“Ship-in-a-Bottle” Integration of Ditin(IV) Sites into a Metal–Organic Framework for Boosting Electroreduction of CO₂ in Acidic Electrolyte

The electrochemical CO₂ reduction reaction (eCO₂RR) under acidic conditions has become a promising way to achieve high CO₂ utilization because of the inhibition of undesirable carbonate formation that typically occurs under neutral and alkaline conditions. Herein, unprecedented and highly active ditin(IV) sites were integrated into the nanopores of a metal-organic framework, namely NU-1000-Sn, by a "ship-in-a-bottle" strategy. NU-1000-Sn delivers nearly 100% formic acid Faradaic efficiency at an industry current density of 260 mA cm⁻² with a high single-pass CO₂ utilization of 95% in an acidic solution (pH = 1.67). No obvious degradation was observed over 15 hours of continuous operation at the current density of 260 mA cm⁻², representing the remarkable eCO₂RR performance in acidic electrolyte to date. The mechanism study shows that both oxygen atoms of the key intermediate *HCOO can coordinate to the two adjacent Sn atoms in a ditin(IV) site simultaneously. Such bridging coordination is conducive to the hydrogenation of CO₂, thus leading to high performance.