Electrochemical deposition of PB on Pt microelectrodes (diam. 25 µm) was carried out according to previously published procedures . In brief, four cycles in a potential range of 0.4 and 0.75 V vs. Ag/AgCl at a scan rate of 0.02 V/s were applied in a freshly prepared solution of 1.25 mM K3[Fe(CN)6] and 1.25 mM FeCl3 in 0.1 M HCl / 0.1 M KCl solution. After the deposition of PB, electrodes were rinsed with ultrapure water and activated by applying another 10 cycles in the electrolyte solution (0.1 M KCl / 0.1 M HCl). Finally, the electrodes were again rinsed with ultrapure water and then tempered at 80 °C for 1 h. In-situ H2O2 measurements were performed in a four-electrode setup (i.e., using two working electrodes, WE1 and WE2) by positioning a PB-modified Pt microelectrode (diam. 25 µm, biased at -0.05