How do sulfate and nitrate impurities affect the voltammetric response of Pt(111) in HClO₄ solutions?

Label:chem

Topic
The presence of trace impurities such as sulfate and nitrate in HClO₄ solutions can alter the voltammetric response of Pt(111) surfaces. These impurities can adsorb onto the electrode surface, affecting the adsorption and desorption of hydrogen and hydroxyl species.

From: "Effect of trace impurities in perchloric acid on blank voltammetry of Pt(111)", Electrochimica Acta, Volume 466, 20 October 2023, 143035
Answer
Sulfate and nitrate impurities in HClO₄ solutions cause a marked attenuation in the charge density across the cyclic voltammogram (CV) of Pt(111). The presence of these impurities results in site-blocking effects, leading to a decrease in the current density of the hydrogen underpotential deposition (Hupd) and hydroxyl adsorption (OHads) regions. Specifically, sulfate ions cause a shift in the onset potential of the sharp OHads peak to more positive values, while nitrate ions lead to the formation of nitric oxide (NO) at 0.32 V, as confirmed by in situ FTIR spectroscopy. These impurities can significantly impact the efficiency of electrocatalytic processes and should be minimized to ensure accurate electrochemical measurements.
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