The two-step electroreduction of CO2 to CO followed by CO to multi-carbon products is a promising alternative to the direct CO2 electroreduction for both efficiency and stability. The catalyst features which control selectivity in CO electroreduction (CORR) remain unclear, which limits further advancement in the overall performance. Herein, we map the CORR sensitivity to the catalyst features exploiting well-defined copper nanocrystals (NCs) with tunable shape and size. After clarifying the dependence of ethylene, methane and acetate on the exposed surfaces, we reveal that copper nanospheres uniquely promote n-propanol selectivity. We point at the importance of strain as one of the key factors underlying the observed propanol selectivity. Inspired by these insights, we achieve n-propanol production via electrosynthesis with a copper-only catalyst.