Separator coatings as efficient physical and chemical hosts of polysulfides for high-sulfur-loaded rechargeable lithium–sulfur batteries

Lithium-sulfur batteries(LSBs)are promising alternative energy storage devices to the commercial lithium-ion batteries.However,the LSBs have several limitations including the low electronic conductivity of sulfur(5×10^-30S cm^-1),associated lithium polysulfides(PSs),and their migration from the cathode to the anode.In this study,a separator coated with a Ketjen black(KB)/Nafion composite was used in an LSB with a sulfur loading up to 7.88 mg cm^-2to mitigate the PS migration.A minimum specific capacity(Cs)loss of 0.06%was obtained at 0.2 C-rate at a high sulfur loading of 4.39 mg cm^-2.Furthermore,an initial areal capacity up to 6.70 mAh cm^-2 was obtained at a sulfur loading of 7.88 mg cm^-2.The low Cs loss and high areal capacity associated with the high sulfur loading are attributed to the large surface area of the KB and sulfonate group(SO3^-)of Nafion,respectively,which could physically and chemically trap the PSs.

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.

Electrochemical Surface Restructuring of Phosphorus-Doped Carbon@MoP Electrocatalysts for Hydrogen Evolution

The hydrogen evolution reaction(HER) through electrocatalysis is promising for the production of clean hydrogen fuel. However,designing the structure of catalysts,controlling their electronic properties,and manipulating their catalytic sites are a significant challenge in this field. Here,we propose an electrochemical surface restructuring strategy to design synergistically interactive phosphorus-doped carbon@MoP electrocatalysts for the HER. A simple electrochemical cycling method is developed to tune the thickness of the carbon layers that cover on MoP core,which significantly influences HER performance. Experimental investigations and theoretical calculations indicate that the inactive surface carbon layers can be removed through electrochemical cycling,leading to a close bond between the MoP and a few layers of coated graphene. The electronsdonated by the MoP core enhance the adhesion and electronegativity of the carbon layers;the negatively charged carbon layers act as an active surface. The electrochemically induced optimization of the surface/interface electronic structures in the electrocatalysts significantly promotes the HER. Using this strategy endows the catalyst with excellent activity in terms of the HER in both acidic and alkaline environments(current density of 10 mA cm^(-2) at low overpotentials,of 68 mV in 0.5 M H_(2)SO_(4) and 67 mV in 1.0 M KOH).

Organic ligand nanoarchitectonics for BiVO_(4) photoanodes surface passivation and cocatalyst grafting

Bismuth vanadate(BiVO_(4))is a promising photoanode material for efficient photoelectrochemical(PEC)water splitting,whereas its performance is inhibited by detrimental surface states.To solve the problem,herein,a low-cost organic molecule 1,3,5-benzenetricarboxylic acid(BTC)is selected for surface passivation of BiVO_(4) photoanodes(BVOs),which also provides bonding sites for Co^(2+)to anchor,resulting in a Co-BTC-BVO photoanode.Owing to its strong coordination with metal ions,BTC not only passivates surface states of BVO,but also provides bonding between BVO and catalytic active sites(Co^(2+))to form a molecular cocatalyst.Computational study and interfacial charge kinetic investigation reveal that chemical bonding formed at the interface greatly suppresses charge recombination and accelerates charge transfer.The obtained Co-BTC-BVO photoanode exhibits a photocurrent density of 4.82 mA/cm^(2) at 1.23 V vs.reversible hydrogen electrode(RHE)and a low onset potential of 0.22 VRHE under AM 1.5 G illumination,which ranks among the best photoanodes coupled with Co-based cocatalysts.This work presents a novel selection of passivation layers and emphasizes the significance of interfacial chemical bonding for the construction of efficient photoanodes.

Solar energy conversion on g-C3N4 photocatalyst:Light harvesting,charge separation,and surface kinetics

Photocatalysis. which utilizes solar energy to trigger chemical reactions, is one of the most desirable solar-energy-conversion approaches. Graphitic carbon nitride （g-C3N4）. as an attractive metal-free photocatalyst, has drawn worldwide research interest in the area of solar energy conversion due to its easy synthesis, earth-abundant nature, physicochemical stability and visible-light-responsive properties. Over the past ten years, g-C3N4 based photocatalysts have experienced intensive exploration, and great progress has been achieved. However, the solar conversion efficiency is still far from industrial applications due to the wide bandgap, severe charge recombination, and lack of surface active sites. Many strategies have been proposed to enhance the light absorption, reduce the recombination of charge carriers and accelerate the surface kinetics. This work makes a crucial review about the main contributions of various strategies to the light harvesting, charge separation and surface kinetics of g-C3N4 photocatalyst. Furthermore, the evaluation measurements for the enhanced light harvesting, reduced charge recombination and accelerated surface kinetics will be discussed. In addition, this review proposes future trends to enhance the photocatalytic performance of g-C3N4 photocatalyst for the solar energy conversion.

