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Surface studies of developed fingerprints have aided in the elimination of criminal cases before moving to the court. The combination of X-ray photoelectron spectroscopy (XPS) with the aryldiazonium gold(III), 4-O2NC6H4N2+AuCl4-, surface modifier has been shown to be a novel approach in latent fingerprint detection and development for the quantification of film elements. The robust gold-aryl film was developed on the reducing chemicals excreted in the sebaceous fingerprints without the need for external stimuli and at a lesser extent after contacting the free metal surface. The concurrent reduction of the diazonium functional group and gold(III) from [AuCl4]- developed a robust gold-aryl film, which showed increasing gold(0) quantity in the time range of 30-120 min over copper coins and model flat sheets. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) support the presence of reduced gold on the top of the latent fingerprints and the presence of CuO resulting from the reaction of the diazonium salt with copper metal. This research combines the quantification of deposits using XPS, a surface-sensitive technique for chemical analysis, in addition to surface imaging.

International audience; Surface modifiers through redox routes emerged as the most preferred in forensic science. Aryldiazonium salts stabilized with tetrachloroaurate(III) are excellent redox modifiers in the development of latent fingerprints on nickel surfaces. Nickel coins were fingerprinted and developed with a stable diazonium salt [O 2 N-4-C 6 H 4 N≡N]AuCl 4. The developed surfaces were studied using XPS which showed the presence of the characteristic gold and organic modifier peaks. In addition, imaging analysis using SEM showed clusters of gold. EDS quantitative analysis estimated a good amount of gold presence on the fingerprinted compared to the nonfingerprinted area. Our results are important in the analysis of nickel coins using a spontaneous route by simply depositing diazonium salt solution drops on the nickel surface without any additional reducing agent. This work brings strong supporting evidence for the efficient combination of diazonium surface chemistry and high-performance surface analytical tools (XPS, SEM-EDS) in the fast, spontaneous developing of fingerprints and their morphological and chemical composition assessments.

Herein, we utilize freestanding sheets of multi-walled carbon nanotube (MWCNT), fabricated through a surface-engineered and controlled approach, to provide direct measurements of activities of MWCNT toward the hydrogen evolution reaction (HER). Since conventional fabrication methods of MWCNT materials can result in different carbonaceous residue contents (as reported in literature), the effect of carbonaceous impurities on the activity of MWCNT toward the HER becomes interesting (not previously recognized). Our results show that increasing amounts of carbonaceous impurities (in the form of carbon black additives) can initially increase the catalytic activity of MWCNT toward the HER, but will result in a lower electrochemical stability and lower activity at higher rates of charge transfer or longer times of charging, for which we propose an electrolytic transport mechanism, related to a debris-formation phenomenon occurring over carbonaceous impurities. The work suggests that carbonaceous impurities’ content should be accounted for during electrochemical studies of MWCNT toward the HER.

Degradation of commercially available CdTe and CIGS PV modules installed in the desert conditions, are not well understood, because they have been in operation for relatively short period compared to crystalline silicon PV technology. In this paper, we investigate the degradation rate of both these thin-film technologies using indoor characterization methods. The calculated annual degradation rate of CdTe technology (1.3-2.2 percent/year) is lower than CIGS (5.3-8.8 /year). The main cause of this degradation is the reduction in fill factor caused by formation of permanent shunts. These shunts were characterized using Electroluminescence and microscopic imaging.

Lithium iron phosphate (LiFePO4)/multi-walled carbon nanotubes (MWCNT) composite electrodes were prepared via a wet-filtration-zipping technique. Mechanical, thermal and electrical properties of the composite electrodes at various temperatures were studied. The composite electrodes exhibited electrical conductivity in the range of 1.1 × 101–3.56 × 101 S/cm. Further, the thermal conductivity, effusivity and volumetric heat capacity were measured. Cyclic voltammograms confirmed good electrochemical performances and high stability during Li+ ion intercalation/de-intercalation.

