Evaluating Analytical Expressions for Scanning Electrochemical Cell Microscopy (SECCM)

Scanning electrochemical cell microscopy (SECCM) mapsthe electrochemicalactivity of a surface with nanoscale resolution using an electrolyte-fillednanopipette. The meniscus at the end of the pipet is sequentiallyplaced at an array of locations across the surface, forming a seriesof nanometric electrochemical cells where the current-voltageresponse is measured. Quantitative interpretation of these responsestypically employs numerical modeling to solve the coupled equationsof transport and electron transfer, which require costly softwareor self-written code. Expertise and time are required to build andsolve numerical models, which must be rerun for each new experiment.In contrast, algebraic expressions directly relate the current responseto physical parameters. They are simpler to use, faster to calculate,and can provide greater insight but frequently require simplifyingassumptions. In this work, we provide algebraic expressions for currentand concentration distributions in SECCM experiments, which are formulatedby approximating the pipet and meniscus using 1-D spherical coordinates.Expressions for the current and concentration distributions as a functionof experimental parameters and in various conditions (steady stateand time dependent, diffusion limited, and including migration) allshow excellent agreement with numerical simulations employing a fullgeometry. Uses of the analytical expressions include determinationof expected currents in experiments and quantifying electron-transferrate constants in SECCM experiments.

Automated summary

Scanning electrochemical cell microscopy (SECCM) uses an electrolyte-filled nanopipette to map the electrochemical activity of a surface with nanoscale resolution. This study provides algebraic expressions for current and concentration distributions in SECCM experiments, which show excellent agreement with numerical simulations and can be used to determine expected currents and quantify electron-transfer rate constants.