Fig. 1.

DEMS measurements. (A) Electrochemical current density based on the geometric area of the electrode, (B) ${\mathrm{H}}_2$ partial pressure ($m/z=2$ for ${\mathrm{H}}_2^{+}$), and (C) ${\mathrm{C}}_2{\mathrm{H}}_4$ partial pressure ($m/z=26$ for ${\mathrm{C}}_2{\mathrm{H}}_2^{+}$) recorded during the electroreduction of CO on Cu in the presence of different cations as indicated. The sequence of potential steps in these experiments is described in the main text.