Graphene is expected to enable superior corrosion protection due to its impermeability and chemical inertness. Previous reports, however, demonstrate limited corrosion inhibition and even corrosion enhancement of graphene on metal surfaces. To enable the reliable and complete passivation, the origin of the low inhibition efficiency of graphene was investigated. Combining electrochemical and morphological characterization techniques, nanometer-sized structural defects in chemical vapor deposition grown graphene were found to be the cause for the limited passivation effect. Extremely fast mass transport on the order of meters per second both across and parallel to graphene layers results in an inhibition efficiency of only ∼50% for Cu covered with up to three graphene layers. Through selective passivation of the defects by atomic layer deposition (ALD) an enhanced corrosion protection of more than 99% was achieved, which compares favorably with commercial corrosion protection methods.

The development of Li-O2 battery electrocatalysts has been extensively explored recently. The Co3O4 oxide has attracted much attention because of its bifunctional activity and high abundance. In the present study, toxic Co(2+) has been replaced through the substitution on the tetrahedral spinel A site ions with environmental friendly metals (Mn(2+), Fe(2+), Ni(2+), and Zn(2+)), and porous nanorod structure are formed. Among these spinel MCo2O4 cathodes, the FeCo2O4 surface has the highest Co(3+) ratio. Thus, oxygen can be easily adsorbed onto the active sites. In addition, Fe(2+) in the tetrahedral site can easily release electrons to reduce oxygen and oxidize to half electron filled Fe(3+). The FeCo2O4 cathode exhibits the highest discharging plateau and lowest charging plateau as shown by the charge-discharge profile. Moreover, the porous FeCo2O4 nanorods can also facilitate achieving high capacity and good cycling performance, which are beneficial for O2 diffusion channels and Li2O2 formation/decomposition pathways.

Increasing demand for clean energy has motivated considerable effort to exploit the properties of various materials in photovoltaics and related solar-harvesting devices. [1] Splitting of water by sunlight to generate hydrogen is one of the forms of energy production with the most potential. Metal oxides such as TiO 2 , ZnO, and WO 3 with various morphologies have been investigated for use in splitting water. [2][3][4][5][6] However, most of these metal oxides have large band gaps, which limit light absorption in the visible region and overall efficiency. To reduce the band gaps of nanostructured metal oxides, doping and utilization of transition metals, carbon, or nitrogen have been investigated. [7][8][9] One possibility is the use of semiconductor nanocrystals, known as quantum dots (QDs), as an alternative to photosensitive dyes. Quantum dots generally offer various significant advantages over dyes. [10] It was recently established that QDs generate multiple electronhole pairs per photon, improving device efficiency. [11] Quantum dot sensitized nanostructures are widely studied for use in solar cells. [12,13] However, little work has been done on metal oxide and semiconductor QD-based composite structures for use in water-splitting nanodevices.To elucidate this fundamental issue, we examined a combination of CdTe QDs and ZnO nanowires for splitting water photoelectrochemically (Scheme 1). One-dimensional nanostructures offer the additional potential advantage of improved charge transport over zero-dimensional nanostruc-tures such as nanocrystals. [6] Additionally, the typical electron mobility in ZnO is 10-100 times higher than that in TiO 2 , so the electrical resistance is lower and the electron-transfer efficiency higher. [14] However, since the overall water-splitting reaction is tough, sacrificial reagents are commonly adopted to evaluate the photocatalytic activity for water splitting. When the photocatalytic reaction is carried out in an aqueous solution that contains a reductant, electron donors, or hole scavengers such as sulfide ions or selenium ions, photogenerated holes irreversibly oxidize the reductant rather than the water. Employment of CdTe QDs in water splitting system has major advantages. CdTe with a more favorable conduction band energy (E CB = À1.0 V vs. NHE) can inject electrons into ZnO faster than CdSe (E CB = À0.6 V vs. NHE). In addition, monolayer deposition of CdTe QDs on the surface of ZnO nanowires would further improve the stability in electrochemical reaction, by avoiding anodic decomposition/corrosion of CdTe and thus enhancing the overall watersplitting performance. During the photoirradiation of CdTe, two reactions can be expected to dominate after initial charge separation [Eqs. (1) and (2)]. [15] Anodic decomposition : CdTe ðe þ hÞ ! Cd 0 þ Te 0Anodic corrosion : CdTe ðhÞ ! Cd 2þ þ TeC ÀMonolayer deposition of QDs can facilitate transfer from CdTe to ZnO and improve QD stability, so that the efficiency in the overall water-splitting reaction can be exactly measured in aqu...

This study reports the successful synthesis of ternary spinel-based ZnCo2O4 nanoflakes (NFs) with mesoporous architectures via the combination of a urea-assisted hydrothermal reaction with calcination in an air atmosphere. Owing to their favorable mesostructures and desirable bifunctional oxygen reduction and evolution activities, the resulting mesoporous ZnCo2O4 NFs yielded stable cyclability at a cut-off capacity of 500 mA h gcarbon(-1) in the case of aprotic Li-O2 batteries.

The colloids of YVO4 nanoparticles on microtextured Si surface are demonstrated to have promising potential for efficient solar spectrum utilization in crystalline Si solar cells. The solar cells showed an enhancement of 4% in short‐circuit current density and approximately 0.7% in power conversion efficiency when coated with YVO4 nanoparticles. The properties of cells integrated with YVO4 nanoparticles were characterized to identify the role of YVO4 in improved light harvesting. The current experiments conclude that the colloids of YVO4 nanoparticles not only act as luminescent down‐shifting centers in the ultraviolet region but also serve as an antireflection coating for enhancing the light absorption in the measured spectral regime. Copyright © 2012 John Wiley & Sons, Ltd.

A ZnO–ZnS solid solution nanowire array photoanode is developed based on an alternative sensitization of a ZnO–ZnS solid solution nanowire array for solar hydrogen generation with considerably enhanced photocurrent – more than 195% greater compared to pristine ZnO nanowires. This solid solution structure demonstrates a better photoactivity enhancement effect than traditional quantum dot sensitization, as well as allowing hydrogen generation.

Herein, mesoporous sodium vanadium phosphate nanoparticles with highly sp(2) -coordinated carbon coatings (meso-Na3 V2 (PO4 )3 /C) were successfully synthesized as efficient cathode material for rechargeable sodium-ion batteries by using ascorbic acid as both the reductant and carbon source, followed by calcination at 750 °C in an argon atmosphere. Their crystalline structure, morphology, surface area, chemical composition, carbon nature and amount were systematically explored. Following electrochemical measurements, the resultant meso-Na3 V2 (PO4 )3 /C not only delivered good reversible capacity (98 mAh g(-1) at 0.1 A g(-1) ) and superior rate capability (63 mAh g(-1) at 1 A g(-1) ) but also exhibited comparable cycling performance (capacity retention: ≈74 % at 450 cycles at 0.4 A g(-1) ). Moreover, the symmetrical sodium-ion full cell with excellent reversibility and cycling stability was also achieved (capacity retention: 92.2 % at 0.1 A g(-1) with 99.5 % coulombic efficiency after 100 cycles). These attributes are ascribed to the distinctive mesostructure for facile sodium-ion insertion/extraction and their continuous sp(2) -coordinated carbon coatings, which facilitate electronic conduction.

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