Residual hydrogen-induced irreversibility in insulator-metal transition of VO₂ film

Vanadium dioxide (VO₂) is a strongly correlated oxide that undergoes an insulator–metal transition (IMT) near 68 °C, driven by strong electron-lattice coupling. Hydrogen incorporation offers a promising way to tune this transition, enabling low-temperature hydrogen storage. However, the fundamental reversibility and the structural stability of hydrogenation-dehydrogenation processes remain unclear. In this study, we investigate the evolution of electrical, structural, and electronic properties of VO₂ films during hydrogenation and dehydrogenation processes using in-situ analysis techniques and synchrotron-based X-ray spectroscopy. Our results reveal that electrical resistivity and the crystal structure do not fully recover after dehydrogenation due to the presence of residual hydrogen ions in the VO₂ film. These residual hydrogen ions donate electrons to the d_∥* states, suppressing the intrinsic IMT behavior. Furthermore, Raman spectroscopy reveals that hydrogen incorporation expands the V–V dimer and unexpectedly enhances the uniformity of their zigzag distortion. Our findings offer critical insights into designing more reliable hydrogen-modulated correlated oxides and highlight the need for strategies to control residual hydrogen for practical energy applications.