Superconducting joints using reacted multifilament MgB_(2)wires:A technology toward cryogen-free MRI magnets

The development of superconducting joining technology for reacted magnesium diboride(MgB_(2))conductors remains a critical challenge for the advancement of cryogen-free MgB_(2)-based magnets for magnetic resonance imaging(MRI).Herein,the fabrication of superconducting joints using reacted carbon-doped multifilament MgB_(2)wires for MRI magnets is reported.To achieve successful superconducting joints,the powder-in-mold method was employed,which involved tuning the filament protection mechanism,the powder compaction pressure,and the heat treatment condition.The fabricated joints demonstrated clear superconducting-to-normal transitions in self-field,with effective magnetic field screening up to 0.5 T at 20 K.To evaluate the interface between one of the MgB_(2)filaments and the MgB_(2)bulk within the joint,serial sectioning was conducted for the first time in this type of superconducting joint.The serial sectioning revealed space formation at the interface,potentially caused by the volume shrinkage associated with the MgB_(2)formation or the combined effect of the volume shrinkage and the different thermal expansion coefficients of the MgB_(2)bulk,the filament,the mold,and the sealing material.These findings are expected to be pivotal in developing MgB_(2)superconducting joining technology for MRI magnet applications through interface engineering.

Recent progress in MgB_(2)superconducting joint technology

Magnesium diboride(MgB_(2))magnets have the potential to be the next-generation liquid-helium-free magnet for magnetic resonance imaging(MRI)application due to their relatively high superconducting transition temperature,high current density and low raw material cost compared with current commercial niobium-titanium(Nb-Ti)magnets.A typical superconducting magnet includes several coils.To produce an ultra-stable magnetic field for imaging in MRI,a superconducting electromagnet operating in a persistent mode is crucial.Superconducting coils of the electromagnet in MRI are short-circuited to operate in the persistent mode by connecting coils with superconducting joints.Per-sistent joints have been demonstrated for in-situ and ex-situ wires of both mono-and multi-filamentary structures,made predominantly by PIT techniques similar to those used in wire production.To realise further engagement of MgB_(2)in MRI applications,enhancing the performance of MgB_(2)superconducting joints is essential.This literature review summarises research and development on MgB_(2)superconducting joining technology.

Cobalt phthalocyanine-based conjugated polymer as efficient and exclusive electrocatalyst for CO_(2) reduction to ethanol

Electrocatalytic conversion of carbon dioxide to high value-added chemicals is a promising method for solving the energy crisis and global warming.Electrochemical active metal-containing conjugated polymers have been widely studied for heterogeneous carbon dioxide reduction.In the present contribution,we designed and synthesized a stable cobalt phthalocyanine-based conjugated polymer,named CoPPc-TFPPy-CP,and also explored its electro-catalytic application in carbon dioxide reduction to liquid products in an aqueous solution.In the catalyst,cobalt phthalocyanine acts as building blocks connected with 1,3,6,8-tetrakis(4-formyl phenyl)pyrenes via imine-linkages,leading to mesoporous formation polymers with the pore size centered at 4.1nm.And the central co-balt atoms shifted to a higher oxidation state after condensation.With these chemical and structural natures,the catalyst displayed a remarkable electrocatalytic CO_(2) reduction performance with an ethanol Faradaic efficiency of 43.25%at-1.0V vs RHE.While at the same time,the electrochemical reduction process catalyzed by cobalt phthalocyanine produced only carbon monoxide and hydrogen.To the best of our knowledge,CoPPc-TFPPy-CP is the first example among organic polymers and metal-organic frameworks that produces ethanol from CO_(2) with a remarkable selectivity.

