The Heteroatom-doped Nanocarbon-Based Catalysts With Multihybridized Structures:Controllable Preparation And Mechanism

As the traditional metal catalysts suffers from serious problems,such as low stability,unsatisfied activity and environmental hazards,metal-free carbon-based catalysts are emerging as potential solution.There have been reports on heteroatom-doped carbon catalysts with multihybridized structures,which exhibits excellent performance in important reactions for future carbon-balanced society.However,the controllable fabrication of heteroatom-doped nanocarbon with multihybridized have not been fully explored and the details of mechanism of carbon catalysis remains unelucidated.Herein,combining first-principles calculations and experiments,we make efforts listed below:(a)Revealing the role of sp2@sp3 structure of nanodiamond in alkane with density functional theory(DFT)calculations for the first time.The superior performance of alkane dehydrogenation on nanodiamond catalyst is investigated thoroughly with DFT calculations.The C-H bond activation,complete reaction pathway,effect of nanodiamond diameter,electronic structures are studied and the results indicate that the sp2@sp3 core-shell structure is crucial for dehydrogenation activity of nanodiamond.The oxygen group on nanodiamond is comparably more electrophilic than that on CNT,which is beneficial for activation of C-H bond.The sp2@sp3 core-shell structure is more effective for distributing the charge from H atom,therefore improve the charge transfer from reactant to catalysts.(b)Proving the effectiveness of phosphorus-doping for improving the activity of carbon catalysts for CO2 electroreduction reaction.Two methods are applied for phosphorus doping,and results show that chemical state of phosphorus is key to reaction activity.P-doped carbon with phosphorus-carbon bond is better than that with phosphorus-oxygen bond.The P-doped carbon exhibits excellent activity in CO2 reduction,and more than 80%selectivity towards CO production.DFT calculations show that reactant and intermediates such as CO2,CO2-and*COOH is more stable on the P-C bonding sites,and the electronic transfer is favored on P-C,shedding lights on the future development of heteroatom-doped carbon catalysts for CO2 electroreduction.(c)Proposing the single-atom catalyst(SAC)supported on nitrogen-or boron-doped graphene.Using DFT calculations,it is found that the doped nitrogen and boron atoms are better than carbon atoms as anchoring sites for single metal atom,which is beneficial for stability of SACs.The parasite hydrogen evolution reaction is significantly suppressed on SACs.Moreover,by tuning the number of nitrogen and boron adjacent to metal atom,the overpotential for CO,HCOOH,CH3OH and CH4 are greatly reduced.The lowest overpotential of CH3OH is-0.49 V,which is one of the lowest reported in literatures.It is found that the linear scaling law,which governs the adsorption energy of*CO and*CHO on bulk metal,is not applicable on SAC.The doped boron and nitrogen could weaken the adsorption between*CO and metal atom,which is crucial for breaking the linear scaling law.(d)Fabricating novel nitrogen-doped CNT@graphene(N-G@CNT)composite structure for CO2 electrochemical reduction.It is shown in microscopy that the CNT and graphene are linked closely.The pyridinic and amine species is dominant in the nitrogen doped in N-G@CNT,which provides the active sites for CO2 electroreduction.The N-G@CNT exhibits higher reactivity comparing to N-G or N-CNT,with faradaic efficiency of 54%and 30%for CO and CH4,respectively,which is It is suggesting that CNT-graphene composite is beneficial for bridge defects and basal sheets of graphene,enhancing charge transferring.