High Electronic Efficiency Research Articles

Conductive polymer protection strategy to promote electrochemical nitrate reduction to ammonia in highly acidic condition over Cu-based catalyst

Electrochemical nitrate reduction (NO3-RR) is a promising way to produce ammonia by alternating Haber-Bosch process. As one promising catalyst, copper suffers from low activity and instability in acidic electrolyte that hinders practical applications. Herein, we report a conductive polymer protection strategy by decorating polypyrrole on Cu nanoparticles (Cu-PPy), achieving high NO3-RR efficiency under strong acidic conditions. In 0.5 M H2SO4, Cu-PPy exhibits high NH3 yield rate of 0.55 mmol h−1 cm−2 with NH3 selectivity of 99.99 % and FE of 96.0 % at high NO3– conversion. Experimental and theoretical results reveal that PPy plays a pluripotent role for the enhanced NO3-RR, consisting of protecting Cu from corrosion in highly acidic electrolyte, promoting the adsorption of NO3– and NO2– in local environment, stabilizing Cu in intermediate valence state, and accelerating the electron transfer rate. Furthermore, a co-production system of NH3 and adipic acid is constructed and achieves high combined electron efficiency.

Reversed Cherenkov radiation amplifier with compact structure and high efficiency

Based on the reversed Cherenkov radiation excited in metamaterials, a novel S-band reversed Cherenkov radiation amplifier (RCRA) with two output ports is proposed in this paper. Its metamaterial slow-wave structure (MSWS) consists of a hollow circular waveguide periodically loaded with all-metal double-ridge complementary electric split-ring resonators (CeSRRs). The CeSRR exhibits subwavelength and strong resonance characteristics, which lead to miniaturization and high interaction impedance of the MSWS. The period of the MSWS is optimized using the phase velocity jump technique to further increase the output power and electronic efficiency. The simulation results demonstrate that when the microwave signal of 7.8 W at 2.286 GHz is inputted at port 2, the output power at port 1 is 307 W, and the saturated output power and saturated gain at port 3 are 5.48 kW and 28.47 dB, respectively. Notably, the total electronic efficiency of the RCRA is predicted as 33.84%. The RCRA features high electronic efficiency and miniaturization and may meet special application scenarios that require two output microwave signals at the same frequency.

Manipulating electron extraction efficiency in microbial electrochemical carbon fixation via single-atom engineering

Microbial electrochemical carbon fixation can directly convert CO2 to renewable fuels, holding the promise of reducing greenhouse gas emissions. Whereas its further development is largely shadowed by the unclear correlation between the coordination environment and carbon-fixation biohybrids. Here, we report a single-atom engineering approach to control extracellular and interspecies charge exchange pathways for high electron efficiency via synergistic effects of Co-N4 coordination and microbiome biohybrids in the electro-methanogenesis system. Optimized carbon-fixation microbial community structures composed of electroactive methanogens and boosted extracellular polymeric substance-mediated charge exchange achieved a 21.49 times methane production rate of 568.7 mmol/m2/day (up to a maximum value of 1014 mmol/m2/day at −1.0 V vs. Ag/AgCl) and a 4.76 times faradic efficiency of 90.1% at −0.9 V vs. Ag/AgCl compared to control groups. Density functional theory calculations indicate that high Co-N/Co-C incorporation promotes the conversion of redox electron carriers for CO2 reduction, and Co-N/Co-C reduced the energy barrier of conductive substances and facilitated the electron storage at the bio/abiotic interface. The synergistic effect between Co-N4 structure and microbiome biohybrids facilitates an effective electron transfer, serving as reliable guiding principles for other microbial electrochemical systems to synthesize sustainable and value-added products.

