Potential Dependence of Nitrate Adsorption and Dissociation across Metals and Dilute Alloys: a Grand Canonical Study

Aqueous nitrate (NO ⁻ ₃ ) can be electrocatalytically reduced to value-added or benign products. However, the impact of the electrochemical potential on key reaction steps remains poorly understood. Using explicit and analytical grand-canonical density functional theory (eGC-DFT and aGC-DFT), we investigate the potential dependence of nitrate adsorption and dissociation on pure metals and Cu-based single-atom alloys (SAAs). With aGC-DFT, we find electrosorption valencies for NO ⁻ ₃ adsorption on stable/metastable SAAs (stability evaluated with eGC-DFT) and pure metals range between −0.60 eV/V to −0.80 eV/V. These values correlate with the extent of the computed partial charge transfer to the surface, which trends with the fractional d-band filling of the metal. NO* ₃ dissociation exhibits weak potential dependence, with symmetry factors between −0.04 eV/V and −0.20 eV/V. For Ni ₁ Cu, an experimentally studied SAA for nitrate reduction, aGC-DFT predicts potential-dependent adsorption and activation energies that can differ significantly from conventional approximations, such as the computational hydrogen electrode model. However, we demonstrate that aGC-DFT computed energies and hence these differences vary drastically with the assumed double-layer properties. Overall, this work clarifies potential dependent nitrate adsorption and dissociation trends across SAAs and pure metals, emphasizing the need to account for electrochemical conditions in mechanistic studies of nitrate reduction.