Pulse Symmetry Impacts the C2 Product Selectivity in Pulsed Electrochemical CO2 Reduction

Pulsed electrochemical CO2 reduction has emerged as an attractive approach to direct product selectivity and activity. The versatility of the pulse profile creates opportunities to study fundamental processes and optimize reaction conditions. We examined the effects of applied pulse potential, duration, and shape to understand the interfacial reaction environment with an eye toward optimized C-2 product formation. We present an electrochemical analysis to show that upper pulse potentials with positive anodic current (indicative of anion coadsorption) improve reaction stability and enhance C-2 selectivity (reaching 76% FE). Interestingly, whereas changing pulse duration had little to no effect on C-2 selectivity, we found that pulse symmetry significantly affected selectivity. Notably, symmetric pulses most selectively produce C-2 products. We discuss the relationship between pulse symmetry and selectivity in the context of COads coverage and C-C coupling reaction energy landscape as a result of anion coadsorption, increased interfacial charge, and electric field variation effects.