Platinum black coated microdisk electrodes for the determination of high concentrations of hydrogen peroxide in phosphate buffer solutions

The performance of a series of platinum black coated microdisk electrodes (Pt-Bs) was investigated in H₂O₂ solutions over the concentration range 0.1–500 mM, in phosphate buffer media pH 7. The Pt-Bs were prepared by electrodeposition of Pt onto the surface of microdisk electrodes 12.5 μm of nominal radius, from aqueous solutions containing hexachloroplatinic acid. The resulting roughness factors (RF, i.e., the ratio of the effective surface area to the geometric electrode area) varied between about 10 and 100. The voltammograms recorded with these electrodes, at relatively low H₂O₂ concentrations (up to 50–100 mM), displayed rather steep mixed anodic–cathodic waves, which attained well-defined and stable current plateaus. At the higher hydrogen peroxide concentrations, additional waves both in the anodic and cathodic region or dramatic current drop phenomena were observed. The wave split phenomenon was attributed to the insufficient buffering capacity of the base electrolyte solution within the pores of the platinum black, induced by the large amounts of hydrogen ions produced in the oxidation process. The current drop was attributed to either the formation of oxygen bubbles, which limit diffusion of H₂O₂ down the pores, or saturation of the active sites responsible for the decomposition of H₂O₂ to O₂ and H₂O. The H₂O₂ concentration at which the above phenomena occurred depended either on the phosphate buffer concentration in the bulk solution or the RF factor of the electrodes. The latter conditions also affected the dynamic range of detection, the sensitivity and low detection limits. Advantageous analytical characteristics were obtained with a Pt-B of RF of about 24, which provided a dynamic range between 0.5 and 230 mM, a sensitivity of 1.93(±0.06) A M⁻¹ cm⁻² and a low detection limit of 0.05 mM. The reproducibility was also very good, it being within 2–3%. The usefulness of the Pt-Bs for real samples analysis was tested in an antiseptic solution containing large amounts of H₂O₂.