Metalloporphyrins As Precursors For Preparation Of M-N-C Type Catalysts And Their Nitrogen Reduction Behaviors

Ammonia（NH₃）is one of the most important chemicals in the world,which can be used as raw material to prepare or process important compounds such as N-containing fertilizers,explosives,polymers,drugs,dyes,plastics,etc.So far,the leading industrial route for NH₃synthesis is the Haber-Bosch technique that uses N₂ and H₂as feed gases,but the process operates at high temperature（350-550°C）and high pressure（150-350 atm）,heavily depending on fossil fuels.As a result,it not only causes environmental pollution,but also intensifies the generation of greenhouse gases.With the depletion of fossil fuels and the deterioration of global climate,environmental protection has become a focus of topics.To meet the demand for ammonia,it is urgent to seek sustainable,renewable and environment-friendly energy to satisfy the future production need.Electrocatalytic N₂ reduction provides an alternative and effective way to solve this problem.Metal atoms fixed on carbon substrates by nitrogen（M-N-C）have been a rising star in the field of catalysis in recent years,especially in the field of electrocatalysis.In M-N-C catalyst,metal atoms can be stably anchored on carbon substrates by nitrogen.In addition,the electronic structures of metal and carbon atoms can be effectively adjusted so as to optimize the adsorption and desorption of intermediates and thusly improve the catalytic performance.Additionally,the carbon substrate has high conductivity,which can accelerate the electron transfer in the reaction.Metalloporphyrin has a well-defined M-N-C structure.The macrocyclic conjugate structure not only gives itself rich free electrons,but also owns a highly-dispersed central metal atom.Based on the above theoretical and practical basis,this research is divided into four parts:1.Tetraphenyl iron porphyrin（Fe TPP）was used as precursor to self-assemble with reduced graphene oxide（r GO）by simple impregnation method,and annealed together at high temperatures to prepare metalloporphyrin-mediated M-N-C catalyst.Their nitrogen reduction reaction（NRR）catalytic performance was tested.The effects of different annealing temperatures on the catalytic performance of M-N-C catalysts were investigated.It turns out that Fe TPP@r GO-800 exhibits excellent catalytic performance with a smaller electron transfer resistance and larger electrochemical active surface area.Its ammonia yield rate and Faradaic efficiency reach the highest at-0.4 V vs RHE,which are 10.5μg·mg^-1·h^-1,13.49%respectively.2.Tetraphenyl iron porphyrin（Fe TPP）and other transitional metalloporphyrins（MTPP,M=Ni,Mn,Zn,Cu,Co）were mixed in a certain proportion to self-assemble with reduced graphene oxide（r GO）by simple impregnation method,and annealed at high temperature to prepare metalloporphyrin-mediated M-N-C catalyst with dual metal atoms and their nitrogen reduction reaction（NRR）catalytic performance was tested.In this process,we adjust the metal center and concentration of metalloporphyrins respectively for the following aims:（1）The effects of doping Fe with Mn,Ni,Co,Cu and Zn respectively on electrochemical ammonia synthesis were systematically investigated.（2）The ratio of Fe and Ni was tuned to figure out the best doping content of the two metal so as to acquire the optimal ammonia yield rate.It turns out that doping of 5%Ni TPP promotes the catalyst to the best performance,whose ammonia yield rate and Faradaic efficiency are 22.5μg·mg^-1·h^-1,50.7%respectively.3.Natural reed straw was collected to prepare biomass material reed straw carbon（RSC）.Tetraphenyl iron porphyrin and reed straw carbon（RSC）were self-assembled by simple impregnation method and then annealed together at high temperatures to prepare metalloporphyrin-mediated M-N-C catalyst based on RSC.Their nitrogen reduction reaction（NRR）catalytic performance was tested.The effects of different annealing temperatures on the catalytic performance of M-N-C catalyst were investigated.It turns out that Fe TPP@RSC-800 exhibits excellent catalytic performance with a smaller electron transfer resistance and larger electrochemical active surface area.Its ammonia yield rate and Faradaic efficiency reach the highest at-0.3 V vs RHE,which are 12.63μg·mg^-1·h^-1,13.74%respectively.4.Tetraphenyl iron porphyrin（Fe TPP）and a series of 3d,4d,5d transitional metal porphyrins（MTPP,M=Ni,Mn,Zn,Cu,Co,Pd,Pt）were mixed in a certain proportion as precursors to self-assemble with reed straw carbon（RSC）by simple impregnation method and annealed together at high temperature to prepare metalloporphyrin-mediated M-N-C catalyst with dual metal atoms biomass material and their nitrogen reduction reaction（NRR）catalytic performance were tested.It turns out that Fe Pd TPP@RSC-800 exhibits excellent catalytic performance with a smaller electron transfer resistance and larger electrochemical active surface area.Its ammonia yield rate and Faradaic efficiency reach the highest at-0.3 V vs RHE,which are 17.6μg·mg^-1·h^-1,15.1%respectively.