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 CO2 electrolysis. Specifically, a composite electrode composed of Sr2Fe1.5Mo0.5O6−δ perovskite and Ru0.05Ce0.95O2 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 Sr2Fe1.5Mo0.5O6−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 O2–/e– conductivity and CO2 reduction reaction (CO2RR) activity. Impressively, a SOEC supported by an La0.8Sr0.2Ga0.8Mg0.2O3−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.