About the Role of Interfacial Lattice Oxygen in Pd─Pt Alloy for C─C Cleavage in Ethanol Electrooxidation

The electrocatalytic ethanol oxidation reaction is bottlenecked by inefficient C─C bond cleavage. This challenge is epitomized at metal‐oxide heterointerfaces, where the active site identity and cleavage mechanism remain obscured. Here, we decoded this by atomically programming model PdO─Pt 3 Pd heterointerfaces. Through 18 O isotopic labeling, we identify the interfacial lattice oxygen (O Int ) in Pd 2+ ─O Int ─Pd alloy motif as the direct oxygen donor for C─C cleavage. The interfacial built‐in electric field activates O Int as a nucleophilic scalpel by upshifting its p‐band center, resulting in an ultralow cleavage barrier of 0.47 eV. Beyond a single site, we demonstrate that the interface functions as a reaction‐network architect. It creates a dominant O Int ‐mediated “non‐CO” C1 pathway at the PdO─Pt 3 Pd heterointerface while re‐engineering the traditional “CO” pathway on the adjacent Pt 3 Pd domain via threefold optimization: minimizing *CO source, suppressing acetate formation and ensuring rapid *CO removal. This dual‐path integration yields breakthrough performance with a mass activity of 9.09 A mg metal −1 and a C1‐pathway Faradaic efficiency of 75.6%. This work reports a paradigm shift from a passive “scavenger” model to an active “initial‐attack and system‐orchestration” mechanism, redefining heterointerfaces as atomically programmable reaction‐network architects. This paradigm offers a blueprint for mastering complex reaction networks, extending the frontier of rational catalyst design.