(530f) Structural and Electronic Analysis of Chalcogenide-Functionalized Gold Nanoparticles from First Principles

Although there is increased demand to develop renewable fuels such as hydrogen, numerous challenges remain to efficiently carry out this process via electrochemical processes such as the hydrogen evolution reaction (HER). Within the broad space of efforts and materials focused on solving this problem, functionalized nanoparticles have received growing attention for use as HER electrocatalysts. In particular, precious metal nanoparticles can be used to tune the electronic properties of metal chalcogenide ligands for improved catalytic behavior. In our experimental work, tetrathiomolybdate (MoS₄^2-) ligands were deposited on small, colloidal Au nanoparticles. Through this functionalization, it was possible to achieve amorphous MoS_x structures with highly active sulfide sites for the HER. To investigate how the atomic and electronic structures of the MoS₄^2- ligand are modified by the Au nanoparticle surface, we analyze the structure of these catalysts with density functional theory (DFT) calculations. We show how the atomic structure of the catalyst evolves with respect to the surface coverage of MoS₄ moieties. At the coverages observed in the experimental work, Mo – S bond lengths increase, sulfur coordination around each molybdenum atom increases, and the formation of terminal and bridging disulfide species is evidenced. The electronic structure of the catalyst is evaluated with Bader charge analyses, density of states calculations, and vibrational frequency computations. Results of the computational analyses are then used to explain the catalytic behaviors observed in the experimental system. Further, electronic descriptors are identified for the effect of the gold surface modification and correlated with measured/calculated changes in the catalytic properties, thus paving the way for more systematic design efforts for these and related systems.