High Peak Power Research Articles

Well-dispersed NiFe nanoalloy embedded on N-doped carbon nanofibers as free-standing air cathode for all-solid-state flexible zinc-air battery

Flexible zinc-air battery (ZAB) is a viable candidate for energy storage in upcoming flexible-wearable technologies. Non-noble transition metal alloys are used to synthesize oxygen evolution reaction (OER) catalysts to facilitate this development. However, inhibiting self-aggregation and promoting high OER activity in alloy nanoparticles is still challenging. Anchoring metal alloys to carbon support materials may produce a strong metal alloy‑carbon support couple, thereby preventing nanoparticle aggregation. Here, the combination of polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), pyrrole, and Ni/Fe salts resulted in homogeneously NiFe nanoparticles embedded in the free-standing nitrogen-doped‑carbon nanofiber (NiFe-N@CNF), produced via electrospinning and followed by carbonization. The NiFe-N@CNF shows a high OER activity with an overpotential of 351 mV. Importantly, good structural stability of NiFe-N@CNF results in superior OER stability with no voltage change after 14 h of chronopotentiometry stability test. The constructed rechargeable aqueous ZAB with NiFe-N@CNF as the air–cathode displays high peak power density (179 mW cm−2) and high stability up to 500 h. With its flexible properties, free-standing NiFe-N@CNF is also used as all-solid-state ZAB cathode, exhibiting stable performance under both flat and bending conditions, proving the promising application of NiFe-N@CNF for flexible-wearable technologies.

Large cross-effect dynamic nuclear polarisation enhancements with kilowatt inverting chirped pulses at 94 GHz

Dynamic nuclear polarisation (DNP) is a process that transfers electron spin polarisation to nuclei by applying resonant microwave radiation, and has been widely used to improve the sensitivity of nuclear magnetic resonance (NMR). Here we demonstrate new levels of performance for static cross-effect proton DNP using high peak power chirped inversion pulses at 94 GHz to create a strong polarisation gradient across the inhomogeneously broadened line of the mono-radical 4-amino TEMPO. Enhancements of up to 340 are achieved at an average power of a few hundred mW, with fast build-up times (3 s). Experiments are performed using a home-built wideband kW pulsed electron paramagnetic resonance (EPR) spectrometer operating at 94 GHz, integrated with an NMR detection system. Simultaneous DNP and EPR characterisation of other mono-radicals and biradicals, as a function of temperature, leads to additional insights into limiting relaxation mechanisms and give further motivation for the development of wideband pulsed amplifiers for DNP at higher frequencies.

In situ constructing Co/Co-Ox/Co-Nx diverse active sites on hollow porous carbon spheres derived from Co-MOF for efficient bifunctional electrocatalysis in rechargeable Zn-air

Earth-rich, durable, and efficient bifunctional electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is vitally important for the wide application of zinc-air batteries in the future. However, due to the single active site, traditional commercial benchmark catalysts typically exhibit selective activity in only one of the two reactions (ORR or OER), making it difficult to meet the dual functional catalytic requirements. Developing efficient oxygen electrocatalysts that achieve diverse active sites on a single catalyst and understanding their internal synergistic reaction activity remain a challenge. Herein, spherical hollow porous carbon matrix composites (s-Co/CoNC) with the coexistence of diverse intrinsic active sites including Co-Nx and Co-Ox species and metal Co nanoparticles were prepared by pyrolysis with oxygen-enriched Co-MOFs as precursor in the presence of melamine. Owing to the combined advantages of the catalyst including the great specific surface area, good conductivity, abundant diverse intrinsic active sites towards ORR and OER, and the electronic interaction among active sites and the optimized the adsorption/desorption process of oxygen species at the catalyst surface, s-Co/CoNC exhibits desirable electrocatalytic activity for both ORR and OER with an ORR half-wave potential of 0.81 V, an OER potential of 1.53 V(vs. RHE at 10 mA cm−2), providing a small reversible potential difference of 0.72 V, superior to the commercial noble-metal catalysts and the most reported cobalt based ORR/OER catalysts. The assembled s-Co/CoC-based rechargeable Zn-air batteries possess high peak power density of 101.7 mW cm−2. This work provides a significant strategy for constructing high-performance dual functional catalysts for secondary Zn-air batteries.