A combination of carbon nanotubes (CNT) and graphene in the form of macroscopic hybrid buckypaper (HBP), exhibits a unique set of properties that can be exploited for many emerging applications. Here, we present a simple, inexpensive and scalable approach for the synthesis of highly conductive auxetic graphene/CNT HBP via wet-filtration-zipping and demonstrate the electrical, electrochemical and mechanical performance (tensile, mode I and mode III fracture) of synthesized HBP. An overall increase in electrical conductivity of 247% is observed for HBP (50 wt.% graphene and 50 wt.% CNT) as compared to BP (100 wt.% CNT) due to effective electronic percolation through the graphene and CNT. As a negative electrode for lithium-ion batteries, HBP shows 50% higher gravimetric specific capacity and 89% lower charge transfer resistance relative to BP. The graphene content in the HBP influences the mechanical performance providing an auxetic structure to HBP with large negative Poisson’s ratio. The facile green-chemistry approach reported here can be readily applied to any other 1D and 2D materials and solves key challenges associated with existing buckypaper manufacturing methods. The potential of the synthesis method to integrate with current cellulose paper manufacturing technology and its scalability demonstrate the novelty of the work for industrial scale production.

Lithium iron phosphate (LiFePO4) micro-particles (MPs) were synthesized under hydrothermal condition for fabrication of cathode materials based on LiFePO4 MPs/multi-walled carbon nanotube (MWCNT) nanocomposites. Influence of reaction time for the hydrothermal process on structural, morphological, and electrochemical behavior was investigated. Crystal quality was confirmed by X-ray diffraction (XRD) together with Raman analysis. Micrometer-scale seeds and capsule-shaped morphology were observed. Such nanocomposite cathodes based on LiFePO4 MPs/MWCNT were prepared by surface-engineered tape casting technique. The well-crystallized material composed of densely aggregated MPs and interconnected with MWCNTs led to excellent volumetric Li storage properties at a current rate of 0.1 mVs−1 between 2.5 to 4.3 V. However, the half-cell analysis does not show reasonable capacity values, which may be due to the larger particle size and morphology of synthesized LiFePO4, resulting in limiting ionic transportation and electronic conduction path.

We attempt to evaluate Black Silicon (BSi) substrate loaded with water splitting (WS) semiconductor and Au particles as an efficient WS composite material. Further, thermal annealing was performed to study the effect of the WS photocatalyst microstructure evolution on optical properties, crystallinity, photo-response and the hydrophilicity. The thermal annealing was carried out at 450–850 °C range in ambient environment. The WS crystal structure analysis by X-ray Diffraction, shows that TiO 2 turns after annealing at 450 °C to anatase phase known for high photocatalytic behavior. This transformation increases the optical reflection (%R) of the WS material in UV–Vis–Near IR region for both substrates (Si and BSi), however this increase about 1–5% is insignificant for the BSi due its morphology consisting of needles and wells. Nevertheless, this transformation decreases the hydrophilicity of the material surface of BSi due to its inherent structure. In addition, we showed that the photo-response after annealing is associated with lower resistance and higher photocurrent emission compared to non-annealed sample. This result suggests that BSi used as a substrate to receive WS semi-conductor has a great potential to be used as an efficient WS materials compared to Si.

We report on the effect of thermal annealing on the microstructure, optical properties and wettability of TiO 2 -based water-splitting (WS) composite using full solar spectrum as source of energy. The WS material used in this study is composed of three layers (SiO 2 , Al 2 O 3 and TiO 2 ) on top of which a distribution of Localized Surface Plasmon Resonance structures such as gold are formed to obtain a multilayer composite material. The fabricated samples are then annealed at 450−1100 °C temperatures range under atmospheric conditions. The crystal structure and chemical composition are determined using X-ray Diffractometer, Scanning Electron Microscope, Energy Dispersive Spectroscopy, High Resolution Scanning and Transmission Electron Microscope. UV–Vis spectroscopy is used to study the influence of thermal annealing on optical absorption. Besides, wettability alteration is assessed using both in-situ (Environmental Scanning Electron Microscope) and ex-situ (sessile drop technique). Our findings reveal that thermal annealing leads to the transformation of amorphous TiO 2 to its more stable phase anatase. This transformation enhances significantly the optical properties and increases the hydrophilicity of the material surface making it suitable for WS activity. More importantly, the presence of plasmonic nanostructures allow the material to extend its photoactivity from UV region to full solar spectrum. The gold nanocrystals were also found to prefer the orientation during their evolving and growth after thermal annealing. This specific compact orientation is also reported to increase the efficiency of WS.

