Hydrodynamic microgap voltammetry under Couette flow conditions: electrochemistry at a rotating drum in viscous poly(ethylene glycol)

Electrochemical processes in highly viscous media such as poly(ethylene glycol) (herein PEG200) are interesting for energy-conversion applications, but problematic due to slow diffusion causing low current densities. Here, a hydrodynamic microgap experiment based on Couette flow is introduced for an inlaid disc electrode approaching a rotating drum. Steady-state voltammetric currents are independent of viscosity and readily increased by two orders of magnitude with further potential to go to higher rotation rates and nanogaps. A quantitative theory is derived for the prediction of currents under high-shear Couette flow conditions and generalised for different electrode shapes. The 1,1′-ferrocene dimethanol redox probe in PEG200 (D=1.4×10⁻¹¹ m² s⁻¹) is employed and data are compared with 1) a Levich-type equation expressing the diffusion–convection-limited current and 2) a COMSOL simulation model providing a potential-dependent current trace.