Hydrophobic modification of hydroxyl-rich metallic Sn catalysts for acidic CO2 electroreduction at high current densities

Abstract

Acidic CO₂-to-HCOOH electrolysis emerges as a compelling avenue for achieving high CO₂ utilization, but is impeded by the exacerbated hydrogen evolution reaction (HER) under proton-dominated environments. Herein, we report a rationally designed electrocatalyst comprising hydroxyl-rich metallic Sn species embedded within a hydrophobic polytetrafluoroethylene (PTFE)-modified ordered mesoporous carbon (CMK) matrix (OH–Sn@CMK-P) to facilitate selective CO₂-to-HCOOH conversion. Contact angle measurements demonstrated that the PTFE modification endowed the composite with superior hydrophobicity, effectively mitigating corrosion and thereby enhancing system stability under high current densities. In situ and ex situ characterization revealed the in situ transformation of Sn(OH)₄ into OH-rich metallic Sn during electroreduction. As a result, OH–Sn@CMK-P delivered remarkable faradaic efficiency of HCOOH up to 95.1% at an industrial-relevant current density of −400 mA cm⁻² in an acidic electrolyte (pH = 3). Notably, the electrocatalyst can operate stably over 50 h at −200 mA cm⁻². Density functional theory (DFT) calculations unveiled that the surface OH species suppressed competitive adsorption of hydrogen (*H) while lowering the energy barrier for the formation of *OCHO.