Photovoltaic-powered supercapacitors for driving overall water splitting:A dual-modulated 3D architecture

Due to the growing demand for clean and renewable hydrogen fuel,there has been a surge of interest in electrocatalytic water-splitting devices driven by renewable energy sources.However,the feasibility of self-driven water splitting is limited by inefficient connections between functional modules,lack of highly active and stable electrocatalysts,and intermittent and unpredictable renewable energy supply.Herein,we construct a dualmodulated three-dimensional(3D)NiCo_(2)O_(4)@NiCo_(2)S_(4)(denoted as NCONCS)heterostructure deposited on nickel foam as a multifunctional electrode for electrocatalytic water splitting driven by photovoltaic-powered supercapacitors.Due to a stable 3D architecture configuration,abundant active sites,efficient charge transfer,and tuned interface properties,the NCONCS delivers a high specific capacity and rate performance for supercapacitors.A twoelectrode electrolyzer assembled with the NCONCS as both the anode and the cathode only requires a low cell voltage of 1.47 V to achieve a current density of 10 mA cm^(−2) in alkaline electrolyte,which outperforms the state-of-the-art bifunctional electrocatalysts.Theoretical calculations suggest that the generated heterointerfaces in NCONCS improve the surface binding capability of reaction intermediates while regulating the local electronic structures,which thus accelerates the reaction kinetics of water electrolysis.As a proof of concept,an integrated configuration comprising a two-electrode electrolyzer driven by two series-connected supercapacitors charged by a solar cell delivers a high product yield with superior durability.

Interplay between cold densification and malic acid addition (C4H6O5) for the fabrication of near-isotropic MgB2 conductors for magnet application

The effect of cold high pressure densification(CHPD)on anisotropy of the critical current density(Jc)in《in situ》single core binary and alloyed MgB2 tapes has been determined as a function of temperatures at 4.2 K,20 K and 25 K as well as at applied magnetic fields up to 19 T.The study includes binary and C4H6O5(malic acid)doped MgB2 tapes before and after CHPD.It is remarkable that the CHPD process not only improved the Jc values,in particular at the higher magnetic fields,but also decreased the anisotropy ratio,Г=JC^///JC^⊥In binary MgB2 tapes,the anisotropy factor F increases with higher aspect ratios,even after applying CHPD.In malic acid(C4H6O5)doped tapes,however,the application of CHPD leads only to small enhancements ofГ,even for higher aspect ratios.This is attributed to the higher carbon content in the MgB2 filaments,which in turn is a consequence of the reduced chemical reaction path in the densified filaments.At all applied field values,it was found that CHPD processed C4H6O5 doped tapes exhibit an almost isotropic behavior.This constitutes an advantage in view of industrial magnet applications using wires with square or slightly rectangular configuration.

New paradigms of water-enabled electrical energy generation

Nanotechnology-inspired small-sized water-enabled electricity generation(WEG)has sparked widespread research interest,especially when applied as an electricity source for off-grid low-power electronic equipment and systems.Currently,WEG encompasses a wide range of physical phenomena,generator structures,and power generation environments.However,a systematic framework to clearly describe the connections and differences between these technologies is unavailable.In this review,a comprehensive overview of generator technologies and the typical mechanisms for harvesting water energy is provided.Considering the different roles of water inWEG processes,the related technologies are presented as two different scenarios.Moreover,a detailed analysis of the electrical potential formation in each WEG process is presented,and their similarities and differences are elucidated.Furthermore,a comprehensive compilation of advanced generator architectures and system designs based on hydrological cycle processes is presented,along with their respective energy efficiencies.These nanotechnology-inspired small-sized WEG devices show considerable potential for applications in the Internet of Things ecosystem(i.e.,microelectronic devices,integrated circuits,and smart clothing).Finally,the prospects and future challenges of WEG devices are also summarized.

