Impact of charging in constant potential electrochemistry modelling

• Charging can provide a significant stabilization of electrochemical interfaces at more negative potential. • Many approaches don’t include this charging energy, as they use a too simple electrolyte model or omit charging altogether. • I arrive at an estimate for the potential of zero charge based on energies rather than workfunctions. A huge issue in computational electrochemistry is that different modelling approaches, used to study electron transfer reactions, give different results that cannot easily be reconciled with each other. Modeling approaches differ in their handling of interface charging and employed electrolyte model. I study charging of electrolyte-Cu(111) interfaces with electrons and cations (or positive continuum charge) and observe that charging energies (i.e. the energy stabilization from charging the interface with one extra electron and thereby going from one potential to another) depend strongly on the electrolyte model. When the electrolyte is a film containing water molecules, there is a significant stabilization of the energy with more negative potential. This is in contrast to the charging of an interface with implicit solvent, where charge repulsion result in low stabilization of the energy with more negative potential. Therefore, modelling with implicit solvent gives the impression that changing has small effect on constant potential reaction energies and, consequently, that charging can be ignored. This is likely erroneous. I further consider constant potential CO 2 adsorption to highlight the importance of charging and using an electrolyte model with water molecules, and show that other modelling approaches gives significantly different CO 2 adsorption energies.