Design Of Metal Organic Complex Electrocatalyst And Its Electrocatalytic Performance

Fuel cells and Zinc-air batteries have the characteristics of high energy efficiency,high energy density and low environmental pollution,so they have a wide range of application prospects.The fuel cell cathode reaction and the zinc-air battery anode reaction are the final rate-determining steps of the entire reaction,namely,the cathode oxygen reduction reaction(ORR)and the anode oxygen evolution reaction(OER).However,the slow kinetic process and the high price of precious metal catalysts limit its large-scale application.Therefore,it is an urgent to prepare cheap and efficient non-noble metal catalysts to accelerate ORR and OER and which becoming one of the future battery research and development directions.This thesis mainly studies the application of metal-organic complexes in electrocatalytic.By regulating the defects of the structure,improving the electronic conductivity,and inducing the generation of large specific surface and abundant active centers,the active sites can be effectively exposed and contact with the electrolyte to achieve effective mass transfer.At the same time,the synergistic effect of multiple active centers can enhance ORR performance;the electronic structure of the catalyst can be adjusted through heteroatom doping,charge effect,spin density and ligand effect.Increase the density of active sites exposed on the catalyst surface can improve OER/ORR dual-function electrocatalytic properties.The specific research content is as follows:(1)New Fe-based complexes were synthesized as OER catalysts.Firstly,a crystalline phase complex(C-Fe-NDC)was prepared by solvothermal method using naphthalenedicarboxylic acid as an organic ligand.Then,it was reacted with different solvents,and with polarity of the solvent change the crystal restructured,and the amorphous phase complex AP-Fe-NDC was obtained finally.X-ray diffraction(XRD),Fourier transform infrared(FTIR),Thermogravimetric(TG)and X-ray photoelectron spectroscopy(XPS)proved the unique structural properties and thermal stability of the complex;Scanning electron microscopy(SEM)and high-angle annular dark field scanning transmission electron microscope(HAADF-STEM)further confirmed that ethanol solvent successfully transformed the ordered crystal phase(C-Fe-NDC)into disordered amorphous state(AP-Fe-NDC).Studies have found that this crystalline state control strategy reduces the particle size,produces defects,exposes more active sites,and promotes the conduction of electrons.Finally,the OER performance of the catalyst was evaluated by combining linear sweep voltammetry,chronovoltage method,and chemical impedance method.It was found that AP-Fe-NDC has a lower overpotential than C-Fe-NDC regardless of whether it is at low current density(10 m A cm^-2)or high current density(500 m A cm^-2),and has a better long-term stablity.The stability verifies the performance improvement of the above-mentioned crystalline state reconstruction.At the same time,the XRD and XPS before and after the OER reaction were explored,indicating that the Fe OOH generated in situ during the OER process is considered to be the active center of the catalytic reaction.(2)Using dopamine as carbon and nitrogen sources to maintain structural stability and to coat Fe Mn-PBA Prussian blue analogs,a composite composed of Fe₃C and Mn₃O₄ nanoparticles in N-doped carbon was successfully prepared,named as Fe Mn PDA-900.Through XRD,Raman,Brunauer-Emmett-Teller(BET)and XPS tests,it is found that after the introduction of dopamine,the graphitization of carbon increases the electrical conductivity,promotes the formation of large surface area,increases the density of catalytic active sites,and produces abundant Fe-N_x active centers.The size and structure of the catalyst were further confirmed by SEM and high-resolution TEM(HRTEM).The catalytic activity,long-term stability and methanol tolerance test of Fe Mn PDA-900 catalyst at full p H were analyzed by rotation disk electrode(RDE)and rotating ring-disk electrode(RRDE),and compared with commercial Pt/C catalyst.The results show that Fe Mn PDA-900 has excellent ORR catalytic performance at full p H,excellent stability and methanol resistance,comparable to Pt/C catalysts.(3)The Fe Co-PBA Prussian blue analogue was coated with cystine to introduce N and S heteroatoms,and the Fe Co-N-C bifunctional single-atom catalyst was successfully prepared.Through SEM and TEM,it was found that the catalyst had a cubic structure with a concave surface.STEM-EESL was used to demonstrate highly dispersed and uniformly distributed monoatomic Fe and Co.The influence of the element composition of the catalyst on the catalytic activity was analyzed by XRD and XPS techniques.Doping heteroatoms into the carbon lattice can change the atomic charge density and spin density of adjacent carbons,which is beneficial to promote the adsorption of oxygen.The effects of different heat treatments on the catalytic performance were explored through BET and Raman techniques,and it was found that Fe Co-N-C-800 has the highest surface area,and the structural defects caused by the introduction of S and N heteroatoms further increase the density and exposure of catalytic active sites.Finally,the OER/ORR performance of the catalyst was evaluated by combining cyclic voltammetry,linear sweep voltammetry,and chronovoltage method.The results show that the single-atom catalyst has excellent OER and ORR catalytic activity.Its use in zinc-air batteries also shows good cycleability and high power density.