Determining Potentials of Zero Charge of Metal Electrodes versus the Standard Hydrogen Electrode from Density-Functional-Theory-Based Molecular Dynamics

Abstract

We develop a computationally efficient scheme to determine the potentials of zero charge (PZC) of metal-water interfaces with respect to the standard hydrogen electrode. We calculate the PZC of Pt(111), Au(111), Pd(111) and Ag(111) at a good accuracy using this scheme. Moreover, we find that the interface dipole potentials are almost entirely caused by charge transfer from water to the surfaces, the magnitude of which depends on the bonding strength between water and the metals, while water orientation hardly contributes at the PZC conditions. DOI: 10.1103/PhysRevLett.119.016801 Metal-water interfaces are of great technological importance in many energy storage and conversion devices such as fuel cells and batteries. Fundamentally, they are the primary subjects for studying electrochemical processes (i.e., electrocatalysis and corrosion) in electrochemistry and play a crucial role in the development of electric double layer (EDL) theories (i.e., Gouy-Chapman-Stern model). Direct probing of structures and dynamics of the interfaces at a molecular level is extremely challenging for experiment. First principles simulations, on the other hand, can offer detailed microscopic information on the interfaces. However, due to high computational costs, it was not long ago that ab initio modeling of metal-water interfaces became affordable [1,2].Potential of zero charge (PZC) is a fundamental concept in the EDL theories, defined as the potential at which no excess charge exists on metal surfaces, and deviation from the PZC will lead to attraction of counterions to the surfaces, building up the EDL [3]. Because of its significance to the microscopic understanding of an EDL and interfacial potentials, numerous experimental techniques have been developed to determine the PZC of metal electrodes, e.g., surface tension methods, capacitance measurement methods, CO charge-displacement methods, etc [4]. Despite repeated efforts, many measurements are still subject to uncertainties because of difficulties in preparing single crystal electrodes and excluding specific adsorption of electrolyte ions [5][6][7]. In the presence of specific adsorption, electrochemists distinguish the subtlety between the potential of zero total charge (PZTC) and the potential of zero free charge (PZFC), and only the latter is an intrinsic property of metal electrodes [8].First principles calculation of well-defined metal surfaces is ideal for determining the PZFC. There are two issues in computational methods. First, how is the solvent treated in the simulation models? In the literature, water has often been treated with either an implicit dielectric continuum [9][10][11] or some representations of static water structures for efficiency [12]. It, however, has been reported that the dynamics of water on surfaces has significant effects on interface potentials [13]. As yet, very few studies have modeled full metal-water interfaces and accounted for water dynamics using density functional theory based molecular dynamics (DFTMD) [14,15]. Second, how are th...

Double Layer at the Pt(111)–Aqueous Electrolyte Interface: Potential of Zero Charge and Anomalous Gouy–Chapman Screening

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