Quantifying Hydroxyl Adsorption on Copper with Electrochemical-Aware Random Phase Approximation

Accurate adsorption thermodynamics of reactive intermediates at electrified metal interfaces are central to predictive surface science, heterogeneous catalysis, and electrochemical modeling, yet remain challenging for standard density functional approximations and difficult to benchmark experimentally. Here we apply electrochemical-aware random phase approximation (RPA) methods that incorporate solvent dielectric screening and grand-canonical constant-potential control to establish a reference-quality description of hydroxyl (*OH) adsorption on Cu(100) in electrocatalytic conditions. At the potential of zero charge (pzc), we quantify the site dependence of *OH binding across terrace sites and representative defective motifs. Under applied potential, electrochemical-aware RPA reproduces the experimentally inferred *OH desorption fingerprint, predicting an *OH desorption potential of -0.54 V vs SHE, in excellent agreement with experimental value -0.56 V vs SHE at pH = 7, whereas widely used GGA functionals (PBE, RPBE) underestimate *OH stability and compress the stability window under reducing conditions. G₀W₀-RPA electronic structure analysis provides a mechanistic rationale for the discrepancy. Finally, we reassess the Cu(100) surface-state diagram with *OH and *CO coadsorption under electrochemical conditions, including the stability of metastable CuCO(OH)_n motifs, and show that many-body accuracy can qualitatively alter predicted interfacial speciation. Overall, our results establish electrochemical-aware RPA as a broadly applicable, systematically improvable many-body framework for quantitative adsorption thermodynamics at constant potential, enabling predictive surface-state maps for complex electrochemical interfaces.