Size control and electronic manipulation of Ru catalyst over B,N codoped carbon network for high-performance hydrogen evolution reaction

Exploring highly efficient Pt-free catalysts for hydrogen evolution reaction(HER)is of great importance for hydrogen(H2)production.Herein,a novel HER electrocatalyst having abundant ultra-small(2–3 nm)Ru electronically confined by a B,N codoped polar carbon surface(Ru/(B-N)-PC)was constructed.The Ru/(B-N)-PC catalyst exhibits a low overpotential of 15 mV at the current density of 10 mA·cm^(−2),a low Tafel slope of 22.6 mV·dec^(−1),superior durability,which outperforms the benchmark Pt/C catalyst.Both experimental characterizations and theory calculations suggest that an electron communication established between B,N co-doped carbon surface and ultra-small Ru nanoparticles with electrons transferred from N atoms to Ru and backtransferred from Ru to B atoms,which exerts a moderate electronic modification of Ru.This,in turn,affords a modest H adsorption energy and a lower H2O dissociation barrier,leading to the high-performance hydrogen evolution reaction.The work provides meaningful insight into the size control and electronic modulation of Ru catalyst for intrinsic HER activity improvement.

Selection of Fe as a barrier for manufacturing low-cost MgB2 multifilament wires-Advanced microscopy study between Fe and B reaction

The high cost of using the niobium(Nb)barrier for manufacturing magnesium diboride(MgB2)mono-and multi-filamentary wires for large-scale applications has become one of the barriers to replacing current commercial niobium-titanium superconductors.The potential of replacing the Nb barrier with a low-cost iron(Fe)barrier for multifilament MgB2 superconducting wires is investigated in this manuscript.Therefore,MgB2 wires with Fe barrier sintered with different temperatures are studied(from 650°C to 900°C for 1 h)to investigate the non-superconducting reaction phase of Fe-B.Their superconducting performance including engineering critical current density(Je)and n-value are tested at 4.2 K in various external magnetic fields.The best sample sintered at 650°C for 1 h has achieved a Je value of 3.64×10^(4) A cm^(−2) and an n-value of 61 in 2 T magnetic field due to the reduced formation of Fe2B,better grain connectivity and homogenous microstructure.For microstructural analysis,the focused ion beam(FIB)is utilised for the first time to acquire three-dimensional microstructures and elemental mappings of the interface between the Fe barrier and MgB2 core of different wires.The results have shown that if the sintering temperature can be controlled properly,the Je and n-value of the wire are still acceptable for magnet applications.The formation of Fe2B is identified along the edge of MgB2,as the temperature increases,the content of Fe2B also increases which causes the degradation in the performance of wires.

Porphyrin-based framework materials for energy conversion

With the increasing demand for fuel causing serious environmental pollution,it is urgent to develop new and environmentally friendly energy conversion devices.These energy conversion devices,however,require good,inexpensive materials for electrodes and so on.The multifunctional properties of porphyrins enable framework materials(e.g.,metal-organic frameworks and covalent organic frameworks)to be applied in energy conversion devices due to their simple synthesis,high chemical stability,abundant metallic active sites,adjustable crystalline structure and high specific surface area.Herein,the types of porphyrin structural blocks are briefly reviewed.They can be used as organic ligands or directly assembled with framework materials to generate high-performance electro-/photo-catalysts.These types of catalysts applied in electro-/photo-catalytic water splitting,electro-/photo-catalytic carbon dioxide reduction,and electrocatalytic oxygen reduction are also summarized and introduced.At the end of the article,we present the challenges of porphyrin-based framework materials in the above application and corresponding solutions.We expect porphyrin-based framework materials to flourish energy conversion in the coming years.

Superior electrocatalytic activity of mesoporous Au film templated from diblock copolymer micelles

Mesoporous Au films consisting of a network of interconnected Au ligaments around ultra-large pores were found to exhibit a promising electrocatalytic activity towards sluggish reactions. Mesoporous Au films with pore sizes up to 25 nm were successfully fabricated using a polymeric micelle approach. A superior catalytic activity of the mesoporous Au films towards methanol oxidation was confirmed, which was thoroughly analyzed and compared with that of other Au materials. An intrinsic investigation on the high catalytic activity revealed that the superior performance of the as-prepared mesoporous Au film was related to its unique atomic structures around the mesopores with well- crystallized facets and several step/kink sites on the Au surfaces. These findings showcase a strategic and feasible design for preparing highly active Au-based catalysts that could be used as promising candidates in electrocatalytic applications.

