Michiel Sprik

An electrochemical cell is a device converting the sum of potentials across a series of electrochemical interfaces into a measurable voltage between the external leads connected to the electrodes. This is very far from the geometry of the periodic model systems used in electronic structure calculation of condensed phases. A further fundamental complication is that electrostatic potentials across interfaces between phases of different composition are not accessible to direct experimental determination. What is measured are work functions. Trasatti has shown how cell voltage can be resolved in a sum of absolute single electrode potentials consisting of free energies for transfer to vacuum and contact potentials across electrode-electrolyte junctions. This talk starts out with a brief review of how the Trasatti scheme has been implemented in the computation of the potential of uncharged ideally polarizable electrodes (no electron transfer between metal and bulk solution). The particular challenge for us was to do this the Car-Parrinello way treating metal electrode and the molecular electrolyte at the same level of DFT based electronic structure calculation. We also rather want to avoid introducing explicit vacuum interfaces which are after all not a functional part of an electrochemical cell[1]. This worked out rather well[2]. We then continue with outlining the much more demanding task of computing the potential of charged (electrified) interfaces again keeping a fully atomistic electronic and statistical mechanical description of the electrolyte. This is work in progress. There remain a number of difficult issues to be resolved which we will try to explain.

1. Jun Cheng and Michiel Sprik. “Alignment of electronic energy levels at electrochemical interfaces.” Physical Chemistry Chemical Physics 14.32 (2012): 11245-11267.
2. Jiabo Le, Marcella Iannuzzi, Angel Cuesta and Jun Cheng. “Determining potentials of zero charge of metal electrodes versus the standard hydrogen electrode from density-functional-theory-basedmolecular dynamics.” Physical review letters 119.1 (2017): 016801.