Fast laser field reconstruction method based on a Gerchberg–Saxton algorithm with mode decomposition

Knowledge of the electric field of femtosecond, high intensity laser pulses is of paramount importance to study the interaction of this class of lasers with matter. A hybrid method to reconstruct the laser field from fluence measurements in the transverse plane at multiple positions along the propagation axis is presented, combining a Hermite–Gauss mode decomposition (MD) and elements of the Gerchberg–Saxton algorithm (GSA). The proposed GSA-MD takes into account the pointing instabilities of high intensity laser systems by tuning the centers of the HG modes. Furthermore, it quickly builds a field description by progressively increasing the number of modes and thus the accuracy of the field reconstruction. The results of field reconstruction using the GSA-MD are shown to be in excellent agreement with experimental measurements from two different high peak power laser facilities.

Space‐Confined Growth of Co9S8 Nanoparticles in Covalent Organic Framework‐Derived Porous Carbon for Efficient Bifunctional Oxygen Electrocatalysis

AbstractFine regulation of the physicochemical structure of carbon‐based electrocatalysts to optimize the adsorption energies of oxygen intermediates is critically important to enhance the reaction kinetics of the oxygen evolution/reduction reaction (OER/ORR) but remains a huge challenge. Herein, nano‐space confined growth of Co9S8 nanoparticles (NPs) in porous carbon is realized through an in situ confined growth strategy by using thiol‐chains functionalized COF (COF‐S‐SH) as a confined template. COF‐S‐SH is used as binding sites to immobilize Co ions to improve the interaction between metal nanoparticles (NPs) and carbon skeletons, and simultaneously serves as a confined void to avoid the aggregation metal NPs. Impressively, as an efficient bifunctional catalyst, the resulting Co9S8/COF‐S800 shows significantly enhanced oxygen electrocatalysis with a small OER‐ORR voltage gap of 0.76 V, vastly superior to that of pristine COF‐S800. Furthermore, the assembled Zn–air battery with Co9S8/COF‐S800 catalyst displays a high peak power density of 181.5 mW cm−2 and great durability over 60 h charge–discharge cycles.

Immobilized hindered amine radical scavenger for durability enhancement of perfluorosulfonic acid membrane in PEMFCs

Membrane durability is one of the crucial considerations that restrict the development of proton exchange membrane fuel cells (PEMFCs). The widely used and inexpensive stabilizer hindered amine 4-amino-2,2,6,6-tetramethylpiperidine (TEMP) was selected as the free radical scavenger and tethered onto the skeleton of carboxyl-functionalized metal-organic frameworks for addressing its migration problem. The resulted inorganic-organic hybrid dopant (UIO-66-TEMP) was then incorporated into the Nafion matrix to alleviate the attacks of free radicals on the membrane in the fuel cell working circumstances. Besides the improved mechanical strength and oxidative stability, and restricted water swelling and hydrogen crossover, the resulted hybrid membranes also possess excellent proton conductivity up to 176 mS cm−1, endowing them with high power density up to 612.78 mW cm−2, 1.5 times higher than recast Nafion. After accelerated durability testing for 120 h, the OCV decay rate of the hybrid membranes decreased to 0.74 mV h−1, only 40% of recast Nafion (1.89 mV h−1). Meanwhile, the optimized hybrid membrane still maintained a high peak power density of 463.62 mW cm−2 and a low hydrogen crossover density of 4.44 mA cm−2, which were superior to recast Nafion after OCV durability tests. Hindered amines can be “regenerated” by the “Denisov cycle” to ensure that they can be used sustainably in the fuel cell. The results demonstrate that the novel UIO-66-TEMP decorated with hindered amine radical scavengers are promising nanofillers for mitigating the membrane degradation and improving the proton conductivity, thereby significantly enhancing the performance and durability of PEMFCs.

