An electrochemical and XPS study of the electrodeposited binary Pd–Sn catalyst: The electroreduction of nitrate ions in acid medium

Optimal conditions for Pd and Sn co-deposition were achieved by voltage cycling between 0.2 and −0.7 V vs. SCE in deaerated solution containing 0.5 mM Na2PdCl6, 0.5 mM SnCl2 and 25 mM HCl. Cyclic voltammetry and chronoamperometric techniques were used to investigate the electrochemical behaviour of the electrodeposited binary film toward the electrochemical reduction of nitrate species in slightly acid solutions. The relevant reduction mechanism was critically discussed. The resulting calibration plots for nitrate analysis performed under voltammetric conditions and in 50 mM H2SO4 solution are linear over the range 1.0–12 mM with correlation coefficients better than 0.984. The X-ray photoelectron spectroscopy technique (XPS) was used in order to evaluate the chemical composition of the binary electrodeposited film. Electrodeposited Pd30Sn70 films, independently of the electrochemical treatment, are composed of 50–60% of Sn metal and 40–50% of SnO of the total tin species, while the palladium species are composed by 60–70% of Pd and 30–40% of palladium oxides (i.e., PdOads and PdO).