Tuning the morphology of sputter-deposited platinum catalyst: From compact layers to dispersed nanoparticles

A comprehensive study on adjusting the morphology of sputter-deposited platinum was performed. Platinum was deposited under various Ar pressure ranging from 0.3 to 3.2 Pa using a conventional magnetron system as well as at 57 Pa using a gas aggregation cluster source integrated into the magnetron sputtering system. The morphology and structure of deposited layers were characterized with a broad portfolio of characterization techniques such as scanning electron microscopy, transmission electron microscopy, grazing incidence small angle X-ray scattering and X-ray diffraction. The results revealed a continuous evolution of the Pt layer morphology from a thin-film-like layer of tightly packed Pt nanoparticles to a deposit composed of dispersed particles of 5-7 nm in size as the Ar pressure increased. The electrochemically active surface area of deposited Pt, as calculated from cyclic voltammograms, increased with deposition pressure from 11.7 m²·g_Pt⁻¹ to 22.3 m²·g_Pt⁻¹ and 24 m²·g_Pt⁻¹ for Pt deposited at 0.3, 3.2 and 57 Pa, respectively. This increase in active sites was reflected in a significant improvement in the mass activity of platinum exemplary confirmed using a methanol electrooxidation reaction.