Controlling Droplet Cell Environment in Scanning Electrochemical Cell Microscopy via Migration & Electroosmotic Flow

Scanning Electrochemical Cell Microscopy (SECCM) has emerged as a powerful technique for understanding nanoscale electrochemical phenomena. The technique’s high spatial resolution allows for further understanding of the heterogeneity of electrochemical interfaces and has applications in electrocatalyst design, correlative microscopy studies, and more. Dual channel nanopipettes can be utilized as the probe, and a voltage bias between the channels can be utilized to control the local electrolyte environment via migration and electroosmotic flow (EOF). The contribution of these transport phenomena is desirable, and in this work, were quantified via finite element modeling (FEM) and fluorescence microscopy. We have shown that redox mediators of high charge, such as Ru(NH3)63+, have a significantly higher contribution of mass transport (5×) via migration to its mass transport limiting current compared to EOF when a voltage bias is applied. Low-charge redox molecules, such as FcTMA+, have a nearly equivalent contribution of migration and EOF. The contributions of either transport method can be manipulated by controlling the surface charge of the electrical double layer (EDL) as well as through the solution’s ionic strength. Our findings allow for the precise control of mass transport flux in dual channel SECCM, potentially allowing for new scanning modes in which high mass transport flux is desirable.