Water Structure, Dynamics, and Sum-Frequency Generation Spectra at Electrified Graphene Interfaces.

The properties of water at an electrified graphene electrode are studied via classical molecular dynamics simulations with a constant potential approach. We show that the value of the applied electrode potential has dramatic effects on the structure and dynamics of interfacial water molecules. While a positive potential slows down the reorientational and translational dynamics of water, an increasing negative potential first accelerates the interfacial water dynamics before a deceleration at very large magnitude potential values. Further, our spectroscopic calculations indicate that the water rearrangements induced by electrified interfaces can be probed experimentally. In particular, the calculated water vibrational sum-frequency generation (SFG) spectra show that SFG specifically reports on the first two water layers at 0 V but that at larger magnitude applied potentials the resulting static field induces long-range contributions to the spectrum. Electrified graphene interfaces provide promising paradigm systems for comprehending both short- and long-range neighboring aqueous system impacts.