Effect of trace impurities in perchloric acid on blank voltammetry of Pt(111)

Abstract

Trace impurities of nitrate and sulphate species have been detected as the cause for the charge quench of existing voltammetric peaks and the appearance of new voltammetric peaks in the blank voltammetry of Pt(111) in high-purity perchloric acid. Cyclic voltammetry of Pt(111) in high concentrations of HClO4 (1 M) electrolyte display anomalous reduction peaks at 0.5 and 0.32 VRHE. The reduction of nitrates to nitric oxide, resulting in the reduction peak at 0.32 VRHE, has been detected using in situ Fourier transform infrared spectroscopy. The peak at 0.5 VRHE, previously assigned in the literature to specific adsorption of perchlorate anions catalytically dissociating to chloride anions, is consistent with sulphate desorption as elucidated by spiking HClO4 electrolyte with trace quantities (10 ppm) of sulphuric acid. The presence of kosmotropic sulphate anions was further confirmed by the positive onset potential shift of the sharp OHads butterfly peak at ∼0.8 VRHE with increasing concentrations of HClO4 (0.01–1 M). Although commonly overlooked, we show here the marked deleterious impact these trace impurities have on the blank voltammetry of Pt(111), and provide recommendations for minimising this impact.