Dewetting of PtCu Nanoalloys on TiO₂ Nanocavities Provides a Synergistic Photocatalytic Enhancement for Efficient H₂ Evolution

We investigate the co-catalytic activity of PtCu alloy nanoparticles for photocatalytic H2 evolution from methanol–water solutions. To produce the photocatalysts, a few-nanometer-thick Pt–Cu bilayers are deposited on anodic TiO2 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 TiO2 shows a synergistic activity enhancement and a significantly higher activity toward photocatalytic H2 evolution than Pt- or Cu-TiO2. 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 H2 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-TiO2 a steeper activity increase compared to Pt-TiO2. A further increase in methanol concentration (up to 80 vol %) causes for Pt-TiO2 a clear activity decay, while PtCu-TiO2 still maintains a high level of activity. This suggests improved robustness of PtCu nanoalloys against poisoning from methanol oxidation products such as CO.