Potential dependent friction: Role of interfacial hydrated molecules

Abstract

The behavior of water molecules at the electrode/aqueous interfaces plays a fundamental role in tribological properties under the regulation of electric potentials. Reversible potential-modulated friction on the gold electrodes is demonstrated by utilizing electrochemical atomic force microscopy (EC-AFM). Applying positive potentials results in an increase in friction compared to that observed under the negative potentials. The stronger intensity of the water signals is detected by the sum-frequency generation (SFG) spectroscopy when the positive potential is applied on the gold surface, mainly ascribed to the absorption of hydrated anion molecules, therefore resulting in weak hydration effects. The electrochemical SFG spectra provide direct experimental evidence to elucidate the underlying mechanisms of potential-dependent friction, which might be related to the arrangement of hydrated cation or anion molecules and surface interactions. This work provides more insights into the molecular-level understanding of tribological behavior on the charged surfaces.