Solvation at Metal/water Interfaces: An Ab Initio Molecular Dynamics Benchmark of Common Computational Approaches

Abstract

<div> <div> <div> <p>Rationalizing the influence of the solvent on electrochemical reaction energetics is a central challenge in our understanding of electrochemical interfaces. To date, it is unclear how well existing methods predict solvation energies at solid/liquid interfaces since they cannot be assessed experimentally. <i>Ab initio</i> molecular dynamics (AIMD) simulations present a physically highly accurate, but also a very costly approach. In this work, we employ extensive AIMD simulations to benchmark solvation at charge-neutral metal/water interfaces against commonly applied continuum solvent models. We consider a variety of adsorbates including *CO, *CHO, *COH, *OCCHO, and *OH on Cu, Au, and Pt facets solvated by water. The surfaces and adsorbates considered are relevant, among other reactions, to electrochemical CO2 reduction and the oxygen redox reactions. We determine directional hydrogen bonds and steric water competition to be critical for a correct description of solvation at the metal/water interfaces. As a consequence, we find that the most frequently applied continuum sol- vation methods, which do not yet capture these properties, do not presently provide more accurate energetics over simulations in vacuum. We find most of the computed benchmark solvation energies to linearly scale with hydrogen bonding or competitive water adsorption, which strongly differs across surfaces. Thus, we determine solvation energies of adsorbates to be non-transferable between metal surfaces in contrast to standard practice. </p> </div> </div> </div>

Electrosorption at metal surfaces from first principles

“…Having said this, we emphasize that the remaining inaccuracies of FGC calculations can still be significant. Notable factors are the approximate DFT exchange-correlation functional and their errors in adsorption energies, the neglect of explicit water 58,59,86 , or missing co-ions 93 . In addition, the present analytical derivations indicate that discrepancies between allimplicit and all-explicit interfacial capacitances 39,55,92,99 and work functions 58 can have an impact as well.…”

“…(1). We stress that this need extends also generally to all interfacial species in the double layer, such as water or solvated ions [57][58][59] . However, in this work we restrict ourselves to implicit solvation models in which only the specifically bound ionic adsorbates a are treated explicitly in Eq.…”

“…As shown convincingly in a recent study by Cheng et al 84 , an increasing distance between metallic surface and interfacial water for higher pH values lead to a decrease in the adsorption energy and thereby to a peak shift of correct magnitude on the RHE scale. In general, any such influence of surface-specific interfacial water 58,59,[85][86][87][88][89][90][91][92] can not be captured in calculations based only on implicit solvation. This highlights that present-day FGC calculations still need to be seen as a numerically efficient approximation-that as a next step might need to be refined by appropriately extending them to mixed explicit/implicit solvation models 39,58 .…”

Sulfate, Bisulfate, and Hydrogen Co-adsorption on Pt(111) and Au(111) in an Electrochemical Environment

“…To consider solvent effects we used an implicit solvation model (Petrosyan et al, 2005 , 2007 ; Letchworth-Weaver and Arias, 2012 ; Gunceler et al, 2013 ; Sakong et al, 2015 ; Bramley et al, 2020 ; Heenen et al, 2020 ) as implemented in the VASP code (Mathew et al, 2014 ). For the permittivity of the solvent we used the one of clean water ( ).…”

Interaction of CO with Gold Under Gas Phase and Electrochemical Environments

“…In the case of (211), the calculated solvation energy is 0.75 eV, while that of (100) is -0.17 eV. The significant destabilization of the adsorbed CO on (211) is due to the competitive adsorption of water, which has also been observed on Cu(211) 20 and Pt(111) 21 (see SI Note 5). In gas phase, less coordinated surfaces bind CO stronger.…”