Gaseous Reactions in Adsorbed Water Present on Transition Metal Oxides

Water from ambient atmosphere is known to adsorb naturally on the surfaces of many transition metal oxides, and this adsorbed water is known to affect electrical, optical, and many functional properties such as catalytic activities. However, the nature of this underlying interaction remains unknown. In this work, we report a new type of semiconductor-adsorbed water interaction in metal oxides that is known as “electrochemical surface transfer doping”, a phenomenon that has previously been observed in hydrogen-terminated diamond. Herein, the adsorbed water on the metal oxide allows dissolution of gaseous species and induces charge transfer processes at the oxide/adsorbed-water interface. We further elucidate, using in situ infrared photoluminescence, electrical resistance, and X-ray photoelectron spectroscopy, the role of vacancy defects in the catalytic process by directly monitoring the charge transfer process between gaseous species and vacancies in defective metal oxides such as p-type nickel oxide and...