Electric Field Generated at the Millisecond Pulse-Polarized Interface Facilitates the Electrolytic Conversion of SO₂ into H₂S

Interfacial electric field holds significant importance in determining both the polar molecular configuration and surface coverage during electrocatalysis. This study introduces a methodology leveraging the varying electric dipole moment of SO 2 under distinct interfacial electric field strengths to enhance the selectivity of the SO 2 electroreduction process. This approach presented the first attempt to utilize pulsed voltage application to the Au/PTFE membrane electrode for the control of the molecular configuration and coverage of SO 2 on the electrode surface. Remarkably, the modulation of pulse duration resulted in a substantial inhibition of the hydrogen evolution reaction (HER) (FE H2 < 3%) under millisecond pulse conditions ( t a = 10 ms, t c = 300 ms, E a = −0.8 V (vs Hg/Hg 2 SO 4 ), E c = −1.8 V (vs Hg/Hg 2 SO 4 )), concomitant with a noteworthy enhancement in H 2 S selectivity (FE H2S > 97%). A comprehensive analysis, incorporating in situ Raman spectroscopy, electrochemical quartz crystal microbalance, COMSOL simulations, and DFT calculations, corroborated the increased selectivity of H 2 S products was primarily associated with the inherently large dipole moment of the SO 2 molecule. The enhancement of the interfacial electric field induced by millisecond pulses was instrumental in amplifying SO 2 coverage, activating SO 2, facilitating the formation of the pivotal intermediate product *SOH, and effectively reducing the reaction energy barrier in the SO 2 reduction process. These findings provide novel insights into the influences of ion and molecular transport dynamics, as well as the temporal intricacies of competitive pathways during the SO 2 electroreduction process. Moreover, it underscores the intrinsic correlation between the electric dipole moment and surface-molecule interaction of the catalyst.