Polycrystalline gold electrode redox behavior in an ammoniacal electrolyte: Part II. A parallel RRDE, EQCM and TOF-SIMS study of copper underpotential deposition

The underpotential deposition (upd) of copper at polycrystalline gold in an ammoniacal electrolyte (0.1 M NH₃+ 0.1 M NaClO₄) was investigated. The rotating ring disk electrode (RRDE), the electrochemical quartz crystal microbalance (EQCM) and time of flight secondary ion mass spectrometry (TOF-SIMS) were all used in parallel to study this process. RRDE experiments showed that upd of Cu(0) occurred at -0.4 V < E < 0.1 V, at three different sites. Bulk deposition of Cu(0) began at -0.4 V. RRDE and EQCM data did not show the involvement of any ionic copper species during the upd discharge process. Static and dynamic TOF-SIMS results are consistent with the above experimental results. The rate-determining step is the reduction of a dissolved copper ammonia species to upd Cu(0).