Wearable electronics require flexible supercapacitors with specially fabricated electrode materials, i.e., foldable and freestanding. Although activated carbon is the most used electrode’s active material for aqueous supercapacitors, it is a challenge to pack the particulates into flexible electrodes. Typically, polytetrafluoroethylene binder and polymeric flexible substrate are used, rendering a large amount of inactive-material. Here, we successfully fabricated multiwalled carbon nanotube/activated-carbon (MWCNT-AC) freestanding sheet via a scalable surface-engineered tape-casting technique to be used as a flexible electrode for aqueous supercapacitors. Instead of focusing on improving MWCNTs as active materials, the sheets act as a conducting matrix that binds together the activated-carbon particulates. MWCNT-AC has a specific capacitance of 135.17 Fg−1 (123.9 Fg−1 after 1000 cycles) at 1 Ag−1 from − 0.8 to 0.2 V vs. Hg/HgO (in three-electrode cell).

The presence of impurities within multiwalled carbon nanotubes (MWCNTs) have major, but as-yet-unrecognized, effects on the electrochemical behavior of MWCNTs in vanadium redox flow batteries. We show that MWCNTs constitute a high-surface-area, electrically conductive, inactive carbon matrix that acts as a bridge between and a support for carbonaceous impurities that are highly active toward the VO2+/VO2+ redox couple. We use freestanding sheets of MWCNTs, either purified and subsequently not modified with impurities (pure) or purified and subsequently contaminated with carbonaceous impurities (impure), as electrodes to eliminate the need for a substrate and thus undesired mixed kinetics. Electrodes fabricated with pure MWCNTs show low activities; attributed to relatively inactive basal sites. In contrast, impure electrodes show high activities due to the increased number of defects and edge sites resulting from the presence of the impurities. Functionalization of pure MWCNTs surface with oxygen-containing groups substantially improve the activity of the electrodes. However, functionalization is not as effective when carbonaceous impurities are present. The carbonaceous impurities form a continuous debris layer over the nanotube fibers, which reduces the effect of the oxidation treatment. Our results indicate that the impurity content of MWCNTs should be considered in studies of their activity and functionalization.

Membraneless redox flow batteries reported to date are microscale designs that have shown poor capacity retention and cyclability due to reactant crossover. Here, we present a new design of macroscale membraneless redox flow battery capable of recharging and recirculation of the same electrolyte streams for multiple cycles and maintains the advantages of the decoupled power and energy densities. The battery is based on immiscible aqueous anolyte and organic catholyte liquids, which exhibits high capacity retention and columbic efficiency during cycling. The aqueous anolyte consists of iron(II) sulfate (FeSO4) as active species, which is immiscible with the catholyte, having iron(III) acetylacetonate (Fe(acac)3) as active species dissolved in water-immiscible ethyl acetate, supported by ionic liquid (1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide). Over 60% of initial discharge capacity was retained and over 80% of columbic efficiency was sustained after 25 cycles in a test flow cell, which is among the highest reported thus far.

