Role of Water Solvation on the Key Intermediates Catalyzing Oxygen Evolution on RuO₂

Abstract

RuO2 and IrO2 are among the most active catalysts for the Oxygen Evolution Reaction (OER). Recently, it was demonstrated that the catalytic surface of these oxides plays a role in the reaction, where a hydrogen bond with a neighbor OH group stabilizes an unconventional −OO intermediate (−OO–H), prior to O2 evolution. Quantum chemical calculations neglecting solvation effects indicated that this intermediate is more stable than the conventional −OOH, and that deprotonation of the stabilizing −OH is the rate limiting step for OER on RuO2(110) and RuO2(100). In this work, we investigate the role of water molecules on the relative stability of −OOH and −OO–H oxygenates on RuO2 (110) by means of density functional theory calculations combined with ab initio Molecular Dynamics simulations (AIMD). We show that the two intermediates participate in a hydrogen bonding network with water to a similar extent, but leading to different interfacial water structures, with possible implications on interfacial proton dynamics and reaction kinetics. Moreover, −OOH can spontaneously convert to −OO–H through a process mediated by water, demonstrating the critical role of explicitly including water in the model. This study provides further mechanistic insights on the role of the oxide surface chemistry in the OER mechanism and highlights the importance of explicitly treating the catalyst/water interfaces including dynamical aspects to assess the stability and the interconversion mechanism of key surface species, since the adoption of static solvation approaches tends to overestimate the energetic difference between −OOH and −OO–H reaction intermediates.

CO2 electroreduction on single atom catalysts: the role of the DFT functional

“…Other approaches should be adopted in order to properly describe the catalyst/water interface including bulk water and explicit solvation spheres. 82,97–101…”

“…It should be mentioned, however, that if one aims at reproducing the experimental complexity, this effect should be accounted for, together with many other effects such as solvation, applied voltage and pH. 81–85 Further details and working equations are reported in the ESI †…”

Predicting the Stability of Single-Atom Catalysts in Electrochemical Reactions

“…Although the PBE functional adopted so far is sufficiently reliable to obtain general trends, systematic improvements can be obtained by adopting higher levels of functionals such as the hybrid functionals. , In a similar way, while some general tendencies can be obtained by using models of SACs without including the solvent, it is clear that this plays a direct role in electrochemical reactions. Even the model can be improved and including solvation is the first step to obtain more quantitative predictions. − Of course, both method and model can be further improved at any desired level, but here we restrict these two aspects to show their impact on the prediction of the thermodynamic stability of SACs under working conditions.…”

Modeling Single‐Atom Catalysis

“…This implies the use of ab initio molecular dynamics (AIMD) simulations. [110][111][112][113] In a recent study the OER has been considered on the surface of a RuO 2 catalyst. Here a hydrogen bond with a surface OH group stabilizes an unconventional ─OO intermediate (─OO─H), besides the classical ─OOH one, before O 2 evolution takes place.…”