Dynamic Hydration Shell Evolution and Charge Transfer Synergy in Hydrated Ti⁰/Ti³⁺ Oxidation

The solvation state of cations during charge transfer in electrolytes represents a fundamental challenge in hydrochemistry, aqueous batteries, electrocatalysis, electrolytic hydrogen production, and anodic corrosion processes, involving intricate coupling between electronic excitation and solvation dynamics. Although substantial experimental progress has been made, the charge transfer behavior and comprehensive kinetics of metal cations remain elusive. Here, titanium is selected as a model system due to its stable intermediate-valence Ti³⁺ species with well-defined ion pairs and solvation structures. By integrating ab initio molecular dynamics (AIMD) and synchrotron radiation techniques, we visualize the excited-electron transfer process from Ti⁰/Ti³⁺ to solvent molecules, resolving the coupled dynamics of structural evolution, electronic behavior, and solvation reorganization. The radial distribution functions and coordination numbers derived from simulations show excellent agreement with experimental observations, validating the charge-transfer-to-solvent (CTTS) states. The Ti³⁺ intermediate exhibits stronger ion-dipole interactions, a denser and more symmetric first hydration shell, and a robust hydrogen-bond network that enhances interfacial stability. In contrast, the ground-state Ti⁰ displays weaker electrostatic interactions and transient hydrogen-bond disruption following excitation. The charge transfer process in both Ti⁰ and Ti³⁺ hydration states proceeds through a three-stage ultrafast dynamical evolution over a femtosecond time scale, consisting of excitation, structural reorganization, and hydrogen-bond-network-mediated charge transfer, critically dependent on the spatial coordination between the titanium center and the excited electron.