Nitrogen vacancy/oxygen dopants designed nanoscale hollow tubular g-C3N4 with excellent photocatalytic hydrogen evolution and photodegradation

In this study, N vacancies and O heteroatoms were decorated onto hollow nanotubes carbon nitride (UMCN-3) via hydrolyzation-precipitation-calcination method to prepare high-performance photocatalyst for hydrogen evolution and photodegradation. Plenty of hollow nanotubes with diameter of 30–50 nm endowed UMCN-3 with abundant active sites and high charge transfer efficiency. Nitrogen vacancies/oxygen dopants not only created defect states but also acted as trapping centers, thus triggering the charge rearrangement to obtain high electronic transport efficiency, as evidenced by experimental results and theoretical calculations (DFT). The hydrogen evolution rate of optimal UMCN-3 sample was 23-times higher than that of pristine g-C3N4, and still at a high level in seawater. The photocatalytic degradation activity for RhB and TC of UMCN-3 also improved greatly. The superb photocatalytic performance can be put down to the three-in-one synergistic effect on N vacancies, O doped and hollow nanotubes.

Interstitial Compound Fe3C-Doped Fe(0) Nanoparticles Embedded in Mesoporous Carbon Efficiently Boosting Cr(VI) Removal

The high reactivity of Fe(0) with Cr(VI) makes it the best choice for Cr(VI) removal. Interstitial compound Fe3C was produced during the carbothermic reduction of mesoporous phenolic resin/ferric ions to form Fe(0)/Fe3C nanoparticles embedded in mesoporous carbon (Fe(0)/Fe3C@MesoC). Fe3C accelerates the electrochemical corrosion process of α-Fe(0) in solution, and the positive/negative equipotential interface that is formed by iron–carbon (Fe–C) microelectrolysis of Fe(0)/Fe3C@MesoC induces the capture of Cr(VI) anions and Cr(III) cations as a result of this process. Cr(VI) was completely reduced to Cr(III) by the Fe(0)/Fe3C@MesoC catalyst with a high electron efficiency (40.5%) relative to nanosized zero-valent iron (1.9%) and Fe@MesoC (32.7%). Surface ferrous ions are the principal reactive species responsible for Cr(VI) reduction (at least 64%); Fe(0)/Fe3C and undetectable surface ferrous ions account for a small part of Cr(VI) reduction (around 28%), and only 8% of Cr(VI) ions are reduced by active hydrogen (H*). The proposed structure of Fe(0)/Fe3C@MesoC provides new insight into iron–carbon material preparation and application in in situ chemical reduction.

Design of a High-Efficiency Ka-Band TWT Power Amplifier for Radar Applications

The design of a high-efficiency traveling-wave tube (TWT) based on a nonconventional folded waveguide slow wave structure (FW-SWS) operating over 34–36 GHz for naval and ground Ka-band radars is presented. The ridge-vane-loaded FW structure allows a good compromise between high interaction impedance and wide bandwidth along with a low weight required for aircraft radar applications and a simple planar manufacturing process structure. Small-signal simulations are performed with a custom interaction impedance evaluation program. The CST suite 2021 3-D electromagnetic simulation code is used for the prediction of the dispersion diagram. Starting from a sensitivity analysis of the FW in terms of width, a high electronic efficiency value of 14.6% is obtained with a reduction in the width of 0.1 mm. To further improve electronic efficiency, a negative phase-velocity step tapering technique is applied and a value of 15.4% from 34 to 36 GHz is obtained. Finally, under an optimized beam voltage and a current of 21 kV and 550 mA, respectively, a peak value of the output power of approximately 1.7 kW and an output power of 800 W with a duty cycle of 12% over the frequency band are obtained. Measurement results of the interaction impedance of a ridge-vane-loaded FWG structure composed of a ten-period high-conductivity oxygen-free copper carried out according to the Langerstrom perturbation method confirm the goodness of the simulation results.

