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.

Hydrogen reduction of molybdenum oxide at room temperature

“…Figure 4 shows the evolution of the Mo 5d states during hydrogenation at 100 mbar. The shape and positions of the peaks change drastically indicating the change of the oxidation state of Mo from Mo 6+ to Mo4 2023323335.…”

“…An important factor in these applications, which was addressed here for the MoO 3 system, is the transient nature of the various states of matter during hydrogen exposure. The time constant in hydrogen W/Mo bronzes is relatively long; however, there are indications of short-lived, but highly mobile and reactive hydrogen states in various other meta-stable systems4, to be studied using the membrane approach.…”

“…Hydroxides do exist, but tend to decompose into the corresponding oxides as well3. However, due to the small atomic diameter and the ambivalent character of hydrogen, hydrogen can intercalate into oxides and act as a donor or acceptor of electrons456, being the origin of various optical and electronic effects with many applications.…”

Experimental and Theoretical Study of Electronic and Hyperfine Properties of Hydrogenated Anatase (TiO2): Defect Interplay and Thermal Stability

“…As V o undergo changes at low temperatures (at 360 K), we focus our understanding on point 2) hydrogen bonds -OH. On the grounds of a few experimental studies on metal oxides, the hydrogen impurities are expected to be in several forms 56,57 . By and large, it is energetically favorable for hydrogen to occupy two states in bulk with different mobilities (i.e.…”

“…Hence, a thorough understanding of defects interaction plays a key role. In this study we report on the results from emission 57 Fe Mössbauer Spectroscopy experiments, using dilute 57 Mn implantation into pristine (TiO2) and hydrogenated anatase held at temperatures between 300-700 K. Results of the electronic structure and local environment are complemented with ab-initio calculations. Upon implantation both Fe 2+ and Fe 3+ are observed in pristine anatase, where the latter demonstrates the spin-lattice relaxation.…”