Characterization of Cu2O/CuO heterostructure photocathode by tailoring CuO thickness for photoelectrochemical water splitting.

Cu2O/CuO heterostructure is a well-known strategy to improve the performance of Cu2O photocathodes for photoelectrochemical (PEC) water splitting. The CuO thickness in the Cu2O/CuO heterostructure is considered as a critical factor affecting the PEC performance because it is highly related to the light utilization and charge separation/transport. In this study, the Cu2O/CuO photocathode tailoring the CuO thickness was investigated to examine the CuO thickness influence on the PEC performance. Cu2O/CuO photocathodes were prepared by the electrodeposition and subsequent thermal annealing process and the Cu2O/CuO heterostructure was controlled by the annealing temperature and time. It was demonstrated that the increased CuO thickness enhances the light absorption in the long wavelength region and improves the charge separation by the reinforced band bending. However, the thick CuO hinders the efficient charge transport in the Cu2O/CuO heterostructure, resulting in the decreased PEC performance. Therefore, it is necessary to optimize the CuO thickness for the enhanced PEC performance of Cu2O/CuO photocathodes. Consequently, the Cu2O/CuO photocathode consisting of the similar CuO thickness with its minority carrier diffusion length (∼90 nm) was fabricated by annealing at 350 °C for 20 min, and it shows the optimal PEC performance (-1.2 mA cm-2 at 0 V vs. RHE) in pH 6.5 aqueous solution, resulting from the enhanced light utilization and the reinforced band bending.

Electrocatalytic Properties of Pulse-Reverse Electrodeposited Nickel Phosphide for Hydrogen Evolution Reaction.

Nickel phosphide (Ni-P) films as a catalytic cathode for the hydrogen evolution reaction (HER) of a water splitting were fabricated by a pulse-reverse electrodeposition technique. The electrochemical behaviors for the electrodeposition of Ni-P were investigated by the characterization of peaks in a cyclic voltammogram. The composition of the electrodeposited Ni-P alloys was controlled by adjusting duty cycles of the pulse-reverse electrodeposition. The HER electrocatalytic properties of the Ni-P electrodeposits with an amorphous phase as a function of phosphorous contents existing in Ni-P were electrochemically characterized by the analysis of overpotentials, Tafel slopes, and electrochemical impedance spectrometry. Additionally, the elemental Ni-embedded crystalline Ni3P was prepared by an annealing process with the amorphous Ni69P31 electrodeposit with high contents of phosphorus. The crystalline structure with Ni inclusions in the matrix of Ni3P was formed by the precipitation of excess Ni. The electrocatalytic properties of crystalline Ni3P with elemental Ni inclusions were also investigated by electrochemical characterization.

Multifunctional Polymer Nanocomposites Reinforced by 3D Continuous Ceramic Nanofillers.

Polymer nanocomposites with inclusion of ceramic nanofillers have relatively high yield strength, elastic moduli, and toughness that therefore are widely used as functional coating and films for optoelectronic applications. Although the mechanical properties are enhanced with increasing the fraction of nanofiller inclusion, there generally is an upper limit on the amount of nanofiller inclusion because the aggregation of the fillers in the polymer matrix, which typically occurs, degrades the mechanical and/or optical performances above 5 vol % of inclusions. Here, we demonstrate an unconventional polymer nanocomposite composed of a uniformly distributed three-dimensional (3D) continuous ceramic nanofillers, which allows for extremely high loading (∼19 vol %) in the polymer matrix without any concern of aggregation and loss in transparency. The fabrication strategy involves conformal deposition of Al2O3 nanolayer with a precise control in thickness that ranges from 12 to 84 nm on a 3D nanostructured porous polymer matrix followed by filling the pores with the same type of polymer. The 3D continuous Al2O3 nanolayers embedded in the matrix with extremely high filler rate of 19.17 vol % improve compressive strength by 142% compared to the pure epoxy without Al2O3 filler, and this value is in agreement with theoretically predicted strength through the rule of mixture. These 3D nanocomposites show superb transparency in the visible (>85% at 600 nm) and near-IR (>90% at 1 µm) regions and improved heat dissipation beyond that of conventional Al2O3 dispersed nanocomposites with similar filler loading of 15.11 vol % due to the existence of a continuous thermal conduction path through the oxide network.

