LIQUID-PHASE ELECTROCHEMISTRY AT ULTRALOW TEMPERATURES

Fluid electrolyte solutions based on mixtures of butyronitrile (PrCN) and ethyl chloride (EtCl) with Bu4NPF6 or Bu4NClO4 as electrolyte freeze below -180-degrees-C and provide excellent media for cryogenic electrochemical experiments. A 1:2 mixture of PrCN and EtCl exhibits the best combination of freezing point and ionic conductivity for ultralow temperature electrochemistry. Diffusion coefficients for bis(pentamethylcyclopentadienyl) iron (Cp2*Fe) are measurable by protential step chronoamperometry down to -160-degrees-C using a conventionally sized electrode, but the resistivity of the solvent mixture is such that potential sweep voltammetry benefits from the use of microdisk (10 and 25-mu-m diam Pt) or microband (0.2-mu-m wide Au) electrodes. Voltammetry at a chemically modified electrode down to -170-degrees-C is presented for the case of thin films of poly-[Os(bpy)2(vpy)2][PF6]2.