Research On Preparation Of Heterogeneous Atom-doped Carbon Nanomaterials And Its Electrocatalytic Performance

Considered as an ideal and highly potential replacement of fossil fuel,hydrogen has its advantages,such as wide sources,high combustion heat value,environment-friendly products,high energy density,and zero emission.The key to hydrogen energy development is finding out efficient and low-cost technologies to produce hydrogen.Among many current technologies to hydrogen generation,electrolytic water hydrogen production attracts considerable attention because of its mild preparation conditions,flexible production mode and high purity of hydrogen production.For electrolytic water hydrogen production technology,catalytic materials are supremely important.Therefore,exploiting efficient,cheap and wide-source non-noble metal catalyst materials becomes the significant research in the field of hydrogen energy.In this paper,a series of nitrogen-doped carbon materials have been prepared by simple hydrothermal-pyrolysis and microwave plasma chemical vapor deposition（MPCVD）methods are used as electrode materials to research their electrochemical performance.The main contents are as follows.Using ferrocene and polyvinylpyrrolidone（PVP）as raw materials to produce polymer gel which consists of evenly dispersed ferric oxide nanoparticles,and Fe₃C/N-doped carbon particles embedded in the nitrogen-doped carbon layer with the assistance of carbamide in high temperature by easy controlled hydrothermal synthesis.What’s more,the paper researches effects of pyrolysis temperature to nanoparticles’microstructure and function of electro-catalysis hydrogen separation,and influences of nitrogen input to the formation of nitrogen-doped carbon layer and its electrocatalytic hydrogen evolution performance.When the pyrolysis temperature is 400℃,there is only amorphous carbon structure.You can barely find iron oxide nanoparticles.And it only exposes few active spots in block structure,showing poor electrochemical hydrogen evolution performance.When the pyrolysis temperature is up to 800℃,XRD,XPS and HRTEM shows that C-N bond decomposition and carbonization reaction forms a typical core-shell structure with iron carbide as the core and nitrogen-doped carbon as the shell,which demonstrates that the pyrolysis temperature triggers amorphous carbon to transform into core-shell-structure iron carbide,increasing samples’crystallinity as well.Meanwhile,Fe₃C/N-doped carbon has the best hydrogen evolution reaction（HER）that other samples in the same conditions.Steady state LSV curve shows that it only demands 211mV current density to drive 10 mA cm^-2 current density,which is less than other pyrolysis temperature conditions.Its exceptional electrochemical activity comes from the synergistic effect of iron carbide and nitrogen-doped carbon.When the pyrolysis temperature rises to 1200^oC,XRD and XPS suggest that carbothermal reduction reduces iron carbide near the carbon bed into element Fe and form iron-iron carbide/carbon core-shell structure.Its electrochemical hydrogen evolution reaction performance deteriorated,and the potential required to drive a current density of 10 mA cm^-2 increased to 272 mV,which reduced the electrocatalytic activity.At the certain pyrolysis temperature under 800℃,Furthermore,Fe₃C/N-doped carbon with different nitrogen content was prepared by changing the input amount of the added nitrogen source and compared its HER performance.XRD and XPS shows that adding nitrogen markedly elevates materials’nitrogen content without affecting materials’phases and structures,efficiently mixing pyridinic-nitrogen and graphitic-nitrogen,increasing the exposed active spots.HER performance points that Fe₃C/N-doped carbon reduced the overpotential by about 28 mV compared to Fe₃C/carbon during the hydrogen evolution reaction,and hints that the doping of pyridinic-nitrogen and graphitic-nitrogen can increase product’s HER activity.For the preparation of hetero-atom-doped carbon-based electrocatalytic materials using abundant and cheap natural carbon sources as raw materials.We use abundant local bush as raw materials,utilizing nitrogen plasma with high chemical activity and good controllability,studying effects of microwave treatment time on carbonization and heterogeneous atom introduction effect and the final effect on HER reaction efficiency.The results show that carbonization of the shrub can be achieved by nitrogen plasma treatment in just 15 minutes,and an amorphous carbon material is formed.The over-potential of the electrocatalytic hydrogen evolution reaction is high,driving a current density of 10 mA cm^-2 required 737 mV.When the microwave plasma processing time is further extended to 1 h,the potential of the obtained product is only slightly reduced when the current density is driven at 10 mA cm^-2（689 mV）,which shows that the product from the material to the performance is extended during the extended processing time.The change is not obvious,and the final material with carbonization and nitrogen doping can be obtained in a short time by nitrogen plasma treatment.In this paper,two types of heteroatom-doped carbon nanomaterials with different structures and electrocatalytic hydrogen evolution properties have been successfully prepared by a simple two-step hydrothermal-pyrolysis method and a unique microwave plasma treatment technology.The electrocatalytic activity of N-doped carbon nanoparticles is significantly higher than that of nitrogen plasma treatment products of natural carbon sources,but the latter has the advantages of rapid,simple,and low-cost processing.Both technical methods are effective ways to obtain abundant sources of electrolytic water catalysts with high efficiency and low-cost.