Highly effective Cs+ removal by turbidity-free potassium copper hexacyanoferrate-immobilized magnetic hydrogels.

Potassium copper hexacyanoferrate-immobilized magnetic hydrogel (MHPVA) has been synthesized via a facile freeze/thaw crosslinking method. The citric acid coated Fe3O4 is embedded into the hydrogel matrix to facilitate the dispersion of nano-sized KCuHCF particles for Cs+ removal, followed by the rapid recovery of the composite in a magnetic field. The Cs+ adsorption behavior of the MHPVA is fitted well with the Langmuir isotherm and the pseudo-second-order kinetic model. The MHPVA exhibits both high Cs+ adsorption capacity (82.8mg/g) and distribution coefficient (Kd) of 1.18×106mL/g (8.3ppm Cs+, V/m=1000mL/g). Sorption of above 90% Cs+ to the MHPVA is achieved in less than 3h of contact time. Moreover, the MHPVA reveals stable and high Cs+ removal efficiency across a wide pH range from 4 to 10. In terms of Cs+ selectivity, the MHPVA shows above 96% removal efficiency in the presence of 0.01M competing cations such as Mg2+, Ca2+, Na+, and K+ with 1ppm of Cs+. From a practical perspective, the MHPVA still exhibits stable and promising selective properties even in groundwater and seawater conditions and after 5days of contact time the used adsorbent is rapidly recovered leaving a turbidity-free aqueous environment.

Highly transparent poly(glycidyl methacrylate-co-acryloisobutyl POSS) for 100 µm-thick submicron patterns with an aspect ratio over 100.

This is the first report on the fabrication of defect-free submicron structures with more than 100 µm thickness and an aspect ratio over 100. Highly transparent poly(glycidyl methacrylate-co-acryloisobutyl POSS) (PGP) was synthesized via radical polymerization. The mechanical properties of the PGP submicron structure displayed a Young's modulus of 6.09 GPa and a hardness of 0.16 GPa, 4.2 and 8 times, respectively, than those of SU8 nanopatterns. These enhancements enable the utilization of ultrathick 2D-/3D-submicron structures as an ideal platform for microelectromechanical systems, big data storage systems, energy devices, etc.

Size-dependent hardness of five-fold twin structured Ag nanowires.

In this study, the size dependent hardness of silver nanowires with a five-fold twin structure was examined using nanoindentation. As the diameter of the nanowires is reduced, the five-fold twin boundaries restrict the dislocation motion, and therefore a size dependent plasticity is expected for these uniquely structured nanowires. The polyol reduction method with modifications was used to synthesize silver nanowires with different diameters in the range of 70 nm to 144 nm. The nanoindentation experiments were performed on silver nanowires deposited on a stiff MgO substrate, and the resulting h, P, and S data were analyzed using the analytical double contact model for nanowire indentation. The hardness of the nanowires determined using the double contact model showed an increase in the hardness with reduction in the diameter of the nanowires, as expected due to the presence of the twin boundaries. The hardness values determined using the analytical double contact model compared favorably to the hardness values calculated from the contact areas that were extracted from finite element method simulations of an elastic indentation into the silver nanowires on the MgO substrate.

Solution-Processed Ag Nanowires + PEDOT:PSS Hybrid Electrode for Cu(In,Ga)Se2 Thin-Film Solar Cells.

To reduce the cost of the Cu(In,Ga)Se2 (CIGS) solar cells while maximizing the efficiency, we report the use of an Ag nanowires (NWs) + poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) ( PEDOT: PSS) hybrid transparent electrode, which was deposited using all-solution-processed, low-cost, scalable methods. This is the first demonstration of an Ag NWs + PEDOT: PSS transparent electrode applied to CIGS solar cells. The spin-coated 10-nm-thick PEDOT: PSS conducting polymer layer in our hybrid electrode functioned as a filler of empty space of an electrostatically sprayed Ag NW network. Coating of PEDOT: PSS on the Ag NW network resulted in an increase in the short-circuit current from 15.4 to 26.5 mA/cm(2), but the open-circuit voltage and shunt resistance still needed to be improved. The limited open-circuit voltage was found to be due to interfacial recombination that is due to the ineffective hole-blocking ability of the CdS film. To suppress the interfacial recombination between Ag NWs and the CdS film, a Zn(S,O,OH) film was introduced as a hole-blocking layer between the CdS film and Ag NW network. The open-circuit voltage of the cell sharply improved from 0.35 to 0.6 V, which resulted in the best cell efficiency of 11.6%.

