W Doping in Ni12P5 as a Platform to Enhance Overall Electrochemical Water Splitting.

Bifunctional electrocatalysts for efficient hydrogen generation from water splitting must overcome both the sluggish water dissociation step of the alkaline hydrogen evolution half-reaction (HER) and the kinetic barrier of the anodic oxygen evolution half-reaction (OER). Nickel phosphides are a promising catalysts family and are known to develop a thin active layer of oxidized Ni in an alkaline medium. Here, Ni12P5 was recognized as a suitable platform for the electrochemical production of γ-NiOOH─a particularly active phase─because of its matching crystallographic structure. The incorporation of tungsten by doping produces additional surface roughness, increases the electrochemical surface area (ESCA), and reduces the energy barrier for electron-coupled water dissociation (the Volmer step for the formation of Hads). When serving as both the anode and cathode, the 15% W-Ni12P5 catalyst provides an overall water splitting current density of 10 mA cm-2 at a cell voltage of only 1.73 V with good durability, making it a promising bifunctional catalyst for practical water electrolysis.

MoS2 and CdMoS4 nanostructure-based UV light photodetectors.

We have developed MoS2 nanosheets and CdMoS4 hierarchical nanostructures based on a UV light photodetector. The surface morphologies of the as-prepared samples were investigated via field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The performance parameters for the present photodetectors are investigated under the illumination of UV light having a wavelength of ∼385 nm. Upon the illumination of UV light, the CdMoS4-based photodetector device showed a better response to UV light compared to the MoS2 device in terms of photoresponsivity, response time (∼72 s) and recovery time (∼94 s). Our results reveal that CdMoS4 hierarchical nanostructures are practical for enhancing the device performance.

Structural Transformation of SnS2 to SnS by Mo Doping Produces Electro/Photocatalyst for Hydrogen Production.

SnS and SnS2 are layered semiconductors, with potential promising properties for electro- and photocatalytic hydrogen (H2 ) production. The vast knowledge in preparation and modification of layered structures was still not employed successfully in this system to fully maximize its potential. Here, the first report of structural transformation of SnS2 into SnS with Mo-doping as a bifunctional catalyst for the hydrogen evolution reaction (HER) is reported. The structural phase transition optimized the properties of the material, providing a more delicate morphology with additional catalytic sites. The electrochemical studies showed overpotential of 377 mV at 10 mA cm-2 for HER with Tafel slopes of 100 mV dec-1 in 0.5 m H2 SO4 for 10 % Mo-SnS. The same structure acts as an efficient photocatalyst in the generation of H2 from water under visible illumination with rate of 0.136 mmol g-1 h-1 of H2 , which is 20 times higher than pristine SnS2 under visible light.

Synergic effects of the decoration of nickel oxide nanoparticles on silicon for enhanced electrochemical performance in LIBs.

Significant efforts continue to be directed toward the construction of anode materials with high specific capacity and long cycling stability for lithium-ion batteries (LIBs). In this context, silicon is preferred due to its high capacity even though it has a problem of excessive volume expansion during electrochemical reactions as well as poor cyclability due to a reduction in conductivity. Hence, the hybridization of silicon with suitable materials could be a promising approach to overcome the abovementioned problems. Herein, we demonstrate the uniform decoration of nickel oxide (NiO) nanoparticles (15-20 nm) on silicon nanosheets using bis(cyclopentadienyl) nickel(ii) (C10H10Ni) at low temperatures, taking advantage of the presence of two unpaired electrons in an antibonding orbital in the cyclopentadienyl group. The formation and growth mechanism are discussed in detail. The electrochemical study of the nanocomposite revealed an initial delithiation capacity of 2507 mA h g-1 with a reversible capacity of 2162 mA h g-1, having 86% retention and better cycling stability for up to 500 cycles. At the optimum concentration, NiO nanoparticles facilitate Li+-ion adsorption, which in turn accelerates the transport of Li+-ions to active sites of silicon. The Warburg coefficient and Li+-ion diffusion at the electrodes confirm the enhancement in the charge transfer process at the electrode/electrolyte interface with NiO nanoparticles. Further, the NiO nanoparticles with uniform distribution suppress the agglomeration of Si nanosheets and provide sufficient space to accommodate a volume change in Si during cycling, which also reduces the diffusion path length of the Li-ions. It also helps to strengthen the mechanical stability, which might be helpful in preventing the cracking of silicon due to volume expansion and maintains the Li-ion transport pathway of the active material, resulting in enhanced cycling stability. Due to the synergic effect between NiO nanoparticles and Si sheets, the nanocomposite delivers high reversible capacity.

