Copper (Cu) is a
unique electrocatalyst, which is able to efficiently
oxidize CO at very low overpotentials and reduce CO
2
to
valuable fuels with reasonable Faradaic efficiencies. Yet, knowledge
of its electrochemical properties at the solid/liquid interface is
still scarce. Here, we present the first two-stranded correlation
of the potential of zero free charge (pzfc) of Cu(111) in alkaline
electrolyte at different pH values through application of nanosecond
laser pulses and the corresponding interfacial structure changes by
in situ
electrochemical scanning tunneling microscopy imaging.
The pzfc of Cu(111) at pH 13 is identified at −0.73 V
SHE
in the apparent double layer region, prior to the onset of hydroxide
adsorption. It shifts by (88 ± 4) mV to more positive potentials
per decreasing pH unit. At the pzfc, Cu(111) shows structural dynamics
at both pH 13 and pH 11, which can be understood as the onset of surface
restructuring. At higher potentials, full reconstruction and electric
field dependent OH adsorption occurs, which causes a remarkable decrease
in the atomic density of the first Cu layer. The expansion of the
Cu–Cu distance to 0.3 nm generates a hexagonal Moiré
pattern, on which the adsorbed OH forms a commensurate (1 × 2)
adlayer structure with a steady state coverage of 0.5 monolayers at
pH 13. Our experimental findings shed light on the true charge distribution
and its interrelation with the atomic structure of the electrochemical
interface of Cu.