Imgon Hwang

Hierarchical DSSC structures based on “single walled” TiO2 nanotube arrays reach a back-side illumination solar light conversion efficiency of 8%

In the present work we introduce a path to the controlled construction of DSSCs based on hierarchically structured single walled, self-organized TiO2 layers. In a first step we describe a simple approach to selectively remove the inner detrimental shell of anodic TiO2 nanotubes (NTs). This then allows controlled well-defined layer-by-layer decoration of these TiO2-NT walls with TiO2 nanoparticles (in contrast to conventional TiO2 nanotubes). We show that such defined multiple layered decoration can be optimized to build dye sensitized solar cells that (under back-side illumination conditions) can yield solar light conversion efficiencies to the extent of 8%. The beneficial effects observed can be ascribed to a combination of three factors: (1) improved electronic properties of the “single walled” tubes themselves, (2) a further improvement of the electronic properties by the defined TiCl4 treatment, and (3) a higher specific dye loading that becomes possible for the layer-by-layer decorated single walled tubes.

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.

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.

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.

TiO2 nanotubes with laterally spaced ordering enable optimized hierarchical structures with significantly enhanced photocatalytic H2 generation

In the present work we grow self-organized TiO2 nanotube arrays with a defined and controlled regular spacing between individual nanotubes. These defined intertube gaps allow one to build up hierarchical 1D-branched structures, conformally coated on the nanotube walls using a layer by layer nanoparticle TiO2 decoration of the individual tubes, i.e. having not only a high control over the TiO2 nanotube host structure but also on the harvesting layers. After optimizing the intertube spacing, we build host-guest arrays that show a drastically enhanced performance in photocatalytic H2 generation, compared to any arrangement of conventional TiO2 nanotubes or conventional TiO2 nanoparticle layers. We show this beneficial effect to be due to a combination of an increased large surface area (mainly provided by the nanoparticle layers) with a fast transport of the harvested charge within the passivated 1D nanotubes. We anticipate that this type of hierarchical structures based on TiO2 nanotubes with adjustable spacing will find even wider application, as they provide an unprecedented controllable combination of surface area and carrier transport.

Large‐Diameter TiO2 Nanotubes Enable Wall Engineering with Conformal Hierarchical Decoration and Blocking Layers for Enhanced Efficiency in Dye‐Sensitized Solar Cells (DSSC)

In the present work we grow anodic TiO

Single-Walled TiO2 Nanotubes: Enhanced Carrier-Transport Properties by TiCl4 Treatment

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Black Magic in Gray Titania: Noble-Metal-Free Photocatalytic H2 Evolution from Hydrogenated Anatase.

nanotube layer with tube diameter ~ 500 nm and an open tube mouth. We use this morphology in dye-sensitized solar cells (DSSCs) and show that these tubes allow the construction of hybrid hierarchical photoanode structures of nanotubes with a defined and wall-conformance TiO2 nanoparticles decoration. At the same time, the large diameter allows the successful establishment of an additional (insulating) blocking layer of SiO

Robust free standing flow-through TiO2 nanotube membranes of pure anatase

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