Templated Dewetting Alloying of NiCu Bilayers on TiO2 Nanotubes Enables Efficient Noble-Metal-Free Photocatalytic H2 Evolution

Photocatalytic H-2 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 H-2 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 H-2 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 H-2 generation rates that can be comparable to those obtained by conventional noble-metal (Pt) decoration of TiO2 nanotube arrays.