Obtaining valuable C3+ products directly from the electrocatalytic reduction of CO2 or CO is an attractive but challenging task, due to the much more complicated reaction pathways and sluggish kinetics of C3+ products than their C1 and C2 counterparts. As different C3+ products and competitive C2 side-products may share the common rate-determining step (e.g. the carbon-carbon coupling), the regulation of subsequent selectivity-determining step(s) is critical for promoting the selectivity of C3+ products. Herein, we focused on tuning the selectivity competition between n-propanol (n-C3H7OH, an important C3+ alcohol) versus ethanol (C2H5OH, a major C2 side product), based on the constant potential computations on Cu surface with different step sites. The critical selectivity-determining steps for the n-C3H7OH and C2H5OH pathways have been identified, and the impact of Cu step sites on the competitive relation between n-C3H7OH and C2H5OH have been explored. Moreover, a descriptor related closely to the n-propanol selectivity has been developed, showing that controlling the competitive hydrogenation of C2 intermediates and C1–C2 coupling processes is vital to differentiate the selectivity of n-propanol from ethanol. This work can inspire the screening and rational design of unconventional electrocatalytic sites for generating more value-added C3+ products from the electrocatalytic CO2 reduction.
