Dewetting of PtCu Nanoalloys on TiO Nanocavities Provides a Synergistic Photocatalytic Enhancement for Efficient H Evolution.

We investigate the co-catalytic activity of PtCu alloy nanoparticles for photocatalytic H evolution from methanol-water solutions. To produce the photocatalysts, a few-nanometer-thick Pt-Cu bilayers are deposited on anodic TiO nanocavity arrays and converted by solid-state dewetting via a suitable thermal treatment into bimetallic PtCu nanoparticles. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results prove the formation of PtCu nanoalloys that carry a shell of surface oxides. X-ray absorption near-edge structure (XANES) data support Pt and Cu alloying and indicate the presence of lattice disorder in the PtCu nanoparticles. The PtCu co-catalyst on TiO shows a synergistic activity enhancement and a significantly higher activity toward photocatalytic H evolution than Pt- or Cu-TiO. We propose the enhanced activity to be due to Pt-Cu electronic interactions, where Cu increases the electron density on Pt, favoring a more efficient electron transfer for H evolution. In addition, Cu can further promote the photoactivity by providing additional surface catalytic sites for hydrogen recombination. Remarkably, when increasing the methanol concentration up to 50 vol % in the reaction phase, we observe for PtCu-TiO a steeper activity increase compared to Pt-TiO. A further increase in methanol concentration (up to 80 vol %) causes for Pt-TiO a clear activity decay, while PtCu-TiO still maintains a high level of activity. This suggests improved robustness of PtCu nanoalloys against poisoning from methanol oxidation products such as CO.