Copper is the only unalloyed metal that can deliver, in a “one-pot” heterogeneous electrochemical reduction of CO₂, a remarkable variety of products, up to fifteen hydrocarbons and oxygenates, in different yields. Its overall activity may be substantial, but its selectivity is far from desirable. In the production of liquid fuels, Cu generates only ethanol at nominal efficiencies that depend upon the particular electrode-surface structure. The optimization of ethanol production may be aided by the correlation, under actual reaction conditions, between the atomic structures of the Cu surfaces and their respective product selectivities. Such operando correlation is made possible by the seriatim (sequential) application of electrochemical scanning tunneling microscopy (ECSTM) and differential electrochemical mass spectrometry (DEMS). The present quasi-review paper describes how seriatim ECSTM-DEMS was utilized to show that ethanol is generated exclusively, sans other hydrocarbons and oxygenates, by a stepped Cu(S)‑[3(100)×(111)], or Cu(511), surface at appreciably low overvoltages.