| Heteroatom doping can effectively modify the band structure,electrical and electrochemical properties of graphene.Thus,the controllable synthesis of heteroatom-doped graphene becomes the research frontier and hotspot of material science.In this dissertation,we focused on the synthesis and the properties of heteroatom-doped graphene films/foams.Firstly,the controllable synthesis and effects of dopant on the structure and electrical properties of nitrogen-or sulfur-doped graphene films were investigated;then,the controllable preparation and effects of dopant on the structure and electrocatalytic performance of sulfur-doped graphene foams and their composites were investigated;finally,the controllable preparation and effects of dopant on the structure and electrocatalytic performance of sulfur and nitrogen co-doped graphene foams and their composites were investigated.The main research content and results are as follows:1.The controllable synthesis and electrical properties of pristine,nitrogen-and sulfur-doped graphene films were investigated.?1?The parameters of chemical vapor deposition?CVD?process and transfer process for pristine graphene films were optimized.The graphene films with high quality and low sheet resistance were obtained.High-performance flexible transparent triboelectric nanogenerator based on graphene film electrode were developed.Its output power density reaches to 10.1?W cm-2 and the peak output voltage reaches up to 56 V,which demonstrates the potential application in energy conversion field.?2?The low-temperature synthesis parameters,structure and electrical properties of CVD grown nitrogen-doped graphene films were investigated by using pyridine as nitrogen doping source and as carbon source.The results show that,when the growth temperature increases from 350 oC to 450 oC,the defect density of N-doped graphene obviously decreases;the content of N doping decreases from 7.6 at%to 3.9 at%,and its mobility increases from 0.3 cm2 V-11 s-11 to 5.7 cm2 V-11 s-1.?3?The CVD growth parameters,structure and electrical properties of sulfur-doped graphene?SG?film were studied by using thianthrene as the sulfur doping source and carbon source.The modulation mechanism of hydrogen flux on the doping content,structure and electrical properties of SG film was revealed.The highest sulfur doping content reaches 4.01 at%and its mobility reaches up to 270 cm2 V-11 s-1,which is the highest value ever reported.2.The controllable preparation and electrocatalytic properties of sulfur-doped graphene foams and their composites were investigated.?1?Three-dimensional sulfur-doped graphene foam?3DSG?was grown on nickel foam by CVD using thianthrene as solid carbon source and as doped sulfur source.The results show that 3DSG treated by Ar plasma?3DSG-Ar?exhibits excellent electrocatalytic hydrogen evolution reaction?HER?,because the defect in 3DSG as catalytic active sites were significantly increased after argon plasma bombardment.The onset potentials of 3DSG and 3DSG-Ar are 259 and 218 mV,respectively and the Tafel slopes are 97 and 64 mV dec-1,respectively.?2?Ultrafine Pt nanoparticles were homogenously deposited on 3DSG?Pt/3DSG?by photochemical reduction of chloroplatinic acid.The results show that Pt/3DSG delivers superior electrocatalytic performance.The Tafel slope of Pt/3DSG with 3.1 wt%Pt loading is only 30.1 mV dec-1,which is smaller than 20 wt%Pt/C(31.2 mV dec-1).The turnover frequencies?TOFs?of Pt/3DSG can reach up to 1.12 s-1,which is much larger than that of 20%Pt/C(0.71 s-1).It was confirmed with Raman,TEM and XPS that the strong chemical bonding and electron transfer between the sulfur atom and the platinum atom in Pt/3DSG,which effectively enhances its catalytic activity and stability.?3?Sulfur-doped graphene/nickel foam composite?3DSG/NF?was synthesized by CVD and its electrocatalytic oxygen evolution reaction?OER?performance was investigated.The results show that 3DSG/NF has excellent OER performance with a Tafel slope of 61.62 mV dec-1,and its overpotential at a current density of 10 mA cm–2 is 291mV.The excellent OER performance is attributed to the enhanced electrocatalytic activity by doped sulfur atoms and the improved stability by the graphene-coated nickel skeleton.3.The controllable preparation and electrocatalytic performance of sulfur and nitrogen co-doped graphene foam and its composites were investigated.?1?Sulfur,nitrogen co-doped graphene foam was synthesized through argon plasma pretreatment for three-dimensional graphene foam?3DG?and then doping by annealing with sulfur,nitrogen source.The results show that the rich defect sites generated by argon plasma pretreatment not only facilitate the doping of sulfur and nitrogen atoms into the graphene lattice,but also become the catalytic active sites for HER;the synergistic effect of co-doping and argon plasma pretreatment greatly enhances the catalytic performance of 3DG and its Tafel slope decrease from 182 to 75 mV dec-1.?2?Sulfur,nitrogen co-doped graphene on nickel foam?3DSNG/NF?was grown by CVD using phenothiazine as carbon,sulfur and nitrogen source.The results show that the3DSNG/NF delivers excellent OER catalytic performance with a low Tafel slope of 45.61mV dec-1.The excellent OER catalytic performance is mainly attributed to the doped sulfur and nitrogen atoms and the partially oxidized nickel from nickel foam.?3?NiSe2/3DSNG/NF was synthesized on 3DSNG/NF by hydrothermal method.The results show that NiSe2/3DSNG/NF has excellent HER catalytic performance in both acidic and alkaline electrolytes,and its Tafel slope in acid?alkali?electrolyte is 28.56?75.95?mV dec-1 and the overpotential at 10 mA cm–2 is 130?177?mV;it also delivers excellent OER catalytic performance in alkaline electrolyte with a low Tafel slope of42.89 mV dec-1,and the overpotential at 100 mA cm–2 is only 256 mV;The electrocatalytic activity and stability of NiSe2/3DSNG/NF were effectively enhanced with NiSe2,sulfur and nitrogen doped atoms as catalytic active sites and combining with conducting three-dimensional framework. |
PDF Full Text Request