Fig. 1. Characterization of the wettability-tunable modified Cu electrode.

a XRD patterns of Cu and Cu-12C show that both Cu catalysts with or without modification tend to expose Cu(111) facet. b HRTEM image of Cu-12C, revealing a 2–3 nm continuous and conformal alkanethiol layer. c Illustration shows Cu catalysts via hydrophobic treatment by alkanethiol. d Cu 2p XPS spectra. e S 2p XPS spectra of Cu and Cu-12C, demonstrating the formation of Cu–S bonds. f The average water droplet contact angle of alkanethiol-treated Cu increases with the increase of the alkyl chain length. The insets show photographs of water droplets. A modified layer with continuously tunable wettability, as well as a homogeneous structure, was obtained. The a.u. stands for arbitrary units. Error bars represent the standard deviation from at least three independent measurements.