Directional Ion Migration Enables Precise Heterointerface Optimization for High-Temperature CO₂ Electrolysis

Heterointerfaces in composite electrodes play critical roles in catalytic performance, but methods for precise optimization of them are still lacking and remain challenging. Here, we propose an innovative ion-directional migration strategy to achieve precise optimization of heterointerfaces in a composite electrode of a solid oxide electrolysis cell (SOEC) for ultraefficient CO₂ electrolysis. Specifically, a composite electrode composed of Sr₂Fe_1.5Mo_0.5O_6-δ perovskite and Ru_0.05Ce_0.95O₂ fluorite with a Ru loading of only 0.89 wt % (denoted as SFM-005Ru@CeO₂) is elaborately designed. Thermal treatment induces directed migration of Ru ions from the fluorite phase to the perovskite-fluorite heterointerfaces and subsurfaces of Sr₂Fe_1.5Mo_0.5O_6-δ, enabling precise optimization of the oxygen vacancy concentration and the electronic environment of Fe cations inside the perovskite phase at the subsurface, thereby markedly enhancing O^2-/e^- conductivity and CO₂ reduction reaction (CO₂RR) activity. Impressively, a SOEC supported by an La_0.8Sr_0.2Ga_0.8Mg_0.2O_3-δ (LSGM, 140 μm) electrolyte and employing the SFM-005Ru@CeO₂ composite with a precisely optimized heterointerface as the cathode delivers an ultrahigh current density of 3.80 A cm^-2 @1.5 V at 800 °C for direct CO₂ electrolysis, superior to all previously reported electrodes. It also shows excellent stability over 200 h under harsh operating conditions (750 °C, 1.6 A cm^-2). This work opens up a new avenue to improve the performance of composite materials in various catalytic systems through precise heterointerface engineering.