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The modified cyanate ester resin(CE) which can be applied stably in the cryogenic environment was prepared by using phenoxy resin(PKHH) and high purity epoxy resin(EP) through the method of melting prepolymerization. The results show that the curing reaction of CE is accelerated by the addition of PKHH, but the reaction pathways are not changed. It is found that PKHH can improve the ductility by the mechanism of the semi-interpenetrating network (SIPN) in the cured CE networks. Especially, the impact strength value of the CE/EP blends with the content of 10% (mass fraction) PKHH reaches to 18.4 kJ/m2 and the modulus is maintained at about 3.5 GPa at –196 ℃, accordingly the cracks are not observed on the surface of specimens after 20 low-high temperature cycles (–196 to 200 ℃).

In this work, the phenolphthalein poly(ether sulfone) (PESC)-modified cyanate ester (CE) and epoxy (EP) blends were prepared. This work mainly discusses the curing behaviors, fracture toughness, dynamic mechanical properties, and thermal and mechanical properties of the blends. The Fourier transform infrared and differential scanning calorimetric analyses are used to confirm the curing behaviors, demonstrating that the main reaction pathways are not varied with the addition of PES-C, but the reaction rate could be evidently accelerated. The fracture morphologies of the blends are observed by Scanning electron microscope (SEM) and the fracture causes of the failed surface are also analyzed. With the addition of PES-C, the modified blends display higher fracture toughness ([K.sub.lc]) and impact strength when compared with neat CE. Domain sizes of the blends first increase then decrease with the addition of PES-C. The results of dynamic mechanical analysis and thermogravimetric analysis show that the [T.sub.g], storage modulus, and thermal stability of the crosslink network slightly decreases with the addition of PES-C. The mechanical strength of blends with the addition of PES-C is far better than that of the blends without PES-C both at ambient temperature and elevated temperature. POLYM. ENG. SCI., 55:2591-2602, 2015. [C] 2015 Society of Plastics Engineers, INTRODUCTION Cyanate ester resins (CE, [T.sub.g]: 255-262°C) are recently used as matrices for high-performance composites and as adhesive materials for advanced random structures in aerospace field because of their high-temperature [...]

To ensure sustainable hydrogen production by water electrolysis, robust, earth‐abundant, and high‐efficient electrocatalysts are required. Constructing a hybrid system could lead to further improvement in electrocatalytic activity. Interface engineering in composite catalysts is thus critical to determine the performance, and the phase‐junction interface should improve the catalytic activity. Here, we show that nickel diphosphide phase junction (c‐NiP2/m‐NiP2) is an effective electrocatalyst for hydrogen production in alkaline media. The overpotential (at 10 mA cm−2) for NiP2‐650 (c/m) in alkaline media could be significantly reduced by 26 % and 96 % compared with c‐NiP2 and m‐NiP2, respectively. The enhancement of catalytic activity should be attributed to the strong water dissociation ability and the rearrangement of electrons around the phase junction, which markedly improved the Volmer step and benefited the reduction process of adsorbed protons. [ABSTRACT FROM AUTHOR]

Rhenium dichalcogenides (ReX2, X = S or Se) are catalysts that have great promise for the photoenhanced hydrogen evolution reaction (PE‐HER) because of their unique physiochemical properties. However, the catalytic performance is still restricted by their low concentration of electrocatalytic activity sites and poor injection of hot electrons. Herein, dual‐enhancement in ReSe2 nanosheets (NSs) with high concentration of active sites and efficient use of hot electrons is simultaneously achieved with moderate Mo doping. Contributions from exposed catalytically active sites, improved electrical conductivity, and enhanced solar spectral response are systematically investigated. Superior PE‐HER catalytical performance is obtained in Re0.94Mo0.06Se2, which has more catalytically active sites and optimized band structure than other Re1−xMoxSe2 samples. Here, it is demonstrated that only doping can reduce the overpotential (η10) from 239 to 174 mV at −10 mA cm−2 (Δ1η10 = 65 mV). Then, η10 is further improved to 137 mV under simulated AM 1.5 sun illumination (Δ2η10 = 37 mV). The total improvement (Δη10) toward PE‐HER is 102 mV (Δ1η10 + Δ2η10 = 102 mV) in optimal Re0.94Mo0.06Se2. This work presents a new perspective for researching high‐efficiency photoenhanced HER ReSe2‐based electrocatalysts and other layered transition metal dichalcogenides. [ABSTRACT FROM AUTHOR]

