Hierarchical nanostructures (Hs) have recently garnered enormous attention due to their remarkable performances in catalysis, electronic devices, energy storage and conversion. Considering the advantage of hierarchical nanostructures, we have formulated a facile and template free method to synthesize novel hierarchical nanospheres (NHNs) of ZnV2O4. Both zinc and vanadium are earth abundant, relatively economical and can offer several oxidation states, which can render a broad range of redox reactions favorable for electrochemical energy storage applications. Keeping these points in mind, we investigated for the first time the electrochemical supercapacitor performance of NHNs. The electrochemical measurements were performed in 2 M KOH solution. The measured specific capacitance of ZnV2O4 electrode is 360 F/g at 1 A/g with good stability and retention capacity of 89% after 1000 cycles. Moreover, the hydrogen storage properties of NHNs were measured at 473, 573, and 623 K with an absorption of 1.76, 2.03, and 2.49 wt %. respectively. These studies pave the way to consider ZnV2O4 as prospective material for energy storage applications.

ZnO is a promising photoanode material for dye-sensitized solar cells (DSCs) due to its high bulk electron mobility and because different geometrical structures can easily be tailored. Although various strategies have been taken to improve ZnO-based DSC efficiencies, their performances are still far lower than TiO 2 counterparts, mainly because low conductivity Zn 2+ −dye complexes form on the ZnO surfaces. Here, cone-shaped ZnO nanocrystals with exposed reactive Oterminated {101̅ 1} facets were synthesized and applied in DSC devices. The devices were compared with DSCs made from more commonly used rod-shaped ZnO nanocrystals where {101̅ 0} facets are predominantly exposed. When cone-shaped ZnO nanocrystals were used, DSCs sensitized with C218, N719, and D205 dyes universally displayed better power conversion efficiency, with the highest photoconversion efficiency of 4.36% observed with the C218 dye. First-principles calculations indicated that the enhanced DSCs performance with ZnO nanocone photoanodes could be attributed to the strength of binding between the dye molecules and reactive O-terminated {101̅ 1} ZnO facets and that more effective use of dye molecules occurred due to a significantly less dye aggregation on these ZnO surfaces compared to other ZnO facets.

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. (2015). Enhanced electron lifetime of CdSe/CdS quantum dot (QD) sensitized solar cells using ZnSe core-shell structure with efficient regeneration of quantum dots. The Journal of Physical Chemistry C: Energy Conversion and Storage, Optical and Electronic Devices, Interfaces, Nanomaterials, and Hard Matter, 119 (5), 2297-2307. Enhanced electron lifetime of CdSe/CdS quantum dot (QD) sensitized solar cells using ZnSe core-shell structure with efficient regeneration of quantum dots AbstractResearch on development of efficient passivation materials for high performance and stable quantum dot sensitized solar cells (QDSCs) is highly important. While ZnS is one of the most widely used passivation material in QDSCs, an alternative material based on ZnSe which was deposited on CdS/CdSe/TiO 2 photoanode to form a semi-core/shell structure has been found to be more efficient in terms of reducing electron recombination in QDSCs in this work. It has been found that the solar cell efficiency was improved from 1.86% for ZnSe0 (without coating) to 3.99% using 2 layers of ZnSe coating (ZnSe2) deposited by successive ionic layer adsorption and reaction (SILAR) method. The short circuit current density (J sc ) increased nearly 1-fold (from 7.25 mA/cm 2 to13.4 mA/cm 2 ), and the open circuit voltage (V oc ) was enhanced by 100 mV using ZnSe2 passivation layer compared to ZnSe0. Studies on the light harvesting efficiency (η LHE ) and the absorbed photon-to-current conversion efficiency (APCE) have revealed that the ZnSe coating layer caused the enhanced η LHE at wavelength beyond 500 nm and a significant increase of the APCE over the spectrum 400-550 nm. A nearly 100% APCE was obtained with ZnSe2, indicating the excellent charge injection and collection process in the device. The investigation on charge transport and recombination of the device has indicated that the enhanced electron collection efficiency and reduced electron recombination should be responsible for the improved J sc and V oc of the QDSCs. The effective electron lifetime of the device with ZnSe2 was nearly 6 times higher than ZnSe0 while the electron diffusion coefficient was largely unaffected by the coating. Study on the regeneration of QDs after photoinduced excitation has indicated that the hole transport from QDs to the reduced species (S 2-) in electrolyte was very efficient even when the QDs were coated with a thick ZnSe shell (three layers). For comparison, ZnS coated CdS/CdSe sensitized solar cell with optimum shell thickness was also fabricated, which generated a lower energy conversion efficiency (η = 3.43%) than the ZnSe based QDSC counterpart due to a lower V oc and FF. This study suggests that ZnSe may be a more efficient passivation layer than ZnS, which is attributed to the type II energy band alignment of the core (CdS/CdSe quantum dots) and passivation shell (ZnSe) structure, leading to more efficient electron-hole separation and slower electron recombination. ABSTRACTResearch on development of efficient passivation materials for high perfor...

Bi2Se3 was synthesized by a room-temperature deposition technique and successive ionic layer adsorption and reaction (SILAR) method with the aim to understand the formation, crystallinity, optical properties, and energy band structure of this material. The Bi2Se3 morphology was found to change from nanoparticles to that of a nanocluster network by increasing the SILAR deposition cycles. The crystalline structure of as-prepared Bi2Se3 determined from the grazing-incidence X-ray diffraction (GI-XRD) pattern was found to have a mixed of metastable orthorhombic and rhombohedral phases which was further confirmed from our analysis of the Raman spectra. The optical bandgap of Bi2Se3 varied from 1.58 to 1.05 eV for 15–90 cycles of deposition, in contrast to the semimetallic 0.3 eV bandgap exhibited by the pure rhombohedral phase. A schematic band diagram of Bi2Se3 prepared by 45 SILAR cycles was constructed for the mixed-phase Bi2Se3. The flat-band potential was determined to be at 0.46 V vs. RHE from Mott–Schottky analysis. Low-temperature annealing at 100 °C for 1 h resulted in the improvement of the rhombohedral phase fraction which was confirmed from analysis of GI-XRD pattern and pronounced E2 g and A2 1g bulk vibrational modes in the Raman spectrum. The absorption cutoff after annealing was found to be red-shifted combined with a sub-bandgap absorption above 0.78 eV. The post-annealing results indicated the onset of an early stage transition from semiconductor to semi-metallic properties for Bi2Se3.