(766e) Electrochemical Barriers Made Simpler

In the study of surface electrochemistry, the calculation of electrochemical reaction energetics is a tremendous open challenge. This is primarily because the driving force of the reaction changes across the reaction coordinate for finite simulation cell sizes. Several methods have been developed to manage this challenge, including extrapolation techniques based on the cell size and the charge of the ion, as well as polarizable continuum charging methods. In this work, we demonstrate that the electrochemical interface can be effectively modeled as multiple capacitors, each corresponding to separate dipole-field interactions. By analogy to the Frumkin correction from classical electrochemistry, we argue that the total excess surface charge density is the appropriate descriptor for the driving force of electrochemical reactions, rather than the work function or applied potential. Specifically, we show that the capacitance associated with each dipole-field interaction need not be the same. Importantly, if the capacitances are not the same, this leads to the striking conclusion that the work function does not uniquely determine the reaction energetics. In other words, any reaction energy can be obtained at a given work function depending on how the surface is charged. Based on the models developed here, we outline a general framework for the calculation of electrochemical reaction energetics. This framework allows, for the first time, the efficient modeling of anions in electrocatalysis, which are important for a number of applications. Finally, we discuss the implication that surface charge as the descriptor for the driving force has on electrocatalyst engineering.