Coulombic Surface-Ion Interactions Induce Nonlinear and Chemistry-Specific Charging Kinetics

TL;DR

This paper develops a theoretical model for solid-liquid interface charging kinetics, revealing how Coulombic interactions influence reaction mechanisms, ion valency, and distinguish reaction types through relaxation dynamics.

Contribution

It introduces a nonlinear differential equation combining Langmuir kinetics and Poisson-Boltzmann theory to analyze surface charging behavior.

Findings

Distinguishes late-time and short-time relaxation rates based on ion valency.

Identifies inflection points as signatures of two-ion reactions and autocatalytic processes.

Reveals Coulombic interactions as an autocatalytic feedback mechanism.

Abstract

While important for many industrial applications, chemical reactions responsible for charging of solids in water are often poorly understood. We theoretically investigate the charging kinetics of solid-liquid interfaces, and find that the time-dependent equilibration of surface charge contains key information not only on the reaction mechanism, but also on the valency of the reacting ions. We construct a non-linear differential equation describing surface charging by combining chemical Langmuir kinetics and electrostatic Poisson-Boltzmann theory. Our results reveal a clear distinction between late-time (near-equilibrium) and short-time (far-from-equilibrium) relaxation rates, the ratio of which contains information on the charge valency and ad- or desorption mechanism of the charging process. Similarly, we find that single-ion reactions can be distinguished from two-ion reactions as the latter show an inflection point during equilibration. Interestingly, such inflection points are characteristic of autocatalytic reactions, and we conclude that the Coulombic ion-surface interaction is an autocatalytic feedback mechanism.