In electrochemical exfoliation, the working electrode is typically a graphite rod or foil, or highly oriented pyrolytic graphite. These electrodes are limited by the surface area that is in contact with the electrolyte and available for exfoliation. In contrast, a powder-based carbon material will have a much larger surface area exposed to the electrolyte, thus leading to an efficient exfoliation process and faster production of graphene. Herein, we have demonstrated the synthesis of few-layer graphene-like (FLG) sheets from carbon black widely available as a fine powder in its native form. It is challenging to run an electric current through a powdery material. Thus, we proposed to bind the carbon black particles together using a pH-independent intrinsically electrically conducting polymer to form a porous working electrode. Raman spectroscopy confirmed the synthesis of FLG from powder-based carbon black. The thickness of our FLG sheets was determined by atomic force microscopy to be between 3 and 8 nm. Transmission electron microscopy revealed that the sheets were ~35 nm in length and ~30 nm in width, similar to the particle size of the carbon black (~50 nm in diameter) starting material. The synthesized FLG was compared to industry standards and found to be of excellent quality. Glass coated with our FLG has a transparency of 85–90% in the 300- to 1000-nm wavelength region. The present study serves as a foundation for the electrochemical synthesis of graphene from various carbonaceous powders generated by many industries.

Typically, multiwalled carbon nanotubes (MWCNTs) are drop-casted on the surface of the underlying carbon substrates; the outcome is a randomly distributed MWCNT layers leading to uncontrollable structure and unreproducible results. Additionally, we suspect that the electrochemical response is influenced by the primary carbon-based substrate. Herein, we propose the use of freestanding sheets of MWCNTs (buckypapers, BP electrodes) as electrode materials for vanadium redox flow batteries to directly probe the electrochemical activity of MWCNTs toward VO 2+ /VO 2 + and V 2+ /V 3+ redox couples; henceforth, eliminating the need for an underlying carbon substrate. The amount of surfactant and the sonication time used during the fabrication of BP electrodes affect their morphological characteristics and electrochemical performances. Although the electrical conductivity of BP electrodes decreases with increasing surfactant amount and increasing sonication time, the heterogeneous rate constants for both redox couples increase as these fabrication variables are increased, indicating that the performance-limiting process is not electrical conductivity but the number of active sites available for the electrochemical reaction. The standard heterogeneous rate constant of the BP electrode with the highest amount of surfactant is comparable to those of state-of-the-art electrodes. Our promising results call for more research on the potential use of BP electrodes in redox flow batteries.

The importance of the choice of solvent in a non-aqueous redox flow battery (NARFB) cannot be overemphasized. Several studies demonstrated the influence of the solvent on electrolyte performance in terms of reaction rates, energy/power densities, and efficiencies. In this work, we investigate capacity decay as a direct consequence of varying reactant crossover rates through membranes in different solvent environments. Specifically, we demonstrate the superiority of an 84/16 vol% acetonitrile/1,3 dioxolane solvent mixture over pure acetonitrile in terms of energy efficiency (up to 89%) and capacity retention for vanadium NARFBs - while incorporating a Nafion 115 membrane. The permeability of Nafion to the vanadium acetylacetonate active species is an order of magnitude lower when pure acetonitrile is replaced by the solvent mixture. A method to estimate relative membrane permeability is formulated from numerical analysis of self-discharge experimental data. Furthermore, tests on a modified Nafion/SiO2 membrane, which generally offered low species permeability, also show that different solvents alter membrane permeability. Elemental and morphological analyses of cycled Nafion and NafionSi membranes in different solvent environments indicate that different crossover rates induced by the choice of solvent during cycling are due to changes in the membrane microstructure, intrinsic permeability, swelling rates, and chemical stability.

Employing solvent mixtures in the electrolyte of non-aqueous redox flow batteries can increase energy density and efficiency. In this paper, active species solubility, electrolyte conductivity, and redox reaction rates were examined systematically among a number of binary and ternary mixtures, consisting of acetonitrile and 5 polar aprotic co-solvents to identify mixtures with enhanced active species solubility and redox reaction rates. Although we used vanadium acetylacetonate as a model, the methodologies presented here are applicable when evaluating solvent mixtures for other active species. Our approach is distinctive in that it elucidated the trade-offs in desirable properties that are necessary when solvent mixtures are used for non-aqueous redox flow batteries. We found that in a vanadium acetylacetonate–based non-aqueous redox flow battery, the use of an 84/16 vol% acetonitrile/1,3-dioxolane binary solvent mixture resulted in an increase in the positive and negative sides reaction rates compared to that observed with pure acetonitrile. This binary mixture resulted in an improvement in reaction rate with no decrease in energy density and is a promising solvent system for other active species used for non-aqueous flow batteries. Keywords: Vanadium acetylacetonate; Non-aqueous electrolyte; Redox flow battery; Organic electrochemistry; Energy Storage

