Surface Adsorbed Hydroxyl: A Double-Edged Sword in Electrochemical CO Reduction over Oxide-Derived Copper.

Oxide-derived Cu (OD-Cu) featured with surface located sub-20 nm nanoparticles (NPs) created via surface structure reconstruction was developed for electrochemical CO reduction (ECO RR). With surface adsorbed hydroxyls (OH ) identified during ECO RR, it is realized that OH , sterically confined and adsorbed at OD-Cu by surface located sub-20 nm NPs, should be determinative to the multi-carbon (C ) product selectivity. In situ spectral investigations and theoretical calculations reveal that OH favors the adsorption of low-frequency *CO with weak C≡O bonds and strengthens the *CO binding at OD-Cu surface, promoting *CO dimerization and then selective C production. However, excessive OH would inhibit selective C production by occupying active sites and facilitating competitive H evolution. In a flow cell, stable C production with high selectivity of ∼60 % at -200 mA cm could be achieved over OD-Cu, with adsorption of OH well steered in the fast flowing electrolyte.