Abstract of Charitha Perera’s talk April 9 2021, Saint Anselm College
A Density Functional Study of Water Splitting Reaction Pathway on ZnO Nanoclusters
Duwage C. Perera
Department of Chemistry, University of Maine, Orono, ME 04469
Due to the rapid depletion of fossil fuel, the world is turning towards searching for new sources of renewable energies. Hydrogen is a promising green fuel of the future with zero carbon emission when burnt with oxygen. Numerous studies have been developed to produce hydrogen by splitting water after Fujishima and Honda first showed photocatalytic water splitting in the presence of a TiO2 catalyst in 1972. H2 evolution is 1.9 times efficient than with pure TiO2, when it is absorbed on a graphene oxide (GO) sheet, because TiO2 can form a p-n heterojunction with GO for visible light absorption. Zinc Oxide (ZnO) also can form a p-n heterojunction with GO which functions as a semiconductor with a wide band gap (3.4 eV) that could be used as a substitute catalyst instead of TiO2. But its efficiency for water splitting is unknown. The goal of this work is to understand the reaction pathway of ZnO and GO in the water splitting reaction using density functional theory (DFT) and optimize the efficiency of the catalyst.
After studying (ZnO)n nanoclusters where the size varies from n=1-6, the (ZnO)3 nano cluster was chosen for specific study based on the singlet-triplet energy difference, 57.8 kcal/mol at B3LYP/DGDZVP2 level of theory (Energy of a visible photon at ̴555 nm is 52 kcal/mol). We have divided this study into two major parts: the reaction (a) on the individual (ZnO)3 cluster and (b) on the GO-ZnO surface using Gaussian 16. The production of H2 and O2 occurs after forming a Zn-H bond generated from the hydrolyzed product of ZnO with two H2O molecules. I will discuss results for the transition state of the reaction using the Synchronous Transit-Guided Quasi-Newton (STQN) method following calculations of the Intrinsic Reaction Coordinate (IRC). In part (b) we study the hydrogen production on GO-ZnO surfaces corresponding to five different GO models obtained by changing the positions of hydroxyl, epoxy, and carboxylic functional groups on a graphene sheet.
- Fujishima, A.; Honda, K. Electrochemical Photolysis of water at a Semiconductor Electrode. Nature 1972,238, 37-38
- Fang, Z.; Dixon, D. Computational study of H2 and O2 production from water splitting by small (MO2)n Clusters (M=Ti,Zr,Hf). J.Phys.Chem.A 2013,117,3539-3555