Yuriy Pihosh

Photocatalytic generation of hydrogen by core-shell WO 3 /BiVO 4 nanorods with ultimate water splitting efficiency

Efficient photocatalytic water splitting requires effective generation, separation and transfer of photo-induced charge carriers that can hardly be achieved simultaneously in a single material. Here we show that the effectiveness of each process can be separately maximized in a nanostructured heterojunction with extremely thin absorber layer. We demonstrate this concept on WO3/BiVO4+CoPi core-shell nanostructured photoanode that achieves near theoretical water splitting efficiency. BiVO4 is characterized by a high recombination rate of photogenerated carriers that have much shorter diffusion length than the thickness required for sufficient light absorption. This issue can be resolved by the combination of BiVO4 with more conductive WO3 nanorods in a form of core-shell heterojunction, where the BiVO4 absorber layer is thinner than the carrier diffusion length while it’s optical thickness is reestablished by light trapping in high aspect ratio nanostructures. Our photoanode demonstrates ultimate water splitting photocurrent of 6.72 mA cm−2 under 1 sun illumination at 1.23 VRHE that corresponds to ~90% of the theoretically possible value for BiVO4. We also demonstrate a self-biased operation of the photoanode in tandem with a double-junction GaAs/InGaAsP photovoltaic cell with stable water splitting photocurrent of 6.56 mA cm−2 that corresponds to the solar to hydrogen generation efficiency of 8.1%.

Nanostructured WO3/BiVO4 Photoanodes for Efficient Photoelectrochemical Water Splitting

Nanostructured photoanodes based on well-separated and vertically oriented WO3 nanorods capped with extremely thin BiVO4 absorber layers are fabricated by the combination of Glancing Angle Deposition and normal physical sputtering techniques. The optimized WO3 -NRs/BiVO4 photoanode modified with Co-Pi oxygen evolution co-catalyst shows remarkably stable photocurrents of 3.2 and 5.1 mA/cm(2) at 1.23 V versus a reversible hydrogen electrode in a stable Na2 SO4 electrolyte under simulated solar light at the standard 1 Sun and concentrated 2 Suns illumination, respectively. The photocurrent enhancement is attributed to the faster charge separation in the electronically thin BiVO4 layer and significantly reduced charge recombination. The enhanced light trapping in the nanostructured WO3 -NRs/BiVO4 photoanode effectively increases the optical thickness of the BiVO4 layer and results in efficient absorption of the incident light.

Photocatalytic Properties of TiO2 Nanostructures Fabricated by Means of Glancing Angle Deposition and Anodization

Structural, optical, and photocatalytic properties of various TiO 2 nanostructures prepared by glancing angle deposition (GLAD) and by electrochemical anodic oxidation of Ti have been studied. The TiO 2 nanorods were prepared on unheated glass substrates by using reactive sputtering of Ti in the GLAD regime. TiO 2 nanotubes and brush-type nanostructures were fabricated by anodic oxidation of flat Ti films and Ti nanorods prepared by GLAD, respectively. The optical studies revealed that the nanotubes and brush-type nanostructures possess antireflection properties. The photocatalytic activity of TiO 2 nanostructures was characterized by following decomposition of isopropanol under visible and UV light irradiation and found to be significantly higher in nanostructured samples than in their flat counterparts. Also, TiO 2 nanotubes and brush-type nanostructures showed superior photocatalytic activity in comparison with nanorods due to a significantly higher specific surface area.

Optical near-field induced visible response photoelectrochemical water splitting on nanorod TiO2

Here we report a way to induce the visible response of non-doped TiO2 in the photocatalytic electrochemical water splitting, which is achieved by utilizing the optical near-field (ONF) generated on nanorod TiO2. The visible response is attributed to the ONF-induced phonon-assisted excitation process, in which TiO2 is excited by sub-bandgap photons via phonon energy. Our approach directly gets involved in the excitation process without chemical modification of materials; accordingly it is expected to have few drawbacks on the photocatalytic performance. This study may offer another perspective on the development of solar harvesting materials.

Nanocomposite Ti/hydrocarbon plasma polymer films from reactive magnetron sputtering as growth support for osteoblast-like and endothelial cells

