Spatial Ion Redistribution Enables Stable Ethylene Synthesis in Acidic CO 2 Electrolysis

Electrocatalytic CO₂ reduction (eCO₂R) under acidic conditions mitigates carbon crossover and energy losses, yet selective multicarbon synthesis remains challenging due to competing hydrogen evolution. Conventional efforts manipulate the electrochemical double layer to enrich alkali cations but reach steric limits at industrially relevant current densities, compromising selectivity and stability. Here, we introduce an ion-gated porous overlayer (IGPO) that extends beyond nanometric constraints, creating a volumetric ion-management zone decoupling catalytic surfaces from bulk electrolyte dynamics. Our hierarchical architecture comprises porous carbon nanocages (PCNs) and polymeric triazine nanocage layers on the Cu catalyst. Theoretical modeling reveals this design displaces K⁺ concentration peaks from the catalyst to outer PCN surfaces while attenuating H₃O⁺ across the porous network. Protonated triazine groups enforce the Donnan exclusion of H₃O⁺ and retard OH^- egress, sustaining locally alkaline microenvironments. Incorporating single-atom nickel sites enables in situ CO generation, enhancing multicarbon formation through tandem catalysis. The optimized electrode achieves 61.1% Faradaic efficiency for ethylene and 86.2% for total C₂₊ products at 400 mA cm^-2 under acidic conditions, with stable operation exceeding 220 h. This ion-gated strategy provides a generalizable framework for overcoming selectivity-stability trade-offs, advancing carbon-neutral chemical manufacturing.