Two‐dimensional layered MoSe2 has been proved to be promising electrocatalyst toward hydrogen evolution reaction (HER), although the typical disadvantages of poor conductivity and limited density of active sites in 2H‐phase restrict further development. Here, a clear evidence is presented in partially‐crystallized 2H‐MoS2xSe2(1‐x) nanosheets (NS) to demonstrate that: i) in both 2H‐ and 1T‐phase, single factor such as phase, conductivity, or defects will not determine or restrict the catalytic activity in MoSe2, and ii) synergistic tuning at least two factors will greatly enhance the overall HER performance than single factor no matter in 2H‐ or 1T‐MoSe2 crystal structures. The enhanced catalytic activity with η10=136 mV vs RHE, and a Tafel slope of 50 mV dec−1 are achieved in the optimized 2H‐MoS0.2Se1.8‐160 NS, which is the best among pure MoSSe materials without heterogeneous atom doping to our knowledge. In addition, 2H‐MoS0.2Se1.8/rGO anodes exhibit a stable reversible capacity of 396 mA h g−1 after 100 cycles at 0.5 A g−1. These discoveries provide a unique opportunity to comprehensively understand the single factor or multi‐factors mechanism for HER, which serves as the general design and modulation principles for further synthesize and applications of MoSe2‐based materials toward HER and other catalytic applications. [ABSTRACT FROM AUTHOR]

Perovskite oxides have been explored as promising electrocatalysts for the oxygen evolution reaction (OER), while a lack of understanding of key factors impacting the catalytic activity restricts their further design and development. Here, for the first time, the contributions of oxygen vacancy (VO) and orbital occupancy of B‐site cations to the catalytic activity of NdNiO3 films are systematically investigated. It is found that OER activity follows a typical volcano‐shaped dependence on the oxygen pressure. In the range of 0.2–10 Pa, proper concentration of VO can provide a moderate bonding strength with intermediate hydroxyl OH* and the increased ratio of Ni3+/Ni2+ provides a more favorable occupancy of eg orbital for the catalytic activity; while in the range of 10–60 Pa, insufficient concentration of VO leads to an enhanced strength of hybridization between Ni 3d and O 2p band and thus deteriorated catalytic activity. The superior OER catalytic performance can be only achieved with both appropriate concentration of VO and the ratio of B‐site metal cations with different valences. [ABSTRACT FROM AUTHOR]

Perovskite oxides have been explored as promising electrocatalysts for the oxygen evolution reaction (OER), while a lack of understanding of key factors impacting the catalytic activity restricts their further design and development. Here, for the first time, the contributions of oxygen vacancy (VO) and orbital occupancy of B‐site cations to the catalytic activity of NdNiO3 films are systematically investigated. It is found that OER activity follows a typical volcano‐shaped dependence on the oxygen pressure. In the range of 0.2–10 Pa, proper concentration of VO can provide a moderate bonding strength with intermediate hydroxyl OH* and the increased ratio of Ni3+/Ni2+ provides a more favorable occupancy of eg orbital for the catalytic activity; while in the range of 10–60 Pa, insufficient concentration of VO leads to an enhanced strength of hybridization between Ni 3d and O 2p band and thus deteriorated catalytic activity. The superior OER catalytic performance can be only achieved with both appropriate concentration of VO and the ratio of B‐site metal cations with different valences. [ABSTRACT FROM AUTHOR]

To ensure sustainable hydrogen production by water electrolysis, robust, earth-abundant, and high-efficient electrocatalysts are required. Constructing a hybrid system could lead to further improvement in electrocatalytic activity. Interface engineering in composite catalysts is thus critical to determine the performance, and the phase-junction interface should improve the catalytic activity. Here, we show that nickel diphosphide phase junction (c-NiP 2 /m-NiP 2 ) is an effective electrocatalyst for hydrogen production in alkaline media. The overpotential (at 10 mA cm -2 ) for NiP 2 -650 (c/m) in alkaline media could be significantly reduced by 26 % and 96 % compared with c-NiP 2 and m-NiP 2 , respectively. The enhancement of catalytic activity should be attributed to the strong water dissociation ability and the rearrangement of electrons around the phase junction, which markedly improved the Volmer step and benefited the reduction process of adsorbed protons., (© 2020 Wiley-VCH GmbH.)

MoSe 2 is a promising earth-abundant electrocatalyst for the hydrogen-evolution reaction (HER), even though it has received much less attention among the layered dichalcogenide (MX 2 ) materials than MoS 2 so far. Here, a novel hydrothermal-synthesis strategy is presented to achieve simultaneous and synergistic modulation of crystal phase and disorder in partially crystallized 1T-MoSe 2 nanosheets to dramatically enhance their HER catalytic activity. Careful structural characterization and defect characterization using positron annihilation lifetime spectroscopy correlated with electrochemical measurements show that the formation of the 1T phase under a large excess of the NaBH 4 reductant during synthesis can effectively improve the intrinsic activity and conductivity, and the disordered structure from a lower reaction temperature can provide abundant unsaturated defects as active sites. Such synergistic effects lead to superior HER catalytic activity with an overpotential of 152 mV versus reversible hydrogen electrode (RHE) for the electrocatalytic current density of j = -10 mA cm -2 , and a Tafel slope of 52 mV dec -1 . This work paves a new pathway for improving the catalytic activity of MoSe 2 and generally MX 2 -based electrocatalysts via a synergistic modulation strategy., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)