Tailoring Active Components of Nanoparticles via Sequential In Situ Exsolution for High‐Performance Solid Oxide CO ₂ Electrolyzers

Anchored on oxide supports through in situ exsolution, nanoparticles (NPs) with embedded structures exhibit outstanding activity, making them central to heterogeneous catalysis. To meet the growing demand for multifunctional active NPs with precise tunability, we propose a strategy that employs oxygen partial pressure (pO 2 ) as a key control parameter for the accurate customization of exsolved NP composition. Using Sr 2 Fe 1.2 Cu 0.2 Co 0.2 Mo 0.4 O 6‐δ perovskite as a model, we demonstrate that a pO 2 gradient drives the sequential exsolution of Cu and Co, allowing precise compositional control from unitary Cu to binary CuCo alloys. This process concurrently triggers a phase reconstruction of the perovskite host into a Ruddlesden‐Popper structure, accompanied by a sixfold increase in NP population density from 27.31 to 163.64 µm −2 . The targeted formation of CuCo alloys optimizes the electronic states of active sites and strengthens interface stability. When applied as a cathode for high‐temperature CO 2 reduction, the CuCo@SFO electrode achieves a remarkable current density of 1.81 A·cm −2 at 1.5 V and 800°C. Our results provide an atomic‐level design principle that enables superior catalytic activity in high‐temperature electrolysis cells and establishes a new paradigm for nanointerface engineering in exsolution systems.