Prerequisite of Oxygen Local Environment for Facile Proton Intercalation into Transition-Metal Oxides

Hydrogen is an abundant element poised to play a central role in future energy systems. When a lightweight hydrogen ion (proton, H⁺) is used as a charge carrier in Faradaic storage, it enables rapid solid-state conduction, offering strong potential for high-capacity, fast-charging electrochemical energy storage. However, the development of proton-based systems has been limited by the scarcity of suitable proton-host materials. In this study, we investigate the mechanisms of proton (de)intercalation in transition metal oxides using VO₂ polymorphs as a model system, with a focus on the role of lattice oxygen environments. Our findings reveal that protons preferentially occupy less-coordinated oxygen sites, which are energetically and structurally favorable. In addition, the presence of continuous H···O hydrogen-bonding networks facilitates solid-state proton transport via a Grotthuss-like mechanism. These insights provide a foundation for identifying and designing new proton-host materials, offering a promising strategy and design principle for advancing high-rate, high-capacity energy storage systems.