Insights into the Voltammetry of Cavity Microelectrodes Filled with Metal Powders: The Value of Square Wave Voltammetry

Cavity microelectrodes (CMEs) offer a valuable platform to evaluate the electrocatalytic performance of micro‐ and nanoparticulate materials. The technical factors and physicochemical processes affecting the electrochemical response at CMEs are to be recognized; specifically, the accessibility of redox species to the electrocatalyst surface. With this aim, the voltammetric response of CMEs is investigated through a joint experimental and theoretical approach including a comparative study of cyclic and square wave voltammetry (SWV). Experiments reveal a capacitive distortion of the response that increases with the powder surface area, but with a faradaic response analogous to that of recessed or inlaid microdisks, that is, with electrochemical reactions occurring essentially on the first layer of the powder load. We show that SWV is well suited to discriminate faradaic processes at CMEs and we present accurate mathematical expressions to describe it. These results provide guidelines for the design and analysis of CME voltammetric measurements. Ride the wave: Cyclic and square wave voltammetry (CV and SWV, respectively) for the reduction of Ru(NH3)63+ with a cavity microelectrode filled with large surface area platinum powders. SWV effectively supresses non‐faradaic distortions, being advantageous over CV to discriminate faradaic processes. Equations describing SWV responses at CMEs are derived for first time.