Photo-enhanced rechargeable high-energy-density metal batteries for solar energy conversion and storage

Solar energy is considered the most promising renewable energy source.Solar cells can harvest and convert solar energy into electrical energy,which needs to be stored as chemical energy,thereby realizing a balanced supply and demand for energy.As energy storage devices for this purpose,newly developed photo-enhanced rechargeable metal batteries,through the internal integration of photovoltaic technology and high-energy-density metal batteries in a single device,can simplify device configuration,lower costs,and reduce external energy loss.This review focuses on recent progress regarding the working principles,device architectures,and performances of various closed-type and open-type photo-enhanced rechargeable devices based on metal batteries,including Li/Zn-ion,Li-S,and Li/Zn-I_(2),and Li/Zn-O_(2)/air,Li-CO_(2),and Na-O_(2) batteries.In addition to provide a fundamental understanding of photo-enhanced rechargeable devices,key challenges and possible strategies are also discussed.Finally,some perspectives are provided for further enhancing the overall performance of the proposed devices.

Metal−Organic Frameworks:A Robust Platform for Creating Nanoarchitectured Carbon Materials

CONSPECTUS:Nanoporous carbon(NPC)materials with various architectures have attracted considerable attention because of their distinctive properties and great application potential in environmental remediation,energy conversion and storage,advanced sensors,and other applications.Traditional methods for the synthesis of NPCs,for example,the pyrolysis of natural products or polymers,template-assisted synthesis,and using deep-eutectic solvents,always involve toxic precursors and complex procedures,which greatly hinder further applications.Therefore,it is highly desirable to explore simple and feasible ways to prepare NPCs.Furthermore,to improve the performance and extend the application fields of NPCs,efficient strategies should be developed to regulate the components at the atomic level and construct multidimensional architectures.

Spatial-controlled etching of coordination polymers

Nanoarchitectonics provide versatile opportunities for modifying the properties of coordination polymers(CP) other than molecular engineering.Spatial-controlled etching focuses on the controlled disassembly of the frameworks.The etching method provides an excellent opportunity for tailoring the properties and functions of the CPs.Here,we discuss the mechanism for controlled etching of the CPs and summarized the two main strategies utilized so far.Several examples are illustrated to demonstrate recent developments in this area.Moreover,advantages of the etched CPs are summarized in several important applications,including energy storage,catalysis and nanomedicine.

Porous Metal Nanocrystal Catalysts:Can Crystalline Porosity Enable Catalytic Selectivity?

Catalytic selectivity is a central issue in the efficiency of catalytic processes.A large number of strategies have been developed to improve the catalytic selectivity of metal catalysts at the atomic and molecular levels,for instance,alloying secondary elements,fabricating metal-support interactions,and introducing surface ligands.Recently,macro/mesoscopic pores and cavities have been demonstrated as an alternative route to promote catalytic selectivity of metal nanocrystal catalysts.The promotion effects of continuous crystalline porosity include(1)more catalytically active sites that accelerate the favorable catalytic routes to targeted products,(2)confined spaces that increase the retention time of key intermediates and remarkably promote the selective catalysis toward desired products,and(3)an optimized electronic structure and coordination environment of active metal sites that tailor the reaction trends of selective catalysis toward desired products.In this minireview,we summarize recent advances in porosity-enabled catalytic selectivity of metal nanocrystal catalysts with focused discussions of CO_(2) reduction electrocatalysis and selective hydrogenation reactions.The mechanisms that allow for the continuous porosity that enables the catalytic selectivity of metal nanocrystal catalysts are discussed in detail.We end this minireview by proposing current challenges and offering future opportunities in this research field.