Charge-Separated Pd δ- -Cu δ+ Atom Pairs Promote CO 2 Reduction to C 2 .

Positively charged Cu sites have been confirmed to significantly promote the production of multicarbon (C 2 ) products from an electrochemical CO 2 reduction reaction (CO 2 RR). However, the positively charged Cu has difficulty in existing under a strong negative bias. In this work, we design a Pd δ- -Cu 3 N catalyst containing charge-separated Pd δ- -Cu δ+ atom pair that can stabilize the Cu δ+ sites. In situ characterizations and density functional theory reveal that the first reported negatively charged Pd δ- sites exhibited a superior CO binding capacity together with the adjacent Cu δ+ sites, synergistically promoting the CO dimerization process to produce C 2 products. As a result, we achieve a 14-fold increase in the C 2 product Faradaic efficiency (FE) on Pd δ- -Cu 3 N, from 5.6% to 78.2%. This work provides a new strategy for synthesizing negative valence atom-pair catalysts and an atomic-level modulation approach of unstable Cu δ+ sites in the CO 2 RR.