Intrinsic Origin of Anomalous Double-Layer Capacitance on Pt(111) Revealed by Grand Canonical Density Functional Theory

Abstract

Interfacial solvent structure is a key determinant of electrocatalytic kinetics, yet the anomalous capacitance of Pt(111) remains a subject of ongoing debate. Using grand-canonical density functional theory and an ab initio molecular dynamics-informed hybrid solvation model, we demonstrate that the capacitance minimum at negative potentials is an intrinsic property. The calculations show that negative bias stabilises a hydrogen-down configuration of interfacial water, which slightly increases the Pt-water separation and strengthens hydrogen-bond ordering to suppress the dielectric response. This work provides a molecular-level baseline for the Pt(111) interface, offering a rigorous framework for predicting how the electrochemical environment influences electrocatalytic pathways.