Plasmonic Pt nanoparticles triggered efficient charge separation in TiO2/GaN NRs hybrid heterojunction for the high performance self-powered UV photodetectors

Solar radiation, especially the UV-A light rays (320–400 nm) exposure causes severe health hazard such as skin-related cancer and premature aging. Owing to the significance of UV-A photodetection, a high-performance UV-A photodetectors (PD) with high sensitivity, large detectivity and fast response time, have attracted great attention in various optoelectronic applications. Herein, we report a self-powered (SP) UV PD based on Pt nanoparticles (NP) decorated TiO2/GaN nanorods (NRs) hybrid heterojunction. The proposed Pt NP@TiO2/GaN NRs hybrid device demonstrates pronounced photoelectric performances including a large responsivity (44.6 A/W), superior detectivity (1.57 × 1014 Jones) and high electronic quantum efficiency (8.65 × 103 %) under the UV light intensity (λ = 382 nm, 1.32 mW/cm2) at zero bias, which are relatively much higher as compare to the pristine counterparts. In addition, the hybrid PD showed a short response/recovery times of 180 ms/200 ms, with a remarkable reproducibility and long-term stability towards the UV light. The impressive photoresponse properties of the hybrid SP PD are ascribed to the large photon absorption endorsed by the localized surface plasmonic resonance effect of Pt NP and the adequate built-in potential at the TiO2 and GaN NRs heterojunction interface, which further endows the effective separation and transport of photogenerated charge carriers. Furthermore, the plausible mechanism for the high-performances of hybrid UV PD is demonstrated in detailed using the energy band diagram. Our work reveals that the integral advantages of hybrid heterostructures, have a significant potential for the practical applications of advanced optoelectronics and high-performance SP UV-A PD.

Recent progress on the synthesis, morphology and photocatalytic dye degradation of BiVO4 photocatalysts: A review

ABSTRACT Bismuth vanadate (BVO) has been established as an efficient photocatalyst for water remediation and energy applications. Its crystal structure stability, high light quantum and electronic transmission efficiency, and outstanding energy utilization capacity are the main reasons for its enhanced utilization as a robust photocatalytic material. Several studies have reported many synthesis methods and strategies to design highly efficient BVO photocatalysts with different shapes, morphologies, facets, oxygen vacancies. This review systematically encapsulates the effects of morphologies on the photodegradation properties. Here, we have surveyed the synthesis methods of BVO photocatalysts followed by their different synthesized morphologies. The photosensitization mechanism whereby the organic dye plays both the role of photosensitizer as well as sample to be degraded is addressed. Further, we have highlighted the general sequential photocatalytic processes and the recent advances on degradation of three model pollutants (Methylene Blue, Rhodamine B and Methyl Orange). The 3 steps photocatalytic mechanism of BVO photocatalysts have discussed. This review provides also the effects of crystal facets, heterojunction BVO materials and elemental doping on the photocatalytic efficiency. Finally, current status, challenges to improve the photoactivity and the future possible scenarios are summarized.

Even Incorporation of Nitrogen into Fe0 Nanoparticles as Crystalline Fe4N for Efficient and Selective Trichloroethylene Degradation.

Surface modification of microscale Fe powder with nitrogen has emerged recently to improve the reactivity of Fe0 for dechlorination. However, it is unclear how an even incorporation of a crystalline iron nitride phase into Fe0 nanoparticles affects their physicochemical properties and performance, or if Fe0 nanoparticles with a varied nitridation degree will act differently. Here, we synthesized nitridated Fe0 nanoparticles with an even distribution of N via a sol-gel and pyrolysis method. Nitridation expanded the Fe0 lattice and provided the Fe4N species, making the materials more hydrophobic and accelerating the electron transfer, compared to un-nitridated Fe0. These properties well explain their reactivity and selectivity toward trichloroethylene (TCE). The TCE degradation rate by nitridated Fe0 (up to 4.8 × 10-2 L m-2 h-1) was much higher (up to 27-fold) than that by un-nitridated Fe0, depending on the nitridation degree. The materials maintained a high electron efficiency (87-95%) due to the greatly suppressed water reactivity (109-127 times lower than un-nitridated Fe0). Acetylene was accumulated as the major product of TCE dechlorination via β-elimination. These findings suggest that the nitridation of Fe0 nanoparticles can change the materials' physicochemical properties, providing high reactivity and selectivity toward chlorinated contaminants for in situ groundwater remediation.

