Alkyl Thiol Surface Engineering for Efficient Acidic CO ₂ Electroreduction

The electrochemical reduction of CO2 (CO2RR) to value-added chemicals and synthetic fuels represents a promising strategy for mitigating carbon emissions using renewable electricity. Notably, performing CO2RR in acidic electrolytes to produce formic acid (HCOOH) offers several advantages, including reduced flooding issues, enhanced CO2 utilization, and lower separation costs. However, the competing hydrogen evolution reaction (HER) in acidic media significantly undermines CO2RR efficiency. In this work, we demonstrate that the interfacial wettability of SnO2 catalysts can be precisely controlled via alkyl thiol modification, effectively suppressing HER. Through integrated in situ spectroscopic characterization and theoretical calculations, we reveal that dual bonding orbitals between Sn and S drive electronic reconstruction, providing the electronic basis for stabilizing Sn oxidation states. This enhances the *OCHO intermediate formation on the SnO2 surface while strengthening its adsorption. Consequently, the optimized catalyst achieves a Faradaic efficiency (FE) of 91% for formic acid in an acidic electrolyte (pH≈1), maintaining stable operation for approximately 90 h at a current density of 200 mA·cm–2. By simultaneously regulating the electronic structure and local chemical environment, this surface engineering approach offers a paradigm for developing robust and efficient electrocatalysts under acidic conditions.