Polycrystalline gold electrode redox behavior in an ammoniacal electrolyte

Abstract

Abstract The redox behavior of a gold electrode in an ammoniacal electrolyte (0.1 M NH 3 and 0.1 M NaClO 4 ) 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 AuNH 2 , 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 AuNH 2 from AuO and AuOHNH 2 . When the potential is held at +0.6 V for longer times, other oxidized gold surface species may form, e.g. AuO, AuOHNH 2 , [OH(NH 2 )Au] 2 NH, AuNH 2 , Au 2 O 3 ·2NH 3 and Au 2 O 3 ·3NH 3 . During the gold electrode oxidation process, NH 3 is probably oxidized to N 2 . 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.