Controllable Synthesis And Electrocatalytic Applications Of Iron Series Metal-organic Frameworks Derived Materials

Energy plays an important role in the development of industry.Since the Industrial Revolution,all countries face an energy crunch due to the large-scale exploitation and utilization of fossil energy.At the same time,the large amounts of exhaust gases produced during combustion has caused a series of environmental problem.Researchers have gradually realized the importance of developing and utilizing of renewable energy and efficient energy conversion technology.Water electrolysis and CO₂ electrocatalytic reduction reaction could use the electric energy generated by solar energy and other renewable resources to produce hydrogen and high value-added hydrocarbons,respectively.At present,researches in the field of electrocatalysis mainly focus on the metal electrodes,which are mainly precious metals with low reserves and high prices.Therefore,it is important to design high activity transition metal-based materials with low price and abundant reserves.Metal-organic frameworks material（MOFs）can be used as precursor to prepare functional carbon-based transition metal composite based on its special physical and chemical properties.In this work,we fabricated a series of MOFs derivatives with specific morphology structure and chemical composition based on the flexible design feature of MOFs precursor.The intrinsic relstionships among the preparation strategies,catalyst structures and catalyst performances were systematacially explored in virtue of advanced characterization methods,electrocatalytic experiemnts and DFT calcualtions.Baced on the above exploration result,this work submitted a general plan for the design of precious metals/transition metal complex catalysts,multi-dimensional catalysts,multi-metal oxide catalysts and transition metal single-atom catalyst,and propose a theory of structure-activity relationship between MOFs derivatives and their electrocatalytic activity.The electronic structure and properties of carbon matrix could be modulated by the doping of nitrogen.Metal nanoparticles could be anchored due to the strong interaction between the nitrogen-doped carbon matrix and metal nanoparticles,surface charge distribution could be modulated at the same time.A novel Co-MOFs（Co-BDC-NH₂）has been fabricated and used as the precursor to synthesize two-dimensional Co/Co O_x@NC catalyst equipped with small Co/Co O_x particle（4.45±0.22 nm）and nitrogen doped carbon base.The synergistic effect between nitrogen doped carbon base and Co/Co O_x nanoparticles effectively avoid the aggregation of nanoparticles and modulate the charge distribution of active sites.Co/Co O_x@NC-500 showed outstanding OER performance and stability,the overpotential at 10,100 m A cm^-2 were 307,375 m V,maintained 97.4%activity after 24 h electrolysis at 1.66 V vs.RHE.Based on the rich channel structure of MOFs,introduce precious metal ions through physical adsorption.And get an ultra-dispersion double metal oxide compound through post-treament process.Due to the strong interaction,noble metal oxide disperses uniformly on the transition metal oxide,in addition to that,improve the electrocatalytic performance through synergistic effect.ZIF-9 was used as the precursor to introduce second metal ions.Ru³⁺was adsorbed on the surface of ZIF-9 throght physical adsorption process.Through a simple calcination method,a complex catalyst Ru O_x/Co O_x with small particle size and uniform element distribution was prepared.At the same time,electron density distribution was improved through the electron migration from Co atom to Ru atom.Positively charged Co atom has stronger electron collector ability,and negatively charged Ru atom has stronger proton trap ability.Then shown excellent electrocatalytic water splitting performance.Compared with the two-dimensional materials,the multidimensional materials with large specific surface area and multilevel pore structure are more favorable for the mass transfer of the reaction species.In addition,the synergistic effect between different metals in ternary metal oxides can effectively regulate the charge distribution on the surface of the active metal and improve the electrocatalytic activity.Fe-MIL-101-NH₂ was used the precursor,Co²⁺and Ni²⁺were introduced through a novel cation substitution process,and then fabricated a multidimensional Co Ni Fe-MOF derivate through a“decomposition-reconstruction”process.Co Ni Fe O_x-NC was fabricated through a simple oxidation process.The optimal charge distribution and the hierarchical structure endowed Co Ni Fe O_x-NC the excellent OER performance.Reached 50 m A cm^-2 current density only requires 265 m V overpotential,and still remained 96.6%initial activity after 40 h continuous electrolysis.Compared with traditional nanomaterials,single-atom electrocatalyst shows nearly 100%atomic availability in electrochemical reation.ZIF-8 was chosen as a precursor to fabricated Fe single-atom electrocatalyst（Fe-N_x/NC-900T）.Due to the strong interaction between Fe single-atom and nitrogen-doped porous carbon matrix,Fe-N_x/NC-900T showed outstanding CO₂electrochemical reduction performance,and reached high CO Faradaic Efficiency（92.19%）and high current density(-10.06 m A cm^-2)at the lowest overpotential（0.57 V）.