Somnath Chanda Roy

Semiconductor heterostructures such as TiO2/Sb2S3 and ZnO/Sb2S3 are promising for photoelectrochemical applications. In this work, we demonstrate the photoelectrochemical performance with enhanced current densities of Sb2S3 sensitized nanorods of TiO2 (TNR) and ZnO (ZNR) photoanodes. ZNR and TNR are synthesized by the hydrothermal method and annealed in the air (AA) and hydrogen (HA) ambient. Stoichiometric Sb2S3 are coated on ZNR and TNR by a facile one-step method using thermolysis of Sb-MPA precursor in air ambient. Structural, optical and microstructural studies are carried out to confirm the formation of phase pure Sb2S3 on ZnO and TiO2 oxide nanorods in the TiO2/Sb2S3 and ZnO/Sb2S3 heterojunction photoanodes. Photoelectrochemical studies show enhanced performance from the Sb2S3 sensitized photoanodes in comparison to the bare TNR or ZNR photoanodes. TNR-AA/Sb2S3(MPA) and TNR-HA/Sb2S3(MPA) heterostructures exhibit current densities of 1.79 mA/cm2 and 1.58 mA/cm2, respectively, which is six times higher than the uncoated photoanodes (0.38 mA/cm2 for TNR-AA and 0.20 mA/cm2 for TNR-HA). In the case of ZNR, we see a 10 to 15 fold increase in current density (~3.3 to 4 mA/cm2) upon sensitizing with Sb2S3 on photoanodes. Further hydrogen annealed ZNR sensitized with Sb2S3 (ZNR-HA/Sb2S3(MPA)) shows a slightly higher current density (3.9 mA/cm2) than the air annealed ZNR-AA/Sb2S3(MPA) (3.32 mA/cm2). Hydrogen annealing is beneficial for ZNR, whereas air-annealing is favored for TNR. Also, stability studies and photocurrent measurements are discussed for these photoanodes.

We report the direct growth of self-aligned single crystalline GaN nanorod array on flexible Ta metal foil using laser molecular beam epitaxy. Scanning electron microscopy reveals the vertically aligned nanorods on Ta surface having diameters in the range of 60–80 nm. The nanorods show well-defined hexagonal facets and are quite uniformly distributed across the metal foil. Transmission electron microscopy shows single crystalline nature of the individual rods having c-axis oriented growth with wurtzite structure. Room temperature photoluminescence study exhibits a sharp, intense band-to-band emission without any deep-level bands indicating the excellent optical quality of the GaN nanorod array. X-ray photoemission spectroscopy to elucidate the electronic structure of the nanorods confirms Ga–N bonding and the calculated chemical composition turns out to be slightly Ga rich. Location of valence band maxima also suggests the n-type character of GaN nanorods. The photoelectrochemical water-splitting behaviour of the self-aligned GaN nanorod arrays on Ta foil has been investigated using 1 M oxalic acid as the electrolyte with AM 1.5 G simulated solar radiation under 1 Sun (100 mW/cm2) conditions. The results demonstrate an effective way of fabricating well-aligned GaN nanorods on flexible metal foils for developing simple, relatively inexpensive, and flexible photo-electrodes for photocatalytic solar water-splitting applications.

Fe2O3 is a stable and low bandgap photocatalyst capable of absorbing a wide range of solar spectra. However, a shorter hole diffusion length impedes its performance as an efficient photocatalyst. The formation of a type II heterojunction is an effective approach to facilitate the quick separation of photogenerated carriers. In this work, we report photo-electrochemical characteristics of WS2 functionalized Fe2O3 nanorod arrays fabricated on FTO coated glass substrate. The Fe2O3 nanorods fabricated by chemical bath deposition and WS2 nanosheets by the hydrothermal technique are characterized by X-ray diffraction, scanning and transmission electron microscopy, energy dispersive X-ray analysis (EDS), X-ray photoelectron spectroscopy, optical absorption, Raman spectra, and FT-IR. A heterojunction architecture formed between these resulted in a higher photocurrent density compared to that of bare Fe2O3 nanorods. Electrochemical impedance spectroscopy and Mott-Schottky measurements reveal lower charge transfer resistance and higher interfacial charge density for WS2 functionalized Fe2O3 nanorods. An energy band diagram for the heterojunction has been proposed to show the charge separation at the interface.