Carbon nanotube/metal-sulfide composite flexible electrodes for high-performance quantum dot-sensitized solar cells and supercapacitors.

Carbon nanotubes (CNT) and metal sulfides have attracted considerable attention owing to their outstanding properties and multiple application areas, such as electrochemical energy conversion and energy storage. Here we describes a cost-effective and facile solution approach to the preparation of metal sulfides (PbS, CuS, CoS, and NiS) grown directly on CNTs, such as CNT/PbS, CNT/CuS, CNT/CoS, and CNT/NiS flexible electrodes for quantum dot-sensitized solar cells (QDSSCs) and supercapacitors (SCs). X-ray photoelectron spectroscopy, X-ray diffraction, and transmission electron microscopy confirmed that the CNT network was covered with high-purity metal sulfide compounds. QDSSCs equipped with the CNT/NiS counter electrode (CE) showed an impressive energy conversion efficiency (η) of 6.41% and remarkable stability. Interestingly, the assembled symmetric CNT/NiS-based polysulfide SC device exhibited a maximal energy density of 35.39 W h kg-1 and superior cycling durability with 98.39% retention after 1,000 cycles compared to the other CNT/metal-sulfides. The elevated performance of the composites was attributed mainly to the good conductivity, high surface area with mesoporous structures and stability of the CNTs and the high electrocatalytic activity of the metal sulfides. Overall, the designed composite CNT/metal-sulfide electrodes offer an important guideline for the development of next level energy conversion and energy storage devices.

Enhancing the photovoltaic performance and stability of QDSSCs using surface reinforced Pt nanostructures with controllable morphology and superior electrocatalysis via cost-effective chemical bath deposition.

To make quantum-dot sensitized solar cells (QDSSCs) competitive, photovoltaic parameters such as the power conversion efficiency (PCE) and fill factor (FF) must become comparable to those of other emerging solar cell technologies. In the present study, a novel strategy has been successfully developed for a highly efficient surface-modified platinum (Pt) counter electrode (CE) with high catalytic activity and long-term stability in a polysulfide redox electrolyte. The reinforcement of the Pt surface was performed using a thin passivating layer of CuS, NiS, or CoS by simple chemical bath deposition techniques. This method was a more efficient method for reducing the electron recombination in QDSSCs. The optimized Pt/CuS CE shows a very low charge transfer resistance of 37.01 Ω, which is an order of magnitude lower than those of bare Pt (86.32 Ω), Pt/NiS (53.83 Ω), and Pt/CoS (73.51 Ω) CEs. Therefore, the Pt/CuS CEs show much greater catalytic activity in the polysulfide redox electrolyte than Pt, Pt/NiS and Pt/CoS CEs. As a result, under one-sun illumination (AM 1.5G, 100 mW cm(-2)), the Pt/CuS CE exhibits a PCE of 4.32%, which is higher than the values of 1.77%, 2.95%, and 3.25% obtained with bare Pt, Pt/CoS, and Pt/NiS CEs, respectively. The performance of the Pt/CuS CE was enhanced by the improved current density, Cu vacancies with increased S composition, and surface morphology, which enable rapid electron transport and lower the electron recombination rate for the polysulfide electrolyte redox couple. Electrochemical impedance spectroscopy and Tafel polarization revealed that the hybrid CEs reduce interfacial recombination and exhibit better electrochemical and photovoltaic performance compared with a bare Pt CE. The Pt/CuS CE also shows superior stability in the polysulfide electrolyte in a working state for over 10 h, resulting in a long-term electrode stability than Pt CE.

Enhanced photovoltaic performance and time varied controllable growth of a CuS nanoplatelet structured thin film and its application as an efficient counter electrode for quantum dot-sensitized solar cells via a cost-effective chemical bath deposition.

For the first time we report a simple synthetic strategy to prepare copper sulfide counter electrodes on fluorine-doped tin oxide (FTO) substrates using the inexpensive chemical bath deposition method in the presence of hydrochloric acid (HCl) at different deposition times. CuS nanoplatelet structures were uniformly grown on the FTO substrate with a good dispersion and optimized conditions. The growth process of the CuS nanoplatelets can be controlled by changing the deposition time in the presence of HCl. HCl acts as a complexing agent as well as improving S(2-) concentration against S atoms in this one-step preparation. The photovoltaic performance was significantly improved in terms of the power conversion efficiency (PCE), short-circuit density (J(sc)), open-circuit voltage (V(oc)), and the fill factor (FF). The optimized deposition time of CuS 60 min resulted in a higher PCE of 4.06%, J(sc) of 12.92 mA cm(-2), V(oc) of 0.60 V, and a FF of 0.52 compared to CuS 50 min, CuS 70 min, and a Pt CE. The superior performance of the 60 min sample is due to the greater electrocatalytic activity and low charge transfer resistance at the interface of the CE and the polysulfide electrolyte. The concentration of Cu/S also had an important role in the formation of the CuS nanoplatelet structures. The optical bandgaps for the CuS with different morphologies were measured to be in the range of 1.98-2.28 eV. This improved photovoltaic performance is mainly attributed to the greater number of active reaction sites created by the CuS layer on the FTO substrate, which results large specific surface, superior electrical conductivity, low charge transfer resistance, and faster electron transport in the presence of HCl. Cyclic voltammetry, electrochemical impedance spectroscopy and Tafel-polarization measurements were used to investigate the electrocatalytic activity of the CuS and Pt CEs. This synthetic procedure not only provides high electrocatalytic activity for QDSSCs but could also be a cost-effective way to fabricate flexible electrodes in dye-sensitized solar cells or supercapacitor applications.

The effect of TiO2 nanoflowers as a compact layer for CdS quantum-dot sensitized solar cells with improved performance.

