Frequency-dependent impedance of nanocapacitors from electrode charge fluctuations as a probe of electrolyte dynamics Giovanni Pireddu and Benjamin Rotenberg CNRS, Sorbonne Université, France The frequency-dependent impedance is one of the most important properties of electrical components, and it is routinely used to characterize energy storage and conversion devices. The frequency-dependence reflects the multiscale dynamics of the charge carriers in these systems. Until recently, there was no direct link between the microscopic mechanisms and the impedance measurements, whose interpretation is often indirect and relies on equivalent circuit models. Building on previous work introducing a fluctuation-dissipation relation between the capacitance to the variance of the electrode charge distribution [1], we show how to compute the full impedance spectrum from the equilibrium dynamical fluctuations of the electrode charge in constant potential molecular simulations [2], with the above- mentioned relation for the capacitance being recovered in the zero-frequency limit. This approach offers a bridge between electrochemical measurements and molecular mechanisms. We illustrate the potential of this approach in the case of nanocapacitors using gold electrodes and pure water or NaCl solutions as a dielectric medium, highlighting how some of the dynamical properties of the electrolyte are reflected in the fluctuations of the electrode charge. We finally show how the electrolyte conductance can be estimated from the impedance results computed from simulations, and compare it with experimental measurements. This work is part of the ERC project SENSES (grant No. 863473). Project website: https://benrotenberg.github.io/erc-senses/ References 1. D. T. Limmer, C. Merlet, M. Salanne, D. Chandler, P. A. Madden, R. van Roij, and B. Rotenberg. Phys. Rev. Lett. 2013, 106102. 2. G. Pireddu and B. Rotenberg, Phys. Rev. Lett. 2023, 130, 098001.
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