2.79-μm high peak power LiNbO3 acousto-optic Q-switched Er,Cr:YSGG laser with thermal lensing effect compensation

A new type of lithium niobate (LiNbO3) acousto-optic Q-switched Er,Cr:YSGG laser with high peak power was designed and the thermal lensing effect compensation was studied. The values of thermal focal length in the gain medium were calculated theoretically and measured experimentally. The experimental results validate the designed plane-convex resonator validity, and the output performance of the 2.79 μm Er,Cr:YSGG laser was obviously improved. When the laser operated at free running region, the maximum values of pulse energy was 160 mJ at 60 Hz, compared with the plane-parallel resonator, the pulse energy was increased by 2 times in the plane-convex resonator. When the LiNbO3 Q-switched laser operated at 60 Hz, the maximum values of pulse energy was 8.5 mJ, and the minimum values of pulse duration was 60.8 ns, and the corresponding peak power approximately was 140 kW, respectively. Compared with the plane-parallel resonator, the pulse energy was increased by 1.6 times in the plane-convex resonator, the corresponding peak power was increased by 2.3 times.

Electrically Tunable Nonlinearity at 3.2 Terahertz in Single-Layer Graphene.

Graphene is a nonlinear material in the terahertz (THz) frequency range, with χ(3) ∼ 10-9 m2/V2 ∼ 15 orders of magnitude higher than that of other materials used in the THz range, such as GaAs or lithium niobate. This nonlinear behavior, combined with ultrafast dynamic for excited carriers, proved to be essential for third harmonic generation in the sub-THz and low (<2.5 THz) THz range, using moderate (60 kV/cm) fields and at room temperature. Here, we show that, for monochromatic high peak power (1.8 W) input THz signals, emitted by a quantum cascade laser, the nonlinearity can be controlled using an ionic liquid gate that tunes the graphene Fermi energy up to >1.2 eV. Pump and probe experiments reveal an intense absorption nonlinearity at 3.2 THz, with a dominant 3rd-order contribution at EF > 0.7 eV, hence opening intriguing perspectives per engineering novel architectures for light generation at frequencies > 9 THz.

Occupational Exposure to Electromagnetic Fields-Different from General Public Exposure and Laboratory Studies.

The designs of in vivo, in vitro and in silico studies do not adequately reflect the characteristics of long-term occupational EMF exposure; the higher exposure levels permitted for employees are nevertheless extrapolated on this basis. Epidemiological studies consider occupational exposure only in a very general way, if at all. There is a lack of detailed descriptive data on long-term occupational exposure over the duration of the working life. Most studies reflect exposure characteristics of the general population, exposures which are long-term, but at a comparably low level. Occupational exposure is often intermittent with high peak power followed by periods with no exposure. Furthermore, the EU EMF-Directive 2013/35/EU states a demand for occupational health surveillance, the outcome of which would be of great help to epidemiologists studying the health effects of EMF exposure. This paper thus aims to outline and specify differences between public and occupational exposure and to increase the understanding of specific aspects of occupational exposure which are important for long-term health considerations. This could lead to a future protection concept against possible hazards based on adequate descriptions of long-term exposures and also include supplementary descriptive features such as a "reset time" of biological systems and accurate dose quantities.

Confined covalent organic framework anchored Fe sites derived highly uniform electrocatalysts for rechargeable aqueous and solid-state Zn-air batteries

Exploiting clean, highly efficient energy storage and conversion device like Zn-air battery is of significance for alleviating the energy and environmental crises of this society. Metal organic coordination polymers/frameworks have been regarded as ideal templates to synthesize non-noble metal catalysts for a long time. However, the high density of metal nodes inevitably leads to the heavy aggregation of metal nanoparticles during thermolysis transformation process, which greatly hinders the maximizing of electrochemical performances. Herein, covalent organic framework (COF) has been employed to anchor the quantificational Fe ions (COF-Fe) and then confined into the macropores of g-C3N4 to improve the dispersion of metal active sites and avoid severe aggregation during high temperature pyrolysis. After calcination, the metal nanoparticles highly dispersed Fe-CFN catalysts can be obtained. The optimal Fe-CFN-800 catalysts exhibit excellent ORR and OER performances with the potential difference between ORR and OER of merely 0.723 V. Moreover, experimental way and DFT theoretical calculations are also employed to disclose the reaction mechanism. Finally, the all-solid-state and aqueous Zn-air batteries assembled with the optimized Fe-CFN-800 as cathode present excellent performances with high peak power density, flexible rate performance, strong discharge stability and long-term charge–discharge cycling performance.

