Scanning electrochemical cell microscopy for the study of (nano)particle electrochemistry: From the sub-particle to ensemble level

Scanning electrochemical cell microscopy (SECCM) is a scanning-droplet-based technique that allows electrochemical fluxes and/or interfacial reactivity to be measured and visualized with high spatiotemporal resolution. This minireview spotlights the use of SECCM for studying the electrochemistry of (nano)particles, highlighting recent works spanning multiple timescales (i.e., microseconds to seconds) and lengthscales (i.e., nanometers to micrometers) to probe physicochemical phenomena at the sub-particle, single particle, and/or (micro)ensemble levels. In SECCM, single (nano)particles (or small particle ensembles) are electrochemically interrogated-directly from colloidal solution (i.e., by investigating electrochemical nanoimpacts with a substrate electrode) or supported on an electrochemically inert support electrode-with a pipette probe that is operated in either a stationary (point measurement) or dynamic scanning/imaging mode. Nanoscale-resolved electrochemical information (e.g., local rates of electron- or ion-transfer, catalytic activity, corrosion resistance, etc.) from SECCM is readily related to (nano)particle structure and properties, collected at a commensurate scale with complementary, co-located microscopy/spectroscopy techniques, allowing structure and function to be resolved directly and unambiguously down to the sub-particle level. Understanding structure-function on this scale enables macroscopic "particle-on-support" electrode behavior to be rationalized and further predicted, guiding the discovery, design, and engineering of novel electromaterials with enhanced function, which is a "holy grail" in materials science.