Theoretical Exploration Of Atomically Dispersed Cactalysts And Two-Dimensional Materials Toward The Activation And Conversion Of Nitrogen And Oxygen

Electrochemical activation and conversion of small molecules,such as N2,O2,H2O,and CO2,into high value-added basic chemicals are of great significance in development of sustainable energy and reduction of emission of CO2.Specifically,considering the abundance of N2 and O2 in air,direct conversion of these two molecules into NH3 and H2O2 respectively holds great industrial prospects,but still faces great difficulties.Two-dimensional(2D)materials have emerged as promising candidates for these catalytic processes,because of their large basal plane area which could potentially provide more active sites.However,in spite of a series of 2D electrocatalysts have been proposed on electrocatalysis,the possible active sites,as well as reaction mechanisms have not been fully proved,and further optimization strategies have not been systematically proposed.Meanwhile,due to the great complexity of 2D materials in their composition space,exploration of new efficient 2D electrocatalysts on a large scale remains challenging.In this thesis,focusing on two important basic chemicals,ammonia and hydrogen peroxide,a set of atomically dispersed 2D catalysts and 2D materials were studied and designed for the electrochemical nitrogen reduction reaction(eNRR)and the oxygen reduction reaction(ORR)via the first-principles computations,through rational tuning the coordination environment,electronic properties of active sites and composition of catalysts.The major research results are as follows:1.Unveiled the important role of metal spin polarization in eNRRThe control of spin polarization of single Fe atom was achieved on the single vacancy defective graphene by coordination modulation strategy.It is found that the enhanced spin polarization of Fe atom can significantly strengthen the binding strength and charge transfer with adsorbed species,and the Fe-N3 moiety with high spin polarization possesses excellent catalytic activity for the eNRR.2.Modulation of coordination microenvironment of single atom catalysts to improve the activity and selectivity of for the eNRRThe catalytic performance of seven kinds of Fe-Nx single atom catalysts(SACs)supported on the double vacancy defective graphene were systematically investigated.It is found that the coordination environment had a significant effect on the catalytic activity and selectivity of metal active sites,and the Fe-N2 moiety with counterpointed nitrogen atoms were demonstrated to have superior catalytic performance for the eNRR.Moreover,by constructing the activity volcano plot,the possible optimization strategy for improving the catalytic activity of carbon-based SACs was proposed.3.High-throughput design of stable and efficient biatom catalysts for the eNRRA branch of 2D phthalocyanine supported biatom site catalysts,namely biatom catalysts(BACs),were demonstrated that can achieve efficient eNRR with robust ability to suppress the competitive hydrogen evolution reaction through the high-throughput first-principles calculations.A universal design strategy to evaluate the stability,activity and selectivity of BACs was developed,and the activity map of complex heteronuclear BACs was constructed using activity descriptor.Three homonuclear and 28 heteronuclear BACs were finally identified that can break the metal-based activity benchmark toward the efficient eNRR.4.Discovery of boron-analogues of MXenes for the NRRA class of boron-analogues of MXenes,namely MBenes,were demonstrated that can cope with the challenge and achieve the high activity and large reaction region simultaneously toward eNRR.The different characteristics between the MBenes and the MXenes in structure and catalytic performance were revealed,and the design principle of "phase diagram analysis plus activity study" was proposed for theoretical exploration of 2D electrocatalyst.A ternary phase CrFeB2 was found to have a record activity and selectivity for the eNRR with a theoretical limit potential of-0.22 V.5.Exploration of stable SACs with improved activity and selectivity for the H2O2 productionDemonstrated that SACs can tackle the trade-off between activity and selectivity of traditional metal catalysts in the production of H2O2 and simultaneously achieve high activity and selectivity toward H2O2 production.On the basis of 210 kinds of SACs,a universal screening strategy was developed to evaluate the stability,activity and selectivity of SACs.Additionally,the internal factors affecting the catalytic performance of SACs were revealed by combining the multivariable linear regression with machine learning method,and the structure-activity relationship between catalysts and catalytic performance was established.