TiO 2 nanotube arrays (TNTAs) sensitized by palladium quantum dots (Pd QDs) exhibit highly efficient photoelectrocatalytic hydrogen generation. Vertically oriented TNTAs were prepared by a three-step electrochemical anodization. Subsequently, Pd QDs with uniform size and narrow size distribution were formed on TiO 2 nanotubes by a modified hydrothermal reaction (i.e., yielding nanocomposites of Pd QDs deposited on TNTAs, Pd@TNTAs). By exploiting Pd@TNTA nanocomposites as both photoanode and cathode, a substantially increased photon-to-current conversion efficiency of nearly 100% at λ = 330 nm and a greatly promoted photocatalytic hydrogen production rate of 592 μmol·h −1 ·cm −2 under 320 mW·cm −2 irradiation were achieved. The synergy between nanotubular structures of TiO 2 and uniformly dispersed Pd QDs on TiO 2 facilitated the charge transfer of photoinduced electrons from TiO 2 nanotubes to Pd QDs and the high activity of Pd QDs catalytic center, thereby leading to high-efficiency photoelectrocatalytic hydrogen generation. P hotoelectrocatalytic water splitting is widely recognized as one of the most promising routes to large-scale production of hydrogen as a potential fuel for renewable energy.1 Among the various catalysts, the noble metal palladium has attracted much attention as one of the most versatile candidates utilized in hydrogen-relevant reactions.2 In particular, Pd immobilized on diverse supports, including carbon, silicates, amorphous or mesoporous silica, and porous biomaterials or polymers, exhibits remarkable performance in organic transformations and especially coupling and hydrogenation reactions.3−6 Onedimensional highly ordered TiO 2 nanotube arrays (TNTAs) fabricated by electrochemical anodization have been demonstrated as a promising photoanode for use in photocatalytic water splitting and solar energy conversion with markedly improved efficiency.7−13 Modified TNTAs were found to possess attractive activities for photoelectrocatalytic water splitting.14,15 However, due to the fast recombination of photogenerated electrons and holes, it remains a major challenge to successfully capitalize on TNTAs for photocatalytic applications.It is well known that the catalytic properties of composites of transition metal particles and supporting materials depend heavily upon the metal particle size, dispersion, composition, etc. 16,17 In this context, it is of high importance to prepare such composites with uniform dispersion, tunable particle size, and narrow size distribution to promote their catalytic activities.
18Catalysts made of Pd nanoparticles supported on TNTAs (i.e., Pd@TNTA nanocomposites) are expected to enhance TiO 2 photocatalysis for hydrogen generation; this can be ascribed to their prominent charge-transfer and separation properties and stability against photocorrosion. 19 The latter contrasts sharply with most of semiconductors, such as CdS, which cause photocorrosion and are not suitable for water splitting.19 As the Fermi level of Pd is lower than that of TiO 2 , photoex...
