Carbon Nanogrid-Directed Interfacial Electric Field Engineering Boosts Selective CO₂-to-Formate Electrosynthesis

Efficient and durable electrochemical conversion of CO₂ to formate at industrially relevant current densities remains challenging, as Sn-based catalysts often suffer from poor conductivity, structural degradation, and overly strong binding to key reaction intermediates. Here, we introduce a nanogrid-directed interfacial electric field engineering strategy that addresses these limitations by spatially confining Sn nanoparticles within a conductive carbon nanotube nanogrid framework (Sn@CNT). The hierarchical architecture induces intense and well-distributed interfacial electric fields, which accelerate charge transport, optimize the adsorption-desorption kinetics of *HCOOH intermediates, and promote interfacial H₂O dissociation while maintaining a favorable local ion environment. As a result, the Sn@CNT catalyst delivers a Faradaic efficiency (FE) of 95.6% for formate at 300 mA cm^-2, and maintains over 90% FE for 200 h in a flow cell in alkaline conditions. In the solid-electrolyte cell, the formate combines with protons to yield formic acid, enabling stable production of 1.1 m formic acid at 400 mA for more than 300 h without observable performance decay. Operando spectroscopy and theoretical simulations reveal that the CNT nanogrid establishes a confined interfacial field that redistributes local charges, facilitates H₂O activation, and lowers the desorption barrier of *HCOOH intermediates. This cooperative field modulation also establishes a mild microenvironment that enhances CO₂ reduction kinetics while suppressing the competing hydrogen evolution reaction. This work demonstrates nanogrid-directed interfacial field engineering as a broadly applicable approach for tailoring electrochemical interfaces, offering design principles for efficient and stable CO₂-to-formate electrosynthesis.