Noble Metals Alloys Deposition from Non-Aqueous Solvents

Abstract

Binary alloys of Pd and Pt were successfully deposited from 1-butyl-3-methyl imidazolium tetrafluoroborate (BMIM-BF4-Cl) ionic liquid and from a deep eutectic solvent (DES) based on a mixture of choline chloride and urea (ChCl-UA) at ambient atmosphere conditions. Ag, Ni and Sn were used as alloy components. Cyclic voltammetry experiments on glassy carbon electrode showed the reduction and dissolution of the alloys in the investigated solvents. Pulse plating and potentiostatic deposition techniques were used to deposit PdAg, PdNi, PdSn and PdPt alloys on cylindrical Cu substrate. The composition of the layers could be varied either by the concentration of the metals in the electrolyte solution or by changing the deposition mode (pulsed current or potentiostatic deposition). In order to determine the surface morphology and the thickness of the electrodeposited noble metal alloy films, a high resolution scanning electron microscope (SEM/EDX) and an energy dispersive X-ray fluorescence spectrometer (XRF) were used. The surface morphology of the layers was remarkable affected by the composition of the alloys. Scanning electron micrographs of the different electrodeposits showed that Pd alloys deposited by pulse current were generally nodular and relatively compact, whereas the films deposited by potentiostatic deposition were less dense and covered with dendrite-like and sharp-edged crystallites. The addition of a second metal (e.g. Ag+ or Sn2+) to a basic Pd or Pt electrolytes enhanced the overall metal deposition rate in comparison to solutions without alloying components and caused a remarkable increase of the layer thickness of the alloys. XRD measurements confirm that it was possible to deposit different binary metal alloys from both non-aqueous electrolytes by applying different deposition techniques. First adhesion tests and measurements of the microhardness of Pd-Ag deposits showed good properties of the produced alloy films. Also the hydrogen embrittlement of selected samples was proved by a hydrogen analyzer. These results confirmed that the quantity of hydrogen was negligible in the Pd alloy films produced from ionic liquids in comparison to films obtained from conventional aqueous solutions.