High‐Entropy Rare Earth Oxides Anchoring Tunable Cuδ+ Nanochimneys for Self‐Tandem C‐C Coupling Catalysis

Abstract Copper (Cu)‐based materials are promising for carbon‐carbon bond (C─C) coupling catalysis, but they are limited to poor structural stability, high activation energy, and low selectivity toward C 2+ products. Here a customized synthetic protocol is defined for the fabrication of 2D ultrathin high‐entropy rare earth (RE) oxides (HE‐REOs) with rich lattice distortions and oxygen vacancies, which act as robust supports for anchoring Cu δ+ serial domains with tunable oxidation states. The rationally integrated HE‐REOs‐Cu δ+ heterostructures feature largely exposed synergistic multi‐site driving rapid *CO spillover, and multiple stabilized Cu δ+ chimneys promoting cascade *CO coupling, together with intrinsic electron activation channels enabling RE 4f electron delocalization to lower the energy barrier. The optimal CeZrZnAgPbO‐Cu 0.44+ self‐tandem catalysts achieve a high Faradaic efficiency (FE) of 51.7% for C 2+ gaseous products at a low potential of ‐0.9 V versus (vs) reversible hydrogen electrode (RHE) in H‐type cell. The study proposes an “all‐in‐one” design principle for advanced RE‐based catalysts through integrating advantageous individuals in a predictable manner.