Disproportionation Reaction of Gallium during Electrodeposition from an Ionic Liquid, Monitored by In Situ Electrochemical XPS

The electrochemical reduction of gallium(III) species in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide ([Py1,4]TFSI) was studied under ultrahigh-vacuum (UHV) conditions. In situ electrochemical X-ray photoelectron spectroscopy (XPS) was employed to investigate the surface electronic and chemical states of the species during the cathodic polarization of 0.1 mol/L GaCl3/[Py1,4]TFSI on a copper working electrode in UHV. The focus was on the electrochemical reactions at the electrolyte/electrode interface, and the XPS spectra of the components were directly followed as a function of electrode potential. The core electron binding energies of the IL components experience a ∼ −1.0 eV/V shift as the applied potentials vary from 0 to −2.5 V. Detailed evidence by XPS of the formation of the low-oxidation-state gallium (Ga(I) or Ga(II)) and of their disproportionation reactions have been demonstrated for the first time. The work opens the possibility to monitor the electrochemical reactions at the electrolyte/electrode interface using in situ XPS in ultrahigh vacuum.