Detailed analysis of the voltammetry of decamethylferrocene at micro and macrodisc electrodes has been carried out in scCO2/MeCN (15 wt%), 20 mM [NBu(n)4][BF4] and 309 K and 17.5 MPa. A passivating film needs to be removed from platinum electrodes before stable, reproducible voltammetry can be obtained. At low concentrations (0.22 mM) reversible 1e(-) behaviour is observed. Significant effects from natural convection are also present and it is demonstrated that fitting a baffle to the electrode dampens this effect. Limiting currents at microdisc electrodes at concentrations ranging from 0.22 to 11 mM and radii of 10 to 25 μm all obey the microdisc equation. The diffusion coefficient is calculated to be 4.06 × 10(-5) cm(2) s(-1) in scCO2/MeCN (15 wt%) with 20 mM [NBu(n)4][BF4] and 309 K at 17.5 MPa. The solubility of decamethylferrocene is in excess of 11 mM for these conditions.

A wide range of supercritical fluids (SCFs) have been studied as solvents for electrochemistry with carbon dioxide and hydrofluorocarbons (HFCs) being the most extensively studied. Recent advances have shown that it is possible to get well-resolved voltammetry in SCFs by suitable choice of the conditions and the electrolyte. In this review, we discuss the voltammetry obtained in these systems, studies of the double-layer capacitance, work on the electrodeposition of metals into high aspect ratio nanopores and the use of metallocenes as redox probes and standards in both supercritical carbon dioxide–acetonitrile and supercritical HFCs.

No abstract

The voltammetry of decamethylferrocene, cobaltocene and decamethylcobaltocene at micro and macro disc electrodes in supercritical difluoromethane at 360 K and 17.6 MPa has been studied. In all cases the voltammetry is distorted to some degree by the effects of random convection but these can . Finally we have briefly investigated the voltammetry of cobaltocene and decamethylcobaltocene in supercritical difluoromethane under the same conditions. We find that reduction of the cobaltocenium cation leads to fouling of the Pt microdisc electrode which limits its use as a model redox system and that reduction of the decamethylcobaltocenium cation was not observed before electrolyte reduction at around -1.6 V vs. Pt.

The paper describes a reactor suitable for high pressure, particularly supercritical fluid, electrochemistry and electrodeposition at pressures up to 30 MPa at 115 • C. The reactor incorporates two key, new design concepts; a plastic reactor vessel and the use of o-ring sealed brittle electrodes. These two innovations widen what can be achieved with supercritical fluid electrodeposition. The suitability of the reactor for electroanalytical experiments is demonstrated by studies of the voltammetry of decamethylferrocene in supercritical difluromethane and for electrodeposition is demonstrated by the deposition of Bi. The application of the reactor to the production of nanostructures is demonstrated by the electrodeposition of ∼80 nm diameter Te nanowires into an anodic alumina on silicon template. Key advantages of the new reactor design include reduction of the number of wetted materials, particularly glues used for insulating electrodes, compatability with reagents incompatible with steel, compatability with microfabricated planar multiple electrodes, small volume which brings safety advantages and reduced reagent useage, and a significant reduction in experimental time.