Synthesis and Electrocatalytic Property Study of Doped Graphdiyne

Author:Zhao Ya Song

Supervisor:wang dan


Degree Year:2019





Developing green efficient energy conversion device is an important strategy to solve the problems of environmental pollution and energy shortage.At present,the energy conversion systems such as metal air batteries and fuel cells are still limited by slow kinetics of oxygen electrode reactions.Designing highly efficient electrocatalysts is the core for improving catalytic activity of oxygen electrode reactions.Although the platinum(Pt),iridium(Ir)and ruthenium(Ru)show excellent catalytic performance,the high price and limited reserves hinder commercial application.The introduction of heteroatoms,such as boron(B),nitrogen(N),phosphorus(P)and sulphur(S),can activate the carbon skeleton,resulting in high activity.Graphdiyne,a new type of carbon allotropes,consists of benzene ring and diacetylenic linkages.The unique sp hybrid structure makes novel doping configurations possible.In this thesis,few-layer oxidized graphdiyne was obtained by exfoliating bulk graphdiyne with oxidation process.And on this basis,a series of heteroatom-doped graphdiyne were prepared by controlling doping positions,configurations,ratios and sequences.These catalysts were applied into oxygen electrode reactions,and structure-activity relationship was explored.The sp-hybridized nitrogen atoms were doped into diacetylenic linkages of graphdiyne by a pericyclic reaction,in which,the doping configuration and amount were controlled.The electrocatalytic activity of sp-hybridized nitrogen atom doped graphdiyne for oxygen reduction reaction was studied.It was found that the catalysts showed excellent electrocatalytic activity,stability,and methanol-resistance property both in alkaline and acidic media.The half-wave potential(0.87 V),kinetic current density(38.0 mA cm-2,0.75 V)and Tafel slope(60 mV dec-1)were superior to commercial Pt/C under alkaline condition.The overall performance of sp-hybridized nitrogen atom doped graphdiyne for oxygen reduction reaction approached to the commercial Pt/C in acidic medium,better than those of reported metal-free catalysts.Besides,the effect of sp configuration on catalytic performance has also been investigated.It has been shown that the sp configuration is vital for the catalysis,and with the amount of sp-hybridized nitrogen atoms increasing,the electrochemical performance improved significantly.Density functional theory calculation has been used to explore the origin of high activity.Compared with other nitrogen configurations such as pyridinic nitrogen and graphitic nitrogen,sp-hybridized nitrogen atoms make the surrounding carbon atoms possess much more positive charges.The larger charge density is beneficial for oxygen adsorption,and promoting the oxygen reduction reaction.A series of boron and nitrogen atoms doped graphdiyne were synthesized by sequential doping method,and their electrochemical activity for oxygen reduction reaction was investigated.It has been indicated that boron and nitrogen atoms doped graphdiyne possessed superior electrocatalytic activity,methanol resistance property and stability(remaining 96%after 10000 s test).The cathodic peak located at the same potential(0.87 V)with commercial Pt/C,exhibiting a good prospect of commercial applicaiton.In addition,the influence of the doping sequence of boron and nitrogen atoms on the catalytic performance was further studied.It should be stressed that graphdiyne firstly doped with nitrogen atom then boron atom presented the highest electrocatalytic activity.And the performance is better than those of boron and nitrogen co-doped graphdiyne,and graphdiyne firstly doped with boron atom then nitrogen atom.A series of sp-hybridized nitrogen and sulphur atoms co-doped graphdiyne were prepared by one-pot method,and the relative stereo distance of sp-hybridized nitrogen and sulphur atoms can also be controlled.The catalysts displayed prominent performance towards oxygen evolution reaction.The sp-hybridized nitrogen and sulphur atoms co-doped graphdiyne showed ultralow overpotential(299 mV),high current density(1.6 V,47.2 mA cm-2),the reaction kinetics and durability(remaining 95%after 20000 s test)were better than that of commercial RuO2.Density functional theory calculations investigated the relationship between the electrocatalytic performance and the doping configurations and relative distance.It can be concluded that sp-hybridized nitrogen and sulphur atoms located closely,and can produce effectively synergistic effect,facilitating the oxygen evolution reaction.Among the various configurations doped with sp-hybridized nitrogen and sulphur atoms,the form of sp-hybridized nitrogen and thiophenic sulphur possessed the highest activity.