Removal of Water Adsorbates on GaN Surfaces via Hopping Processes and with the Aid of a Pt4 Cluster: An Ab Initio Study

Abstract

In one of our previous works (Du, Y. A.; Chen, Y.-W.; Kuo, J.-K. Phys. Chem. Chem. Phys. 2013, 15, 19807–19818), it had been found that nonpolar and polar facets of gallium nitride (GaN) nanoparticles may play different roles in water splitting processes because of their different redox characters for O2 and H2 evolution. The mechanism of removing other water adsorbates on different facets was left undetermined. In this work, we investigate the hopping processes of water adsorbates on GaN (101̅0) nonpolar and (0001) polar surfaces and also the effect of a Pt4 cluster on nonpolar surface for water splitting. The hopping of O adatoms from polar to nonpolar surface is found to be feasible at room temperature and hence can facilitate the O2 evolution. However, the mobility of H adatoms from nonpolar to polar surface is relatively limited for higher barriers. On the other hand, the Pt4 cluster offers mediate states to facilitate water splitting and H2 evolution on GaN nonpolar surface. The features of Pt4 projected density of states show suitable properties of being a cocatalyst for H2 evolution but also a shortcoming as an electron–hole recombination center.