Study On The Construction And Electrocatalytic Performance Of Novel Metal-Organic Frame Composite Materials

With regard to growing environmental problems and the rapid depletion of fossil fuels,the development of renewable and sustainable energy sources is very necessary.Electrolyzed water technology can efficiently and massively store electrical energy in chemical bonds,thereby solving the problem of difficult storage of electrical energy,and simultaneously obtaining zero pollution,high heating value and recyclable hydrogen energy.It is considered a promising and competitive new energy.Extensive studies show that platinum group metals(PGMs)such as Ru/Ir O₂ and Pt/C materials are the state-of-the-art catalysts for oxygen evolution reaction(OER)and hydrogen evolution reaction(HER)because of their excellent electronic conductivity and highly efficient active sites.However,their high cost,scarcity,and poor stability greatly hinder the wide commercialization of water-splitting devices.In recent years,researchers at home and abroad have devoted themselves to designing and developing electric catalysts with earth-abundant,low-cost,high efficiency and stability to improve the efficiency of electrolyzed water and reduce the cost of catalysts.Therefore,it is very important and urgent to construct an excellent electrocatalytic material with uniform active site exposure through the composite of metal organic frameworks(MOFs)and other materials.Herein,starting from the construction of a nano-electrocatalyst with a uniform active site distribution by regulating the morphology and structure of MOFs-based materials,a series of novel electrocatalysts with excellent catalytic performance,as well as controllable size and morphology were successfully prepared.And their electrocatalytic performances were explored.The effects of different electrocatalytic materials for the reaction performance were also investigated.To analyze the inherent correspondence between morphology,size of the composite materials and electrocatalytic performance,the as-fabricated electrocatalysts were characterized in detail by SEM,TEM and XPS,etc.The intrinsic relationship between the performance and structure of materials in electrocatalytic reactions was studied,and possible electrocatalytic mechanisms were explored.The main results are summarized as follows:(1)Mesoporous cobalt-iron-organic frameworks:a plasma-enhanced oxygen evolution electrocatalystAn innovative approach is implemented to produce highly-active and stable OER electrocatalyst by plasma-enabled Fe doping of Co-based 2D metal-organic frameworks(MOFs)nanosheets,followed by carbonization process to fabricate unique triangle shaped“cheese-like”Fe/Co-carbon nanosheets with mesoporous structure,densely and evenly distributed reactive centers,and without damaging the frameworks.The O₂-Ar radio frequency(RF)plasma ensured two critical effects,namely oxygen vacancy generation as well as forming and modifying oxidation states of the catalytically active metals in the framework leading to high OER performance.It is shown that filling the oxygen vacancies with Fe heteroatoms helps tune atomic sites of the two metals in the MOFs and achieve unique heterostructure where electron currents can be directed between metal sites of different oxidation states.Benefiting from the demonstrated unique advantages of our plasma-enabled approach,the optimized Fe₁Co₃/V_O-800 exhibits a significantly enhanced OER performance and long-term stability,evidenced by a low overpotential of 260 m V at10 m A cm^-2 and a small Tafel slope of 53 m V dec^-1,which was superior to its counterparts and other MOFs-based electrocatalysts.(2)Ni-Co hydroxide nanosheets grown on plasma-reduced ZIF-67 nanocages for electrocatalytic water oxidationA novel porous 3D hybrid nanostructure is obtained with nickel cobalt layered double hydroxides(Ni Co LDH)on the surface of functional ZIF-67 template with rich oxygen vacancies(V_O)etched by O₂-Ar radio frequency(RF)plasma.The as-prepared Ni Co LDH@ZIF-67-V_O/NF hybrid materials exhibit excellent OER performance evidenced by the competitive potential of 1.52V at the current density of 10 m A cm^-2 in alkaline medium.Moreover,the Tafel slope of 58 m V dec^-1 is much lower compared to noble metal oxide and other counterpart catalysts.Our experimental and theoretical calculation results reveal that by incorporating V_O into the Ni Co LDH@ZIF-67-V_O/NF composite can efficiently tune the electronic structure and also increase the water adsorption energy,ultimately accelerating OER process.(3)Interface coupling of Ni-Co layered double hydroxide nanowires and cobalt-based zeolite organic frameworks for efficient overall water splittingThe Ni Co layered double hydroxide salt was prepared by hydrothermal method using Ni-Fe foam as a support,and ZIF-67 was grown in situ on its surface to prepare a 3D flower-shaped nanocomposite.In order to improve interfacial coupling and catalytic performance,simple oxidation,carbonization,sulfidation,and selenization were carried out to make the interface between Ni Co LHSs nanowires and ZIF-67.Among the prepared catalysts,the optimized S-doped catalyst reveals the highest electrocatalytic characteristic quantified by the low overpotentials of170 and 100 m V for OER and HER at 10 m A cm^-2 in 1 M KOH,respectively.This outstanding electrocatalytic property is ascribed to strong interfacial coupling between the Ni Co-LHSs and ZIF-67 derivatives,as well as the rational electronic structures,dense catalytic active sites and large specific surface area.This work opens new prospects for fabricating efficient and low-cost electrocatalysts for renewable hydrogen energy production.(4)Hierarchical porous bimetal-sulfide bi-functional nanocatalysts for overall water electrolysisA new bi-functional catalyst that has a cobalt-based nano-architecture with ordered,Ni-doped two-dimensional(2D)defect-rich nanosheets is developed.Innovative combination of doping,annealing,and sulfidation is developed to fabricate the hierarchical porous metal sulfide(denoted as Ni-Co-S)nanosheets arrays(HPNA)directly on conductive carbon cloth(CC).Owing to the unique architecture with the specific surface area and porous structure,short ion diffusion paths,the Ni-Co-S HPNA exhibits excellent electrocatalytic activitiy for hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)in alkaline solution,featuring low overpotentials of 110 and270 m V at a current density of 10 m A cm^-2,respectively.The excellent catalytic performance is attributed to the unique porous structure,abundant active sites and efficient mass transport.More importantly,when the Ni-Co-S HPNA serves as both the anode and cathode,it achieves a 1.62 V at10 m A cm^-2 and remains stable over 12 h of the overall water splitting process.This work opens new avenues for rational design of high-efficiency and stable bifunctional electrocatalysts for water electrolysis and a broader range of clean energy and sustainable chemistry applications.(5)Nickel-doped and 2-methylimidazole induced layered bihydroxy compound for overall water splittingThe Co_xNi_10-x layer double hydroxide salts with controllable structure and morphology induced by 2-methylimidazole to derive ZIF-67 on Ni/Fe foam is reported.The as-prepared 3D Co_xNi_10-xlayer double hydroxide microspheres are constructed by self-assembly of 2D nanoflake and 1D nanorod with ZIF-67 particles due to the double influence of Ni and 2-methylimidazole.It is discovered that the Ni and 2-methylimidazole can simultaneously modulate morphology and structure of Co_xNi_10-x layer double hydroxide to distinctly increase the electrochemical active surface area for exposing more accessible active sites.Notably,the 3D microsphere heterogeneous catalysis of the self-assembly combines the merits of low dimensions(1D and 2D)materials,providing high structural void porosity and fast charge transport channels.Particularly,the Co₇Ni₃layer double hydroxide salts@ZIF-67/Ni/Fe foam exhibits the highest electrocatalytic activity with the lower overpotentials of 260 and 165 m V toward oxygen evolution reaction and hydrogen evolution reaction at current density of 10 m A cm^-2,respectively.The outstanding activity originates from the strong electronic coupling between the 3D microsphere and ZIF-67.