A computational study on the Pd-decorated ZnO nanocluster for H2 gas sensing: A comparison with experimental results

Abstract

Recently, an experimental work has shown that the Pd-decoration implicitly increases the ZnO nanostructure sensitivity toward H 2 gas. In this work, density functional theory calculations are used to explain the origin of this phenomenon. It was found that the Pd metal on a ZnO nanocluster (ZnONC) catalyzes the dissociation of O 2 gas by a π-backdonation process, facilitating the O ion formation. Then the H 2 gas reacts with the pre-chemisorbed O ions on the Pd–ZnONC and generates H 2 O molecules, releasing some of the trapped electrons (by the O anions) back into the cluster. This process needs to overcome an energy barrier of 1.3 kcal/mol, which is close to the experimental value of 0.88 kcal/mol. The generated H 2 O molecules weakly adsorb on the surface of the Pd–ZnONC with adsorption energy of −14.7 kcal/mol per molecule. The calculated recovery time of the H 2 O molecules from the Pd–ZnONC surface is 0.7 ms. After the H 2 adsorption and H 2 O production, the HOMO-LUMO gap of Pd–ZnONC somewhat backs toward its initial value because of an electron back-donation, increasing the resistivity. By Pd-decoration the sensor response increases from 0.11 to 123.53, in agreement with the experiment. • Pd metal catalyzes O 2 dissociation on the ZnO nanocluster (ZnONC). • H 2 reacts with the O ions on the Pd–ZnONC and generates H 2 O gas. • This process needs to overcome an energy barrier of 1.3 kcal/mol. • The recovery time of the H 2 O molecules from the Pd–ZnONC surface is 0.7 ms. • By Pd-decoration the sensor response increases from 0.11 to 123.53.