Electrocatalyic Performance Of Metal-free Doped Functional Carbon Materials

Oxygen Reduction Reaction(ORR)and Oxygen Evolution Reaction(OER)are always the research hotspots in the field of electrocatalysis,as they play a key role in a wide range of energy storage and conversion technology.At present,the catalysts for ORR and OER developed are mainly Pt,Ru,Ir and other noble metal catalysts,and some progress have been made.However,the amount of noble metal storage in the earth is limited,and the cost is expensive,leading to it diffcult to scale applications.Recent studies reveal that the inexpensive nonmetal doped carbon materials exhibit excellent catalytic activity for ORR and OER and are considered to be one of the most promising alternatives to noble metal catalysts.In order to develop the nonmetal doped carbon catalyst with better activity,this paper attempt to synthesis As doped,As/N codoped carbon nanotubes and N-containing ordered mesoporous carbon(N-OMC)prepared for Electrocatalysis of ORR and OER,and discuss the catalytic mechanism of As doping and N doping.The results are as follows:(1)Preparation and Electrocatalyic Performance of As-doped Carbon NanotubesAs-doped Carbon Nanotubes(As-CNTs)were prepared by the thermolyses of triphenylarsine(TP)xylene solutions using Chemical vapor deposition(CVD),The morphologies and elemental compositions of as-prepared samples were characterized,the results showed that the successful doping of As with large radius into the framework of CNTs.Electrichemical tests demonstrated that the prepared As-CNTs exhibited better electrocatalytic activity for ORR and OER in alkaline medium,showing that the doping of As atoms could significantly improve the ORR and OER activities of CNTs.Density functional theory calculations indicated that the net charges of carbon atoms around As changed from neutral to negative and the energy gaps decreased,further demonstrating that the As doping could improve the ORR and OER activity of CNTs in alkaline medium.(2)Preparation and Electrocatalyic Performance of As and N-codoped Carbon NanotubesIn order to further improve the catalytic activity of As-doped Carbon materials,this paper tried to synthesize As and N-codoped Carbon Nanotubes(AsN-CNTs),the morphologies and elemental compositions of obtained materials were characterized.The results confirmed the successful doping of As and N elements.Electrichemical tests showed AsN-CNTs with much higher ORR activity than N-CNTs indicated the existence of synergistic effect between As and N atoms.Theoretical calculations showed the net charges of carbon atoms around As and N changed to show more active sites.Moreover,the As/N codoping could reduce the energy gaps,it was in more favor of the improvement of the electrocatalytic activity for ORR and OER.(3)Effects of N species on electrocatalytic activities for ORR and OERDespite remarkable progresses has been made in the application of N-doped carbon materials as novel bifunctional electrocatalysts.However,there is not a clear answer about active N species for the ORR and OER up to now.this paper used tobacco as cheap materials to fabricate N-OMC.Meanwhile,to adjust N species distribution by dicyandiamide.Electrocatalytic activity tests results indicated that the as-prepared N-OMC with more pyrrolic and pyridinic Ns exhibited much higher activities for ORR and OER than ones with more graphitic N in both acidic and alkaline media,suggesting that the increase of pyrrolic and pyridinic Ns favors the improvement of ORR and OER activities of N-OMC.It is of guiding significance for the design of bifunctional catalysts in the future.