Influence of Ga2O3, CuGa2O4 and Cu4O3 phases on the sodium-ion storage behaviour of CuO and its gallium composites.

CuO and its gallium composites with various compositions are successfully fabricated by using a hydrothermal technique followed by calcination at 900 °C. The added Ga precursors formed oxides in the composites, such as Ga2O3, CuGa2O4 and Cu4O3, as confirmed through the X-ray diffraction patterns as well as the HRTEM and SAED patterns. Further HRTEM analysis also confirmed that Cu4O3 and CuGa2O4 phases reside on the surface of CuO in the composites with a CuO : Ga ratio of 90 : 10. The contents of various oxide phases varied when we increased the amount of Ga in the CuO composites. Changing the ratios of CuO and Ga precursors in the composites is quite effective in tailoring the sodium-ion storage behaviour of CuO. The resultant CuO/Ga composites exhibit remarkable electrochemical performance for sodium-ion batteries in terms of capacity, rate capability and cycling performance. The composite containing 90% CuO and 10% Cu/Ga oxides delivers the highest charge capacity of 661 mA h g-1 at a current density of 0.07 A g-1 with a capacity retention of 73.1% even after 500 cycles. The structure and morphology of the composite (90% CuO and 10% Cu/Ga oxides) was successfully retained after 500 cycles, which was confirmed through ex situ XRD, SEM and HRTEM analyses. The composite also exhibited remarkable rate capability in which it delivered 96 mA h g-1 even at a high current density of 6.6 A g-1. The enhanced electrochemical performances of CuO and its gallium composites are attributed to the presence of Cu4O3 and CuGa2O4 phases. The Cu4O3 phase is actively involved in the redox reaction and the CuGa2O4 phase stabilizes the CuO phase and buffers the volume expansion of CuO during cycling. The present approach eplores great opportunities for improving the electrochemical performance of oxide based anode materials for sodium-ion batteries.

Heterostructure of two different 2D materials based on MoS2 nanoflowers@rGO: an electrode material for sodium-ion capacitors.

Sodium ion capacitors are under extensive investigation as companionable pre-existing lithium ion batteries and sodium ion batteries. Finding a suitable host for sodium ion storage is still a major challenge. In this context, here we report a MoS2 nanoflowers@rGO composite produced via a hydrothermal method followed by an ultra sonication process as a sodium ion symmetric hybrid supercapacitor. The structural and electrochemical performances of the electrode material were investigated to establish its applicability in sodium ion capacitors. The electrochemical performance was evaluated using metallic sodium in a half cell configuration which delivered a maximum specific capacitance of 226 F g-1 at 0.03 A g-1. When examined as a symmetric hybrid electrode (full cell) it delivered a maximum capacitance of 55 F g-1 at 0.03 A g-1. This combination may be a new gateway for upcoming research work which deals with sodium ion storage applications. The results confirmed that the as-synthesized MoS2 nanoflowers@rGO heterostructure electrode exhibited notable electrochemical behaviour.

A Mn3O4 nanospheres@rGO architecture with capacitive effects on high potassium storage capability.

A two dimensional (2D) Mn3O4@rGO architecture has been investigated as an anode material for potassium-ion secondary batteries. Herein, we report the synthesis of a Mn3O4@rGO nanocomposite and its potassium storage properties. The strong synergistic interaction between high surface area reduced graphene oxide (rGO) sheets and Mn3O4 nanospheres not only enhances the potassium storage capacity but also improves the reaction kinetics by offering an increased electrode/electrolyte contact area and consequently reduces the ion/electron transport resistance. Spherical Mn3O4 nanospheres with a size of 30-60 nm anchored on the surface of rGO sheets deliver a high potassium storage capacity of 802 mA h g-1 at a current density of 0.1 A g-1 along with superior rate capability even at 10 A g-1 (delivers 95 mA h g-1) and cycling stability. A reversible potassium storage capacity of 635 mA h g-1 is retained (90%) after 500 cycles even at a high current density of 0.5 A g-1. Moreover, the spherical Mn3O4@rGO architecture not only offers facile potassium ion diffusion into the bulk but also contributes surface K+ ion storage. The obtained results demonstrate that the 2D spherical Mn3O4@rGO nanocomposite is a promising anode architecture for high performance KIBs.

Unravel the interaction of protoporphyrin IX with reduced graphene oxide by vital spectroscopic techniques.

Probing interaction between dyes and reduced graphene oxide (rGO) is of contemporary research interest. Since, rGO is widely used as electron acceptor in photovoltaic and optoelectronic devices. Hence, we have investigated the interaction between protoporphyrin IX (PPIX) and rGO by vital spectroscopic techniques. The adsorption of PPIX on rGO is studied by Attenuated total reflection-Fourier transform infrared (ATR-FTIR) and X-ray photoelectron spectroscopic (XPS) measurements. The fluorescence quenching measurements are also performed and the fluorescence intensity of PPIX is quenched by rGO. The quenching of PPIX with rGO is evaluated by the Stern-Volmer equation and time-resolved fluorescence lifetime studies. The results revealed that the fluorescence quenching of PPIX with rGO is due to the static quenching mechanism. The dominant process for this quenching has been attributed to the process of electron transfer from excited state PPIX to rGO. Fluorescence lifetime measurements were used to calculate the rate of electron transfer process between excited state of PPIX and rGO. Transient absorption studies demonstrated the formation of PPIX cation radical for the evidence of electron transfer between PPIX and rGO.

