Descriptor-guided Design Of N-doped-graphene Based Single-and Bimetallic-atomic Catalysts For Electrochemical CO₂ Reduction

The massive consumption of fossil fuels can bring about problems such as energy exhaustion and greenhouse effect.Electrochemical CO₂reduction reaction（CO₂RR）can convert CO₂into CH₃OH,CH₄,CO,HCOOH and other useful chemicals,and reduce excess CO₂emissions.However,due to the very stable chemical properties of CO₂,CO₂RR requires high overpotentials and is accompanied by the competing hydrogen evolution reaction（HER）,resulting in low catalytic activity and selectivity of CO₂RR.Thus,the high-performance catalysts are urgently needed.In recent years,single-atom catalysts（SACs）and bimetallic atomic catalysts（BACs）have been extensively studied in CO₂RR because they combine the advantages of homogeneous and heterogeneous catalysis and have 100%utilization of the atoms in active center.However,there is only one metal atom in the active center in SACs,and the single adsorption site limits the regulation of their catalytic properties.The interaction between the metal atoms in BACs can effectively modulate the electronic structure of the active center.Meanwhile,the diversity of the combinations of metal atoms and their coordination environments provides more space for the regulation of catalytic performance,but also makes the design of high-performance BACs a great challenge.Therefore,it is important to use descriptors based on intrinsic properties of the catalysts to achieve fast screening of high performance BACs.At present,the types and quantities of synthesized BACs are still limited,so the effective modulation strategies are needed to expand the scale of high-performance BACs.In this paper,we first studied the effect of local coordination environment of active center on the catalytic properties of transition metals（TMs）and SACs by the descriptorψ.On this basis,we designed high-performance BACs for CO₂RR through effective regulation of the coordination environment.We further modulate the properties of BACs by introducing dangling bonds and applying charges,and study the effects of dangling bonds and charging on the catalytic properties of BACs by using the descriptorψ.The content of this thesis mainly includes the following three parts:1.The key to designing advanced catalysts is to study the correlations between the intrinsic atomic and electronic structures of catalysts and their catalytic properties.We propose a general descriptorψbased on the electronegativity and the valence electron number of the active center to describe the reactivity and selectivity of CH₄,CO,HCOOH,and H₂formation in CO₂RR on TMs and SACs.The descriptorψsuccessfully reveal the effect of coordination environment on the adsorption and catalytic properties of TMs and SACs.Compared with the previous descriptors,our intrinsic descriptorψbridges the gap between catalytic properties of the active center and its intrinsic properties.Because the parameters in the descriptor are easily accessible,we can easily understand the activity and selectivity of the catalysts and quickly screen advanced catalysts.2.To establish an effective strategy for the design of high-performance BACs,we extend the descriptorψto MX-N₆-Gra,where M and X represent the doped metal atoms,and study the adsorption properties of key intermediates of CO₂RR,such as*CO,*COOH and*HCOO.We investigate the local environmental effect of the active center and reveal the different roles of M,X and N atoms in adsorption and reaction.M atom determines the range of adsorption energy of BACs,X atom determines the difference of adsorption energy between different BACs,and N atom improves the regulation efficiency of BACs adsorption energy of metal atoms.Based on these results,we successfully screen out the potential high-performance BACs of CO₂reduction to CO.Therefore,our design strategy can provide guidance for the experimental synthesis of high-performance BACs.Besides,we can design high-performance atomic catalysts for other reactions by using the descriptorψand study their catalytic properties.3.Although some high-performance BACs have been synthesized experimentally,the quantity and types are still limited,so we need effective strategies to expand their scale.On the basis of previous research,we introduce the dangling bonds in the coordinatively saturated BACs and apply charges to regulate their catalytic properties.We used the descriptorψto investigate the effect of dangling bonds and charging on the catalytic properties of BACs.Our study shows that the linear relationships between the adsorption energy of C-species are broken under the effect of the dangling bonds,while the linear relationships are restored after charging.However,charging has little effect on the adsorption properties of O-species.This is due to the different effects of the dangling bonds and charging on the adsorption configuration of C-and O-species.On this basis,we successfully screen out high-performance BACs for CH₃OH formation.Therefore,we propose effective strategies for regulating atomic catalysts and provide guidance for expanding the scale of advanced catalysts.