Polycrystalline gold electrode redox behavior in an ammoniacal electrolyte: Part I. A parallel RRDE, EQCM, XPS and TOF-SIMS study of supporting electrolyte phenomena

The redox behavior of a gold electrode in an ammoniacal electrolyte (0.1 M NH₃ and 0.1 M NaClO₄) was investigated using four techniques. These were the rotating ring disk electrode (RRDE), the electrochemical quartz crystal microbalance (EQCM), X-ray photoelectron spectroscopy (XPS) and time of flight secondary ion mass spectrometry (TOF-SIMS). Two different gold surface compounds, AuO and AuNH₂, are formed in relative amounts that depend on the holding time at + 0.6 V (versus SCE). XPS and SIMS studies were used to distinguish the surface species AuO and AuNH₂ from AuO and AuOHNH₂. When the potential is held at + 0.6 V for longer times, other oxidized gold surface species may form, e.g. AuO, AuOHNH₂, [OH(NH₂)Au]₂NH, AuNH₂, Au₂O₃-2NH₃ and Au₂O₃-SNH₃. During the gold electrode oxidation process, NH₃ is probably oxidized to N₂. During the surface gold species reduction process, some soluble Au(III) species form that can be reduced to an adsorbed Au(I) species at -0.4 V.