Bi2 O3 @Reduced Graphene Oxide Nanocomposite: An Anode Material for Sodium-Ion Storage.

The high capacity, excellent cyclability, and good rate capability of reduced graphene oxide (rGO) anchored with Bi2 O3 nanocomposite for sodium-ion batteries is reported. A simple reduction method is adapted to deposit spherical Bi2 O3 nanoparticles on the surface of rGO sheets. The surfactant cetyltrimethylammonium bromide (CTAB) plays a major role in controlling the morphology of the Bi2 O3 nanoparticles. This Bi2 O3 @rGO nanocomposite has the advantages of high reversible capacity with a capacity retention (at high rate) of 70.2 % after 200 cycles at a current density of 350 mA g-1 . This superior performance can be attributed to the fact that rGO sheets hamper the volume expansion of Bi2 O3 nanoparticles and result in faster diffusion of Na+ ions (diffusion coefficient: 5.12×10-8  cm2 s-1 ) and smaller internal resistance (84.17 Ω) compared with pristine Bi2 O3 nanoparticles. The results suggest that anchoring rGO sheets with metal oxides is one of the simplest ways to enhance the electrochemical performance of sodium-ion batteries.

2,3'-diamino-4,4'-stilbenedicarboxylic acid sensitizer for dye-sensitized solar cells: quantum chemical investigations.

The metal-free organic dye sensitizer 2,3'-diamino-4,4'-stilbenedicarboxylic acid has been investigated for the first time for dye-sensitized solar cell applications. Density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations (performed using the hybrid functional B3LYP) were carried out to analyze the geometry, electronic structure, polarizability, and hyperpolarizability of 2,3'-diamino-4,4'-stilbenedicarboxylic acid used as a dye sensitizer. A TiO2 cluster was used as a model semiconductor when attempting to determine the conversion efficiency of the selected dye sensitizer. Our TD-DFT calculations demonstrated that the twenty lowest-energy excited states of 2,3'-diamino-4,4'-stilbenedicarboxylic acid are due to photoinduced electron-transfer processes. Moreover, interfacial electron transfer between a TiO2 semiconductor electrode and the dye sensitizer occurs through electron injection from the excited dye to the semiconductor's conduction band. Results reveal that metal-free 2,3'-diamino-4,4'-stilbenedicarboxylic acid is a simple and efficient sensitizer for dye-sensitized solar cell applications.

Reduced graphite oxide/nano Sn: a superior composite anode material for rechargeable lithium-ion batteries.

The electrochemical performance of reduced graphite oxide (RGO) anchored with nano Sn particles, which are synthesized by a reduction method, is presented. The Sn nanoparticles are uniformly distributed on the surface of the RGO matrix and the size of the particles is approximately 5-10 nm. The uniform distribution effectively accommodates the volume expansion experienced by Sn particles during cycling. The observed electrochemical performance (97 % capacity retention) can be ascribed to the flexible RGO matrix with uniform distribution of Sn particles, which reduces the lithium-ion diffusion path lengths; therefore, the RGO matrix provides more stability to the Sn particles during cycling. Such studies on Sn nanoparticles anchored on RGO matrices have not been reported to date.

High-performing LiMgxCuyCo1-x-yO2 cathode material for lithium rechargeable batteries.

Sustainable power requirements of multifarious portable electronic applications demand the development of high energy and high power density cathode materials for lithium ion batteries. This paper reports a method for rapid synthesis of a cobalt based layered cathode material doped with mixed dopants Cu and Mg. The cathode material exhibits ordered layered structure and delivers discharge capacity of ∼200 mA h g(-1) at 0.2C rate with high capacity retention of 88% over the investigated 100 cycles.

LiCo(x)Mn(1-x)PO4/C: a high performing nanocomposite cathode material for lithium rechargeable batteries.

Pristine and Co-doped LiMnPO(4) have been synthesized by the sol-gel method using glycine as a chelating agent and the carbon composites were obtained by the wet ball mill method. The advantage of this method is that it does not require an inert atmosphere (economically viable) and facilitates a shorter time for synthesis. The LiCo(0.09)Mn(0.91)PO(4)/C nanocomposites exhibit the highest coulombic efficiency of 99 %, delivering a capacity of approximately 160 mAhg(-1) and retain a capacity of 96.3 % over the investigated 50 cycles when cycled between 3-4.9 V at a charge/discharge rate of 0.1 C.