Computational Study of H2O Adsorption, Hydrolysis, and Water Splitting on (ZnO)(3) Nanoclusters Deposited on Graphene and Graphene Oxides

Graphene and graphene oxide (GO)-based metal oxides couldplayan important role in using metal oxide like zinc oxide (ZnO) as photocatalyststo split water. The & pi; conjugation structure of GO shows greaterelectron mobility and could enhance the photocatalytic performance of the bare ZnOcatalyst by increasing the electron-hole separation. In this work,we use density functional theory (DFT) with the B3LYP exchange functionaland DGDZVP2 basis set to study the impact of adsorbing (ZnO)(3) nanoparticles on graphene and four different GO models (GO1, GO2,GO4, and GO5) on the hydration and hydrolysis of water that precedeswater splitting to produce H-2 and O-2 atoms inthe gas phase and compare them with our previous studies on the barecatalyst in the absence of the substrate. The potential energy curvesand activation energies are similar, but the triplet states are lowerin energy than the singlet states in contrast to the bare (ZnO)(3) catalyst. We extend our calculations to water splitting fromthe hydrolyzed (ZnO)(3) on GO1 (GO1-(ZnO)(3)). Thetriplet state energy remains lower than the singlet state energy,and hydrogen production precedes the formation of oxygen, but thereis no energy inter-crossing during the formation of O-2 thatoccurs in the absence of a GO1 substrate. Although the hydrolysisreaction pathway follows similar steps in both the bare and GO1-(ZnO)(3), water splitting with (ZnO)(3) absorbed on the GO1substrate skips two steps as it proceeds toward the production ofthe second H-2. The production of two hydrogen moleculesprecedes oxygen formation during water splitting, and the first Zn-Hbond formation step is the rate-determining step. The ZnO trimer depositedon GO systems could be potentially attractive nanocatalysts for watersplitting.

Automated summary

Graphene and graphene oxide (GO)-based metal oxides can enhance the photocatalytic performance of zinc oxide (ZnO) as a water-splitting photocatalyst. The adsorption of (ZnO) nanoparticles on GO promotes hydrogen production during water splitting, with hydrogen formation preceding oxygen formation. However, this phenomenon is not observed when (ZnO) nanoparticles are adsorbed on graphene.