Templated dewetting-alloying of NiCu Bilayers on TiO2 nanotubes enables efficient noble-metal-free photocatalytic H2 evolution

Photocatalytic H2 evolution reactions on pristine TiO2 is characterized by low efficiencies that are due to trapping and recombination of charge carriers and due to a sluggish kinetics of electron transfer. Noble-metal (mainly Pt, Pd, Au) nanoparticles are typically decorated as co-catalysts on the TiO2 surface to reach reasonable photocatalytic yields. However, because of the high cost of noble metals, alternative metal co-catalysts are being developed. Here, we introduce an approach to fabricate an efficient noble-metal-free photocatalytic platform for H2 evolution based on alloyed NiCu co-catalytic nanoparticles at the surface of anodic TiO2 nanotube arrays. NiCu bilayers are deposited onto the TiO2 nanotubes by plasma sputtering. A subsequent thermal treatment is carried out that leads to dewetting, that is, because of surface diffusion, the Ni- and Cu-sputtered layers simultaneously mix with each other while splitting into NiCu nanoparticles at the nanotube surface. The approach allows for a full control over key features of the alloyed nanoparticles, such as their composition, work function, and co-catalytic ability toward H2 generation. Dewetted–alloyed co-catalytic nanoparticles composed of equal Ni and Cu amounts not only are significantly more reactive than pure Ni or Cu nanoparticles, but also lead to H2 generation rates that can be comparable to those obtained by conventional noble-metal (Pt) decoration of TiO2 nanotube arrays.