Study on Impact of Different Electrode Materials on the Collector Performance in TWTs

Attaining good collector performance in terms of high collector efficiency, low backstreaming, and body interception current has been a prime motive for traveling wave tube (TWT) designers. Selection of appropriate electrode material can result in enhancement of collector performance for the same electrical design (with same electrode potentials and electrode geometry). Here, attempts have been made to quantitatively demonstrate the unexplored impact of electrode material selection on the collector performance systematically. The effect of electrode material on collector efficiency, backstreaming current, body interception current, and their fluctuations arising in a practical scenario due to the variations in input power drives and electrode potentials has been studied. This study has been extended for two different types of TWTs–one with high electronic efficiency and another with medium electronic efficiency at different operating frequencies. Five different electrode materials have been studied with precise recommendations provided for each of the two types of TWTs.

Mechanism of galvanic reduction of selenate oxyanions and surface immobilization by nano zero-valent iron aggregates under anaerobic conditions: towards high electron efficiency

Elucidation of the galvanic mechanism of selenate reduction by nZVI leads to >99.95% removal and record electron efficiency by suppressing H2 evolution via in situ Se doping.

In-situ prepared MIL-53(Fe)/BiOI photocatalyst for efficient degradation of tetracycline under visible-light driven photo-Fenton system: Investigation of performance and mechanism

In this work, a series of MIL-53(Fe)/BiOI composites were synthesized by a combined hydrothermal and facile co-precipitation method. The heterojunctions were further used as photocatalysts for tetracycline (TC) degradation in photo-Fenton system. The TC degradation rate constant for MIL-53(Fe)/BiOI (0.0906 min−1) was 2.1 and 2.3 times higher than that for MIL-53(Fe) (0.0432 min−1) and BiOI (0.0389 min−1), respectively. The photoelectrical characterization results suggested that the enhanced photocatalytic activity of the MIL-53(Fe)/BiOI composite was attributed to the high electron and holes separation efficiency. The scavenging experiment results and electron spin resonance analysis demonstrated that h+ and singlet oxygen were the main reactive species in the degradation process. The possible photo-Fenton degradation mechanism was further elucidated based on the band structures of MIL-53(Fe) and BiOI with the generation process of reactive species. This work provided a new idea to construct metal-organic-framework-based composite photocatalysts for photo-Fenton system, and it is also promising for the applications in environmental restoration and protection field.

Design and analysis of a quasi-TM03 mode G-band extended interaction radiation source

A disk-loaded coupled cavity structure operating in the quasi-TM03 mode has been used here to develop a high electron efficiency, high output power terahertz radiation source, demonstrating that it is possible to concentrate the axial field energy along the source’s central axis within a large cavity. Compared with traditional extended interaction devices operating at the same frequency band, the operating mode of this present device provides a sizable beam tunnel capacity that can support efficient energy conversion between the electron beam and the high frequency field. The developed electron optical system is based on a cylindrical electron beam of 0.3 mm radius and is capable of producing a beam current of 0.65 A at a bias of 16.4 kV. Particle in cell simulations show that such new design approaches can achieve kilowatt-level output power at 0.22 THz with a high electron efficiency of 11.5%.

Insight into electrosorption behavior of monovalent ions and their selectivity in capacitive deionization: An atomic level study by molecular dynamics simulation

Nanopore in capacitive deionization (CDI) plays a key role in selective removal of target ions. In this work, we investigate the transport behavior of ions in the electrosorption process on an atomic level using molecular dynamics (MD) simulations, and explore the selectivity between two typical ions, namely Cl− and NO3− characterized by identical valence but distinct molecular geometry. We show that dehydration effect enables smaller pores to accommodate more ions relative to its inner volume, but it requires higher electronic potential. However, high electronic potential decreases energy efficiency by enhancing the competence between anions and waters as highly polar molecules. It is also found that ion dehydration is crucial for selectivity with complicated dependency on pore size and electronic potential, as well as ion geometry. Planar geometry of NO3− helps removing the surrounding solvated waters while these waters are weakly coordinated around the O atom of NO3−. NO3− also promotes its entrance into the nanopore by altering its angle of the structive plane towards the longitudinal direction of the nanotube. With strong affinity to carbon, NO3− are preferred even when the carbon is not charged. In addition, a maximal selectivity (above 8 for 1.0-nm, 1.5-nm and 2.0-nm pores) can be obtained with certain electronic potential, but further increasing of the electronic potential will lead to lower selectivity.

