The Design And Study Of Electrochemical Properties For Carbon-based Materials Derived From MOFs/Three-dimensional Porous Carbon Composites

The utilization of renewable energy is paramount for the development of our society,and the zinc air battery（ZAB）is a viable chemical power source to store and convert this energy due to its ample material sources,safety,reliability,and low cost.The Oxygen Reduction Reaction（ORR）is a critical semi-reaction that affects the discharge process of the ZAB,and its large reaction overpotential and multiple reaction intermediates can lead to a decline in the discharge effect.To improve the ORR performance,it is necessary to enhance the intrinsic catalytic activity of the electrocatalyst from a chemical composition and electronic structure control perspective,as well as to design a rapid mass transfer structure on the micro and nano scales to expedite the ORR diffusion process.This thesis examines carbon-based materials derived from honeycomb three-dimensional porous carbon loaded zeolite imidazole frameworks（ZIFs）and aims to optimize the intrinsic activity of ORR electrocatalysts through the alteration of the morphology,structure,composition and other characteristics of ZIFs.Additionally,the open and multi-level pore structure based on the three-dimensional porous carbon substrate can improve the accessibility and apparent density of active sites.Through physical and chemical characterization,electrochemical testing,ZAB application and theoretical calculation simulation,the structure-activity relationship and design guidelines of three-dimensional porous carbon loaded ZIFs derived carbon are systematically demonstrated.The primary research theme and discoveries presented in this thesis can be summarized as follows:（1）The preparation method and ORR activity of 3D honeycomb-like porous carbon in situ loaded Co@N-CNTs hierarchical structure material.Based on 3D honeycomb-like porous carbon（referred to as 3DHC）,a series of variables in the nucleation-growth process were used to uniformly load Co Zn contained zeolite-imidazole-frameworks（denoted as BZIF）in the form of ultrafine nanoparticles on the 3DHC interface.Simultaneous thermogravimetry/quadrupole mass spectrometry/Fourier transform infrared（TG/QMS/FTIR）analysis,combined with ex situ characterization,was conducted to reveal the formation mechanism of nitrogen-doped carbon nanotubes（N-CNTs）-coated Co nanoparticle structure（Co@N-CNTs）.This research proposed a detailed synthetic strategy to obtain a three-dimensional porous carbon-based composite material with dense and uniform Co@N-CNTs distribution.The Co@N-CNTs/3DHC catalyst demonstrated remarkable performance,with a half-wave potential of 0.88 V,a limiting current density of-5.50 m A·cm^-2,an average electron transfer number of approximately 3.75,and a Tafel slope value of 47.6 m V·dec^-1,which are all superior to commercial Pt/C electrocatalysts.Theoretical analysis suggests that N-doped CNTs facilitate the redistribution of electronic structures,particularly the directional electron transfer process from the Co core to the N-doped carbon layer,thereby increasing the interaction between the p_zorbitals of C atoms and O2 molecules and the electron transfer effect,thus enhancing the ORR activity.The Co@N-CNTs/3DHC-based zinc-air battery showed a high discharge voltage of 1.36 V,a discharge capacity of 801.8m Ah·cm^-2,a maximum discharge power of 235.5 m W·cm^-2,and a stable continuous discharge effect.（2）The preparation of 3D honeycomb-like porous carbon in situ supported Fe Co@CNTs hierarchical structure material and its study on multifunctional electrocatalytic activity.The introduction of Prussian blue analogues（Fe Co PBA）containing Fe Co components onto a uniform and densely loaded cubic ZIF-8（c-ZIF8）on 3DHC as the medium layer has been proposed as a strategy to further expand the preparation method and application direction of 3DHC-loaded CNTs carbon-based composite materials.By controlling the nucleation-growth process of an ultra-fine-sized nanorod precursor material,a composite electrocatalyst Fe Co@CNTs/3DHC with densely loaded Fe Co nanoalloys embedded in CNTs（Fe Co@CNTs）on a3DHC carbon substrate was successfully prepared.The tight coverage of the Fe Co active phase by CNTs suppresses the tendency of non-noble metals to be easily dissolved,oxidized,and poisoned,thus improving the tolerance effect of the catalyst.Additionally,the multi-level morphology of Fe Co@CNTs/3DHC increases the electrochemically active specific surface area of the catalyst,which further enhances the contact between oxygen and metal-nitrogen coordination sites（M-Nx）and the structure of Fe Co@CNTs,thus improving the electrocatalytic activity.As an ORR catalyst,Fe Co@CNTs/3DHC exhibited a half-wave potential of 0.85 V,a limiting current density of-5.24 m A·cm^-2,and an average electron transfer number of approximately 3.87.Additionally,when used as a catalyst for HER and OER electrolysis of water,Fe Co@CNTs/3DHC displayed a HER overpotential of138.3 m V@-10 m A·cm^-2and an OER overpotential of 290.7 m V@10m A·cm^-2.Furthermore,a liquid zinc-air battery based on Fe Co@CNTs/3DHC showed a discharge voltage of 1.31 V,a discharge capacity of 780.9 m Ah·cm^-2,and a maximum discharge power of 229.7 m W·cm^-2.Additionally,a flexible zinc-air battery based on Fe Co@CNTs/3DHC demonstrated superior discharge performance and stability during bending cycle charge and discharge when compared to a noble metal-based comparative zinc-air battery.