Entropy governs the structure and reactivity of water dissociation under electric fields

TL;DR

This study uses ab initio molecular dynamics to show that electric fields significantly increase water dissociation rates, transforming the process from entropy-hindered to entropy-driven, with implications for electro-catalyst design.

Contribution

It provides new insights into how electric fields influence water dissociation thermodynamics and solvent structure, revealing a shift to entropy-driven reactions under strong fields.

Findings

Electric fields dramatically increase water dissociation equilibrium constant.

Strong electric fields transform the reaction from entropy-hindered to entropy-driven.

Electric fields alter ion structuring, affecting solvent reactivity.

Abstract

The response of water to electric fields is critical to the performance and stability of electrochemical devices, and the selectivity of enzymatic, atmospheric, and organic reactions. A key process in this context is the water (auto)dissociation reaction (WD), which governs acid-base aqueous chemistry and shapes reaction rates and mechanisms. Despite its significance, the thermodynamics of the WD reaction in electrified environments remains poorly understood. Here, we investigate the WD reaction under external electric fields using ab initio molecular dynamics simulations within the framework of the modern theory of polarization. Our results reveal that strong electric fields dramatically enhance the WD reaction, increasing the equilibrium constant by several orders of magnitude. Moreover, we show that the applied field transforms the WD reaction from an entropically hindered process to an entropy-driven one. Analysis shows that this is because the electric field alters the tendency of ions to be structure makers or structure breakers. By highlighting how strong electric fields reshape solvent organization and reactivity, this work opens new avenues for designing aqueous electro-catalysts that leverage solvent entropy to enhance their performance.