Interface engineering to improve electrochemical performance of intermediate-temperature solid oxide fuel cells

The interface between the cathode and the electrolyte is critical in the electrochemical performance of intermediate-temperature solid oxide fuel cells (IT-SOFCs). In this study, the correlation between the structural properties at the interface and the electrochemical performance is investigated with a focus on the ohmic resistance. Electrostatic spray deposition (ESD) is used to optimize the cathode particle size and distribution by controlling the solvent evaporation rate. A mechanical pull-off test is performed to directly assess the structural properties at the interface. Furthermore, electrochemical impedance spectroscopy (EIS) is employed with an equivalent circuit model to establish a quantitative correlation between the contact coverage at the interface and the interfacial resistance. By maximizing contact coverage, a significantly high peak power density of 1.87 W cm−2 is achieved at 600 °C in a Ni-Gd0.1Ce0.9O1.95 (GDC)-based single cell. The findings indicate that the proposed approach effectively achieves the desired structural properties, thereby enhancing the performance of IT-SOFCs with significant implications for the design and optimization.

Mn-Doped Zn Metal-Organic Framework-Derived Porous N-Doped Carbon Composite as a High-Performance Nonprecious Electrocatalyst for Oxygen Reduction and Aqueous/Flexible Zinc-Air Batteries.

Developing low-cost, efficient, and stable oxygen reduction reaction (ORR) electrocatalysts is crucial for the commercialization of energy conversion devices such as metal-air batteries. In this study, we report a Mn-doped Zn metal-organic framework-derived porous N-doped carbon composite (30-ZnMn-NC) as a high-performance ORR catalyst. 30-ZnMn-NC exhibits excellent electrocatalytic activity, demonstrating a kinetic current density of 9.58 mA cm-2 (0.8 V) and a half-wave potential of 0.83 V, surpassing the benchmark Pt/C and most of the recently reported non-noble metal-based catalysts. Moreover, the assembled zinc-air battery with 30-ZnMn-NC demonstrates high peak power densities of 207 and 66.3 mW cm-2 in liquid and flexible batteries, respectively, highlighting its potential for practical applications. The excellent electrocatalytic activity of 30-ZnMn-NC is attributed to its unique porous structure, the strong electronic interaction between metal Zn/Mn and adjacent N-doped carbon, as well as the bimetallic Mn/Zn-N active sites, which synergistically promote faster reaction kinetics. This work offers a controllable design strategy for efficient electrocatalysts with porous structures and bimetallic active sites, which can significantly enhance the performance of energy conversion devices.

A Wide Spectrum Yb-Doped All-Fiber-Integrated Chirped Pulse Amplification System Based on Parabolic Shaping

Nonlinear effect in an ultrafast fiber laser has always been a major obstacle in realization of laser with narrow pulse width and high energy. To achieve higher peak power, we herein introduce pre-chirping management and pre-amplification before the chirped pulse amplification (CPA) system. The self-phase modulation effect is used to effectively stretch the spectrum when the pulse reaches a high peak power, and then the parabolic pulse and spectrum are obtained in a fiber amplifier. This parabolic pulse effectively reduces the impact of nonlinear effect in subsequent fiber amplifier and realizes the amplification of chirped pulse with a higher peak power compared with conventional CPA system. We finally achieved a mode-locked pulse with 143 fs pulse duration, 8.57 W average power, 85.7 μJ single pulse energy, M2 &lt; 1.10 beam quality, and without obvious pulse degeneration. The reported pulse energy is the highest among all-fiber CPA systems based on nonlinear amplification technology.

