Covalent surface coordination enables efficient and stable formaldehyde-water co-electrolysis over non-stoichiometric cuprous oxide.
The activity-stability trade-off of copper-based oxide catalysts in formaldehyde oxidation remains a fundamental challenge. Here, we resolve this trade-off by grafting N-heterocyclic carbenes (NHCs) onto non-stoichiometric Cu2+1O nanocubes (denoted as Cu2+1O, a Cu+-rich single-phase oxide) through covalent CuC bonds. This molecular surface coordination strategy delivers two concurrent benefits. First, strong σ-electron donation from NHCs shifts the Cu d-band center from -2.106 eV to -2.416 eV, weakening intermediate adsorption and lowering the reaction free-energy change of the rate-determining step (CHOOH⁎ desorption) from 2.56 eV to 1.38 eV. Second, the covalent CuC anchors suppress copper leaching in alkaline electrolyte by a factor of 160 (from 8 mg L-1 to 0.05 mg L-1 over 100 h). The resulting Cu2+1O-NHC catalyst drives formaldehyde oxidation at an onset potential of 0.1 V vs. RHE (Tafel slope: 590 ± 2 mV dec-1, versus 96 ± 3 mV dec-1 for unmodified Cu2+1O; mean ± SD, n = 3), achieving near-unity Faradaic efficiency for both formate (98.65 ± 0.32%) and anodic H2 evolution from CH bond cleavage (99.14 ± 0.28%). Isotope-labeled DEMS confirms that anodic H₂ originates predominantly from the CH bond of formaldehyde, as no HD or D2 was detected when the reaction was performed in D2O. After 100 h of continuous operation, the cubic morphology remains largely intact. This work establishes covalent surface coordination as a promising molecular strategy to decouple activity and stability in oxide electrocatalysts, potentially extendable beyond the specific case of Cu2+1O for aldehyde oxidation.