Intermetallic Differences at CdS-Metal (Ni, Pd, Pt, and Au) Interfaces: From Single-Atom to Subnanometer Metal Clusters

Metal co-catalysts tipped at a photocatalyst surface form a crucial component in the nanoheterostructures designed for the photocatalytic hydrogen evolution reaction. To examine the intermetallic differences and size effects at these interfaces, we use spin-polarized density functional theory to study single-atom, 13-atom, and 55-atom cluster depositions of Ni, Pd, Pt, and Au on the CdS(1010) surface. For the single metal atoms, the ground-state configuration was the same site for all of the elements. Analysis of the metal-CdS bonding and of the charge transfers revealed a Ni-Cd bonding complex leading to depletion of electronic charge at the Ni single atom and at deposited Ni clusters, in contrast to charge accumulation observed for the other three metals Pd, Pt, and Au. For scaling up sizes of the metal deposition, six subnanometer cluster types were selected over a wide range of cluster's effective coordination number, and their interfaces were differentiated by charge redistributions, structure and adhesion energies, highest occupied molecular orbital-lowest occupied molecular orbital (HOMO-LUMO) gaps, and Schottky barrier heights. Although all considered clusters are semiconducting in the gas phase, 9 out of 28 clusters became (semi)metallic after deposition on the CdS semiconductor surface. Intermetallic differences and common trends are discussed.