title: Highly mobile and reactive state of hydrogen in metal oxide semiconductors at room temperature.
abstract: Hydrogen in metal oxides usually strongly associates with a neighboring oxygen ion through an O-H bond and thus displays a high stability. Here we report a novel state of hydrogen with unusually high mobility and reactivity in metal oxides at room temperature. We show that freshly doped hydrogen in Nb₂O₅ and WO₃ polycrystals via electrochemical hydrogenation can reduce Cu²⁺ ions into Cu⁰ if the polycrystals are immersed in a CuSO₄ solution, while this would not happen if the hydrogenated polycrystals have been placed in air for several hours before the immersion. Time-dependent studies of electrochemically hydrogenated rutile single crystals reveal two distinct states of hydrogen: one as protons covalently bonded to oxygen ions, while the other one is highly unstable with a lifetime of just a few hours. Observation of this mobile and reactive state of hydrogen will provide new insight into numerous moderate and low temperature interactions between metal oxides and hydrogen.
authors.affiliation: Key Laboratory of Artificial Micro- and Nano-structures of Ministry of Education and School of Physics and Technology, Wuhan University, Wuhan 430072, China.
authors.forename: Wan Ping
authors.initials: WP
authors.lastname: Chen
authors.forename: Ke Feng
authors.initials: KF
authors.lastname: He
authors.forename: Yu
authors.initials: Y
authors.lastname: Wang
authors.forename: Helen Lai Wah
authors.initials: HL
authors.lastname: Chan
authors.forename: Zijie
authors.initials: Z
authors.lastname: Yan