Promoted CO₂ Electrolysis to Formic Acid Using Single Atom Cobalt Alloyed Tin

Electrochemical CO₂ reduction with renewable electricity offers a promising path for accessing carbon-neutral liquid chemicals. Although post-transition metals, especially tin (Sn), are intrinsically selective for formate, most catalysts still require high overpotentials to reach industrially relevant current densities and lose activity under sustained operation. Here, we report a single-atom alloy catalyst, comprising isolated cobalt (Co) atoms in a Sn matrix (Co₁Sn), that drives CO₂-to-formate with near-unity selectivity at high rates. Co₁Sn achieves an FE_formate of up to 99% at current densities exceeding -1 A cm^-2. At current densities ranging from -100 to -1000 mA cm^-2, Co₁Sn maintained >92% formate selectivity. When integrated in a porous solid electrolyte reactor, a continuous production of pure formic acid was enabled for 130 h at a current density of -50 mA cm^-2 with an FE_HCOOH of ∼95%. In situ spectroscopy and theoretical simulation demonstrated that the incorporation of single Co atoms finely tuned the electronic structure of the Sn matrix, enhanced CO₂ activation, and lowered barriers along the O-bound *OCHO pathway, thereby facilitating formate generation. This work resolves the rate-selectivity-durability trade-off in formic acid electrosynthesis by leveraging a single-atom alloying strategy.