Nanocomposite Ti/hydrocarbon plasma polymer (Ti/ppCH) films were deposited by DC magnetron sputtering of titanium target in n-hexane, argon, or a mixture of these two gases. The resultant films were heterogeneous, with inorganic regions of nanometer scale distributed within a plasma polymer matrix. The titanium content was controlled by adjusting the argon/n-hexane ratio in the working gas. In the pure n-hexane atmosphere, the Ti concentration was found to be below 1 at %, whereas in pure argon it reached 20 at %, as measured by Rutherford backscattering spectroscopy and elastic recoil detection analysis (RBS/ERDA). A high level of titanium oxidation is detected with TiO(2), substoichiometric titania, and titanium carbide, composing an inorganic phase of the composite films. In addition, high hydrogen content is detected in films rich with titanium. Ti-deficient and Ti-rich films proved equally good substrates for adhesion and growth of cultured human osteoblast-like MG 63 cells. In these cells, the population densities on days 1, 3, and 7 after seeding, spreading area on day 1, formation of talin-containing focal adhesion plaques as well as concentrations of talin and osteocalcin (per mg of protein) were comparable to the values obtained in cells on the reference cell culture materials, represented by microscopic glass coverslips or a polystyrene dish. An interesting finding was made when the Ti/ppCH films were seeded with calf pulmonary artery endothelial cells of the line CPAE. The cell population densities, the spreading area and also the concentration of von Willebrand factor, a marker of endothelial cell maturation, were significantly higher on Ti-rich than on Ti-deficient films. On Ti-rich films, these parameters were also higher or similar in comparison with the reference cell culture materials. Thus, both types of films could be used for coating bone implants, of which the Ti-rich film remains effective in enhancing the endothelialization of blood contacting artificial materials.

Hierarchically Organized Micro/Nano-Structures of TiO2

We have developed a technique for the fabrication of hierarchically organized micro/nano-structures of TiO2 by means of anodic oxidation of Ti nanorods prepared by glancing angle deposition. The fabricated nanostructures consist of small TiO2 nanotubes that form brush-type shells around long central oxide cores. This multiscale organization of the nanostructures satisfies requirements for large and accessible surface area while providing direct path for electrons, which are desirable for photocatalytic applications.

Tandem photovoltaic–photoelectrochemical GaAs/InGaAsP–WO3/BiVO4 device for solar hydrogen generation

We demonstrated highly efficient solar hydrogen generation via water splitting by photovoltaic–photoelectrochemical (PV–PEC) tandem device based on GaAs/InGaAsP (PV cell) and WO3/BiVO4 core/shell nanorods (PEC cell). We utilized extremely thin absorber (ETA) concept to design the WO3/BiVO4 core/shell heterojunction nanorods and obtained the highest efficiencies of generation, separation and transfer of the photo-induced charge carriers that are possible for the WO3/BiVO4 material combination. The PV–PEC tandem shows stable water splitting photocurrent of 6.56 mAcm−2 under standard AM1.5G solar light that corresponds to the record solar-to-hydrogen (STH) conversion efficiency of 8.1%.

Implantation of perylene molecules into glass plates through a water layer using a laser induced molecular micro-jet

Perylene molecules have been successfully implanted onto borosilicate glass plates, forming fluorescent features of 420 nm in diameter, using a method involving laser induced molecular micro-jet ejection through a water layer. The technique utilises a polymer source film in which perylene molecules are dispersed, a borosilicate glass substrate as a target and a pulsed laser. The space gap between the source film and the target is filled with liquid water. Perylene molecules dispersed in the polymer source films are photo-excited using 4-ns laser pulses resulting in the ejection of the molecules from the source matrix after which they become implanted into the target after passing through the water layer. This new advanced implantation method, using a laser induced molecular micro-jet through water, gives fine spatial control for fixing functional organic molecules in a designated region on hard dielectric materials and will have application in the fabrication of molecular devices, molecular sensors, and opto-electronics.

On-Chip Step-Mixing in a T-Nanomixer for Liquid Chromatography in Extended-Nanochannels

Miniaturization of liquid chromatography separation columns is a key trend in chemical and biochemical areas, particularly in genomics, proteomics, and single-cell analysis. The work at this level relies upon a novel analytical platform that can deal with sample volumes that are much smaller than a cell. An extended-nanospace is within a scale of 101-103 nm and defines the space between a single molecule and normal liquid. Our group has realized high-performance liquid chromatography (HPLC) separation in extended-nanospace with sample injections of hundreds of attoliters and a separation efficiency of hundreds of thousands of plates/m that can overcome the limitations of a conventional packed column by a magnitude of several orders. However, gradient flow is needed to improve the separation performance, and in this work we present reversed-phase chromatography with step-mixing in extended-nanospace and describe its application. Six fluorescently labeled amino acids were separated in 16 s, followed by separation of 17 labeled amino acids in only 50 s with a plate height for most of the peaks of less than 1 μm.

Ubiquitous element approach to plasmonic enhanced photocatalytic water splitting: the case of Ti@TiO2 core-shell nanostructure

We demonstrate a new approach to plasmonic enhanced photocatalytic water splitting by developing a novel core-shell Ti@TiO2 brush nanostructure where an elongated Ti nanorod forms a plasmonic core that concentrates light inside of a nanotubular anodic TiO2 shell. Following the ubiquitous element approach aimed at providing an enhanced device functionality without the usage of noble or rare earth elements, we utilized only inexpensive Ti to create a complex Ti@TiO2 nanostructure with an enhanced UV and Vis photocatalytic activity that emerges from the interplay between the surface plasmon resonance in the Ti core, Vis light absorption in the Ti-rich oxide layer at the Ti/TiO2 interface and UV light absorption in the nanotubular TiO2 shell.