Construction And Electrocatalytic Properties Of Transition Metal Based Nitrogen-doped Composites

Due to the energy shortage and environmental pollution caused by fossil fuels,there is an increasing demand for developing a kind of efficient clean energy.As for fuel cells,Pt catalyst is the most ideal catalytic material because the change value of free energy of instantaneous adsorption H*on Pt surface is almost zero.However,since Pt is scarce and expensive,it is a general trend to construct a low or no Pt based high efficiency fuel cell catalyst.Based on the above considerations,we developed the transition metal based nitrogen-doped composites,and explored their properties and internal mechanism.（1）In this study,three-dimensional reticulated N-Ni Se2 nanosheets（N-Ni Se2/CP）uniformly grown on carbon paper were prepared by hydrothermal and pyrolysis methods.Firstly,Ni Se2/CP was successfully synthesized by hydrothermal reaction.Secondly,the carbon paper with uniformly loaded Ni Se2 was soaked in ammonia water.Then,it was pyrolysis at400℃in a tubular furnace.Nitrogen dopant can adjust the electronic structure of Ni Se₂nanosheet array to optimize the adsorption and dissociation behavior of water and promote the OER process.When the sample was used in the OER process,we were surprised to find that the sample has good catalytic performance of OER.In 0.1 M KOH,the potential of N-Ni Se2/CP is 1.35 V and 1.61 V（vs.RHE）at the current density of 10 m A/cm² and 40 m A/cm²,respectively.It is much lower than the Ni Se2/CP without N doping electrode.We speculate that the doping of N heteroatoms promotes the formation of mott-Schottky heterojunction structure inside the material,and the electronic structure and interface energy band of this heterojunction structure have obvious mutations.Therefore,the adsorption of reactants,desorption of products and the activity of active sites are improved at the heterogeneous interface.This interfacial adjustment continuously changes the work function of catalyst at Schottky barrier,changes the electron cloud density of catalyst,and induces the negative charge to accumulate on the side with higher work function,accordingly improving the catalytic performance of the material.The material can be easily prepared and has excellent properties,which provides a new path for OER catalyst in the future.（2）In this study,Pt Ni Fe based rigid and bamboo like N-doped carbon nanotubes（Pt Ni Fe/N-CNTS）were prepared by a simple one-step pyrolysis process.First of all,under vacuum conditions,the premixed platinum chlorate,iron nitrate and nickel nitrate were dried on the porcelain boat,and then the dried porcelain boat was turned upside down on the porcelain boat containing melamine and pyrolyzed at 800℃.Finally,uniform growth of Pt Ni Fe based rigid and bamboo like N-doped carbon nanotubes was obtained.We chose melamine as the source of heteroatom doping,and the introduction of heteroatom is an effective way to introduce material defects,improve electron transfer rate and active site.The ORR test of the materials showed that the onset potential（Eonset）and half-wave potential（E1/2）in 0.1 M KOH were 1.01V and 0.92 V（vs.RHE）,respectively.The nano-particles encapsulated at the tip of carbon nanotubes are Pt,Fe and Ni-based alloys,and they are coated by a carbon shell.In Pt Ni Fe/N-CNTs,Pt Fe alloy catalyzes the rapid growth of Pt Ni Fe/N-CNTs,adjusts the electron cloud of tip nanoparticles,and catalyzes the ORR reaction more easily.Fe Ni bond and Fe Pt bond are relatively stable,which can effectively resist the Fenton effect between carbon corrosion and iron ions,reduce iron leaching and improve stability.The material has the advantages of simple preparation,easy operation and superior catalytic performance,making it a new path for the development of ORR catalyst.