Spectroscopic ellipsometry was used to check the changes of the

Working solutions were prepared with NaOH pellets (Merck), suprapure HClO4 (Merck), H2O2 (Merck) and Milli-pure water and they Biotin-HPDP were either deaerated by N2 (99.9995%, Messer), or saturated by O2 (99.9995%, Messer). All experiments were performed at room temperature.
3.1. CV characterization of Pd(poly) surface
Fig. 1. Cyclic voltammetry curves of Pd(poly) recorded in: a) 0.1 M HClO4; b) 0.1 M NaOH. Sweep rate was 50 mV/s.Figure optionsDownload full-size imageDownload as PowerPoint slide
The formation of Pd oxide in 0.1 M NaOH solution, Fig. 1b, begins at -0.4 V, and the first reversible oxidation/reduction peak at approx. -0.27 V as well as a small prepeak at -0.36 V are attributed to the formation of PdOHads submonolayer [29]. The oxidation of palladium proceeds at higher potentials up to the positive potential limit. The main Pd oxide formation peak at -0.08 V has a counterpart in the negative going scan, which appears at -0.2 V as the main Pd oxide reduction peak, indicating a strong irreversibility of Pd oxide formation/reduction at higher potentials. There is only a slight suppression of Pd oxide formation/reduction peaks during repeating cycling as can be seen from CV recorded after 30 cycles. The presence of the excess of OH− anions in alkaline solutions is supposed to facilitate the formation of PdOH on the surface, thus showing more stable CV in basic than in acid electrolytes.