Unique CdS@MoS2 Core Shell Heterostructure for Efficient Hydrogen Generation Under Natural Sunlight.

The hierarchical nanostructured CdS@MoS2 core shell was architectured using template free facile solvothermal technique. More significantly, the typical hexagonal phase of core CdS and shell MoS2 has been obtained. Optical study clearly shows the two steps absorption in the visible region having band gap of 2.4 eV for CdS and 1.77 eV for MoS2. The FESEM of CdS@MoS2 reveals the formation of CdS microsphere (as a core) assemled with 40-50 nm nanoparticles and covered with ultrathin nanosheets of MoS2 (Shell) having size 200-300 nm and the 10-20 nm in thickness. The overall size of the core shell structure is around 8 µm. Intially, there is a formation of CdS microsphre due to high affinity of Cd ions with sulfur and further growth of MoS2 thin sheets on the surface. Considering band gap ideally in visible region, photocatalytic hydrogen evolution using CdS@MoS2 core shell was investigated under natural sunlight. The utmost hydrogen evolution rate achieved for core shell is 416.4 µmole h-1 with apparent quantum yield 35.04%. The photocatalytic activity suggest that an intimate interface contact, extended visible light absorption and effective photo generated charge carrier separation contributed to the photocatalytic enhancement of the CdS@MoS2 core shell. Additional, the enhanced hole trapping process and effective electrons transfer from CdS to MoS2 in CdS@MoS2 core shell heterostructures can significantly contribute for photocatalytic activity. Such core shell heterostructure will also have potential in thin film solar cell and other microelectronic devices.

Correction: Unique perforated graphene derived from Bougainvillea flowers for high-power supercapacitors: a green approach.

Correction for 'Unique perforated graphene derived from Bougainvillea flowers for high-power supercapacitors: a green approach' by Rajendra P. Panmand et al., Nanoscale, 2017, 9, 4801-4809.

Hierarchical CdMoO4 nanowire-graphene composite for photocatalytic hydrogen generation under natural sunlight.

Herein, a facile in situ solvothermal technique for the synthesis of a CdMoO4/graphene composite photocatalyst is reported. Graphene oxide (GO) was synthesised by an improved Hummers' method and was further used for the in situ synthesis of graphene via GO reduction and the formation of a CdMoO4 nanowire/graphene composite. The structural phase formation of tetragonal CdMoO4 was confirmed from X-ray diffraction measurements. The small nanoparticle assembled nanowires, prismatic microsphere morphology and crystalline nature of the synthesized material were investigated using field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Due to its unique morphology and stability, the CdMoO4/graphene composite was used as a photocatalyst for H2O splitting. In comparison to pristine CdMoO4, the CdMoO4/graphene composite showed the best hydrogen evolution rate, i.e. 3624 µmole h-1 g-1, with an apparent quantum yield of 30.5%. The CdMoO4/graphene composite has a higher photocatalytic activity due to the inhibition of charge carrier recombination. H2 production measurements showed that the ternary semiconductor/graphene composite has enhanced photocatalytic activity for H2 generation.

Surface modified Li4Ti5O12 by paper templated approach for enhanced interfacial Li+ charge transfer in Li-ion batteries.

