Tuning the CO-Reduction Product Distribution by Structural Modification of the Cu Electrode Surface

The electrochemical reduction of CO_2 on copper electrodes is known to generate a wide variety of products that include low-molecular-weight hydrocarbons and oxygenates. The product distribution can be regulated to yield a single liquid fuel by the control, at the atomic level, of the structure of the electrode surface. The reaction of interest was the selective CO-to-C_2H_5OH reduction at low potential in alkaline solution. The seriatim or sequential use of electrochemical scanning tunneling microscopy and differential electrochemical mass spectrometry allowed the identification of a particular surface structure responsible for a specific product selectivity. Monolayer-limited Cu ↔ Cu_2O oxidation-reduction cycles (ORC) in 0.1 M KOH transformed the reconstructed Cu(pc)-[Cu(100)] surface to an ordered stepped surface, Cu(S)-[3(100)×(111)], or Cu(511) that led to the exclusive production of ethanol. Despite the potential cycles, Cu(111) and (110) surfaces did not produce ethanol. The Cu(111) surface retained its pristine arrangement after a potential hold at -0.9 V and subsequent ORC. Under similar potentiostatic conditions, the Cu(110) surface became Cu(110)-[Cu(100)]; ORC of the reconstructed surface ultimately formed Cu(110)-[Cu(111)].