Reversible Hydrogen Electrode (RHE) Scale Dependent Surface Pourbaix Diagram at Different pH

Area of Science:

• Electrocatalysis
• Surface Science
• Computational Chemistry

Background:

• Surface coverage is critical for electrocatalysis mechanisms and catalyst design.
• Surface Pourbaix diagrams predict adsorbate coverage from water activation but can be inconsistent with experimental data at the reversible hydrogen electrode (RHE) scale, especially in alkaline conditions.
• Existing models do not fully account for pH-dependent surface energetics at the RHE scale.

Purpose of the Study:

• To develop a pH-dependent surface Pourbaix diagram applicable at the RHE scale.
• To improve the accuracy of theoretical predictions for electrocatalyst surface coverage.
• To provide a refined methodology for analyzing surface coverage in electrocatalysis.

Main Methods:

• Density functional theory (DFT) calculations with Bayesian Error Estimation Functional with van der Waals corrections (BEEF-vdW) were used to compute energetics.
• Incorporation of electric field effects, adsorption-induced dipole moment, polarizability, and potential of zero charge.
• Derivation of a pH-dependent surface Pourbaix diagram at the RHE scale, validated using Pt(111).

Main Results:

• The proposed RHE-dependent surface Pourbaix diagram significantly reduces the discrepancy between theoretical predictions and experimental surface coverage.
• The improved model shows particular accuracy under neutral-alkaline and moderate-potential conditions.
• The methodology provides a more precise analysis of surface coverage for electrocatalyst evaluation.

Conclusions:

• The developed pH-dependent surface Pourbaix diagram offers a more accurate theoretical framework for understanding electrocatalysis.
• This work establishes guidelines for precise surface coverage analysis, enhancing electrocatalyst design and activity evaluation.
• The findings are crucial for advancing the field of electrocatalysis, particularly for applications in neutral to alkaline environments.