On using the bulk electrolysis equation for stochastic microdroplet electrochemistry
摘要
Micro- and nanodroplet electrochemistry has recently been used to explore chemical reactions in tiny volumes. Within such scholarly pursuits, the bulk electrolysis equation is often used to quantify the contact radius of the microdroplet on the ultramicroelectrode surface. In this study, we explore common pitfalls for acquiring data for such an analysis. We demonstrate how the peak transient current, i0, and the shape of the transient itself can depend highly on the measurement sample rate, a phenomenon that is often not considered when fitting stochastic transients. Using finite element modeling, we provide a framework that shows the bulk electrolysis equation is only accurate within 10% error when the contact radius of the droplet is less than one-fifth the size of the radius of the droplet before contact with the electrode. We also discuss that the basic criterion for using bulk electrolysis is that the concentration of the redox species is completely homogeneous throughout a volume, V, across all time, t. If a droplet is too large, mixing within the droplet is not fast enough to maintain this important criterion. Thus, this work demonstrates that to accurately use the bulk electrolysis equation, one must sample quickly enough and analyze droplets that are small enough such that the concentration of redox species is homogeneous within the sample rate. These results will allow for a more quantitative workflow for stochastic droplet electrochemistry.
Graphical abstract