Electrochemical conversion of CO2 to valuable fuels is appealing for CO2 fixation and energy storage. The Cu‐based catalysts feature unique superiorities, but achieving high ethylene selectivity is ...still restricted. In this study, we propose the anchoring of an ionic liquid (IL) on a Cu electrocatalyst for improving the electrochemical CO2 reduction to ethylene. In a water‐based electrolyte and a commonly used H‐type cell, a high ethylene Faradaic efficiency of 77.3 % was achieved at −1.49 V (vs. RHE). Experimental and theoretical studies reveal that an IL can modify the electronic structure of a Cu catalyst through its interaction with Cu, making it more conducive to *CO dimerization for ethylene formation.
The ionic liquid 1‐butyl‐3‐methylimidazolium nitrate (BmimNO3) was anchored into Cu, through which the atomic coordination and electronic properties of Cu can be optimized to facilitate C−C coupling. This electrocatalyst can reduce CO2 to C2H4 with high selectivity. The Faradaic efficiency of C2H4 reaches 77.3 % at −1.49 V (vs. RHE) in KHCO3 aqueous solution using a H‐type cell, much higher than that over pure Cu catalyst (31.2 %).
Graphene oxide (GO) membrane, bearing well-aligned interlayer nanochannels and well-defined physicochemical properties, promises fast proton transport. However, the deficiency of proton donor groups ...on the basal plane of GO and weak interlamellar interactions between the adjacent nanosheets often cause low proton conduction capability and poor water stability. Herein, we incorporate sulfonated graphene quantum dots (SGQD) into GO membrane to solve the above dilemma via synergistically controlling the edge electrostatic interaction and in-plane π–π interaction of SGQD with GO nanosheets. SGQD with three different kinds of electron-withdrawing groups are employed to modulate the edge electrostatic interactions and improve the water swelling resistant property of GO membranes. Meanwhile, SGQD with abundant proton donor groups assemble on the sp2 domain of GO via in-plane π–π interaction and confer the GO membranes with low-energy-barrier proton transport channels. As a result, the GO membrane achieves an enhanced proton conductivity of 324 mS cm–1, maximum power density of 161.6 mW cm–2, and superior water stability when immersed into water for one month. This study demonstrates a strategy for independent manipulation of conductive function and nonconductive function to fabricate high-performance proton exchange membranes.
Simultaneous manipulation of topological and chemical structures to induce ionic nanochannel formation within solid electrolytes is a crucial but challenging task for the rational design of ...high‐performance electrochemical devices including proton exchange membrane fuel cell. Herein, a novel generic approach is presented for the construction of tunable ion‐conducting nanochannels via direct assembly of graphene oxide (GO)/poly(phosphonic acid) core–shell nanosheets prepared by surface‐initiated precipitation polymerization. Using this simple and rapid approach to engineer GO/polymer nanosheets at the molecular‐level, ordered and continuous nanochannels with interconnected hydrogen‐bonded networks having a favorable water environment can be created. The resulting membranes exhibit proton conductivities up to 32 mS cm−1 at 51% relative humidity, surpassing state‐of‐the‐art Nafion membrane and all previously reported GO‐based materials.
A novel approach to construct tunable nanochannels via direct assembly of graphene oxide/polymer core–shell nanosheets is developed. Through molecular‐level engineering of the nanosheets, ordered and continuous nanochannels with well‐tailored chemical structures can be created. The resulting membrane exhibits a proton conductivity of 32 mS cm−1 at 51% RH, surpassing state‐of‐the‐art Nafion membrane and all previously reported GO‐based materials.
Rotor clearance is necessary for the safe operation of twin-screw compressors, and it has a major impact on the performance of twin-screw compressors. The purpose of this study was to obtain a rotor ...tooth profile with reasonable meshing clearance on the rotor end surface, so that the clearance on the rotor contact line would be uniform and the rotor could be smoothly meshed. Under ideal conditions, the rotor of a screw compressor should have no clearance or interference. However, owing to assembly errors, thermal compression, stress deformation, and other factors, a rotor without backlash modification will inevitably produce interference during operation. A new design method based on the Alpha shape solution was proposed to achieve an efficient and high-precision design of the clearance of the twin-screw rotor profile. This method avoids the complex analytical calculations in the traditional envelope principle. The best approximation of the points on the rotor conjugate motion sweeping surface in the points is illuminated using a specific color. The sweeping surface of the screw rotor single-tooth profile is roughly scanned to capture the base point set of the sweeping surface boundary points. The chord length and tilt angle of each interval are calculated using the value of the base point set to adjust the position, phase, and magnification of each interval sweeping surface. Finally, the data point set is converted to the same coordinate system to generate the conjugated rotor profile. An example was used to verify the feasibility and adaptability of this method. Based on the equidistant profile method, the clearance between male and female rotors of a screw compressor was obtained under actual operation conditions. Therefore, this study provides a basis for the meshing clearance design in the machining of twin-screw compressor rotors.
