Temperature Effects on the Kinetics of Ferrocene and Cobaltocenium in Methyltriphenylphosphonium Bromide Based Deep Eutectic Solvents

Abstract

The oxidn. of ferrocene (Fc/Fc+) and redn. of cobaltocenium (Cc+/Cc) under different temps. was studied by cyclic voltammetry and double potential step chronoamperometry in deep eutectic solvents (DESs) consisting of methyltriphenylphosphonium bromide salt with tri-ethylene glycol, glycerol or ethylene glycol as H bond donors. The temp. dependence of the measured phys. properties of DESs (such as viscosity and cond.) is discussed. The kinetics of the redox couples were studied using cyclic voltammetry, and the std. heterogeneous electron transfer rate const., k0 is of the order of 10-5 to 10-4 cms-1 at different temps. The diffusion coeff., D, of Fc and Cc+ is detd. to lie 8.28 × 10-10-6.65 × 10-9 cm2 s-1. Both k0 and D increase with temp. in the studied DESs. Better kinetic parameters for the DES with ethylene glycol as H bond donor means that this could be evaluated favorably as both solvents and electrolytes for redox flow cells. [on SciFinder(R)]