Atomic-Scale Analysis of the RuO₂/Water Interface under Electrochemical Conditions

Abstract

The structure of the interface between ruthenium oxide and water was examined using density functional theory calculations for a range of pH and electrode potential values, and the results were summarized in a surface Pourbaix diagram. The results indicate that pH affects the interfacial structure as a consequence of the formation of a stable hydrogen network and the impact of the electric field on the interfacial Gibbs energy. Focusing on the potential region of the oxygen evolution reaction (1.23 V vs a reversible hydrogen electrode (RHE) + overpotential), variations in pH were found to change both the formal Ru valency and the structure of the primary water layer by altering the work function of the interfacial structure. We hypothesize that the effects of pH on the hydrogen bond network and formal valency observed in this work also apply to other transition-metal oxides.

Controlling Stability and Selectivity in the Competing Chlorine and Oxygen Evolution Reaction over Transition Metal Oxide Electrodes

“…Several ab initio studies based on density functional theory (DFT) were devoted to investigate the surface structure of RuO 2 (110) as function of the applied electrode potential [16][17][18][19][20][21][22][23][24] by using the formalism of the computational hydrogen electrode (CHE) approach, as introduced by Nørskov and co-workers. [30] Under CER conditions, i. e., at U > 1.36 V vs., the RuO 2 (110) surface is completely oxygen terminated: all one-fold coordinatively unsaturated Ru surface atoms (Ru cus ) are capped by ontop oxygen (O ot ) and the neighboring Ru 2f atoms are bridged by undercoordinated surface oxygen (O br ).…”

“…[10] While in the corresponding surface stability diagrams in heterogeneous catalysis [58,59] or in battery research [60,61] surface energies, γ, are used in order to comprehend on the stability range of the respective electrode material, Pourbaix diagrams are commonly constructed based on free energies, ΔG, rather than on surface energies, γ. [10,17,18,21,24,28,[54][55][56][57] This finding triggers to expand the Pourbaix approach by adopting the concept of surface energies from the neighboring research communities: [57] the electrode material is unstable, if in a certain (U, pH) range the surface energy γ(U, pH) of a surface phase falls below zero. It shall be noted that this criterion strongly depends on the chosen reference states when calculating surface energies.…”

“…[2,14] The (110) facet as most stable surface termination of the active component RuO 2 is envisioned as an appropriate model system for the investigation of the competing CER and OER on a molecular scale. [15] In the last decade, computational researchers gained in-depth insights into the energetics of adsorbates on the RuO 2 (110) surface under CER/OER conditions [16][17][18][19][20][21][22][23][24] and resolved the reaction mechanism of both mechanistic pathways. [25,26] The concrete knowledge of the kinetics enables a detailed discussion of the pressing selectivity issue for the competing CER and OER.…”

Recent Advancements Towards Closing the Gap between Electrocatalysis and Battery Science Communities: The Computational Lithium Electrode and Activity–Stability Volcano Plots

“…The crudest assumption is that the effect of the surrounding aqueouse lectrolyte solution on the energy change can be neglected, which is often used for materials screening to speed up first-principles calculations. [46][47][48][49][50] Similarly to the proceedings in heterogeneous catalysis, the largestp ossible set of potentiala dsorbate structures on the RuO 2 (110) surface, relatingt ot he availablei ons (H + ,C l À )a nd water molecules in the electrolyte solution, needs to be calculated by meanso fD FT within af ixed unit cell dimension. [9,40] For ad escription of the solvent within firstprinciples calculations, different approaches are available, such as the application of explicit water molecules on top of the investigated surfaces lab [34,41] or additional cluster calculations, [42,43] in which the solvent is included implicitly by its dielectric constant and the probe radius, according to the selfconsistentr eaction field (SCRF) approach.…”

“…[44,45] Recent advancements in the description of the two-phase boundary between the solid-state electrode and the aqueous electrolyte solution can be traced to the investigations of Rossmeisl and co-workers, including the application of ab initio molecular dynamics ChemSusChem 2019ChemSusChem , 12,2330ChemSusChem -2344 www.chemsuschem.org (MD) simulations for ap ropers ampling of solvent configurations. [46][47][48][49][50] Similarly to the proceedings in heterogeneous catalysis, the largestp ossible set of potentiala dsorbate structures on the RuO 2 (110) surface, relatingt ot he availablei ons (H + ,C l À )a nd water molecules in the electrolyte solution, needs to be calculated by meanso fD FT within af ixed unit cell dimension. The CHE concept allows the free energy DG j 0 for the formation of ap otential surface structure jt ob et ranslated to any arbitrary electrode potential, U,orpHvalue based on the corresponding stoichiometric coefficients n(e À )and n(H + )inthe underlying reaction equation of the respective adsorption process [Eq.…”