The Li4Ti5O12 (LTO) and lithium silicate (LS) surface modified LTO have been demonstrated by a unique paper templated method. Comparative study of structural characterization with electrochemical analysis was demonstrated for pristine and modified Li4Ti5O12. Structural and morphological study shows the existence of the cubic spinel structure with highly crystalline 250-300 nm size particles. The LS modified LTO shows the deposition of 10-20 nm sized LS nanoparticles on cuboidal LTO. Further, X-ray photoelectron spectroscopy (XPS) confirms the existence of Li2SiO3 (LS) in the modified LTO. The electrochemical performance was investigated by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and galvanostatic charge-discharge. The modified LTO with 2% LS (LTS2) exhibited excellent rate capability compare to pristine LTO i.e. 182 mA h g-1 specific capacity at a current rate, 50 mA g-1 with remarkable cycling stability up to 1100 cycles at a current rate of 800 mA g-1. The lithium ion full cell of modified LTO with LS as an anode and LiCoO2 as a cathode exhibited a remarkably reversible specific capacity i.e. 110 mA h g-1. Both electronic and ionic conductivities of pristine LTO are observed to be enhanced by incorporation of appropriate amount of LS in LTO due to a larger surface contact at the interface of electrode and electrolyte. More significantly, the versatile paper templated synthesis approach of modified LTO with LS provides densely packed highly crystalline particles. Additionally, it exhibits lower Warburg coefficient and higher Li ion diffusion coefficient which in turn accelerate the interfacial charge transfer process, which is responsible for enhanced stable electrochemical performance. The detailed mechanism is expressed and elaborated for better understanding of enhanced electrochemical performance due to the surface modification.

Unique perforated graphene derived from Bougainvillea flowers for high-power supercapacitors: a green approach.

Herein, we demonstrated a green approach for the synthesis of high surface area (850 m2 g-1) mesoporous perforated graphene (PG) from Bougainvillea flower for the first time using a template free single-step method. The existence of PG was confirmed by XRD, Raman spectroscopy, FESEM, and FETEM. Surprisingly, FETEM clearly showed 5-10 nm perforation on the graphene sheets. More significantly, these mesoporous perforated graphene sheets can be produced in large scale using the present green approach. Considering high surface area and unique perforated graphene architecture, these PGs were studied for supercapacitor applications in detail without any chemical or physical activation. The nanoporosity and high conductivity of PG derived from Bougainvillea flower exhibited excellent supercapacitive performance. According to the supercapacitor study, the synthesized perforated graphene sheets conferred a very high specific capacitance of 458 F g-1 and an energy density of 63.7 Wh kg-1 at the power density of around 273.2 Wh kg-1 in aqueous 1 M Na2SO4. Significantly, the areal capacitance of PG was observed to be very high, i.e. 67.2 mF cm-2. The cyclability study results showed excellent stability of synthesized perforated graphene sheets up to 10 000 cycles. Note that the specific and areal capacitance and the energy density of the synthesized PGs are much higher than the earlier reported values. The high supercapacitive performance may be due to high surface area and mesoporosity of PG. The present approach has a good potential to produce cheaper and high surface area PG. These PGs are good candidates as an anode material in the lithium-ion battery.

Nanostructured CdS sensitized CdWO4 nanorods for hydrogen generation from hydrogen sulfide and dye degradation under sunlight.

In this report, CdS nanoparticles have been grown on the surface of CdWO4 nanorods via an in-situ approach and their high photocatalytic ability toward dye degradation and H2 evolution from H2S splitting under visible light has been demonstrated. The structural and optical properties as well as morphologies with varying amount of CdS to form CdS@CdWO4 have been investigated. Elemental mapping and high resolution transmission electron microscopy (HRTEM) analysis proved the sensitization of CdWO4 nanorods by CdS nanoparticles. A decrease in the PL emission of CdWO4 was observed with increasing amount of CdS nanoparticles loading possibly due to the formation of trap states. Considering the band gap in visible region, the photocatalytic study has been performed for H2 production from H2S and dye degradation under natural sunlight. The steady evolution of H2 was observed from an aqueous H2S solution even without noble metal. Moreover, the rate of photocatalytic H2 evolution over CdS modified CdWO4 is ca. 5.6 times higher than that of sole CdWO4 under visible light. CdS modified CdWO4 showed a good ability toward the photo-degradation of methylene Blue. The rate of dye degradation over CdS modified CdWO4 is ca. 7.4 times higher than that of pristine CdWO4 under natural sunlight. With increase in amount of CdS nanoparticle loading on CdWO4 nanorods the hydrogen generation was observed to be decreased where as dye degradation rate is increased. Such nano-heterostructures may have potential in other photocatalytic reactions.