Various applications of freestanding multi-walled carbon nanotube (MWCNT) sheets (also known as buckypapers), although very promising in the laboratory, failed to meet the technology readiness level for commercialisation due to the use of non-scalable fabrication methods. Herein, we developed a surface-engineered tape-casting (SETC) technique which is a facile and scalable preparation method to fabricate freestanding, flexible and foldable buckypapers using tape-casting on a surface-engineered conveyor-belt without a mould. The SETC technique has several advantages: it can be implemented in both batch and roll-to-roll processing; has a high throughput; produces a large area with tuneable length, thickness, density and composition; and produces sheets from any commercially available carbon nanotubes with superior properties. The SETC technique solves the main challenge of tape-casting which is the separation of the dried MWCNT sheet from the supporting-substrate. This challenge originates from the fact that MWCNTs always tend to stick to the substrate which makes it almost impossible to peel as a perfect sheet. We found out that easy peeling of the buckypaper from a substrate can be achieved if the following conditions are satisfied: (a) enough difference between MWCNTs and substrate surface energies and (b) the micro-pyramid pore structure of the substrate morphology. Moreover, the SETC technique was able to preserve the MWCNT alignment within the sheet. We demonstrated the application of a SETC-made MWCNT–LiFePO4 buckypaper composite in lithium-ion batteries with an excellent specific capacity of 86.79 mA h gLiFePO4−1 (61.20 mA h gMWCNT+LiFePO4−1) at a high discharge rate of 1905 mA gLiFePO4−1 (1270 mA gMWCNT+LiFePO4−1) for 1000 cycles.

Although free-standing sheets of multiwalled carbon nanotubes (MWCNT) can provide interesting electrochemical and physical properties as electrodes for redox flow batteries, the full potential of this class of materials has not been accessible as of yet. The conventional fabrication methods produce sheets with micro-porous and meso-porous structures, which significantly resist mass transport of the electrolyte during high-current flow-cell operation. Herein, we developed a method to fabricate high performance macro-porous carbon nano-foam free standing sheets (Puffy Fibers, PF), by implementing a freeze-drying step into our low cost and scalable surface-engineered tape-casting (SETC) fabrication method, and we show the improvement in the performance attained as compared with a MWCNT sheet lacking any macro pores (Tape-cast, TC). We attribute the higher performance attained by our in-lab fabricated PF papers to the presence of macro pores which provided channels that acted as pathways for electrolytic transport within the bulk of the electrode. Moreover, we propose an electrolytic transport mechanism to relate ion diffusivity to different pore sizes to explain the different modes of charge transfer in the negative and the positive electrolytes. Overall, the PF papers had a high wettability, high porosity, and a large surface area, resulting in improved electrochemical and flow-cell performances.

14 pags., 10 figs., 3 tabs. -- This article belongs to the Special Issue Advances in Elastic Micro-Structured Systems and Metamaterials, A numerical simulation study on elastic wave propagation of a phononic composite structure consisting of epoxy and tungsten carbide is presented for low-frequency elastic wave attenuation applications. The calculated dispersion curves of the epoxy/tungsten carbide composite show that the propagation of elastic waves is prohibited inside the periodic structure over a frequency range. To achieve a wide bandgap, the elastic composite structure can be optimized by changing its dimensions and arrangement, including size, number, and rotation angle of square inclusions. The simulation results show that increasing the number of inclusions and the filling fraction of the unit cell significantly broaden the phononic bandgap compared to other geometric tunings. Additionally, a nonmonotonic relationship between the bandwidth and filling fraction of the composite was found, and this relationship results from spacing among inclusions and inclusion sizes causing different effects on Bragg scatterings and localized resonances of elastic waves. Moreover, the calculated transmission spectra of the epoxy/tungsten carbide composite structure verify its low-frequency bandgap behavior., The authors thank the support from other members in the Advanced Materials Research Centre at Technology Innovation Institute and also thank Abu Dhabi Government’s Advanced Technology Research Council (ATRC), which oversees technology research in the emirate.

