Promoting electrocatalytic CO₂ reduction to n-propanol over ethanol at Cu step sites

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 the 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 has 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.