Surface self-reconstructed amorphous/crystalline hybrid iron disulfide for high-efficiency water oxidation electrocatalysis.

Hybrid electrocatalysts derived from surface self-reconstruction during reaction processes can facilitate charge transfer between different phases and nanostructures by their unique interfaces. Herein, amorphous/crystalline hybrid iron disulfide obtained by self-reconstruction is developed for the first time for the oxygen evolution reaction (OER). The amorphous/crystalline hybrid FeS2 catalyst exhibited a high OER activity with an overpotential of only 189.5 mV (IR-corrected) to deliver 10 mA cm-2 in 1.0 M KOH, which was superior to that of the commercial RuO2. Notably, in the two-electrode system with the amorphous/crystalline hybrid FeS2 as the anode electrocatalyst and Pt/C as the cathode, the catalytic activity towards the overall water splitting was enhanced with a voltage of only 1.43 V at 10 mA cm-2. The phase, composition and surface structure were changed greatly before and after the reaction. All these surface reconstructions after the OER reaction may play significant roles in the high electronic catalytic efficiency. Therefore, the study of the surface reconstruction of catalysts during the reaction process is very important for the structure-performance relationship and the design of efficient hybrid electrocatalysts.

Demonstration of a Pulsed G-Band 50-W Traveling Wave Tube

This letter presents the research progress of a pulsed G-band 50 W traveling wave tube (TWT) with pencil beam focused by periodic permanent magnet (PPM). Three approaches have been combined to improve the tube's operation performances including setting the operating point near the cutoff frequency, using the folded waveguide (FWG) slow wave structure (SWS) with modified circular bends (MCBs), and adopting phase velocity tapering (PVT) technique. The measured output power can be over 50 W at 5% duty cycle with a bandwidth of 3.6 GHz when the beam voltage is 24.25 kV and the beam current is 59 mA. Corresponding electronic efficiency and gain are higher than 3.5% and 35 dB, respectively. The results provide a demonstration of a compact terahertz amplifier with high power, high electronic efficiency and significant bandwidth.

Cellulose/carbon Composites and their Applications in Water Treatment – a Review

Cellulose, as the most abundant natural polymer material on the earth, has attracted worldwide attention due to its characteristics of reproducibility, universality, low cost, biocompatibility and biodegradability. Cellulose-based materials have potential value in supercapacitors, environment and biomedicine. The combination of cellulose and carbon materials can further adjust the microstructure of the composite such as porosity (76–98.8%) and specific surface area (5.07–47.3 m2/g), and enhance the properties of the composite such as the adsorption rate (47–100%) and the degradation rate of pollutants (60–100%), the Young's modulus (1.14–16.6 GPa) and the tensile strength (23.1–277.5 MPa). Besides, composites have the advantages of high electronic transmission efficiency and good reusability, which broaden their applications in water treatment. This review summarizes the molding methods of multi-dimensional cellulose materials, as well as the development status, preparation and modification methods of composites formed by carbon materials such as graphene, carbon nanotubes, activated carbon and nanodiamonds with cellulose, analyzes the research progress and existing problems of the composites in water treatment fields such as adsorption, catalysis, membrane separation and microbial fuel cells, and finally, we make some perspectives for the future researches and applications.

