Alkyl Thiol Surface Engineering for Efficient Acidic CO 2 Electroreduction

The electrochemical reduction of CO 2 (CO 2 RR) to value-added chemicals and synthetic fuels represents a promising strategy for mitigating carbon emissions using renewable electricity. Notably, performing CO 2 RR in acidic electrolytes to produce formic acid (HCOOH) offers several advantages, including reduced flooding issues, enhanced CO 2 utilization, and lower separation costs. However, the competing hydrogen evolution reaction (HER) in acidic media significantly undermines CO 2 RR efficiency. In this work, we demonstrate that the interfacial wettability of SnO 2 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 SnO 2 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.