A Dewetted-Dealloyed Nanoporous Pt Co-Catalyst Formed on TiO₂ Nanotube Arrays Leads to Strongly Enhanced Photocatalytic H₂ Production

Pt nanoparticles are typically decorated as co-catalyst on semiconductors to enhance the photocatalytic performance. Due to the low abundance and high cost of Pt, reaching a high activity with minimized co-catalyst loadings is a key challenge in the field. We explore a dewetting-dealloying strategy to fabricate on TiO₂ nanotubes nanoporous Pt nanoparticles, aiming at improving the co-catalyst mass activity for H₂ generation. For this, we sputter first Pt-Ni bi-layers of controllable thickness (nm range) on highly ordered TiO₂ nanotube arrays, and then induce dewetting-alloying of the Pt-Ni bi-layers by a suitable annealing step in a reducing atmosphere: the thermal treatment causes the Pt and Ni films to agglomerate and at the same time mix with each other, forming on the TiO₂ nanotube surface metal islands of a mixed PtNi composition. In a subsequent step we perform chemical dealloying of Ni that is selectively etched out from the bimetallic dewetted islands, leaving behind nanoporous Pt decorations. Under optimized conditions, the nanoporous Pt-decorated TiO₂ structures show a>6 times higher photocatalytic H₂ generation activity compared to structures modified with a comparable loading of dewetted, non-porous Pt. We ascribe this beneficial effect to the nanoporous nature of the dealloyed Pt co-catalyst, which provides an increased surface-to-volume ratio and thus a more efficient electron transfer and a higher density of active sites at the co-catalyst surface for H₂ evolution.