Bi@Sn Core–Shell Structure with Compressive Strain Boosts the Electroreduction of CO2 into Formic Acid

Abstract As a profitable product from CO 2 electroreduction, HCOOH holds economic viability only when the selectivity is higher than 90% with current density ( j ) over −200.0 mA cm −2 . Herein, Bi@Sn core–shell nanoparticles (Bi core and Sn shell, denoted as Bi@Sn NPs) are developed to boost the activity and selectivity of CO 2 electroreduction into HCOOH. In an H‐cell system with 0.5 m KHCO 3 as electrolyte, Bi@Sn NPs exhibit a Faradaic efficiency for HCOOH (FE HCOOH ) of 91% with partial j for HCOOH ( j HCOOH ) of −31.0 mA cm −2 at −1.1 V versus reversible hydrogen electrode. The potential application of Bi@Sn NPs is testified via chronopotentiometric measurements in the flow‐cell system with 2.0 m KHCO 3 electrolyte. Under this circumstance, Bi@Sn NPs achieve an FE HCOOH of 92% with an energy efficiency of 56% at steady‐state j of −250.0 mA cm −2 . Theoretical studies indicate that the energy barrier of the potential‐limiting step for the formation of HCOOH is decreased owing to the compressive strain in the Sn shell, resulting in the enhanced catalytic performance.