Confining Sn Nanocatalysts via Ship-in-a-Bottle Strategy: Local Alkaline Microenvironment Engineering for High-Selective and Durable Acidic CO2RR to Formic Acid

Acidic CO2 electroreduction (CO2RR) prevents carbonate formation but suffers from severe competition with the hydrogen evolution reaction. Herein, a nanoreactor-structured Sn@MCHS catalyst is fabricated via a ship-in-a-bottle method, synergizing the catalytic activity of metallic Sn with the microenvironment-modulating capability of hollow mesoporous carbon spheres (MCHS). This mesoporous shell acts as a physical barrier, restricting proton replenishment and retaining the in situ generated OH–, thereby forming a local alkaline microenvironment. The nanoreactor enriches K+ and stabilizes *OCHO. In the acidic CO2 reduction system, the FE of the catalyst in an H-type cell reached 90.3%, and in a flow cell it reached 95.1%. It also demonstrated excellent stability for continuous operation for up to 96 h. This study established nanoscale confinement as a powerful strategy for constructing an electrocatalytic microenvironment, opening up a new path for designing highly selective and durable electrocatalysts.