Intensifying Diffusion-Limited Reactions by Using Static Mixer Electrodes in a Novel Electrochemical Flow Cell

Abstract

Surface-mediated reactions require effective mixing for them to be intense and efficient. In electrochemistry where the reactants must contact electrode surfaces for a sufficient time to enable electron tunnelling to occur, exhaustive electrolysis in poorly stirred reactors can take many hours to complete. As a consequence, electrochemical processing in many industries is restricted to batch processing which is more costly and labour intensive than continuous processing and results in significant down time between batches. This is not ideal for bulk production or treatment. Here we describe CSIRO’s novel axial flow electrochemical cell which aims to address these mixing problems by using a bespoke static mixer electrode (SME), designed by computational fluid dynamics (CFD) and manufactured using additive manufacturing (AM) technology to retain the fidelity of the original design. This electrode was characterized by SEM-EDS and electrosorption measurements. The performance of the electrochemical flow cell was evaluated by probing the ferricyanide ([Fe(CN)6]3−) reduction reaction on a platinum-coated SME under controlled mass transport conditions using cyclic voltammetry (CV), linear sweep voltammetry (LSV) and chronoamperometric measurements. This reaction was chosen because it has fast electron transfer kinetics, so the rate of reaction in dilute solutions is limited only by mass transport of the reactant to the electrode surface. Under the highest flow rate used (400 ml min−1) the cell enhanced the rate of reduction of ([Fe(CN)6]3− in a 10−3 M solution by 45 times compared with the no flow result. The impact the cell has diminishes as the concentration increases where mass transport plays a diminishing role in controlling the reaction rate. The performance of the cell is compared with a rotating disk electrode and a tubular flow cell and mass transfer coefficients are also presented for different reactant concentrations and flow conditions.