Computing the local ion concentration variations for electric-double-layer-modulation microscopy

Abstract

Modulation of the electric potential on a conducting electrode is presented to generate an optical contrast for scattering microscopy that is sensitive to both surface charge and local topography. We dub this method electric-double-layer-modulation microscopy. We numerically compute the change in the local ion concentration that is the origin of this optical contrast for three experimentally relevant geometries: nanosphere, nanowire, and nanohole. In absence of plasmonic effects and physical absorption, the observable optical contrast is proportional to the derivative of the ion concentration with respect to the modulated potential. We demonstrate that this derivative depends on the size of the object and, less intuitively, also on its surface charge. This dependence is key to measuring the surface charge, in an absolute way, using this method. Our results help to identify the experimental conditions such as dynamic range and sensitivity that will be necessary for detecting the elementary charge jumps. We conclude that the nanohole is the most suitable geometry of the three for achieving elementary charge sensitivity.

Operando imaging in electrocatalysis: insights into microstructural materials design

“…Notably, the investigation highlights the crucial role played by metal hydroxide nano‐shells in enhancing electrocatalysis. Moreover, DFM was utilized to spatially resolve the reconfiguration of the electric double layer [140,141] . Spatial and temporal characterization of the scattering signal reveals that the potential‐dependent optical contrast is directly proportional to the accumulated charge of polarizable ions at the interface.…”

“…Moreover, DFM was utilized to spatially resolve the reconfiguration of the electric double layer. [140,141] Spatial and temporal characterization of the scattering signal reveals that the potential-dependent optical contrast is directly proportional to the accumulated charge of polarizable ions at the interface. Additionally, the time derivative of the accumulated charge provides insight into the nanoscale ionic current.…”

Iontronic microscopy of a tungsten microelectrode: “seeing” ionic currents under an optical microscope

“…We have dubbed our method EDLmodulation microscopy, which can be categorized as a subclass of iontronic microscopy methods. Recent advances in interferometric scattering microscopy and computational modeling of the electric double layer formation indicate that sensing a single surface charge alteration is within technical reach 21 . Merryweather et al resolved nanoscopic lithium-ion dynamics in solid-state battery based on interferometric scattering microscopy 22,23 .…”

“…We have dubbed our method EDLmodulation microscopy, which can be categorized as a subclass of iontronic microscopy methods. Recent advances in interferometric scattering microscopy and computational modeling of the electric double layer formation indicate that sensing a single surface charge alteration is within technical reach 21 (IRM) to monitor interfacial processes the SECCM meniscus status with high spatial and temporal resolution 24 . Utterback et al spatiotemporally resolved electrochemically-induced ion concentration gradient evolution in solution using the interference reflection microscopy 25 .…”

“…Recent advances in interferometric scattering microscopy and computational modeling of the electric double layer formation indicate that sensing a single surface charge alteration is within technical reach. 21 Merryweather et al resolved nanoscopic lithium-ion dynamics in a solid-state battery based on interferometric scattering microscopy. 22,23 Valavanis et al demonstrated the combination of scanning electrochemical cell microscopy (SECCM) and interference reection microscopy (IRM) to monitor electrochemically-driven phase formation phenomena with high spatial and temporal resolution.…”