Tailored Selectivity for CO and C₂₊ in CO₂ Reduction: Insights into the Dynamic Evolution of Electrocatalysts

Controlling product selectivity in electrochemical CO₂ reduction (eCO₂R) is critical for efficient CO₂ conversion. However, the dynamic structural changes of Cu-based catalysts during operation complicate mechanistic understanding. Here, we investigate fluorine-modified copper pre-catalysts with varying doping levels and reveal how their structural evolution governs eCO₂R activity and selectivity. Through operando spectroscopy characterizations and theoretical simulations, we show that fluorine leaches rapidly during electrolysis, transforming Cu²⁺ precursors into metallic Cu⁰ with distinct local structures. Cu-F-4, with the lowest coordination number, exhibits high eCO₂R activity and favors CO formation with a Faradaic efficiency (FE_CO) of 81% at -0.45 V. In contrast, Cu-F-1, enriched in grain boundaries and Cu(100) facets, achieves a high FE_C2+ of 80% at -0.65 V. Differences in local pH, *OH coverage, and *CO binding energies further modulate catalytic pathways. Our findings highlight the importance of dynamic catalyst reconstruction in steering product selectivity and offer design principles for advancing CO₂-to-chemicals conversion.