Oxygen Reduction And Hydrogen Evolution Reactions

The development of efficient,stable,and cost-effective electrocatalysts is essential for the applications of fuel cells,water splitting,and metal-air batteries.Noble metal materials（such as Pt,Rh and Ir）have excellent electrocatalytic properties,but their resource shortage,high cost and low stability greatly limit the commercial application.In recent years,carbon-based materials have been widely developed due to their excellent electrocatalytic performance,high electrical conductivity,robust stability and abundant resources.Metal organic frameworks（MOFs）have uniformly distributed metal nodes and organic ligands at the atomic level.Carbon based materials,especially carbon-based materials at micro/nano scales,which are prepared with MOFs as the precursors,usually have uniform structures and compositions,rich active sites and high specific surface area.Therefore,the preparation of micro/nano-scale carbon based electrocatalytic materials from MOFs has attracted great attention of researchers.The dissertation focuses on the applications of carbon micro/nanocomposites designed and synthesized with MOFs as precursors in electrocatalytic oxygen reduction and hydrogen evolution reactions.The optimization of electrocatalytic properties of the materials was mainly investigated through regulating the compositions and configurations of active sites（transition metals,nitrogen,sulfur）and constructing hierarchical structures（one-dimensional/two-dimensional）.The main research contents of this thesis are as follows:1.The self-templated strategy was utilized for fabricating hierarchical 2D-1D structured Co/N decorated carbon matrix via the pyrolysis of bimetallic Zn/Co metal-organic-framework（MOF）nanosheets.The Zn/Co-MOF nanosheets,formed by the coordination of Zn²⁺/Co²⁺in a certain proportion and the dimethyl imidazole,serve as both the self-template for the carbonized 2D framework morphology and C/N source for the in-situ growth of N-doped 1D carbon nanotubes.The constructed hierarchical architecture of N-Co@NC-NSs effectively integrates the active sites into frameworks with highly exposed accessible surface,enhanced mass-transport kinetics and increased electrical conductivity,thus exhibiting superior ORR activity and durability than those of commercial Pt/C in alkaline media.In addition,it also shows promising ORR performance with a half-wave potential of 0.865 V versus reversible hydrogen electrode,four-electron dominated pathway and negligible activity attenuation after 5000 potential cycles in acidic electrolyte.The synthetic strategy in this work can be extended to construct other MOFs-derived carbon matrixes with diverse hierarchical structures and provide an efficient avenue for searching high-performance electrocatalysts.2.Hydrothermally synthesized ZIF-8 nanoparticles were used as precursors.After adsorbing W source,tungsten disulfide nanosheets supported on N,S-doped carbon matrix（WS₂@SNC-NPs）were prepared via pyrolysis in H₂S atmosphere.WS₂@SNC-NPs exhibit high activity for hydrogen evolution reaction.When the current density is 10 m A cm^-2,the overpotential is 163 m V,and the catalyst shows good stability.The excellent electrocatalytic activity of WS₂@SNC-NPs stems from the synergy between tungsten disulfide nanosheets and porous carbon materials derived from ZIF-8.