Ordered Three Dimensional Electrodes for Enhanced Mass Transfer

Abstract

Over the last decade, the use of nanotechnology in electrochemical catalysis has become extreme popular [1]. Sole electrocatalytic nanoparticles, however, do not yet constitute an electrode. Hence, deposition on a conducting support structure is indispensable. While the electrocatalytic activity is in general well understood using typical electrochemical techniques such as cyclic and linear voltammetry whether or not coupled with controlled mass transfer conditions like rotating disk electrodes, the impact of concentration polarization is often neglected. Operating under current limiting regime, mass transfer enhancement in electrochemical reactors is a key factor not only for current density but also for the selectivity and stability [2]. Inducing convective transport, however, is limited to the incorporation of turbulence promoters. Either stating an increase in inter-electrode distance or a large power dissipation to pump the feed. Looking at electrochemical reactors (e.g. fuel cell, chloor-alkali process, water electrolyzer) the conductive support typically consist of a flat substrate with the electrolyte flowing sideways along the electrode [3]. Inevitably a stagnant boundary layer arises which reacting species have to surpass to reach the electrocatalytic surface, even when using turbulence promotors. As transport across this stagnant layer is solely due to diffusion it has a major impact on the mass transfer resistance and concomitantly on the position of the limiting current plateau. However, when the electrode is no longer considered as a flat substrate a plethora of options arise, where not only the surface area can be increased, but also where the electrode itself can provoke mixing effects, reducing this boundary layer. In the present work such integrated mixer and electrode configurations have been constructed and evaluated using additive manufacturing technology. Doing so these electrode mixers shift the limiting current plateau with over 70%. At the one hand this is attributed due to shear forces reducing the stagnant boundary layer, at the other hand as no longer a turbulence promotor or even a spacer is required the inter-electrode distance can be reduced to sub-millimeter range, having a beneficial impact on the ohmic resistance.