Electrospun fiber membranes from blends of poly(vinylidene fluoride) with fouling‐resistant zwitterionic copolymers

Nonwoven super‐hydrophobic fiber membranes have potential applications in oil–water separation and membrane distillation, but fouling negatively impacts both applications. Membranes were prepared from blends comprising poly(vinylidene fluoride) (PVDF) and random zwitterionic copolymers of poly(methyl methacrylate) (PMMA) with sulfobetaine methacrylate (SBMA) or with sulfobetaine‐2‐vinylpyridine (SB2VP). PVDF imparts mechanical strength to the membrane, while the copolymers enhance fouling resistance. Blend composition was varied by controlling the PVDF‐to‐copolymer ratio. Nonwoven fiber membranes were obtained by electrospinning solutions of PVDF and the copolymers in a mixed solvent of N,N‐dimethylacetamide and acetone. The PVDF crystal phases and crystallinities of the blends were studied using wide‐angle X‐ray diffraction and differential scanning calorimetry (DSC). PVDF crystallized preferentially into its polar β‐phase, though its degree of crystallinity was reduced with increased addition of the random copolymers. Thermogravimetry (TG) showed that the degradation temperatures varied systematically with blend composition. PVDF blends with either copolymer showed significant increase of fouling resistance. Membranes prepared from blends containing 10% P(MMA‐ran‐SB2VP) had the highest fouling resistance, with a fivefold decrease in protein adsorption on the surface, compared to homopolymer PVDF. They also exhibited higher pure water flux, and better oil removal in oil–water separation experiments. © 2018 Society of Chemical Industry     

Hardness and fracture toughness of thermoelectric La<Subscript>3−<Emphasis Type="Italic">x</Emphasis></Subscript>Te<Subscript>4</Subscript>

Lanthanum telluride (La_3?x Te₄) is a state-of-the-art n-type high temperature thermoelectric material that behaves as a weak and brittle ceramic. Vickers microindentation hardness testing was explored as a rapid analysis technique to characterize the mechanical properties of this material. An indentation size effect was observed with hardness values ranging from 439 ± 31 kgf/mm² (0.01 kgf/10 s contact time) to 335 ± 6 kgf/mm² (0.5 kgf/10 s contact time). The Vickers indentation fracture toughness, K _VIF, based on measurements of crack lengths emanating from the corners of the Vickers indents was 0.70 ± 0.06 MPa m^1/2.     

Preparation and characterization of the platinum metal phosphides RuP2 and IrP2

Single crystals of iridium and ruthenium diphosphide have been grown from a tin flux. Both compounds are diamagnetic semiconductors exhibiting extrinsic electrical conductivity from ～77 to ～300°K. Optical measurements indicate absorption edges of 1.1(1) and 0.8(1) eV for IrP₂ and RuP₂, respectively.     

Nanostructured Bulk Silicon as an Effective Thermoelectric Material

Thermoelectric power sources have consistently demonstrated their extraordinary reliability and longevity for deep space missions and small unattended terrestrial systems. However, more efficient bulk materials and practical devices are required to improve existing technology and expand into large‐scale waste heat recovery applications. Research has long focused on complex compounds that best combine the electrical properties of degenerate semiconductors with the low thermal conductivity of glassy materials. Recently it has been found that nanostructuring is an effective method to decouple electrical and thermal transport parameters. Dramatic reductions in the lattice thermal conductivity are achieved by nanostructuring bulk silicon with limited degradation in its electron mobility, leading to an unprecedented increase by a factor of 3.5 in its performance over that of the parent single‐crystal material. This makes nanostructured bulk (nano‐bulk) Si an effective high temperature thermoelectric material that performs at about 70% the level of state‐of‐the‐art Si_0.8Ge_0.2 but without the need for expensive and rare Ge.     

Exploration of Advanced Electrode Materials for Approaching High‐Performance Nickel‐Based Superbatteries

The surging interest in high performance, low‐cost, and safe energy storage devices has spurred tremendous research efforts in the development of advanced electrode active materials. Herein, the in situ growth of zinc–iron layered double hydroxide (Zn–Fe LDH) on graphene aerogel (GA) substrates through a facile, one‐pot hydrothermal method is reported. The strong interaction and efficient electronic coupling between LDH and graphene substantially improve interfacial charge transport properties of the resulting nanocomposite and provide more available redox active sites for faradaic reactions. An LDH–GA||Ni(OH)₂ device is also fabricated that results in greatly enhanced specific capacity (187 mAh g^?1 at 0.1 A g^?1), outstanding specific energy (147 Wh kg^?1), excellent specific power (16.7 kW kg^?1), along with 88% capacity retention after >10 000 cycles. This approach is further extended to Ni–MH and Ni–Cd batteries to demonstrate the feasibility of compositing with graphene for boosting the energy storage performance of other well‐known Ni‐based batteries. In contrast to conventional Ni‐based batteries, the nearly flat voltage plateau followed by a sloping potential profile of the integrated supercapacitor–battery enables it to be discharged down to 0 V without being damaged. These findings provide new prospects for the design of high‐performance and affordable superbatteries based on earth‐abundant elements.     

Three-dimensional core-shell hybrid solar cells via controlled in situ materials engineering

Three-dimensional core-shell organic-inorganic hybrid solar cells with tunable properties are demonstrated via electropolymerization. Air-stable poly(3,4-ethylenedioxythiophene) (PEDOT) shells with controlled thicknesses are rapidly coated onto periodic GaAs nanopillar arrays conformally, preserving the vertical 3D structure. The properties of the organic layer can be readily tuned in situ, allowing for (1) the lowering of the highest occupied molecular orbital level (|ΔE| ～ 0.28 eV), leading to the increase of open-circuit voltage (V(OC)), and (2) an improvement in PEDOT conductivity that results in enhanced short-circuit current densities (J(SC)). The incorporation of various anionic dopants in the polymer during the coating process also enables the tailoring of the polymer/semiconductor interface transport properties. Systematic tuning of the device properties results in a J(SC) of 13.6 mA cm(-2), V(OC) of 0.63 V, peak external quantum efficiency of 58.5%, leading to a power conversion efficiencies of 4.11%.