Core-shell Nanoarrays Research Articles

C@SiNW/TiO2 core-shell nanoarrays with sandwiched carbon passivation layer as high efficiency photoelectrode for water splitting.

One-dimensional heterostructure nanoarrays are efficiently promising as high performance electrodes for photo electrochemical (PEC) water splitting applications, wherein it is highly desirable for the electrode to have a broad light absorption, efficient charge separation and redox properties as well as defect free surface with high area suitable for fast interfacial charge transfer. We present highly active and unique photoelectrode for solar H2 production, consisting of silicon nanowires (SiNWs)/TiO2 core-shell structures. SiNWs are passivated to reduce defect sites and protected against oxidation in air or water by forming very thin carbon layer sandwiched between SiNW and TiO2 surfaces. This carbon layer decreases recombination rates and also enhances the interfacial charge transfer between the silicon and TiO2. A systematic investigation of the role of SiNW length and TiO2 thickness on photocurrent reveals enhanced photocurrent density up to 5.97 mA/cm2 at 1.0 V vs.NHE by using C@SiNW/TiO2 nanoarrays with photo electrochemical efficiency of 1.17%.

Fast and low-cost synthesis of 1D ZnO–TiO2 core–shell nanoarrays: Characterization and enhanced photo-electrochemical performance for water splitting

We report on a simple, fast and low-cost synthesis procedure for the complete covering of zinc oxide (ZnO) 1D nanostructures with a protective shell of titania (TiO2) nanoparticles. ZnO nanowires (NWs) were grown on transparent F-doped Tin Oxide (FTO) conductive layer on glass by seed layer-assisted hydrothermal route in aqueous media, while the titania shell was deposited on the ZnO NWs through an in situ non-acid sol–gel synthesis. The nanowires impregnation time in the titania sol was varied from 3 to 10min. The resulting core–shell ZnO–TiO2 structures were characterized by different techniques, including Scanning and Transmission Electron Microscopy, X-ray diffraction and UV–Vis spectroscopy, confirming the uniform coverage of the wurzite ZnO NWs with anatase TiO2 nanoparticles (NPs), with a shell thickness dependent on the impregnation time in the titania synthesis bath. Photoelectrochemical (PEC) tests of the ZnO–TiO2 material, used as anode for the water splitting reaction, confirmed the formation of the heterojunction by the enhanced photocurrent densities, reaching values of about 0.7mA/cm2 under simulated solar light (AM1.5G, 100mW/cm2). The core–shell photo-anodes performance was about twice and forty- times better than the ones with a film of equivalent thickness of bare ZnO NWs and TiO2 NPs, respectively. Steady-state measures of the photocurrent over the time and FESEM analysis confirmed that this procedure could be effectively used to both protect the nanostructured ZnO from photo-corrosion into different electrolytic media and enhance its photocatalytic properties.

Changes of Voc in Hybrid Solar Cells by TiO2 Nanoarray with Different Crystallinity of Shell

Polymer-inorganic hybrid solar cells with pure vertically aligned TiO2 nanorod arrays (TiO2-NRA) normally suffer from a rather low (<0.4 V) open-circuit voltage (Voc). Recently, it has been demonstrated that the Voc in polymer/TiO2-NRA solar cells can be improved to 0.7 V by formation of homostructured core-shell structures with single-crystalline TiO2 nanorod as core and the polycrystalline TiO2 quantum dots aggregation layer as shell. However, the Voc was not achieved high enough, and effects of different crystallinity of shell on device performance have not been investigated. In this paper, we obtained three types of homostructured TiO2 core-shell nanoarrays with different crystallinity of TiO2 shell (amorphous, amorphous&crystalline, and polycrystalline) through controlling shell reaction time. The changes of device performance (in particular, the Voc) in solar cells with these arrays are studied. Results show that the device Voc gradually decreases when crystallinity of shell changes from amorphous to crystalline. Moreover, the reason for a larger Voc by amorphous shell is analyzed. More dipoles could be produced at α-TiOx shell/polymer interface than crystalline TiO2 shell/polymer interface, which results in a further up-shifting conduction band edge in TiO2 nanorod core toward the local vacuum level of the polymer, along with a further enhanced Voc.

Magnetic properties of electroless-deposited Ni and Ni–NiO core–shell nano-arrays

Ni and Ni–NiO core–shell nano-arrays were fabricated by means of electroless deposition, where the latter was covered by a NiO shell of ∼10 nm by annealing the former at 350 °C for 30 min in an atmospheric condition. HRTEM showed that the NiO shell was developed at the expense of Ni at the array's surface. Ferromagnetic ordering of the Ni–NiO arrays was found to be suppressed compared with those of the less oxidized reference Ni arrays. This is attributed to the screening effect of the NiO shell, and weak ferromagnetism of inner Ni arrays resulted from the development of the NiO. X-ray absorption spectrum reveals that the reference Ni is partially oxidized. Also, X-ray magnetic circular dichroism suggests that the magnetic suppression of the Ni–NiO arrays is associated with a reduced spin moment.