Controlled Synthesis Of Metal-organic Frameworks Derived Cobalt/Nickel-based One Dimension Nano-assembled Materials For Electrocatalytic Applications

The development of science technology brings great convenience to human society.However,most advanced technologies still rely on carbon-based fuels such as natural gas,coal,and petroleum.The depletion of these resources and their impact on the environment has motivated many researchers to pursue alternative new energy.Numerous ideas have been proposed to achieve more efficient energy conversion or storage systems such as alkaline fuel cells,water electrolysis,and metal-air batteries.Although the noble metal based catalysts,such as Platinum?Pt?,Ruthenium?Ru?and Iridium?Ir?possess superior catalytic activity;the poor stability and high cost seriously limit their application.So the construction of non-precious catalysts is very important for the pratical application of these novel energy conversion devices.In this thesis,the overview of rechargeable zinc-air batteries and the reaction mechnism of oxygen reduction reaction?ORR?and oxygen evolution reaction?OER?are presented.The research background of the electrocatalysts and the application of metal organic framework and its derivatives in electrocatalytic are described in detail.The current main problems about non-precious metal catalysts,the way to solve these problems are proposed.The simple synthesis method for synthsis of a series of metal-organic frameworks?MOFs?with special morphologies was explored.Then,a series of one-dimensional?1D?cobalt/nickel-base nano-assembled structures with larger specific surface area,porous and hetero-atom doping non-precious catalysts were sysnthsised with the MOFs used as precursors by regulating the preparation conditions.Finally through a variety of characterization testing methods,the research results show that the catalysts with special structure have a superior electric catalytic performance.And also it has potential application prospects.The relationship between composition,structure and performance was studied.The specific contents of the paper are as follows:Firstly,1D nano-assembled Ni nanopaticles and N codoped carbon nanotube catalyst were synthesized.And the OER properties of this catalyst were tested.First,the Ni-MOF was synthesized using 4,4?-bipyridine?Bpy?and D-?+?-camphoric acid as a dual organic ligand in the hydrothermal reaction,followed synthesis of the Ni NPs@N-CNTs catalyst by pyrolysis of the Ni-MOF in N₂.By regulating the pyrolysis temperature,we find that the catalyst pyrolyzed at 600 ^oC performance is the best one.Nitrogen species disappear when temperature is higher than 700 ^oC.NiO form at 800 ^oC.When the pyrolysis temperature is higher than 700 ^oC,the mesoporous of the catalysts disappear,As expected,the obtained catalyst owns the advantageous features towards OER.Benefiting from the favorable features,the Ni NPs@N-CNTs exhibits a better OER performance than commercial RuO₂ in alkaline medium,which includes a lower onset potential?1.45 V vs.RHE?and the overpotential at the current density of 10 mA cm^-2 is 460 mV.The stability is also higher than some reported nickel-based catalysts and commercial RuO₂.Secondly,Co nanopaticles embedded in S,N codoped hollow carbon nanoprism catalyst?Co@SN-CNP?was synthesized and the ORR property of this catalyst was tested.The Co-MOF was synthesized with Bpy and thiophene-2,5-dicaboxylate?Tdc?acid used as a dual organic ligand in the hydrothermal reaction at first.The non-precious metal catalyst Co@SN-CNP with high specific surface and porous was synthesized by pyrolysis of the Co-MOF in N₂.The cayalyst maintains the 1D nanostructure of precursor and the composite mesoporous holes appears on the basis of the precuresor micropore,which benefits to mass transport.Meanwhile the sulfur and nitrogen were successfully doped into the catalysts for improving the electrocatalytic percformace.Then,its ORR properties were studied.The research results showed that the Co@SN-CNP catalyst owned better ORR performance.It possesses similar ORR activity but superior durability compared to the commercial 20 wt%Pt/C in 0.1 M KOH solution.Thirdly,1D nano-assembled Co nanoparticles and N codoped carbon nanotube catalyst were synthesized.The ORR and OER bifunction properties of this catalyst were tested.The preformance of Co@N-CNR electrocatalyst employed in the air electrode of aqueous ZnABs were conducted also.The Co-MOF was synthesized with Bpy and D-?+?-camphoric acid used as dual organic ligands in the hydrothermal reaction at first.Then the 1D Co@N-CNR catalyst with large surface area and porous was synthesized by pyrolysis of the Co-MOF in N₂.The electrocatalytic properties of the catalyst toward ORR and OER were studied.The reseach results showed that the catalyst had better ORR and OER bifuctional activity.As expected,the Co@N-CNR could be used as highly active bifunctional catalyst for ZnABs.When the Co@N-CNR electrocatalyst was employed in the air electrode of aqueous Zn ABs,the ZnAB prototype displayed the excellent performance(a maximum power density of 63 mW cm^-2 during discharge)and long cycle stability,making it highly promising for widespread implementation of rechargeable ZnABs.The relationship between the performance and the morphology and composition of the catalyst at different pyrolysis temperature was also studied.The research results showed that the pyrolysis temperature was critical to the catalyst.The catalyst performance was the best under 600 ^oC.The electrocatalytic performance decreased dramatically when the temperature was higher than 700 ^oC,as the one dimensional structure collapsed,specific surface reduced rapidly and mesoporous disappear.Fourthly,1D nano non-precious metal catalyst Co-MOF assembled by core-shell nanoparticles was synthesized and their ORR,OER and HER trifunction properties were studied.The Co-MOF was synthesized by the method proposed in third part of this thesis.Then it was use as precursor to obtain the1D hybrid structure that comprised of double-core@shell structure is composed of an inner metallic Co and a Co₉S₈ core and an outer carbonaceous layer shell and the double-core@shell nanoparticles can hybridize to form one dimensional nanotubes.As expected,the prepared catalyst with hybrid nanostructure integrated the advantageous features of 1D nanostructures and core-shell nanostructures displayed a higher catalytic performance.The research results showed that the catalyst had tri-functional catalytic activity.It showed a considerable activity toward ORR with commercial Pt/C,superior activity and stability to commercial Ir/C in the alkaline medium.It also had better catalytic activity toward HER.When the electrocatalyst was employed in the air electrode of aqueous ZnABs,the ZnAB prototype displays the excellent performance(a maximum power density of 93 mW cm^-2)and better cycling stability compared to commercial Pt/C or Ir/C integrated in zinc air batteries.Meanwhile,it was used as electrodes for full water splitting and displayed good performance and excellent stability for more than 15 h.Finally,The influence of the morphology and composition of the precursor and the different pyrolysis conditions on the morphology and composition of the 1D catalyst structure were discussed based on above studies.The research results showed the same precursor could produced the different morphology and composition of catalysts through controlling the pyrolysis conditions,and then affected the perfomance of the catalyst.These research results can provide the reference for the synthesis of one dimensional non-precious metal material with multilevel composite structures;the studies of composition and properties also provide the reference for the preparation of electrocatalytic materials.In addition,the results of this paper also provide some experimental and theoretical basis for the preparation of hetero-atom doped catalysts.