Here we report studies of photoelectrochemical (PEC) properties and ultrafast charge carrier relaxation dynamics of hydrogen-treated TiO2 (H:TiO2) nanowire arrays. PEC measurements showed the photocurrent density of the H:TiO2 was approximately double that of TiO2, attributed to increased donor density due to the formation of oxygen vacancies in H:TiO2 due to hydrogen treatment Charge carrier dynamics of H:TiO2, measured using fs transient absorption spectroscopy, showed a fast decay of ∼20 ps followed by slower decay persisting to tens of picoseconds. The fast decay is attributed to bandedge electron-hole recombination and the slower decay is attributed to recombination from trap states. Visible absorption is attributed to either electronic transitions from the valence band to oxygen vacancy states or from oxygen vacancy states to the conduction band of the TiO2, which is supported by incident photon to current conversion efficiency (IPCE) data. H:TiO2 represents a unique material with improved photoelectrochemical properties for applications including PEC water splitting, solar cells, and photocatalysis.

Photoelectrochemical properties of nitride semiconductors are paid attention due to their possibilities of water splitting by visible light absorption. However, the photocurrent density of InxGa1-xN, which absorbs visible light, is usually lower than that of GaN, which has larger band-gap and absorbing only UV light. The reasons of this are thought to be the band-edge position at the semiconductor-electrolyte interface and the crystal quality. The conduction band-edge decreases with increasing of indium composition and across the hydrogen generation energy at around the indium composition of 0.2. This means that the hydrogen generation ability decreases with increasing of indium composition. Low crystal quality is obtained because the lower growth temperature of InxGa1-xN than that of GaN to achieve the indium incorporation. In order to improve the photocurrent density, band-edge energy control and quantum tunneling effect are tried using the structure of thin GaN layer on InxGa1-xN here. The effect for the photocurrent densities is also discussed.

Recent trend in thin film solar cells is to use earth abundant materials such as zinc and iron. Zinc phosphide (Zn3P2) has been has been explored as a choice for solar cell absorber and is currently reviving attention. Zinc phosphide is synthesized from earth-abundant constituents. We have already optimized zinc phosphide phase both in nanocrystalline and bulk thin film form. The purpose of this study is to study growth conditions at different temperatures. In this study, Trioctylphosphine (TOP) is used as a source of phosphorous which reacts with zinc and results in the growth of Zn3P2. The synthesized zinc phosphide phase has been characterized using SEM, EDS, XRD and XPS. We report a simple and repeatable process for synthesis of Zn3P2 phase.

The electrochemical decomposition of water is an attractive method, however, the performance of the electrodes and efficiencies are of great concern in its large scale production. In this context, we wish to report here the superior performance of Ni-multiwalled carbon nanotube composite as cathode in the decomposition of water. The current voltage curves recorded with this electrode in different media showed a significant electrocatalysis in the reduction of hydrogen ion; the background electrolysis is shifted in the anodic direction. The nanocomposite composition has been found to be crucial in the efficient production of hydrogen. A coulombic efficiency of about 68% has been obtained at this electrode with a hydrogen production rate of 130L/m2 d. This electrode is more efficient than the 316L stainless steel (composition in percentage: C 0.019, Cr 17.3, Mo 2.04, Ni 11.3, Mn 1.04, N 0.041, Fe bulk) cathode that produces 10 ml/h at an area of 20 cm2 (5L/m2.h) (2). The results obtained with different electrolytes, performance variation with electrode composition, and current densities will be presented. The trials carried out using solar panel instead of DC power source showed similar hydrogen production rates and efficiencies.

ZnO was electrochemically grown on ITO coated polyethylene (PET) substrate. By sandwiching the electrolyte (sodium para-toluene sulfonate) with so grown ZnO/ITO/PET substrate with another ITO/Plastic substrate, a transparent ZnO based flexible PV cells was fabricated. The efficiency of 0.3% was obtained when shined under UV light. It was concluded that there will be a significant trade-off between with its performance although the optical transparency is very attractive.

In this work, the synthesis of carbon nanotubes/hematite hybrids was investigated. The hybrids were produced by solvothermal method and a systematic study exploring different reaction parameters such as treatment duration, temperature and solvent was performed. Results from different characterization techniques demonstrate that the CNTs were effectively decorated with hematite (α-Fe2O3). The size and concentration of the NPs varies with the reaction parameters and the smallest obtained NPs have ∼100 nm diameter. It was demonstrated that translucent and homogeneous thin films made of the resulting hybrid material can be deposited on indium-tin oxide substrates by electrophoretic deposition or by vaccum filtration.

This investigation reports the synthesis of Ni-ferrite and ZrO2 added Ni-ferrite powdered materials for H2 generation from thermochemical water-splitting reaction. NiFe2O4 was synthesized using sol-gel technique in which salts of Ni and Fe were sonicated in ethanol until a visually clear solution was obtained. To this solution, propylene oxide was added to achieve the gel formation. As-prepared gel was dried at 100oC for 1 h and calcined upto 600oC at a ramp rate of 40oC/min. The calcined sample from the furnace was removed at 600oC and cooled down at room temperature in air. To synthesize NiFe2O4/ZrO2 powdered mixture, ZrO2 nanoparticles were mixed with the calcined ferrite powder using vortex mixer. These powdered materials were analyzed using powder x-ray diffractometer (XRD), BET surface area analyzer and scanning (SEM) and transmission electron microscopy (TEM). As-prepared NiFe2O4 and ZrO2 added NiFe2O4 powdered materials were loaded in an Inconel tubular reactor to investigate H2 generation from four consecutive thermochemical cycles where water-splitting and regeneration was performed at 900o and 1100oC, respectively.

We report a study on catalytic water oxidation by cobalt in oxygen ligand environments because such systems are as promising as any in the water oxidation component of solar fuel production. We have re-examined the catalytic activity of Co(II) in aqueous solution using either [Ru(bpy)3]3+ as a stoichiometric oxidant or in visible-light-driven reactions with persulfate as a sacrificial electron acceptor. In both systems a distinctive induction period is observed. A simple kinetic model is proposed that describes the experimental data well. The presence of an induction period is explained by relatively slow formation of the true catalyst from aquacobalt(II).