Revisits the Selectivity toward C₂₊ Products for CO₂ Electroreduction over Subnano-Copper Clusters Based on Structural Descriptors

Subnanometal catalysts usually possess significant catalytic performance due to their unique ″finite size effect″. The nanoengineering of copper (Cu) catalysts is a crucial approach for CO2 electroreduction (CO2ER) toward multicarbon (C2+) products. However, whether subnano-Cu clusters (0.5–2 nm) are a forbidden or promising zone for C2+ products through CO2ER remains controversial. To shed light on the feasibility and potential of Cu subnanoclusters as catalysts for CO2ER toward C2+ products, we employ global optimization by Revised Particle Swarm Optimization algorithm, density functional theory calculations, and microkinetic modeling on a range of Cu subnanoclusters with varying sizes to investigate CO2ER reactivity. We propose a geometric–electronic composite structural descriptor that characterizes the reaction energies and construct a theoretical reaction rate contour map based on the structural descriptor. The contour map reveals that Cu sites, reaching an optimal balance between the C–C coupling energy barrier and coverage of the coupling precursor, tend to exhibit high C2H4 yield. Furthermore, a volcano-like trend is presented between the theoretical turnover frequency of C2H4 products and the size of subnanoclusters, which is experimentally validated. Notably, medium-sized Cu subnanoclusters (around 1 nm) possessing the highest proportion of edge sites with the optimal value of structural descriptor own superior C2H4 yield to the large particles or monocrystal Cu catalysts in experiments. This work represents the first theoretical confirmation regarding the feasibility of subnano-Cu clusters in CO2RR for C2+ production and provides insights into its underlying mechanisms. These findings expand the field in size-dependent reactivity of Cu catalysts toward C2+ products through CO2ER and provide guidance for designing efficient Cu electrocatalysts at the subnanoscale.