The Preparation Of Nitrogen Doped Graphene And Property For Hydrogen Evolution Reaction

Hydrogen energy is reconginzed as a clean new engery in the future owing to its high-efficiency,environment friendly and sustainablity.The hydrogen technologies,such as water splitting,hydrogen storage and fuel cells,have been attracting increasingly intense attention.The fashionable technologies for hydrogen production are electrolysis and photolysis from water.The photolysis of water to produce hydrogen can hardly meet the large scale demands because of its low efficiency,geographical factors and narrow wavelength coverage for light.In the contast,the electrolysis of water is a promising technology to produce hydrogen at industrial scale owing to its high-efficiency and high production.Noble metal,such as Pt,Ru,Ir,is the best catalytic materials for hydgroden evlution reaction(HER),but their commercialization is hindered by the scarcity and exorbitant price of noble metal.Thus,the development of earth abundant alternative catalysts with high-efficiency and low-cost to replace noble metal Pt for HER is urgent needed.In this thesis,we aimed to develop N-doped graphene(NG)as catalytic material for the catalysisi of HER.A space-confinement-induced sythsis is developed to control the nitrogen configurations as well as metal-nitrogen interactions of NG by using cations modified montmorillonite(MMT)as nanoreactors.The relationship between the NG interface structure and HER activity was investaged.We also provided an insight into the active site for HER in this work.Details are listed as follows:Firstly,a space-confinement-induced synthesis of pyridinic-and pyrrolic nitrogen-doped grapheme was studied.Nanoreactors with different layer distances(0.46~0.55 nm)including H-MMT,Ni-MMT,Co-MMT were prepared by using H+,Ni2+,Co2+ modified Na-MMT,respectively.Aniline(AN)monomers were intercalated into the layers of MMT nanoreactor(H-MMT,Na-MMT,Ni-MMT,Co-MMT)by free diffusion and ion-exchange,and then the AN monmers were in situ oxidation polymerization,followed by pyrolyzing at 900?.The confinement effect of MMT ensures that N is incorporated into the structure and that the graphitization is successful without significant loss of N species.Furthermore,planar pyridinic and pyrrolic N can be expected to be dominantly synthesized inside MMT because of the spatial confinement.Our results even indicate that the content of the planar pyridinic and pyrrolic N is inversely proportional to the interspace width(d)of MMT.For comparison,N doped carbon(NC)obtained by AN polymerization and pyrolysis without MMT and that obtained from a simple mixture of MMT were termed NCOMMT and NC?Na-MMT,respectively.Secondly,the study of electrocatalytic acitivity for HER.We found that,for the first time,the HER catalytic activity of a metal-free NG catalyst is positively correlated with 3-Dquaternary N content,while with an assistance of trace metal ions,the planar pyridine and pyrrolic N doped NG exihibts a much higher HER activity than that of quaternary N doped NG.The planer N doped NG catalyst coordinated with trace mount of Co irons displays an excellent HER activity with an onset potential of-49 mV(vs.reversible hydrogen electrode,RHE)and achieve a HER current density of 10 mA cm-2 at a much lower overpotential of-215 mV,which is among the best carbon based catalysts for the HER reported so far.NG coordinated with Co irons played a more important role in HER than NC coordinated with Co irons.Such phenomenon is not observed planer-N doped NG coordinated with Ni irons.The nanoreactor MMT showed a rather inferior activity for HER.When about 60 wt.% of MMT was removed in NG catalytic sample,all catalytic NG showed a better activity for HER than that confined in the nanoreactors.The result indicated that the etching of part MMT benifit the exposion of NG active sites for HER.While all MMT were removed,the active sites of NG would be recovered by NG restacking.