Electrochemical Behavior of Different Diffusional Redox Probes on a Porous Acetylene Black Electrode: Mass Transport Modes and Electrostatic Effects

The need for high-performance electrodes for electrical energy generation, conversion, and storage has increased the use of carbon nanomaterials as smart surface modifiers of working electrodes. Among carbon nanomaterials, common and inexpensive carbon blacks have spurred the scientific community’s interest due to their outstanding capabilities as electrode nanomodifiers, typically combined with an ionomer forming carbonaceous inks. Determining the key factors that can limit or enhance the overall electrochemical response of the employed redox-active species is essential to ascertain the impact on the performance of a hypothetical device, as well as to understand and elucidate reaction mechanisms. Moreover, maximizing the use of the area actually available for the electrochemical active species inside the carbon matrix is of paramount importance. Thus, in this work, the analysis of the electrochemical responses of six redox solution-soluble probes is investigated by cyclic voltammetry and a rotating disk electrode at a GC electrode modified with a metal-free carbon ink formed by a mixture of acetylene black and the ionomer Nafion. The experimental responses show mixed thin-layer and semi-infinite behavior to different degrees depending on the charge of the redox probe. The study of the causes underlying these findings reveals a strong electrostatic influence of the ionomer, leading to the appearance of blocking or trapping effects depending on the charge number of the redox probe. Such effects can compromise the validity of the well known and broadly used procedures of data analysis for porous electrodes, which is critically analyzed.