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 (FECO) of 81% at -0.45 V. In contrast, Cu-F-1, enriched in grain boundaries and Cu(100) facets, achieves a high FEC2+ 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.