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

Abstract

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.

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

“…This can be ascribed to the formation of a Pt/TiO 2 Schottky junction that aids TiO 2 CB electron extraction and transfer to the environment, as well as to the intrinsic catalytic activity of Pt for hydrogen recombination. The activity of NTs decorated with dewetted, pure Ni nanoparticles was investigated in a recent report of ours . Depending on the Ni film nominal thickness (e.g.…”

“…The activity of NTs decorated with dewetted, pure Ni nanoparticles was investigated in a recent report of ours. [60] Depending on the Ni film nominal thickness (e.g. 5-10 nm), the resulting r H2 was found to vary in the 0.2-0.5 mL h À1 cm À2 range; this confirms that the dewetted Ni co-catalyst is significantly less active than pure, dewetted Pt.…”

Dewetted Au Nanoparticles on TiO2 Surfaces: Evidence of a Size-Independent Plasmonic Photoelectrochemical Response

“…TiO2, to fabricate photocatalysts and photo-electrodes. [26][27][28][29] In the present work, the Au-films deposited at the TiO2 surfaces were dewetted by a thermal treatment in air at 450°C (1 h); this is well in line with the melting point of Au (Tm,Au = 1064°C), as depending on the metal film thickness, solid state dewetting is expected to occur at temperatures well below the metal melting point, e.g. between 1/3 and 1/2 of Tm,Au.…”

High-Field Growth of Semiconducting Anodic Oxide Films on Metal Surfaces for Photocatalytic Application

“…Photoanodes based on TiO 2 nanotube layers have been reported to be more promising than nanoparticle layers, due to their well-defined geometry on the one hand, but especially because it is more feasible to incorporate cocatalysts, for example, by electrocrystallization and/or simple chemical reduction. Additionally, after the generation of charge carriers by sunlight, the electrons go to the back contact of the photoanode, then, electron lifetime and conductivity become determinant factors for the overall efficiency [17,22,26,130].…”

“…Additionally, Spanu et al [130] remarked that the photocatalytic H 2 evolution reaction on pristine TiO 2 occurred with low efficiencies due to (i) trapping and recombination of charge carriers and (ii) sluggish electron transfer kinetics.…”