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(101̅0) 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.