Voltammetric behavior of Pd(II) and Ni(II) ions and electrodeposition of PdNi bimetal in N-butyl-N-methylpyrrolidinium dicyanamide ionic liquid

In this study, the voltammetric behavior of Pd(II), Ni(II), and mixtures of Pd(II) and Ni(II) was carried out in room-temperature N-butyl-N-methylpyrrolidinium dicyanamide ionic liquid (BMP-DCA IL). Electrodeposition of PdNi bimetal was achieved by controlled-potential electrolysis at iron wire electrodes from BMP-DCA containing various molar ratios of PdCl2/NiCl2. BMP-DCA shows good solubilities to PdCl2 and NiCl2, respectively, leading to the convenience for preparing the electrodepositing baths. By tuning the molar ratios of Pd(II)/Ni(II) in the electrodepositing baths and/or the applied potentials, PdNi coatings with various atomic contents of Pd could be obtained. Among these PdNi bimetallic coatings, the PdNi coatings with atomic ratios of ∼80/20 had the highest oxidation current in methanol oxidation reaction (MOR) in 1 M NaOH and exhibited the best poisoning tolerance. Powder X-ray diffraction analysis indicated that two separate metallic phases belonging to Pd and Ni existed in the PdNi coatings. The diffraction signal of Pd was very broad, indicating the tiny crystal size of Pd in the bimetal coatings. The scanning electron spectroscopic micrographs of PdNi coatings demonstrated that the Pd∼80Ni∼20 coatings had three-dimensional structures. This morphological characteristic implied that the composition and the surface morphology of the PdNi coatings equivalently contributed to the electrocatalytic activity toward MOR. The Pd∼80Ni∼20-coated iron-electrode (Fe/Pd∼80Ni∼20) was used to detect methanol and the linearity was observed in 3.53 μM to 758.88 μM using hydrodynamic chronoamperometry where a potential of −0.1 V (vs. Ag/AgCl) was applied.