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

Abstract

As a profitable product from CO₂ electroreduction, HCOOH holds economic viability only when the selectivity is higher than 90% with current density (<i>j</i>) 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 CO₂ electroreduction into HCOOH. In an H-cell system with 0.5 m KHCO₃ as electrolyte, Bi@Sn NPs exhibit a Faradaic efficiency for HCOOH (FE_HCOOH) of 91% with partial <i>j</i> for HCOOH (<i>j</i> _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 KHCO₃ electrolyte. Under this circumstance, Bi@Sn NPs achieve an FE_HCOOH of 92% with an energy efficiency of 56% at steady-state <i>j</i> 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.