Size-Dependency of Electrochemically Grown Copper Nanoclusters Derived from Single Copper Atoms for the CO Reduction Reaction

Electrochemically grown copper nanoclusters (CuNCs: <3 nm) from single-atom catalysts have recently attracted intensive attention as electrocatalysts for CO₂ and CO reduction reaction (CO₂RR/CORR) because they exhibit distinct product selectivity compared with conventional Cu nanoparticles (typically larger than 10nm). Herein, we conducted a detailed investigation into the size dependence of CuNCs on selectivity for multicarbon (C₂₊) production in CORR. These nanoclusters were electrochemically grown from single Cu atoms dispersed on covalent triazine frameworks (Cu-CTFs). Operando X-ray absorption fine structure analysis revealed that Cu-CTFs containing 1.21 wt % and 0.41 wt % Cu (Cu(h)-CTFs and Cu(l)-CTFs, respectively) formed CuNCs of 2.0 and 1.1 nm, respectively, at −1.0 V vs. RHE. The selectivity for CORR products was particularly dependent on the size of CuNCs, with the Faraday efficiencies of C₂₊ products being 52.3 % and 32.7 % at −1.0 V vs. RHE with Cu(h)-CTFs and Cu(l)-CTFs, respectively. Spherical CuNCs modeling revealed that larger cluster sizes led to a greater proportion of a surface coordination number (SCN) of 8 or 9. Density functional calculations revealed that the CO dimerization reaction was more likely to proceed at SCNs of 8 or 9 compared to SCN of 7 because of the stability of the *OCCO intermediate.