Electrochemical Strain Measurements with Atomic Force Microscopy: Principles and Applications

Mechanical cyclic voltammetry (mCV) is a recently developed characterization technique for studying local electrochemical processes operando. This method is a subset of electrochemical atomic force microscopy (EC-AFM) that investigates electrochemical processes on electrode surfaces. In many materials, electrochemically driven ion insertion leads to electrode volume expansion or contraction, which can be measured with EC-AFM. If the volume change scales with the amount of inserted charge, the rate of electrode expansion is proportional to the electrochemical current, forming the basis for the mechanical analogs of electrochemical characterization methods. Here, we provide a technical tutorial of mCV, including data recording, processing, evaluation of measurement artifacts, and considerations for 3D volume changes. We discuss the advantages and disadvantages of different measurement modalities, including noise levels and drift. We demonstrate mapping capabilities to obtain spatially resolved information about electrochemical processes using proton insertion into monoclinic tungsten oxide (WO3) as a model system. Our insights, which address key experimental challenges in EC-AFM, extend to a wide range of systems and establish EC-AFM as a broadly accessible platform for developing mechanical analogs to conventional electrochemical characterization techniques.