Reconciling the Experimental and Computational Hydrogen Evolution Activities of Pt(111) through DFT-Based Constrained MD Simulations

Abstract

The computational hydrogen evolution activity of Pt(111) remains controversial due to apparent discrepancies with experiments concerning rate-determining activation free energies and equilibrium hydrogen coverages. A fundamental source of error may lie within the static representations of the metal−water interface commonly employed in density functional theory (DFT)based kinetic models neglecting important entropic effects on reaction dynamics. In this work, we present a dynamic reassessment of the Volmer−Tafel hydrogen evolution pathway on Pt(111) through DFT-based constrained molecular dynamics simulations and thermodynamic integration. Hydrogen coverage effects are gauged at two distinct surface saturations, while the critical potential dependence and constant potential conditions are accounted for using a capacitive model of the electrified interface. The uncertainty in the highly nontrivial treatment of the electrode potential is carefully examined, and we provide a quantitative estimation of the error associated with dynamically simulated electrochemical barriers. The dynamic description of the electrochemical interface promotes a substantial decrease of the Tafel free energy barrier as the coverage is increased to a full monolayer. This follows from a decreased entropic barrier due to suppressed adlayer dynamics compared to the unsaturated surface, a detail easily missed by static calculations predicting notably higher barriers at the same coverage. Due to observed endergonic adsorption of active hydrogen intermediates, the Tafel step remains ratedetermining irrespective of the coverage as illustrated by composed Volmer−Tafel free energy landscapes. Importantly, our explicitly dynamic approach avoids the ambiguous choice of frozen solvent configuration, decreasing the reliance on error cancellation and paving the way for less biased electrochemical simulations.

Hydrogen Coupling on Platinum Using Artificial Neural Network Potentials and DFT

“…This process proceeds with a barrier of 0.67 eV to overcome the transition state (TS) located at an H−H separation distance of 1.05 Å. Our calculated barrier is in excellent agreement with recent constrained-AIMD calculations by Kronberg and Laasonen, 48 in which the barrier for the Tafel mechanism exhibits a coverage dependence, decreasing from 0.80 eV (0.66 ML) to 0.53 eV (1.00 ML). To validate the reliability of our calculated free energy, we compare the HDNN with AIMD simulations, resulting in a mean averaged error (MAE) of ∼0.1 eV between the two calculation methods, as shown in Figure S6 and Table S2 (Supporting Information).…”

“…The inverse behavior is predicted for the Tafel mechanism barrier, which has been shown to increase at lower coverage. 48 This is significant, as it suggests the dual mechanistic nature for HER on Pt(111) which is highly coverage-dependent.…”

“…Experimentally, the low resolutions obtained from spectroscopic analyses are inadequate for analyzing the complicated solid–liquid interfacial structure; the exact nature of weakly bound adsorbates on (111) surfaces cannot be directly identified using current experimental methods because of high surface mobilities and diffusion rates . To this end, theoretical modeling of solid–liquid interfaces has been extensively used. − Notable progress has been made, showcasing the inherent value of ab initio molecular dynamics (AIMD) and related methods in understanding experimental findings. − However, several pitfalls emerge depending on the choice of method, while extracting free energy profiles at the solid–liquid interface with explicit solvent remains a formidable task. Additionally, more open challenges remain, such as determining the extent to which the solvent environment and surface adsorbed hydrogen species influence the reactivity.…”

Unraveling the Activity and Selectivity of CO2 Electrochemical Reduction on Single Atom Catalyst by Potential Based Scaling Relationship

“…Interestingly, we found that the configuration of deprotonated H2O at final state is not as usual as previous report about metal catalyst. 67 Specifically, one hydrogen atom of H2O is pointed to the adsorbed hydrogen rather than the O atom of H2O from our observation (Figure 5a). This is owing to that the adsorbed H is actually negatively charged by -0.17 |e| and thus have strong affinity to hydrogen atom of H2O.…”

On the optimum binding energy for the hydrogen evolution reaction: How do experiments contribute?

“…18 This finding, however, contrasts with the most recent DFT studies for the HER over Pt(111), reporting that the active hydrogen species is bonded weakly when considering the aqueous electrolyte by means of implicit or explicit solvation approaches (ΔG H of about 200 to 400 meV). 19,20 The author ascribed these differences to a type II error. 21 The Sabatier principle in its thermodynamic form at zero overpotential purports thermoneutral bonding as the optimum situation for a twoelectron process.…”