High current density electrodeposition of silver from silver-containing liquid metal salts with pyridine-N-oxide ligands

Abstract

New cationic silver-containing ionic liquids were synthesized and used as non-aqueous electrolytes for the electrodeposition of silver layers. In the liquid state of these ionic liquids, a silver (i) cation is coordinated by pyridine-N-oxide (py-O) ligands in a 1 : 3 metal-to-ligand ratio, although in some cases a different stoichiometry of the silver center crystallized out. As anions, bis(trifluoromethanesulfonyl)imide (Tf2N), trifluoromethanesulfonate (OTf), methanesulfonate (OMs) and nitrate were used, yielding compounds with the formulae [Ag(py-O)3][Tf2N], [Ag(py-O)3][OTf], [Ag(py-O)3][OMs] and [Ag(py-O)3][NO3], respectively. The compounds were characterized by CHN analysis, FTIR, NMR, DSC, TGA and the electrodeposition of silver was investigated by cyclic voltammetry, linear potential scans, scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometry (EDX). With the exception of [Ag(py-O)3][Tf2N], which melts at 108 °C, all the silver(i) compounds have a melting point below 80 °C and were tested as electrolytes for silver electrodeposition. Interestingly, very high current densities were observed at a potential of -0.5 V vs. Ag/Ag(+) for the compounds with fluorine-free anions, i.e. [Ag(py-O)3][NO3] (current density of -10 A dm(-2)) and [Ag(py-O)3][OMs] (-6.5 A dm(-2)). The maximum current density of the compound with the fluorinated anion trifluoromethanesulfonate, [Ag(py-O)3][OTf], was much lower: -2.5 A dm(-2) at -0.5 V vs. Ag/Ag(+). Addition of an excess of ligand to [Ag(py-O)3][OTf] resulted in the formation of the room-temperature ionic liquid [Ag(py-O)6][OTf]. A current density of -5 A dm(-2) was observed at -0.5 V vs. Ag/Ag(+) for this low viscous silver salt. The crystal structures of several silver complexes could be determined by X-ray diffraction, and it was found that several of them had a stoichiometry different from the 1 : 3 metal-to-ligand ratio used in their synthesis. This indicates that the compounds form crystals with a composition different from that of the molten state. The electrochemical properties were measured in the liquid state, where the metal-to-ligand ratio was 1 : 3. Single crystal X-ray diffraction measurements showed that silver(i) is six coordinate in [Ag(py-O)3][Tf2N] and [Ag(py-O)3][OTf], while it is five coordinate in the other complexes. In [Ag3(py-O)8][OTf]3, there are two different coordination environments for silver ions: six coordinate central silver ions and five coordinate for the outer silver ions. In some of the silver(i) complexes, silver-silver interactions were observed in the solid state.

Liquid Nickel Salts: Synthesis, Crystal Structure Determination, and Electrochemical Synthesis of Nickel Nanoparticles

“…In general, the melting points and the viscositieso ft hese liquid nickel salts are higher than those of previously reported copper(I) and silver(I) salts. [23][24][25][26][27][28][29][30] This is due to the fact that most of the liquid copper and silver salts are composed of monovalent cations and one anion,w hereas nickel has a + II valency state. This resultsi n ah igherC oulombic attraction between cations and anions and therefore, ahigherviscosity and melting point.…”

“…[8][9][10][11][12][13] Several examples of electrodepositiono fm etals from liquid metal salts can be found in the literature. [14][15][16][17][18][19][20][21][22] Our research group has obtainedv ery promising resultsf or the electrodeposition of copper, [23][24][25] silver, [26][27][28][29][30] palladium [31] and lithium. [32] Metal coatings of ag ood quality were achieved at very high current densities,e ven withoutt he use of additives.…”

Influence of an Additive on Zinc Electrodeposition in the Ionic Liquid 1‐Ethyl‐3‐methylimidazolium Trifluoromethylsulfonate

“…The influence of additiveso nt he electrodeposition of metalsi ni onic liquids is an ew area of interesta nd much more attention should be paid to it. The influence of additives on the electrodeposition of cobalt, [3] nickel, [4] silver, [5] and lithium [6] from ionicl iquids and of tin [7] and zinc [8,9] from deep eutectic solvents have been reported.…”

Liquid silver tris(perfluoroethyl)trifluorophosphate salts as new media for propene/propane separation

“…Low melting silver salts have been studied by the group of Binnemans for electrodeposition purposes. [18][19][20][21][22] It has been shown that by adding different ligands to the silver center, the melting point of usually high melting silver salts can be significantly reduced by disturbing the crystal packing. Depending on the number and structure of the ligand in combination with a suitable anion, melting points below 100 Synthetic procedures for the silver propene complexes…”