The voltammetry of decamethylferrocene and coboltacene in supercritical difluoromethane (R32)

- Decamethylferrocene has been studied at microelectrodes in supercritical R32.
- The natural convection of scR32 can be dampened by using a baffle.
- The diffusion coefficient of DMFc in scR32 has been determined.
- A baffled macroelectrode was also used and the results compared to simulated data.
- Studies of cobaltocene complexes led to a fouling of the Pt electrode in scR32.

The voltammetry of decamethylferrocene, cobaltocene and decamethylcobaltocene at micro and macrodisc 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 be suppressed by adding a baffle around the electrode. The voltammetry of decamethylferrocene is well behaved with fast electrode kinetics at Pt microdisc electrodes. The limiting currents, corrected for random convection, obey the normal microdisc equation and are linear in electrode radius for decamethylferrocene up to the highest concentration (11 mM) used in this study. Based on the microelectrode studies, we find that the diffusion coefficient of decamethylferrocene in supercritical difluoromethane containing 20 mM [NBun4][BF4] at 360 K and 17.6 MPa is 8.3 × 10− 5 cm2 s− 1. 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.