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 m 2  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.