Nhat Truong Nguyen

Efficient Photocatalytic H2 Evolution: Controlled Dewetting-Dealloying to Fabricate Site-Selective High-Activity Nanoporous Au Particles on Highly Ordered TiO2 Nanotube Arrays.

Anodic self-organized TiO2 nanostumps are formed and exploited for self-ordering dewetting of Au-Ag sputtered films. This forms ordered particle configurations at the tube top (crown position) or bottom (ground position). By dealloying from a minimal amount of noble metal, porous Au nanoparticles are then formed, which, when in the crown position, allow for a drastically improved photocatalytic H2 production compared with nanoparticles produced by conventional dewetting processes.

Strongly Enhanced Water Splitting Performance of Ta3 N5 Nanotube Photoanodes with Subnitrides.

Subnitrides strongly enhance the efficiency of Ta3 N5 -nanotube photoanodes in photochemical water splitting. The fabrication of Ta3 N5 nanotube layers with a controlled subnitride layer at the interface to the back contact is demonstrated. The insertion of this subnitride layer has a strong influence on the electron transfer to the back contact, and as a result leads to a drastic shift in photocurrent onset potential and a considerable enhancement of photocurrent conversion efficiency.

Aligned metal oxide nanotube arrays: key-aspects of anodic TiO2 nanotube formation and properties

Over the past ten years, self-aligned TiO2 nanotubes have attracted tremendous scientific and technological interest due to their anticipated impact on energy conversion, environment remediation and biocompatibility. In the present manuscript, we review fundamental principles that govern the self-organized initiation of anodic TiO2 nanotubes. We start with the fundamental question: why is self-organization taking place? We illustrate the inherent key mechanistic aspects that lead to tube growth in various different morphologies, such as ripple-walled tubes, smooth tubes, stacks and bamboo-type tubes, and importantly the formation of double-walled TiO2 nanotubes versus single-walled tubes, and the drastic difference in their physical and chemical properties. We show how both double- and single-walled tube layers can be detached from the metallic substrate and exploited for the preparation of robust self-standing membranes. Finally, we show how by selecting specific growth approaches to TiO2 nanotubes desired functional features can be significantly improved, e.g., enhanced electron mobility, intrinsic doping, or crystallization into pure anatase at high temperatures can be achieved. Finally, we briefly outline the impact of property, modifications and morphology on functional uses of self-organized nanotubes for most important applications.

Plasmon‐Enhanced Photoelectrochemical Water Splitting Using Au Nanoparticles Decorated on Hematite Nanoflake Arrays

Hematite nanoflake arrays were decorated with Au nanoparticles through a simple solution chemistry approach. We show that the photoactivity of Au-decorated Fe2 O3 electrodes for photoelectrochemical water oxidation can be effectively enhanced in the UV/Visible region compared with the bare Fe2 O3 . Au-nanoparticle-decorated Fe2 O3 nanoflake electrodes exhibit a significant cathodic shift of the onset potential up to 0.6 V [vs. reversible hydrogen electrode (RHE)], and a two times increase in the water oxidation photocurrent is achieved at 1.23 VRHE . A maximum photocurrent of 2.0 mA cm(-2) at 1.6 VRHE is obtained in 1 M KOH under AM 1.5 (100 mW cm(-2) ) conditions. The enhancement in photocurrent can be attributed to the Au nanoparticles acting as plasmonic photosensitizers that increase the optical absorption.

Enhanced Charge Transport in Tantalum Nitride Nanotube Photoanodes for Solar Water Splitting

In the present work we grow anodic self-organized Ta2O5 nanotube layers, which are converted by ammonolysis to Ta3 N5 nanotubes, and then are used as photoanodes for photoanalytic water splitting. We introduce a two-step anodization process that not only improves order (reduced growth defects) and overall light absorption in the nanotube layers, but also provides a significantly reduced interface charge resistance at the nitride/metal interface due to subnitride (TaNx ) formation. As a result, such nanotube anodes afford a 15-fold increase of the photocurrent compared with conventional nanotubular Ta3 N5 electrodes under AM 1.5 G simulated sunlight (100 mW cm(-2)) conditions.

