Hydrogenation Dynamics of Electrically Controlled Metal–Insulator Transition in Proton-Gated Transparent and Flexible WO₃ Transistors

Electrolyte gating is widely adopted to electrically control the physical properties of materials, leading to numerous intriguing phenomena and various applications. However, the carrier modulation mechanism remains heavily controversial. Herein, using natural mica pieces as substrates and ionic gel as the dielectric layer, all-transparent and flexible WO₃ transistor configuration is designed to in situ monitor the dynamic doping process of electrolyte gating. A reversible and vacuum-dominant volatile/nonvolatile metal–insulator transition (MIT) is observed in electrolyte-gated WO₃ thin films. In situ X-ray diffraction experiments, together with first-principles calculations, reveal an abrupt and symmetric structural evolution through two distinct hydrogenated metastable phases and phase separation progress. The fast volatility is assigned to a spontaneous dehydrogenation process. A prototype of a flexible vacuum meter is demonstrated on the basis of the unique vacuum-dependent MIT, exhibiting a measurement range down to 1.0 × 10⁻⁶ mbar and no injury of electromagnetic radiation. These findings bring new insights into hydrogenation dynamics, paving a feasible way for the realization of user-friendly flexible electronics.