In this discussion paper we discuss our recent results on the electrodeposition of materials and in situ STM/AFM measurements which demonstrate that ionic liquids should not be regarded as neutral solvents which all have similar properties. In particular, we focus on differences in interfacial structure (solvation layers) on metal electrodes as a function of ionic liquid species. Recent theoretical and experimental results show that conventional double layers do not form on metal electrodes in ionic liquid systems. Rather, a multilayer architecture is present, with the number of layers determined by the ionic liquid species and the properties of the surface; up to seven discrete interfacial solvent layers are present on electrode surfaces, consequently there is no simple electrochemical double layer. Both the electrodeposition of aluminium and of tantalum are strongly influenced by ionic liquids: in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide, [Py_1,4]TFSA, aluminium is obtained as a nanomaterial, whereas in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide, [EMIm]TFSA, a microcrystalline material is made. Tantalum can be deposited from [Py_1,4]TFSA, whereas from [EMIm]TFSA only non-stoichiometric tantalum fluorides TaF_x are obtained. It is likely that solvation layers influence these reactions.

We report on the synthesis of copper nanoparticles in two different water- and air-stable ionic liquids using plasma electrochemical deposition. The copper nanoparticles were deposited in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide ([Py_1,4]Tf₂N) and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([EMIm]Tf₂N). To get information on the dimensions of the particles made, we have applied in situ transmission electron microscopy (TEM) (particles in ionic liquid). The chemical composition was investigated by ex situ X-ray photoelectron spectroscopy (XPS). We found that the copper particles produced in [Py_1,4]Tf₂N were larger in size compared to the particles obtained in [EMIm] Tf₂N (roughly 20 vs. 10 nm). The chemical composition of the particle surface differs too. In both cases the particles are partly oxidised leading to a CuO shell, but the particles obtained in [Py_1,4]Tf₂N carry a lot of residues from the ionic liquid.