Directional Ion Migration Enables Precise Heterointerface Optimization for High-Temperature CO 2 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 CO 2 electrolysis. Specifically, a composite electrode composed of Sr 2 Fe 1.5 Mo 0.5 O 6−δ perovskite and Ru 0.05 Ce 0.95 O 2 fluorite with a Ru loading of only 0.89 wt % (denoted as SFM-005Ru@CeO 2 ) is elaborately designed. Thermal treatment induces directed migration of Ru ions from the fluorite phase to the perovskite–fluorite heterointerfaces and subsurfaces of Sr 2 Fe 1.5 Mo 0.5 O 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 CO 2 reduction reaction (CO 2 RR) activity. Impressively, a SOEC supported by an La 0.8 Sr 0.2 Ga 0.8 Mg 0.2 O 3−δ (LSGM, 140 μm) electrolyte and employing the SFM-005Ru@CeO 2 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 CO 2 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.