Preparation And Electrocatalytic Properties Of Porpyrin MOF-based Composite Materials

Recently,the energy crisis and environmental problems are becoming more and more prominent.As a new type of energy,hydrogen is widely concerned because of its cleanness,efficiency and environmentally friendly.Among the numerous hydrogen production methods,electrochemical water splitting is the most promising large-scale hydrogen production technology.Thus,it is important to develop efficient hydrogen evolution catalysts and promote the commercialization of hydrogen energy to solve the energy crisis and environmental problems.As the representative of precious metal catalyst,platinum is the most efficient electrocatalyst,but its low reserves and high price restrict its large-scale application.Therefore,it is necessary to develop high-performance non noble metal electrocatalysts to reduce the cost in the process of hydrogen production.Porphyrin based metal organic framework materials are formed by the combination of porphyrin or metal porphyrin organic ligands with metal ions.They have the biological and chemical stability of porphyrin,large specific surface area and rich pore structure of metal organic framework,and are expected to replace the metal catalysts.In order to solve the problem of insufficient conductivity of metal organic framework materials,the porphyrin metal organic framework material is compounded with highly conductive graphene by using the π conjugated structure of porphyrin,which can form π-π stacking effect and accelerate electrons.In addition,the porphyrin-based metal organic framework material is a porous material with extremely high carbon and nitrogen content and uniform distribution of metal ions.With this property,the porphyrin-based metal organic framework materials were pyrolyzed at a high temperature to uniformly distribute them in the framework.An electrocatalytic porous material doped with abundant active sites is obtained on the surface.The main research contents are as follows:1.The tetracarboxyphenyl copper porphyrin ligand was coordinated with cobalt metal ions by hydrothermal method to construct a porphyrin-based metal organic framework material(Co-CuTCPP)with the bimetallic active center.Each nanosheet has a diameter of about 200-500 nm.The presence of COO-Co bond makes the electrocatalytic oxygen evolution(OER)performance of Co-CuTCPP superior to that of copper porphyrin.At a current density of 1 mA cm-2,the initial potential is 340 mV.In order to further improve the electrical conductivity of Co-CuTCPP material,it is combined with different proportions of graphene oxide to prepare Co-CuTCPP/rGO-x sheet composite with oxygen evolution activity.The catalyst was placed in a 1.0 M KOH solution for electrochemical testing.At a current density of 10 mA cm-2,the overpotential of Co-CuTCPP/rGO-10 material was the smallest,only 396 mV,which has the highest catalytic activity for OER.At the same time,it exhibits the lowest Tafel slope(58 mV/dec),indicating that the kinetic process is the fastest.In the electrochemical stability test,the constant current electrolysis performance was still not attenuated at a voltage of 1.61 V for 10 hours.In addition,the morphology and structure of Co-CuTCPP nanosheets and Co-CuTCPP/rGO-x were characterized by SEM,TEM,XRD,FTIR,UV-Vis,BET,etc.,and their catalytic OER mechanism was analyzed in depth.2.The porphyrin-based MOF material rich in nitrogen was used as the precursor,and the nickel porphyrin organic ligand and zirconium chloride were synthesized by solvothermal method to form a rod-like porous metal organic framework material PCN-222(Ni).Morphology,crystal structure and specific surface area were characterized by SEM,XRD and SEM.PCN-222(Ni)is rich in nitrogen and homogeneous metal ions.It was calcined at different temperatures by high temperature pyrolysis to obtain carbon material Ni-N-C uniformly dispersed by nickel nitride nanoparticles.The cracking process was analyzed by XRD,FTIR,TG.The porous metal nitride carbon material was subjected to electrochemical hydrogen evolution(HER)test under acidic conditions.At a current of 10 mA/cm2,Ni-N-C 800 exhibited the lowest potential(100 mV),which was close to the commercial Pt/C(76 mV)with excellent electrocatalytic activity.In the AC impedance test,the resistance value is less than PCN-222(Ni),indicating that the calcination process improves the conductivity of the material.Ni-N-C 800 has a lower potential than NiTCPP 800 and N-C 800 because of its rod-shaped frame carbon material and uniformly distributed NiNx active sites,which makes Ni-N-C 800 exhibit excellent HER performanceIn this paper,new catalytic materials such as Co-CuTCPP,Co-CuTCPP/rGO-x,PCN-222(Ni)and Ni-N-C 800 were prepared by hydrothermal method,solvothermal method and calcination method.The morphology and structure of the materials were characterized by SEM,TEM,XRD,FTIR,UV-Vis,BET,XPS and other tests.In addition,the electrochemical test show that the electrocatalytic performance of the porphyrin MOF material after graphene composite and calcination has been greatly improved,and has a good development prospect,which provides a direction for the follow-up workers.