Core‐Shell‐Structured FeNx@Graphite Carbon Nanofibers as Highly Active and Stable Electrocatalysts for Zn‐Air Batteries

AbstractThe exploitation of high‐performance, durable, and low‐cost oxygen reduction reaction (ORR) electrocatalysts is crucial for energy storage and convert devices. Herein, a core‐shell structured catalyst (FeNx@graphite carbon) is developed by coaxial electrospinning. The resulting nanofibers combines the distinguished activity of FeNx and the good conductivity and stability of graphite carbon. This unique core‐shell structure with potential synergistic interaction leads to high activity and outstanding stability. As an excellent cathode catalyst for the Zn‐air battery, FeNx@graphite carbon displays an outstanding open‐circuit voltage (1.592 V), a high peak power density (100 mW cm−2) and stable rechargeability (30 h), outperforming that of Pt/C assembled Zn‐air battery. Our work provides a guide to rational design for achieving both high ORR activity and good stability.

Application of ultrafast laser beam shaping in micro-optical elements

The manufacturing and application of micro-optical elements are constantly evolving toward miniaturization, integration, and intelligence and have important applications in holographic displays, optical imaging, laser processing, information processing, and other fields. Ultrafast lasers, with their ultrashort pulse width, extremely high peak power, high processing resolution, small thermal influence zone, and nondestructive material processing advantages, have become an important processing method for preparing micro-optical elements. However, the laser output from the laser usually has a Gaussian distribution, with limitations in spatial and temporal energy and shape distribution, making it difficult to meet the requirements of processing efficiency and quality, which poses new challenges to ultrafast laser manufacturing technology. Therefore, by shaping the ultrafast laser beam and regulating nonlinear optical effects, the optimization and adjustment of the beam shape can be achieved, thus improving the quality and efficiency of micro-optical element processing. Ultrafast laser beam shaping technology provides a new method for the manufacture of micro-optical elements. This article first introduces the commonly used manufacturing methods for micro-optical elements. Second, from the perspective of the temporal domain, spatial domain, and spatiotemporal domain, the basic principles, methods, and existing problems of ultrafast laser beam shaping are summarized. Then, the application of these shaping technologies in the preparation of micro-optical elements is elaborated. Finally, the challenges and future development prospects of ultrafast laser beam shaping technology are discussed.

CoNiFe‐layered double hydroxide decorated Co‐N‐C network as a robust bi‐functional oxygen electrocatalyst for zinc‐air batteries

AbstractRechargeable zinc‐air batteries (ZABs) are cost‐effective energy storage devices and display high‐energy density. To realize high round‐trip energy efficiency, it is critical to develop durable bi‐functional air electrodes, presenting high catalytic activity towards oxygen evolution/reduction reactions together. Herein, we report a nanocomposite based on ternary CoNiFe‐layered double hydroxides (LDH) and cobalt coordinated and N‐doped porous carbon (Co‐N‐C) network, obtained by the in‐situ growth of LDH over the surface of ZIF‐67‐derived 3D porous network. Co‐N‐C network contributes to the oxygen reduction reaction activity, while CoNiFe‐LDH imparts to the oxygen evolution reaction activity. The rich active sites and enhanced electronic and mass transport properties stemmed from their unique architecture, culminated into outstanding bi‐functional catalytic activity towards oxygen evolution/reduction in alkaline media. In ZABs, it displays a high peak power density of 228 mW cm−2 and a low voltage gap of 0.77 V over an ultra‐long lifespan of 950 h.image

110 MW thin-disk oscillator.

A compact Kerr-lens mode-locked thin-disk oscillator reproducibly delivering 110 MW output peak power, the highest among all oscillators, is reported. This simple and stable femtosecond oscillator delivering a unique combination of high average power (202 W) and peak power, is an ideal driver and an important milestone for the development of extreme ultraviolet transportable frequency comb sources.

