Self-decoration of Pt metal particles on TiO₂ nanotubes used for highly efficient photocatalytic H₂ production

Abstract

Pt decorated TiO 2 has, over the past decades, been a key material for photocatalytic hydrogen production. The present work shows that growing anodic self-organized TiO 2 nanotubes from Ti-Pt alloy with a low Pt content of 0.2 at% leads to oxide nanotube layers that are self-decorated with Pt nanoparticles of 4-5 nm in diameter. The average particle spacing is in the range of~50 nm and is partially adjustable by the anodization conditions. This intrinsic decoration of TiO 2 nanotubes with Pt leads to a highly active photocatalyst for the production of H 2 under UV or visible light conditions.Since Fujishima and Honda in 1972 showed the feasibility to produce hydrogen, the fuel of the future, by photoelectrochemical water splitting using a TiO 2 electrode, vast efforts have been dedicated to optimize systems to enhance the hydrogen yield. 1 The principle of this pathway to hydrogen is based on using a semiconductor for light absorption and formation of excited electron-hole pairs that then on the semiconductor surface react with an environmental H-source. A key requirement of the semiconductor is that it has suitable band-edge positions to allow generation of H 2 (namely a conduction band edge with a negative potential to the H 2 /H + redox potential). If the goal is to achieve a photocatalytic hydrogen production system that operates without external bias (i.e., under open circuit conditions), then also the transfer of holes from the valence band to the environment should be not only thermodynamically possible but also kinetically fast. 2,3 In the case of TiO 2 , most measures to enhance the kinetics are the use of sacrificial agents such as methanol, ethanol and decorating the surface with suitable charge transfer co-catalysts.Other key parameters for an effective hydrogen evolution from TiO 2 are a large surface area and an optimized geometry of the photocatalyst. For the latter reason, one-dimensional nanostructures have attracted wide interest in this field, as they provide a high aspect ratio with an optimized light absorption path and an orthogonal carrier separation. A most straightforward approach towards directional structures is self-organized TiO 2 nanotube arrays. To produce these nanotube structures a Ti metal substrate can be anodized under self-organizing electrochemical conditions. 4 The advantage of an anodic formation is not only simplicity of the process but also the easiness of geometry control (length, diameter, wall thickness) via the selection of suitable anodization parameters. 4 In the context of H 2 production from TiO 2 , as co-catalysts most active are noble metal nanoparticles (mainly Pt) that act very efficiently on TiO 2 nanostructures -in fact in order to obtain measurable contents of H 2 from TiO 2 under non-biased conditions (without the use of a counter electrode and by applying a potential difference) co-catalyst decoration is mandatory. [5][6][7] There are mainly two beneficial effects ascribed to Pt decoration: (i) changes in surface band bending in TiO 2 induced by the meta...

A review on plasmonic metal⿿TiO2 composite for generation, trapping, storing and dynamic vectorial transfer of photogenerated electrons across the Schottky junction in a photocatalytic system

“…Their work showed that both doped and metalized samples had similar photocatalytic activity [59]. Self decorated Pt (0.2 at%) metal deposits on the surface of TiO 2 prepared by anodization of Ti-Pt alloy for 2 h exhibited enhanced photocatalytic hydrogen evolution under both UV/visible light irradiation [61]. These Pt nanoparticle deposits were found to have a diameter of 4-5 nm with inter particle spacing of ∼50 nm and these dimensions were partially adjustable by changing anodization conditions.…”

“…These Pt nanoparticle deposits were found to have a diameter of 4-5 nm with inter particle spacing of ∼50 nm and these dimensions were partially adjustable by changing anodization conditions. Samples prepared at shorter (∼30 min) and longer (∼4 h) anodization time periods exhibited lower hydrogen production which indicates the need of optimum size with particle interspacing for effective photocatalytic performance [61]. (Table 2).…”

One-Dimensional Titanium Dioxide Nanomaterials: Nanotubes

“…An elegant decoration approach for anodic nanotubes with noble metal particles is using low concentration Ti-X (X=Au,Pt) alloys 27,537 that can provide very uniform particle densities and defined particle diameters.…”

Turning Perspective in Photoelectrocatalytic Cells for Solar Fuels

“…Currentd ata indicateaproductivity at best of approximately 0.2-0.5 g H 2 m À2 h À , [110,120] but the value is often much lower.A s an example reporting highly efficient photocatalytic H 2 production, the resultso fS chmuki et al [121] shouldb ec ited. For Ptdoped TiO 2 nanotubes under solar simulator illumination (100 mW cm À2 ), ap roductivity of approximately 0.01 g H 2 m À2 h À1 is reported, whichi ncreasest oa pproximately 0.06 g H 2 m À2 h À1 under UV light (laser,3 25 nm, 60 mW cm À2 )i llumination.…”