H2 sensing mechanism under different oxygen concentration on the hexagonal WO3 (001) surface: A density functional theory study

Abstract

Metal oxides based gas sensors play important role in the detection of dangerous gases. In this work, density functional theory (DFT) has been used to investigate the H2 sensing mechanism on hexagonal WO3 (001) surface. We found that oxygen concentration in the ambient atmosphere, which can be reflected directly by surface oxygen density (denoted as dO), affects the H2 sensing mechanism on WO3 surface greatly. According to oxygen concentration varying from high to low, four surfaces including O-terminated surface, and oxygen pre-adsorbed, clean and oxygen vacancy presented WO-terminated surfaces are considered. At O-terminated surface (dO=1), H2 interacts with the surface onefold coordinated oxygen (O1c) forming H2O with charge transfer of 0.635 e from molecule to surface. At oxygen pre-adsorbed WO-terminated surface (1>dO>0), H2 adsorbs on pre-adsorbed O1c and neighboring O2c forming H2O and hydroxyl with charge transfer of 0.621 e and 0.488 e, respectively. On WO-terminated surface (dO=0) and oxygen vacancy surface (0>dO>−1), H2 exhibits relatively weak adsorption with small adsorption energy and little charge transfer. An oxygen concentration dependent behavior is confirmed for H2 sensing on h-WO3 (001) surface. And the results on the reducing gas H2 here obey the new proposed oxygen density dominated gas sensing mechanism in the CO sensing study well.