Theoretical Study Of Catalytic Performance Of Two-dimensional Carbon-based Materials Confining Transition Metal Single-atom Catalysts

The depletion of fossil fuels,the increasing global energy demand and the increasingly serious environmental problems make it extremely important and urgent to develop the next generation of high-capacity,low-cost,renewable and environment-friendly energy storage and conversion technologies,such as hydrogen energy,fuel cells and metal-air cells.Electrochemical energy storage and conversion can store energy through hydrogen and oxygen generation from hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)process during water splitting.On the other hand,hydrogen can be burned in fuel cell or metal-air cell through hydrogen oxidation reaction(HOR)and oxygen reduction reaction(ORR)so as to realize energy utilization.Nobel metal catalysts play vital role in improving energy storage and conversion efficiency.Nevertheless,their drawbacks,such as scarcity of resources and high price,have severely hindered the large-scale commercial application of relevant technologies.Therefore,the development of catalysts with high activity,low cost and high stability has been a difficult problem in academia and industry for many years.There is no doubt that single atom catalysis(SAC_S)provides a new way to solve the above problems.The main goal of this paper is to efficiently and quickly screen high active single-functional and multi-functional SAC_S,and to further enhance the number of active sites.First of all,we directly selects carbon nitride(g-C₃N₄)two-dimensional material with uniform cavity as the substrate to confine the high active transition metal(TM@g-C₃N₄)to achieve stable SAC_S,and uses carbon monoxide reaction(COR)as the catalytic probe reaction to explore the catalytic performance.Secondly,TM@g-C₃N₄ SAC_S is used to study ORR/OER single-functional and multi-functional catalysis,and then forming structural nitrogen defect of TM@g-C₃N_4-?to further enhance the catalytic activity,so as to screen out the best ORR/OER bifunctional SAC_S.Then,we extend the catalyst support from g-C₃N₄ to?-graphyne(GY)to form SAC_S(TM@GY),and then further expand its application from single-functional SAC_S to multifunctional SAC_S for ORR/OER/HER/HOR.Finally,a new two-dimensional material family(2D-M₂C₁₂)with superior coverage of metal atoms is directly designed.Taking the rare two-dimensional magnetic semimetallic material of2D-Fe₂C₁₂ as an example,the stability and intrinsic catalytic activity are verified,so as to ensure that the intrinsic catalytic activity is improved and the number of active sites is also increased as much as possible.The main research results are as follows:(1)We show that TM@g-C₃N₄ is stable and particularly that Cr@g-C₃N₄ and Mn@g-C₃N₄ are potential CO oxidation agents of SACs at room temperature.It is proved that TM act as active sites and charges memory in catalytic reactions.(2)Based on a systematic study of TM@g-C₃N₄ as ORR/OER SACs,we identified a simple and reliable intrinsic activity descriptor?to characterize the catalytic activity,and proposed a scheme to further enhance the catalytic activity by reducing N coordination number.Specifically,Ag@g-C₃N₄ and Rh@g-C₃N_4-?showed the excellent ORR/OER bifunctional catalytic activity.The active mechanism analysis showed that the enhancement of activity was the result of synergistic effect of g-C₃N₄ and TM.(3)The results of TM@GY based multi-functional SACs show that Fe,Ir,Co,Rh,Cu,Ni,Pd and Pt@GY are potential ORR/OER single-functional/bifunctional SACs.Sc,Ti,Cr,Mn,Fe,Co,Y and Zr@GY are potential HER/HOR single-functional/bifunctional SACs.Fe,Ru and Co@GY are potential ORR/OER/HER/HOR multifunctional SACs,among which Co@GY shows excellent multifunctional catalytic activity.(4)A three-step strategy for screening multifunctional SACs is put forward:(i)screening non-radioactive TM element,(ii)screening single-functional SACs through stability and activity,(iii)screening multifunctional SACs based on the potential single-function SACs candidates.(5)Through self-assembly lattice reconstruction of GY and TM atoms,we design a new family of 2D material with very high TM coverage namely 2D-M₂C₁₂,including metals,semimetals and semiconductors.In this family,2D-Fe₂C₁₂,a rare 2D magnetic semi-metallic material,remains stable at 700 K.Via the catalytic probe reaction COR,we shows that2D-Fe₂C₁₂ has very good intrinsic catalytic activity.The prediction of this new 2D material systems has broadened the way for further research on SACs and spintronic devices.