Currently, TiO2 on a fluorine-doped tin oxide substrate is the most commonly used type of photoelectrode in high-efficiency quantum dot-sensitized solar cells (QDSSCs). The power conversion efficiency (PCE) of TiO2 photoelectrodes is limited because of higher charge recombination and lower QD loading on the TiO2 film. This article describes the effect of a TiO2 compact layer on a TiO2 film to enhance the performance of QDSSCs. TiO2 nanoparticles were coated on an FTO substrate by the doctor-blade method and then the TiO2 compact layer was successfully fabricated on the surface of the nanoparticles by a simple hydrothermal method. QDSSCs were made using these films as photoelectrodes with NiS counter electrodes. Under one sun illumination (AM 1.5 G, 100 mW cm(-2)), the QDSSCs showed PCEs of 2.19 and 2.93% for TCL1 and TCL2 based photoelectrodes, which are higher than the 1.33% value obtained with bare TiO2. The compact-layer-coated film electrodes provide a lower charge-transfer resistance and higher light harvesting. The compact layer on the TiO2 film is a more efficient photocatalyst than pure TiO2 film and physically separates the injected electrons in the TiO2 from the positively charged CdS QD/electrolyte.

Cost-effective and morphology controllable PVP based highly efficient CuS counter electrodes for high-efficiency quantum dot-sensitized solar cells.

Currently, copper sulfide (CuS) is the most commonly used counter electrode (CE) in high-efficiency quantum dot-sensitized solar cells (QDSSCs) because of its superior electrocatalytic activity in the presence of polysulfide electrolyte. For the first time, CuS thin films were prepared by a facile chemical bath deposition method with different concentrations of polyvinylpyrrolidone (PVP) and directly used as CEs in QDSSCs without any further post treatment. The quantum dot photoanode with the optimized 0.25 mM PVP-based CuS CE exhibits higher short circuit current density (Jsc), open circuit voltage (Voc), fill factor (FF), and power conversion efficiency (PCE) of 17.57 mA cm(-2), 0.578 V, 0.514, and 5.22%, respectively, which are much higher values than those of a bare CuS CE (Jsc: 12.36 mA cm(-2); Voc: 0.591 V; FF: 0.436; PCE: 3.18%) and Pt CE (Jsc: 11.25 mA cm(-2); Voc: 0.464 V; FF: 0.296; PCE: 1.54%) under one-sun illumination (AM 1.5 G, 100 mW cm(-2)). Moreover, the 0.25 mM PVP-based CuS CE produces a charge-transfer resistance of only 4.39 Ω with the aqueous polysulfide electrolyte commonly applied in QDSSCs. This value is several orders of magnitude lower than that of a typical Pt electrode (69.75 Ω) and bare CuS electrode (9.27 Ω). This enhancement is mainly attributed to the improved morphology of the 0.25 mM CuS CE with high catalytic activity, which plays a main role in the reduction processes of the oxidized polysulfide electrolyte, as well as the increased sulfur atomic percentage with Cu vacancies. Cyclic voltammetry, electrochemical impedance spectroscopy, and Tafel polarization were performed to study the underlying reasons behind the efficient CE performance.

Environmental enrichment exposure restrains the neuronal damage induced by diabetes and stress in the motor cortex of rat brain.

OBJECTIVE: The present study was intended to assess the effect of environmental enrichment on the diabetes as well as combined actions of diabetes and stress on the neurons of the motor cortex of rat brain. BACKGROUND: Untreated diabetes mellitus causes severe insults to the neurons of the central nervous system. Treatment with environmental enrichment is known for producing significant and reliable neuronal changes in the neurological disorders of central nervous system. MATERIALS AND METHODS: Male albino rats of Wistar strain, aged 35 days were used. The rats were divided into (A) Normal Control (B) Vehicle Control (C) Diabetic (D) Diabetes+Stress (E)Diabetes+Environmental enrichment (F)Diabetes+Stress+Environmental enrichment (n=6) in each group). Blood glucose levels and body weight was measured before the induction of diabetes, on the 2nd day after induction of diabetes and before sacrifice. After exposure to stress and environmental enrichment diabetic rats were sacrificed (Day 30) and brains were processed for cresyl violet staining. The number of survived neurons in the motor cortex was quantified. RESULTS: Quantification of cresyl violet neurons in the motor cortex showed a significant increase in the number of survived neurons in Diabetes+Environmental enrichment and Diabetes+Stress+Environmental enrichment group rats compared to Diabetes and Diabetes+Stress group rats respectively. CONCLUSION: Findings from the present study indicated that the exposure to environmental enrichment can prevent the amount of the neural damage caused by complications of diabetes and combined actions of diabetes and stress to the neurons of the motor cortex (Fig. 5, Ref. 37).

Encoding range minima and range top-2 queries.

We consider the problem of encoding range minimum queries (RMQs): given an array A[1..n] of distinct totally ordered values, to pre-process A and create a data structure that can answer the query RMQ(i,j), which returns the index containing the smallest element in A[i..j], without access to the array A at query time. We give a data structure whose space usage is 2n+o(n) bits, which is asymptotically optimal for worst-case data, and answers RMQs in O(1) worst-case time. This matches the previous result of Fischer and Heun, but is obtained in a more natural way. Furthermore, our result can encode the RMQs of a random array A in 1.919n+o(n) bits in expectation, which is not known to hold for Fischer and Heun's result. We then generalize our result to the encoding range top-2 query (RT2Q) problem, which is like the encoding RMQ problem except that the query RT2Q(i,j) returns the indices of both the smallest and second smallest elements of A[i..j]. We introduce a data structure using 3.272n+o(n) bits that answers RT2Qs in constant time, and also give lower bounds on the effective entropy of the RT2Q problem.