Generating Oscillatory Behavior by Applying a Magnetic Field during Electrocatalytic Oxidation of Glycerol

This work demonstrates how the application of a magnetic field during electrocatalysis can affect the transport of reactants and products at the electrode surface and, under certain conditions, generate complex, oscillatory behavior in amperometric experiments. During the electrocatalytic oxidation of glycerol (EOG), the Lorentz force acts upon hydronium and hydroxide ionic currents to produce fluidic convection, which serves to enhance the mass transport of glycerol and glyceraldehyde. Particle imaging velocimetry shows that the convective fluid flow field depends nonlinearly on the viscosity of the solution (dictated by the concentration of glycerol, which ranged from 2.5% to 40% v/v, to give a viscosity range of 1.3–5.3 mPa s). The nonlinear dependence of velocity of the fluid flow on the viscosity of the electrolyte generates time-delayed negative feedback during EOG and results in chemical oscillations. This time-delayed feedback is due to two coupled steps: (i) oxidation of glycerol rapidly decreases the viscosity of the electrolyte near the anode and (ii) at low viscosities magnetic fields increase the rate of mass transport, which subsequently increases the viscosity of the electrolyte near the anode (by increasing the concentration of glycerol). These chemical oscillations can be used to enhance the selectivity of EOG to glyceric acid by a factor of 2.1. This work focuses on the effects of magnetic fields on EOG using a combination of fluid flow analysis, rotating-disk electrode experiments, and electrochemical simulations.