Theoretical Investigation Of Structure-performance Relationship On Copper Based Catalyst For CO₂ Electroreduction

The massive burning of fossil fuels leads to excessive CO₂ emissions,breaking the carbon cycle in nature and causing a series of problems such as global warming.Electrochemical CO₂ reduction into fuels and feedstocks using renewable energy is a promising way to reduce carbon emissions and store energy.Cu is the only metal that can efficiently reduce CO₂ to high value-added multi-carbon products such as ethylene and ethanol.However,the wide distribution of the products leads to low selectivity of the target carbon-containing products.Therefore,understanding the structure-performance relationship of Cu-based catalysts in CO₂ reduction,and then designing and developing highly active and selective catalysts are the focus of current research.In this thesis,multi-scale simulation methods are used to understand the structure-performance relationship of the catalyst,from identifing the active site of oxide-derived Cu（OD-Cu）,to exploring the mechanism of Cu grain boundaris.Finally,the structural design criteria to improve the activity and selectivity of the Cu-based catalyst is proposed.In the first section of this thesis,the active sites of ethylene and alcohols on OD-Cu catalysts are identified by multi-scale simulations.Firstly,the dynamic reduction process of Cu₂O is simulated by neural network potential based molecular dynamics simulation and the authentic OD-Cu surface models are obtained.Then,three types of C-C coupling active sites are identified by using neural network potential based high-throughput screening and density functional theory calculations.It is found that planar-square site and convex-square site are favorable for ethylene production,while step-square site is the active site for alcohol production.Meanwhile,The C-O bond length in*CH₂CHO can be used as a descriptor of selectivity for ethylene and alcohols.Finally,the accuracy of the active sites screened out are verified by conducting high temperature annealing process theoretically and experimentally.Cu grain boundaries are believed to be the active site for electrochemical CO₂ reduction,but the mechanisms behind are still unclear.In the second section of this thesis,the typical Cu∑3/（111）grain boundary and Cu∑5/（100）grain boundary models are established.Based on the density functional theory calculations,it is found that the lower coordination environment and the longer Cu-Cu bond length can well stabilize the bientate adsorbed intermediates such as*COOH and*CHO,which are beneficial to the initial activation of CO₂ and the deep reduction of*CO.Thermodynamic and kinetic analyses show that*CO-*CHO coupling is the main coupling form at grain boundary sites at relatively high overpotential,and the C-C coupling energy barriers are reduced compared with that at planar sites.When grain boundary is introduced on Cu（100）,the product is converted from ethylene to ethanol due to the stabilization effect for*CH₃CHO intermediate and destabilizing*O adsorption.Finally,based on the above findings,a structural design criterion to improve the ethanol selectivity of Cu-based catalysts is proposed,namely,square sites coupled with low coordination sites,where square sites are responsible for C-C coupling and low-coordinated sites tune the reaction pathway to alcohols by enhancing*CH₃CHO adsorption.