Advancing from Rules of Thumb: Quantifying the Effects of Small Density Changes in Mass Transport to Electrodes. Understanding Natural Convection

作者：Ngamchuea Kamonwad; Eloul Shaltiel; Tschulik Kristina^*; Compton Richard G

来源：Analytical Chemistry, 2015, 87(14): 7226-7234.

DOI：10.1021/acs.analchem.5b01293

Understanding mass transport is prerequisite to all quantitative analysis of electrochemical experiments. While the contribution of diffusion is well understood, the influence of density gradient-driven natural convection on the mass transport in electrochemical systems is not. To date, it has been assumed to be relevant only for high concentrations of redox-active species and at long experimental time scales. If unjustified, this assumption risks misinterpretation of analytical data obtained from scanning electrochemical microscopy (SECM) and generator-collector experiments, as well as analytical sensors utilizing macroelectrodes/microelectrode arrays. It also affects the results expected from electrodeposition. On the basis of numerical simulation, herein it is demonstrated that even at less than 10 mM concentrations and short experimental times of tens of seconds, density gradient-driven natural convection significantly affects mass transport. This is evident from in-depth numerical simulation for the oxidation of hexacyanoferrate (II) at various electrode sizes and electrode orientations. In each case, the induced convection and its influence on the diffusion layer established near the electrode are illustrated by maps of the velocity fields and concentration distributions evolving with time. The effects of natural convection on mass transport and chronoamperometric currents are thus quantified and discussed for the different cases studied.

• 出版日期2015-7-21