The nanoscale structure of the Pt-water double layer under bias revealed

Abstract Atomistic mass and charge distribution at electrified interfaces play a key role in electrochemical phenomena of huge technological relevance for energy production and conversion. However, in spite of its importance, the structure of the double layer at the nanoscale is still to a large extent unknown, even for Pt-water, the most fundamental electrochemical interface. Using a new, general ab initio methodology to model charged electrodes, we simulate the atomistic structure of the Pt-water double layer and its response to an applied potential, in realistic solution conditions. We evaluate the interface capacitance and the absolute electrode potential for three states of charge of the electrode. We reveal that electrode polarisation induces interfacial electronic charge spillover and oscillation, and changes the surface coverage of the first adsorbed water layer. Since the molecules in this layer are all found to be equally charged, the interface dipole is strongly affected by such change of coverage, while water reorientation becomes relevant only from the second water layer. Our findings will be essential to develop highly realistic models for catalytic processes at the Pt-water interface.