Mind the coverage gap: The crucial importance of the pH- and potential-dependent surface coverage in oxygen reduction electrocatalysis
Year: 2026
Type: preprint
Abstract: Understanding the origins of oxygen reduction reaction (ORR) activity and selectivity on gold electrodes remains a longstanding puzzle in electrocatalysis. In particular, it remains unclear why Au(100) in alkaline media is exceptionally active and selective toward the 4-electron ORR while acidic conditions and other gold surfaces catalyze exclusively 2-electron ORR. We address this question through extensive grand-canonical density functional theory calculations and investigate the pH- and potential-dependent surface coverage and its effect on ORR thermodynamics and kinetics on Au(111) and Au(100) electrodes. Our results reveal that ORR thermodynamics and kinetics are highly sensitive to pH- and potential-dependent surface coverage, an effect largely neglected in previous computational studies. The key steps governing ORR activity and selectivity – O 2 adsorption and O–O bond cleavage – are influenced even more strongly by surface coverage than by electrode potential. By integrating pH- and potential-dependent surface coverages with elementary reaction thermodynamics and kinetics, we propose a mechanism that consistently explains a broad range of voltammetric observations on ORR activity and selectivity trends on Au(100) and Au(111) across reaction conditions; neglecting coverage effects leads to qualitatively incorrect mechanistic predictions. Our findings demonstrate that ORR electrocatalysis on gold is not governed only by the intrinsic properties of pristine surfaces. Instead, ORR thermodynamics, kinetics, mechanisms, activity, and selectivity depend explicitly on the interplay between pH, electrode potential, surface coverage, and adsorbate–adsorbate interactions which together define the local reaction environment. More broadly, our work establishes the central importance of pH- and potential-dependent surface coverage in (computational) electrocatalysis.
Source: ChemRxiv
Authors: Kayvan Moradi, Marko M. Melander
Language: English
Field: Energy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7214089343