Revealing the role of aniline in assisting SnO2 electrocatalytic CO2 reduction to HCOOH: via the perspective of the reaction pathway

Abstract

Sn-based electrocatalysts are exceptionally competitive for electrochemical reduction of CO₂ (CO₂ER) applications. The rate-controlling step of Sn-based catalysts, extensively investigated through experiment and theoretical studies, primarily involves the electron transfer process from CO₂ to form surface-adsorbed *CO₂˙⁻. In light of this, the introduction of amines to enhance guest–host interaction for CO₂ adsorption and simultaneously reduce the reaction energy barrier is an innovative tactic that will make a decisive contribution to improving the CO₂ER performance. Herein, an aniline modified tin oxide composite catalyst (SnO₂/PDA_0.5-OCNTs) was constructed and applied to electrocatalytic CO₂ reduction to produce HCOOH. A thin amorphous organic aniline layer was formed on the exterior of oxidized carbon nanotubes (OCNTs), which anchors tin oxide nanoparticles (SnO₂ NPs) and improves the stability of the composite electrocatalysts. Depending on the robust chemical interactions between aniline and CO₂, the captured CO₂ is converted into an intriguing carbamate intermediate (NHCOO*), which reduces the reaction energy barrier through a new reaction pathway and accelerates the reaction kinetics of the rate-determining step for CO₂ER to generate HCOOH. Benefiting from these merits, SnO₂/PDA_0.5-OCNTs delivered an excellent HCOOH faradaic efficiency (FE_HCOOH) of 96% at −1.43 V (vs. RHE) with a satisfactory HCOOH partial current density (j_HCOOH) of 166 mA cm⁻² at −1.83 V in a flow cell.