Unraveling Water’s Behavior in Anisotropic Environments

The structure and reactivity of water in anisotropic environments, such as at interfaces, under external electric fields, or in extremely nano-confined conditions, can differ markedly from those in the bulk. Understanding these differences is crucial for gaining insight into atmospheric and electrochemical processes, as well as nano-fluidic devices, that are central to modern technologies and environmental processes.

In the first part of the talk, I will discuss how ions organize at the water/air interface and show that the conventional electric double-layer model fails to provide a complete microscopic picture of these interfaces [1,2]. Using first-principles simulations and surface-specific vibrational spectroscopy, I will show that the surface of common electrolyte solutions is stratified into two distinct water layers: one depleted of ions and the other enriched in ions.

In the second part of the talk, I will present our recent investigations of the water dissociation reaction (WDR) [3]. Using the modern theory of polarization, we perform periodic ab initio molecular dynamics simulations to study the WDR under external electric fields. Our simulations reveal that the WDR is enhanced under strong electric fields. However, this enhancement is primarily driven by entropic effects rather than the enthalpic contributions that are commonly assumed, providing important insights into recent kinetic measurements of the hydrogen evolution reaction (HER) across various electrochemical systems [4]. Finally, time permitting, I will discuss how nano-confinement and surface chemistry can be used to control the WDR [5]. Together, these studies identify key molecular mechanisms that can be exploited to control water reactivity in interfacial and nano-confined environments.