Electrochemical quartz crystal microbalance analysis of nitrogen oxide-promoted platinum dissolution in HClO₄

To elucidate the mechanism of NaNO₂-promoted Pt dissolution, the weight loss of Pt black-deposited Au quartz resonators was measured in 0.1 mol dm^-3 HClO₄ containing NaNO₂ under potential cycling and constant potential conditions. A continuous weight loss of ca. 50-60 ng cm^-2 cycle^-1 was detected in the presence of 10 mmol dm^-3 NaNO₂ during potential cycling above a high potential limit of 1.2 V vs RHE (V_RHE) and below a low potential limit (E _L) of 0.9 V_RHE. A weight loss was observed at constant potentials (0.6-0.8 V_RHE) when oxides were initially present; the net weight loss (Δw) magnitude increased as the amount of the initially formed Pt oxide increased. These results indicate that Pt dissolution occurred when Pt oxides were reduced in the presence of NaNO₂. The good agreement between the Δw per potential cycle and the Δw at a constant potential (E_L of the potential cycling = constant potential) revealed that the formation of Pt oxides in the positive sweep was required for the continuous weight loss under potential cycling. The Δw value increased for higher concentrations of NaNO₂ under both conditions. The products of NaNO₂ reduction were thought to participate in Pt dissolution.