Highly Conducting Spaced TiO2 Nanotubes Enable Defined Conformal Coating with Nanocrystalline Nb2O5 and High Performance Supercapacitor Applications

Establishing self-organized spacing between TiO2 nanotubes allows for highly conformal Nb2 O5 deposition that can be adjusted to optimized supercapacitive behavior.

Use of Anodic TiO2 Nanotube Layers as Mesoporous Scaffolds for Fabricating CH3NH3PbI3 Perovskite‐Based Solid‐State Solar Cells

We optimize the deposition of CH3NH3PbI3 perovskite into mesoporous electrodes consisting of anodic TiO2 nanotube layers. By a simple spin-coating approach, complete filling of the tube scaffolds is obtained, which leads to interdigitated perovskite structures in conformal contact with the TiO2 tube counterparts. Such assemblies can be used as solid-state solar cells in a hole-transporting-material-free configuration, that is, the tube scaffold serves as electron collector and blocking layer, while the perovskite acts as visible-light absorber and hole-transporting material. We show that the complete filling of the tube scaffold with the perovskite is essential to improve the solar cell efficiency.

Stable Co‐Catalyst‐Free Photocatalytic H2 Evolution From Oxidized Titanium Nitride Nanopowders

A simple strategy is used to thermally oxidize TiN nanopowder (∼20 nm) to an anatase phase of a TiO2:Ti(3+):N compound. In contrast to the rutile phase of such a compound, this photocatalyst provides activity for hydrogen evolution under AM1.5 conditions, without the use of any noble metal co-catalyst. Moreover the photocatalyst is active and stable over extended periods of time (tested for 4 months). Importantly, to achieve successful conversion to the active anatase polymorph, sufficiently small starting particles of TiN are needed. The key factor for catalysis is the stabilization of the co-catalytically active Ti(3+) species against oxidation by nitrogen present in the starting material.

Spaced TiO2 nanotube arrays allow for a high performance hierarchical supercapacitor structure

In this work, we describe the synthesis and electrochemical properties of nitridated hierarchical TiO2 nanotubes as an electrode for supercapacitors. The hierarchical TiO2 nanostructures are formed by a controlled layer-by-layer TiO2 nanoparticle decoration on self-organized spaced TiO2 nanotubes. These structures are then annealed in a NH3 atmosphere at elevated temperature to convert the material to a nitride structure – this drastically enhances their electron-transport properties. The areal capacitance of hierarchical structures can be tuned by changing the number of decorated TiO2 nanoparticle layers. The capacitance enhancement of the hierarchical structures reaches a maximum when the surface area through nanoparticle deposition is highest and the conductivity via nitridation is optimized.

Enhanced Solar Water Splitting by Swift Charge Separation in Au/FeOOH Sandwiched Single-Crystalline Fe2O3 Nanoflake Photoelectrodes

In this work, single crystalline α-Fe2 O3 nanoflakes (NFs) are formed in a highly dense array by Au seeding of a Fe substrate by a thermal oxidation technique. The NFs are conformally decorated with a thin FeOOH cocatalyst layer. Photoelectrochemical (PEC) measurements show that this photoanode, incorporating α-Fe2 O3 /FeOOH NFs rooted on the Au/Fe structure, exhibits significantly enhanced PEC water oxidation performance compared to the plain α-Fe2 O3 nanostructure on the Fe substrate. The α-Fe2 O3 /FeOOH NFs on Au/Fe photoanode yields a photocurrent density of 3.1 mA cm-2 at 1.5 VRHE , and a remarkably low onset potential of 0.5-0.6 VRHE in 1 m KOH under AM 1.5G (100 mW cm-2 ) simulated sunlight illumination. The enhancement in PEC performance can be attributed to a synergistic effect of the FeOOH top decoration and the Au underlayer, whereby FeOOH facilitates hole transfer at the interface of electrode/electrolyte and the Au layer provides a sink for the electron transport to the back contact. This results in a drastically improved charge-separation efficiency in the single crystalline α-Fe2 O3 NF photoanode.