（3）The preparation of 3D honeycomb-like porous carbon in situ supported Fe Cu co-doped composites and their study on the electrocatalytic ORR activity under full p H conditions.The utilization of a3DHC substrate to load a thin-layered,weak crystalline Fe-ZIF8 precursor（Fe-ZIF8/3DHC）has enabled the realization of the four-electron selectivity effect of the ORR process at all p Hs.A high-temperature solid-phase etching mechanism,combined with many defect sites derived from ZIF-8,has been employed to co-dope Cu into the carbon matrix to form a Fe Cu co-doped honeycomb three-dimensional porous carbon-based composite Fe Cu NC/3DHC.The synergistic effect between Fe and Cu has inhibited the formation of Fe and Cu aggregate phases,improved the utilization of Fe and Cu active sites,and facilitated the construction of a Fe-Cu double site structure,which is conducive to the dissociation of the oxygen-oxygen bond and the ideal four-electron transfer process.The Fe Cu NC/3DHC electrocatalyst demonstrated half-wave potentials of 0.89 V,0.63 V,and 0.68 V,and current densities of-6.52 m A·cm^-2,-6.77 m A·cm^-2and-6.28 m A·cm^-2,as well as average electron transfer number of up to 3.93,3.96,and 3.96 in alkaline,neutral,and acidic conditions,respectively.These results are superior to those of commercial Pt/C electrocatalysts to a certain extent.Through electrochemical impedance spectroscopy（EIS）tests and theoretical calculations,it was determined that the efficient ORR catalytic activity is due to the synergistic effect of Fe and Cu,and the M-N_xstructure acting as an active site.Furthermore,the Fe Cu NC/3DHC-based alkaline zinc-air battery exhibited a discharge voltage of 1.33 V,a discharge capacity of 802.7m Ah·cm^-2,and a maximum discharge power of 161.0 m W·cm^-2,while the Fe Cu NC/3DHC-based neutral zinc-air battery showed a discharge voltage of1.15 V,a discharge capacity of 812.1 m Ah·cm^-2,and a maximum discharge power of 88.4 m W·cm^-2,which are all better than those of Pt/C-based comparative batteries.（4）Study on the thermal decomposition mechanism of ZIF-8 core material and its enlightenment to the calcination process of ORR electrocatalysts.The thermal evolution of four different anion-intercalated ZIF-8 was studied in order to gain a deeper understanding of the evolution mechanism of the ZIF-8 core material during the roasting process,particularly the influence of the presence of anions.Four metal sources,zinc nitrate,zinc acetate,zinc sulfate and zinc chloride,were used to synthesize four ZIF-8materials with different internal anions(denoted as ZIF-8-NO₃^-,ZIF-8-Ac^-,ZIF-8-SO₄^2-and ZIF-8-Cl^-).TG/QMS/FTIR and ex situ tests were conducted to analyze the pyrolysis rules and revealed that different anions regulate the morphology and structure of ZIF-8 by interacting with Zn²⁺,and thus have a significant impact on its thermal stability.Subsequently,the multi-step model fitting kinetics method was used to determine that ZIF-8-NO₃^-followed the Am pyrolysis mechanism,ZIF-8-Ac^-and ZIF-8-SO₄^2-followed the Fn pyrolysis mechanism,and ZIF-8-Cl^-follows the pyrolysis mechanism of Fn-Am.Analysis of the fitted activation energy（E_a）and pre-exponential factor A reveals that ZIF-8-Cl^-is most prone to thermal decomposition and its pyrolysis intensifies over time.On the other hand,ZIF-8-NO₃^-is the most difficult to thermally decompose,yet its pyrolysis is the most violent.Thermal decomposition of ZIF-8-Ac^-and ZIF-8-SO₄^2-lies somewhere in between,with their pyrolysis being relatively mild.This provides useful guidance for the application of ZIF-8-NO₃^-in heat treatment,as its pyrolysis can be either inhibited or utilized.This thesis presents a successful and versatile strategy for the preparation of different morphological structures with different active metal loadings through finely tuned and loaded ZIF materials based on 3D honeycomb-like porous carbon,and further through the controllable post-treatment process.Furthermore,the detailed investigation of the pyrolysis mechanism of ZIF-8core materials provides guidance for the rational selection of precursors and design of roasting strategies.By coupling the 3D honeycomb-like porous carbon with various transition metal components,the interaction between the active site and the reactant is optimised,and the mass transfer process is accelerated,thus increasing the utilization rate of the active site and ensuring an efficient ORR process and ZAB performance.This thesis provides a comprehensive theoretical and strategic basis for the development of3DHC-supported ZIFs-derived composite carbon materials.