Tailoring Oxygen Reduction Reaction Kinetics on Perovskite Oxides via Oxygen Vacancies for Low-Temperature and Knittable Zinc-Air Batteries.

High kinetics oxygen reduction reaction (ORR) electrocatalysts under low temperature are critical and highly desired for temperature-tolerant energy conversion and storage devices, but remain insufficiently investigated. Herein, oxygen vacancy-rich porous perovskite oxide (CaMnO3 ) nanofibers coated with reduced graphene oxide coating (V-CMO/rGO) are developed as the air electrode catalyst for low-temperature and knittable Zn-air batteries. V-CMO/rGO exhibits top-level ORR activity among perovskite oxides and shows impressive kinetics under low temperature. Experimental and theoretical calculation results reveal that the synergistic effect between metal atoms and oxygen vacancies, as well as the accelerated kinetics, enhanced electric conductivity and mass transfer over the rGO coated nanofiber 3D network contribute to the enhanced catalytic activity. The desorption of ORR intermediate is promoted by the regulated electron filling. The V-CMO/rGO drives knittable and flexible Zn-air batteries under a low temperature of -40 °C with high peak power density of 56 mW cm-2 and long cycle life of over 80 h. This study provides insight of kinetically active catalyst and facilitates the ZABs application in harsh environment. This article is protected by copyright. All rights reserved.

Nitrogen‐Rich Rigid Polybenzimidazole With Phosphoric Acid Shows Promising Electrochemical Activity and Stability for High‐Temperature Proton Exchange Membrane Fuel Cells

AbstractPolybenzimidazoles (PBIs) are the most promising binders for the catalyst layer (CL) in high‐temperature proton exchange membrane fuel cells (HT‐PEMFC). However, traditional commercial PBIs are not applied in binders because they do not enhance the electrochemical performance and because the related solvents are not environmentally friendly. In addition, proton transfer channels in PBIs are not investigated at the microscopic and atomic scales to date. In this study, a nitrogen‐rich rigid PBI binder containing pyridine, diazofluorene, and partially grafted nitrile (PBPBI‐3CN) is prepared with a functionalized structure, good thermal stability, and good solubility in an environmentally friendly solvent. A membrane electrode assembly (MEA) is fabricated with the PBPBI‐3CN binder, providing a high peak power density, low resistance, and good stability. The protonation, hydrogen bond networks, and platform for proton transfer are confirmed in the CLs. The protonation of PBPBI‐3CN occurs in two steps. First, some phosphoric acid (PA) molecules bind to nitrogen‐containing acidophilic groups via preliminary protonation; second, multiple PA molecules then interact with nitrogen‐containing acidophilic groups via further protonation. With protonation as the foundation, a sufficient amount of PA molecules form a hydrogen bond network, and proton transfer channels are established.

Microlens array device for laser light shaping in laser scanning smart headlights.

We present, what we believe to be, a novel microlens array (MLA) scheme for laser light shaping in laser scanning smart headlight. The laser spot has a Gaussian distribution that may reach a high peak power density in the central part, which is called hot spot. When the laser beam is applied to a phosphor plate for luminous conversion, the hot spot of Gaussian beam causes thermal quench and decreases luminous efficacy. To avoid this effect, an MLA is used, so as to achieve a uniform energy distribution. In this study, we propose a laser scanning smart headlight fabricated by a new MLA structure, with an arrangement providing both light uniformity and shaping. The novel MLA is designed by two-dimensional micro-concave lens array yielding a flat-top beam. The flexible fabrication process employs laser drilling to shape the micro-hole array on the glass substrate surface and then etch it to form MLA without requiring any mask lithography process. The full-width half maximum (FWHM) of light output distribution can be adjusted by the glass etching parameters, and the light distribution could be controlled by the arranged layout of the array. Thus, beams with FWHM divergence ranging from 5° to 34° has been fabricated and characterized. The typical pixel shape is a rectangle with two different FWHMs in two orthogonal directions, and the fabrication method achieves this goal as well. This novel design and unique maskless process of the MLAs is a promising tool for development the next generation laser scanning smart headlight.