Novel S-Band Metamaterial Extended Interaction Klystron

A miniaturized, high electronic efficiency, S-band metamaterial extended interaction klystron (MEIK) is proposed. The metamaterial-based extended interaction resonant cavities were designed, fabricated, and tested, the assembled and cold-tested results confirm the feasibility of miniaturization in MEIK. Furthermore, the particle-in-cell (PIC) simulation predicts that, typically, when the beam voltage and current are 30 kV and 3 A, respectively, the focusing magnetic field is 1000 G, a 3-cavity MEIK yields the output power of 56 kW at 2.453 GHz, with the saturated gain of 47 dB and the electronic efficiency of 62%, and, importantly, with the cavity diameter of its interaction structure being ~1/2 of a conventional extended interaction klystron. As a power amplifier, the emerging MEIK with its miniaturization and high electronic efficiency has potential applications such as in future accelerators and microwave heating systems.

Cadmium toxicity reduction in rice (Oryza sativa L.) through iron addition during primary reaction of photosynthesis.

Cadmium (Cd) pollution is a worldwide concern due to its biotoxicity. Because Cd and Fe are closely associated during plant photosynthesis, this study aims at investigating the mechanism governing Cd toxicity during photosynthetic primary reaction in rice by adjusting Fe concentration. The results show that moderate Fe concentration (1.0gkg-1) added to soil can increase the stomatal conductance (Gs) and SPAD value by stimulating the stomatal opening and chlorophyll synthesis. Moderate Fe concentration can also improve the maximum fluorescence (Fm) and the maximal photochemical efficiency (Fv/Fm) to keep the high reaction center activity and electronic transfer efficiency in photosystems I and II. Thus, moderate Fe can eliminate Cd-induced decrease in Gs, intercellular CO2 concentration (Ci) and net photosynthetic rate (Pn) as well as the disorder of antioxidative system under Cd concentration of 2.0mgkg-1 in the soil. When its application is increased to 2.0gkg-1, Fe can notably decrease Pn, and result in remarkable decrease in the biomass of shoots and grains. Decrease in Pn can be mainly attributed to high Fe concentration which can greatly destroy chloroplast structure and, meanwhile, inhibit the electron transfer between acceptor and donator in photosynthetic chain especially from quinone A (QA) to quinone B (QB). Unlike the situation under moderate Fe concentration, the high Fe application cannot mitigate the Cd-induced decrease in photosynthetic index. Our results indicate that the moderate Fe application is necessary to promote rice performance and production and, in the meantime, to inhibit Cd toxicity in the extensively polluted soils.

Enhanced electrochemical properties of ZnO encapsulated in carbon nanofibers as anode material for lithium-ion batteries

The amorphous ZnO particles encapsulated in porous nitrogen-doped carbon nanofibers (ZnO@PN-CNFs) are synthesized by electrospinning process and heat treatment. The enhanced electrochemical properties of ZnO@PN-CNFs are based on the porous nanostructure, high length/diameter (L/D) ratio, doped nitrogen, and uniform distributed amorphous ZnO nanoparticles. The results show amorphous ZnO particles in carbon nanofibers avoid the pulverization and alleviated the volume expansion, as well as make the cycling of the anode quickly reach stable. Furthermore, the nitrogen-doped carbon improves electron conductivity while one-dimensional (1D) nanofibers with high L/D ratio own a short diffusion path and high electronic transportation efficiency along the longitudinal direction. Meanwhile, the porous nanostructure from urea pyrolysis produces thinner wall and further shortens the ionic transport distance. Therefore, high capacity and long-cycling life are achieved. And the ZnO@PN-CNF electrode shows a high discharge capacity (1073.2 mAh g−1 at 0.1 A−1) after 100 cycles. Moreover, the ZnO@PN-CNF electrode presents a high discharge capacity of 703.1 mAh g−1 even at 1 A−1 after 400 cycles. In this work, urea not only stops the ZnO from crystallization, leading to uniform distributed amorphous small ZnO particles, but also makes numerous pores in the carbon nanofibers, enlarging the touching area with electrolyte and shortening the transport distance to ZnO particles. It is a promising way by adding urea to alleviate volume expansion and pulverization of the crystal particles and then enhance the performance of electrode.