In this paper, a molecular model based on quantum mechanics and molecular dynamics (MD) is developed to study the transfer mechanisms of proton, phosphoric acid (PA) molecule and dihydrogen phosphate anion ( H 2 PO 4 − ) in PA-doped poly(2,5-benzimidazole) (ab-PBI) membrane. This model couples with intermolecular potential energy, interaction force between two particles, linear momentum conservation equation, angular momentum conservation equation, total energy conservation equation, the radial distribution function and Einstein's law of diffusion. The simulated molecular system consisting of ab-PBI macromolecules doped with PA is optimized to obtain an optimal structure of the amorphous cell unit system. The effects of PA doping level, temperature and electric field intensity on the mass transfer in the ab-PBI membrane are studied. A comparison between this simulation results and experimental data gotten from literatures shows this model and its simulation are reliable. Two kinds of proton transfer mechanisms are evaluated, and the first transfer mechanism, in which H 2 PO 4 − takes as a carrier and [ − C = N − ] takes as a stronghold, is considered as the main proton transfer mechanism in an ab-PBI membrane at the studied doping levels. The diffusion coefficient of PA is about 2.5 times of that of H 2 PO 4 − , which indicates the diffusion of H 2 PO 4 − controls the mass transfer in the ab-PBI membrane.

This study investigates the performance of dye-sensitized solar cells constructed with a Fe-Cu metastable material as the mesoporous layer on which a natural organic dye is applied. The synthesis of the Fe-Cu material is done via a high throughput process that produces nanosized particles from elemental metallic powders. Xanthophyll is singled out as the organic natural dye of choice among other dyes that were extracted, as it exhibited wider spectral absorptivity in terms of wavelength range and magnitude. Two compact solar cells were constructed and tested; one is a reference cell with a TiO2 working electrode and the other with a Fe-Cu working electrode. The results show a better power conversion efficiency for the Fe-Cu-based solar cell 0.943% compared to 0.638% for the TiO2, and the number of carriers in the former is found to be orders of magnitude higher than the latter (1019 vs. 1032, respectively). A thorough optical, electrical, and thermal analysis of the Fe-Cu material is conducted and used to explain the obtained results.

In this work, a novel material based on carbon nanostructures (CNS), developed by Applied NanoStructured Solutions, was used with the goal of fabricating scalable CNS-based mats as an alternative to commercially available CNT-based mats. Statistical and experimental methods have been used to determine how the amount of surfactant and the sonication time that is used during fabrication of the mats have affected their mechanical and electrical properties. A strong statistically-significant interaction between surfactant/CNS mass ratio and sonication time was observed. Factorial ANOVA suggested that the combination of a surfactant/CNS mass ratio of approximately 2 and a sonication time of 5 min are optimal for electrical conductivity; this combination used the minimum amount of surfactant and the minimum sonication time of all the values investigated in the study. Samples with combinations of a surfactant/CNS mass ratio of 2 and a sonication time of

The oxygen reduction reaction plays an important role in the performance of high-temperature proton exchange membrane (HT-PEM) fuel cells. In this study, a molecular dynamics model, which is based on the density functional theory and couples the system’s energy, the exchange-correlation energy functional, the charge density distribution function, and the simplified Kohn–Sham equation, was developed to simulate the oxygen reduction reaction on a Pt(111) surface. Additionally, an electrochemical reaction system on the basis of a four-electron reaction mechanism was also developed for this simulation. The reaction path of the oxygen reduction reaction, the product structure of each reaction step and the system’s energy were simulated. It is found that the first step reaction of the first hydrogen ion with the oxygen molecule is the controlling step of the overall reaction. Increasing the operating temperature speeds up the first step reaction rate and slightly decreases its reaction energy barrier. Our results provide insight into the working principles of HT-PEM fuel cells.