NaNbO
3
-based lead-free ceramics are gaining widespread interest in recent years due to their environmental friendliness and low density, which can meet the needs of future advanced pulse power ...electronics for low cost, miniaturization and integration. However, a reversible phase transition of FE-AFE at room temperature for pure NaNbO
3
ceramic will produce a large residual polarization, resulting in a low energy storage capacity. In this work, the ternary system (1-
x
)(0.92NaNbO
3
-0.08Bi(M
g0.5
Ti
0.5
)O
3
)-
x
CaTiO
3
was designed by introducing the linear material CaTiO
3
doped into (0.92NaNbO
3
-0.08Bi(Mg
0.5
Ti
0.5
)O
3
) ceramics to enhance the disorder of A/B sites in the system. The introduce of CaTiO
3
could optimize the relaxation characteristics of the ceramics, refine the grain size to improve the breakdown field strength(
E
b
), which enhance the energy storage properties to
W
rec
= 5.71 J/cm
3
and
η
= 85.7% at 475 kV/cm. Additionally, the 0.8(0.92NN-0.08BMT)-0.2CT ceramic achieves both temperature (20–160 °C) and frequency (5 Hz -120 Hz) stability, while also obtains excellent charge/discharge performance(
C
D
= 607.22 A/cm
2
,
P
D
= 48.58 MW/cm
3
,
t
0.9
= 28 ns), which indicates the great potential application in pulsed power capacities.
Graphical Abstract
Development of proton exchange membranes with sufficiently high proton conductivity, especially at low relative humidity (RH), remains a big challenge in the field of fuel cells. In this study, ...graphene oxide-based nanoscale ionic materials (NIMs-GO) were prepared by sulfonation with 3-(trihydroxysilyl)-1-propanesulfonic acid and subsequent neutralization with amino-terminated polyoxypropylene (PO)–polyoxyethylene (EO) block copolymer. The resultant NIMs-GO with acid–base pairs and hygroscopic EO units were incorporated into sulfonated polysulfone (SPSF) to fabricate nanocomposite membranes. A matrix-softening phenomenon was found due to the extensive interaction between the SPSF matrix and the amphiphilic NIMs-GO, which primarily contributes to the homogeneous dispersion of the NIMs-GO filler in the nanocomposite membranes. The acid–base pairs and the interconnected hydrogen-bonded networks formed between the EO units and water molecules imparted efficient proton transfer via the Grotthuss mechanism. The water uptake and retention ability of the SPSF/NIMs-GO nanocomposite membranes were enhanced due to the hydrophilic EO units on NIMs-GO. As a result, the nanocomposite membrane exhibited a 52% increase compared with the pristine SPSF membrane in proton conductivity at 75 °C, 100% RH and a 24-fold increase at 75 °C, 40% RH. This enhanced proton conductivity led to an elevated fuel cell performance under both hydrous and low RH conditions.
Ferric acetylacetonate/covalent organic framework (Fe(acac)3/COF) composite was synthesized by interfacial polymerization method at room temperature. The crystal structure, morphology and porosity ...property of the composite were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope and nitrogen adsorption. The interaction between Fe(acac)3 and COF was investigated by Fourier transform infrared spectra and X-ray photoelectron spectroscopy. The Fe(acac)3/COF composite was used as a photocatalyst for the oxidation of benzyl alcohol under mild conditions. It exhibits high activity and selectivity for the reaction, of which the mechanism was investigated by determining its photoelectric properties. The Fe(acac)3/COF catalyst developed in this work has application potential in other photocatalytic reactions.
