Fig. 4: Materials characterization of the ternary catalysts.

a SEM image and EDS spectra for Au₆Ag₂Cu₂ and b for Au₄Zn₃Cu₃. All scale bars in (a and b) are 2.5 µm. c Cu 2p, Ag 3d, and Au 4f XPS spectra for Au₆Ag₂Cu₂. d Cu 2p, Zn 2p, and Au 4f XPS spectra for Au₄Zn₃Cu₃.