Microscopic evidence for the dissociation of water molecules on cleaved GaN(11̄00)

Abstract

The dissociation of water molecules absorbed on a cleaved non-polar GaN(11[combining macron]00) surface was studied primarily with synchrotron-based photoemission spectra and density-functional-theory calculations. The adsorbed water molecules are spontaneously dissociated into hydrogen atoms and hydroxyl groups at either 300 or 130 K, which implies a negligible activation energy (<11 meV) for the dissociation. The produced H and OH were bound to the surface nitrogen and gallium on GaN(11[combining macron]00) respectively. These results highlight the promising applications of the non-polar GaN(11[combining macron]00) surface in water dissociation and hydrogen generation.

Investigation into water-induced surface oxidization of GaN lamella structure

“…In addition, no appreciable differences in the Ga2p and Ga3d peak positions were detected between the pristine-GaN and oxidized-GaN samples (figure S2). It has been reported, theoretically and experimentally, that the adsorbed H 2 O molecules at room temperature dissociate to OH − and H + , which easily binds to Ga and N, respectively [31,33,34,38]. A similar bonding effect was observed from other III-V semiconductors, for example GaP, after exposure to H 2 O [6].…”

“…Thus, it is strongly believed that the change in resistance could result from the dissociative adsorption of H 2 O on the GaN surface which has been reported experimentally to have a sticking coefficient of ⩾0.45 and a saturation coverage of 0.46 ML [32,54]. In addition, upon adsorption of H 2 O molecules at room temperature, it was also found that H 2 O molecules were dissociated spontaneously resulting in the formation of Ga-OH and N-H bonds at the surface [33]. The dissociative adsorption of H 2 O molecules on the GaN surface resulted in a decreased surface band bending due to the removal of the dangling bonds, thereby influencing the electrical properties [31].…”

“…When the GaN surface is exposed to H 2 O, the measured electrical resistivity increases continuously with time at room temperature, which might be attributed to the electrochemical reaction at the surface of GaN. The formation of Ga-OH at room temperature has been reported, theoretically and experimentally, to be observed at the H 2 O/GaN interface [31,33,38]. We performed DFT simulations with a nudged elastic band (NEB) method [41] to study the reaction path and energy barrier of water dissociation on pristine and oxidized GaN surfaces.…”

“…Degradation of the electrodes can alter the WS efficiency which is generally related to surface corrosion of the GaN photoanode. In recent years, the H 2 O/GaN interfacial properties have been studied both experimentally [31][32][33] and theoretically [34][35][36]. A few theoretical studies have explored the adsorption of H 2 O molecules on the polar and nonpolar GaN surfaces using firstprinciples density functional theory (DFT) [36][37][38][39].…”

Physisorbed State Regulates the Dissociation Mechanism of H2O on Ni(100)

“…Water dissociation on low index metal surfaces has been considered as a prototype to understand the interactions and dynamics of gas-surface reactions, and so far, numerous efforts have been made. − Available data showed that the catalytic activity varied with metals and was highly structure sensitive. At the level of density functional theory, Wang and Wang predicted that the activation energies of H 2 O decreased in the order Au(111) > Ag(111) > Pt(111) > Pd(111) > Cu(111) > Ir (111) > Rh(111) > Co(0001) > Ni(111) > Ru(0001).…”