Here, we synthesized Fe(acac)3/Bp-COF composite photocatalyst in one step under mild conditions. Compared with Bp-COF, composite photocatalyst has facile preparation and exhibits highly improved light absorbance and transformation of photogenerated electron–hole pairs. The composite photocatalyst can efficiently convert benzyl alcohol into benzaldehyde under the condition of room temperature and air as oxidant without producing other by-products. Display omitted
•A ferric acetylacetonate/covalent organic framework composite was synthesized using interfacial polymerization method.•The composite exhibits excellent light absorbance and transformation of photogenerated electron–hole pairs.•The composite shows high catalytic performance for the selective oxidation of benzyl alcohol under mild conditions.
The construction of efficient proton transport channels in ion-conductive membranes is crucial to proton exchange membrane fuel cells (PEMFCs). Herein, zwitterion-functionalized covalent organic ...framework (Z-COF) with both ammonium groups and sulfonic acid groups was synthesized and blended with Nafion to prepare Nafion/Z-COF composite proton exchange membranes. The polymer-like feature of the Z-COF imparted favorable interactions between Z-COF and Nafion, and thus promoted the dispersion of Z-COF and the reorganization of ion clusters. The incorporation of Z-COF enhanced water retention property and the sulfonic groups on Z-COF provided additional proton-transport sites within the membranes. As a result, the low-energy-barrier paths for proton transport were created. The composite membranes with 10 wt% of Z-COF exhibited the highest proton conductivity of 0.22 S cm−1 at 80 °C and 100% RH, which was 57.1% higher than that of recast Nafion membrane. The enhanced proton conductivity also afforded the composite membrane a 45.7% increase in maximum power density of single fuel cell at 80 °C and 50% RH. The effects of Z-COF loading on membrane morphology, polymer chain mobility, thermal stability, water uptake and dimensional stability were also investigated.
•Covalent organic framework (COF) is functionalized with zwitterions.•Composite membranes are prepared by doping zwitterion-functionalized COF as additive into Nafion.•The composite membrane records a 1.6-fold proton conductivity enhancement.•The thermal stability, dimensional stability and mechanical strength are improved.
High-performance dielectric capacitors are one of the key components of pulsed power systems. Recently, with the rapid development of new energy sources, achieving a large energy storage density and ...a high efficiency in relaxor ferroelectric ceramics becomes the focus of our research. However, owing to the low breakdown strength (Eb), it is still a challenge to achieve high recoverable energy storage density (Wrec) in (Bi0.5Na0.5)0.7Sr0.3TiO3-based ceramics. The doping of Sm(Mg0.5Zr0.5)O3 can effectively increase the activation energy of the ceramics and reduce the oxygen vacancy concentration. Therefore, a giant Wrec of ∼6.2 J/cm3 and a high energy storage efficiency (η) of ∼82.4 % are realized in 0.88(Bi0.5Na0.5)0.7Sr0.3TiO3-0.12Sm(Mg0.5Zr0.5)O3 ceramics at Eb = 455 kV/cm. Besides, the ceramic also possesses a high current density of 611.5 A/cm2, a high-power density of 55.0 MV/cm3 and the fast discharge rate near 10.0 ns. This strategy to improve the energy storage performance opens up a new and effective way for future research on lead-free energy storage ceramics.
•The enhancement of Eb is realized in BNST ceramics.•Wrec of 6.2 J/cm3 and η of 82.5% are achieved in 0.12SMZ ceramic.•The 0.12SMZ ceramic exhibit excellent frequency and temperature stability.•High CD of 611.5 A/cm2 and PD of 55.0 MV/cm3 at an applied electric field of 180 kV/cm.
Inductors that are widely used in wideband filter designs could result in large filter size and high insertion loss. A novel design method using admittance matrix based on direct circuit ...implementation is introduced for wideband bandpass filters. Firstly, a frequency transformation is performed on cross-couplings to realize the conversion between inductor and capacitor, thereby reducing usage of inductors. Moreover, by virtue of an enhanced resonator (type I), an approach of adding extra transmission zero is proposed to improve the out-of-band rejection without any additional usage of inductors. Thirdly, based on the frequency transformation, another enhanced resonator (type II) is introduced to further improve the frequency characteristics without compromising usage of inductors. Finally, by cascading the enhanced resonators of type I and type II, a novel filter can be constructed. This novel filter is designed and fabricated using a glass-based integrated passive device (IPD) technology. The measurement results are highly consistent with the simulation results. It is shown that the proposed design method can reduce the filter size and thus improve the chip integration. It enriches the freedoms during the filter design.
PDF