Highly transparent Au-coated Ag nanowire transparent electrode with reduction in haze.

Ag nanowire transparent electrode has excellent transmittance and sheet resistance, yet its optical haze still needs to be improved in order for it to be suitable for display applications. Ag nanowires are known to have high haze because of the geometry of the nanowire and the high light scattering characteristic of the Ag. In this study, a Au-coated Ag nanowire structure was proposed to reduce the haze, where a thin layer of Au was coated on the surface of the Ag nanowires using a mild [Au(en)2]Cl3 galvanic displacement reaction. The mild galvanic exchange allowed for a thin layer of Au coating on the Ag nanowires with minimal truncation of the nanowire, where the average length and the diameter were 13.0 µm and 60 nm, respectively. The Au-coated Ag nanowires were suspended in methanol and then electrostatically sprayed on a flexible polycarbonate substrate that revealed a clear reduction in haze with a 2-4% increase in total transmittance, sheet resistance ranges of 80-90%, and 8.8-36.8 Ohm/sq. Finite difference time domain simulations were conducted for Au-coated Ag nanowires that indicated a significant reduction in the average scattering from 1 to 0.69 for Au layer thicknesses of 0-10 nm.

Highly reliable ag nanowire flexible transparent electrode with mechanically welded junctions.

Deformation behavior of the Ag nanowire flexible transparent electrode under bending strain is studied and results in a novel approach for highly reliable Ag nanowire network with mechanically welded junctions. Bending fatigue tests up to 500,000 cycles are used to evaluate the in situ resistance change while imposing fixed, uniform bending strain. In the initial stages of bending cycles, the thermally annealed Ag nanowire networks show a reduction in fractional resistance followed by a transient and steady-state increase at later stages of cycling. SEM analysis reveals that the initial reduction in resistance is caused by mechanical welding as a result of applied bending strain, and the increase in resistance at later stages of cycling is determined to be due to the failure at the thermally locked-in junctions. Based on the observations from this study, a new methodology for highly reliable Ag nanowire network is proposed: formation of Ag nanowire networks with no prior thermal annealing but localized junction formation through simple application of mechanical bending strain. The non-annealed, mechanically welded Ag nanowire network shows significantly enhanced cyclic reliability with essentially 0% increase in resistance due to effective formation of localized wire-to-wire contact.

Electrostatic spray deposition of highly transparent silver nanowire electrode on flexible substrate.

In this work, a modified polyol synthesis by adding KBr and by replacing the AgCl with NaCl seed was used to obtain high quality silver nanowires with long aspect ratios with an average length of 13.5 µm in length and 62.5 nm in diameter. The Ag nanowires suspended in methanol solution after removing any unwanted particles using a glass filter system were then deposited on a flexible polycarbonate substrate using an electrostatic spray system. Transmittance of 92.1% at wavelength of 550 nm with sheet resistance of 20 Ω/sq and haze of 4.9% were measured for the electrostatic sprayed Ag nanowire transparent electrode.

Evolutionary design principles of modules that control cellular differentiation: consequences for hysteresis and multistationarity.

MOTIVATION: Gene regulatory networks (GRNs) govern cellular differentiation processes and enable construction of multicellular organisms from single cells. Although such networks are complex, there must be evolutionary design principles that shape the network to its present form, gaining complexity from simple modules. RESULTS: To isolate particular design principles, we have computationally evolved random regulatory networks with a preference to result either in hysteresis (switching threshold depending on current state), or in multistationarity (having multiple steady states), two commonly observed dynamical features of GRNs related to differentiation processes. We have analyzed the resulting evolved networks and compared their structures and characteristics with real GRNs reported from experiments. CONCLUSION: We found that the artificially evolved networks have particular topologies and it was notable that these topologies share important features and similarities with the real GRNs, particularly in contrasting properties of positive and negative feedback loops. We conclude that the structures of real GRNs are consistent with selection to favor one or other of the dynamical features of multistationarity or hysteresis. SUPPLEMENTARY INFORMATION: Supplementary data are available at Bioinformatics online.