Understanding the roles of carbon in carbon/g-C_(3)N_(4)based photocatalysts for H2 evolution

Coupling graphitic carbon nitride(CN)with carbonaceous materials is an effective strategy to improve photocatalytic performance,but the contributions of carbonaceous materials are not fully understood.Herein,a new type of carbon/CN(CCN)complex photocatalyst is synthesized with a 6-fold enhancement of H2 evolution rate compared to that of pristine CN.The role of carbon in photocatalytic H2 evolution reaction is systemically studied and it is experimentally and theoretically revealed that carbon mainly contributes to the improved capability of exciton dissociation and enhanced electric conductivity for charge transfer,leading to an increased population of photo-carriers for photocatalytic reactions.Interestingly,the enhanced light absorption originated from carbon barely generates charge carriers for H2 evolution activity.These new findings will inspire the rational design of carbon-based photocatalysts for efficient solar fuel production.

An orientated mass transfer in Ni-Cu tandem nanofibers for highly selective reduction of CO_(2) to ethanol

Electrochemically reducing CO_(2)to ethanol is attractive but suffers from poor selectivity.Tandem catalysis that integrates the activation of CO_(2)to an intermediate using one active site and the subsequent formation of hydrocarbons on the other site offers a promising approach,where the control of the intermediate transfer between different catalytic sites is challenging.We propose an internally self-feeding mechanism that relies on the orientation of the mass transfer in a hierarchical structure and demonstrate it using a one-dimensional(1D)tandem core-shell catalyst.Specifically,the carbon-coated Ni-core(Ni/C)catalyzes the transformation of CO_(2)-to-CO,after which the CO intermediates are guided to diffuse to the carbon-coated Cu-shell(Cu/C)and experience the selective reduction to ethanol,realizing the orientated key intermediate transfer.Results show that the Faradaic efficiency for ethanol was 18.2%at-1 V vs.RHE(V_(RHE))for up to 100 h.The following mechanism study supports the hypothesis that the CO_(2)reduction on Ni/C generates CO,which is further reduced to ethanol on Cu/C sites.Density functional theory calculations suggest a combined effect of the availability of CO intermediate in Ni/C core and the dimerization of key∗CO intermediates,as well as the subsequent proton-electron transfer process on the Cu/C shell.

Hollow Multishelled Structure: Synthesis Chemistry and Application

Hollow multishelled structure(HoMS),a promising and complex multifunctional structural system,features at least two shells that are separated by internal voids.The unique structure endows it with numerous advantages including low density,high loading capacity,large specific surface area,facilitated mass transport,and multiple spatial confinement effect.In the past twenty years,benefiting from the booming development of synthesis methods,various HoMS materials have been prepared and show promising applications in diverse areas.

The role of functional materials to produce high areal capacity lithium sulfur battery

The lithium sulfur batteries(LSBs) are considered as one of the promising next generation energy storage devices due to the high theoretical specific capacity of sulfur(1675 m Ah g-1), naturally available, low cost.However, the practical LSBs are impeded by the well-known "shuttle effect" combined with other technical drawbacks. The "shuttle effect" causes rapid capacity decay, severe self-discharging and low active material utilization. The polysulfide(PS) which has lone pair electrons in each sulfur atom is considered as Lewis base and shows strong affinity to various polar, Lewis acid and catenation interactive materials but very weakly interacts with the non-polar conductive carbons. The "shuttle effect" occurs due to the diffusion of high order PS from the cathode to the anode and then low-order PS back to the cathode. The PS is polar and, due to a lone pair of electrons associated with the sulfur atom, is considered a Lewis base. As such, the PS shows a strong affinity with various polar and Lewis acid materials. In addition, a more novel trapping can be performance through a catenation reaction. For LSBs to compete with the state-of-the-art lithium ion batteries(LIBs), the LSB areal capacity need to be ~6 m Ah cm-2(which is proportional to sulfur loading). To achieve this target the PS shuttling needs to mitigate, which can be achieved through using functional materials. This review addresses the aforementioned phenomena by considering the PS phase interacts with the various functional materials and how this impacts areal capacity and cycling stability of LSBs.

Recent progress of tungsten-and molybdenum-based semiconductor materials for solar-hydrogen production

Semiconductor-based solar water splitting is regarded as one of the most promising technologies for clean hydrogen produc-tion.The rational design of semiconductor materials is critically important to achieve high solar-to-hydrogen(STH)con-version efficiencies towards practical applications.A rich family of tungsten-and molybdenum-based materials have been developed as both photocatalysts and cocatalysts for solar-hydrogen production in the past years,providing more opportunities to achieve high solar-to-hydrogen(STH)efficiencies.In this review article,we comprehensively review the recent progress of tungsten-and molybdenum-based materials for solar-hydrogen production.In particular,the strengths and drawbacks of each material system are critically discussed,followed by an overview of the emerging strategies to improve their performances.Finally,the key challenges and possible research directions of tungsten-and molybdenum-based materials are presented,which would provide useful information for the design of efficient semiconductor materials for solar-hydrogen production.

Scalable fabrication and active site identification of MOF shell-derived nitrogen-doped carbon hollow frameworks for oxygen reduction

Nitrogen-doped carbon materials as promising oxygen reduction reaction(ORR) electrocatalysts attract great interest in fuel cells and metal-air batteries because of their relatively high activity, high surface area, high conductivity and low cost. To maximize their catalytic efficiency, rational design of efficient electrocatalysts with rich exposed active sites is highly desired. Besides, due to the complexity of nitrogen species, the identification of active nitrogen sites for ORR remains challenging. Herein, we develop a facile and scalable template method to construct high-concentration nitrogen-doped carbon hollow frameworks(NC), and reveal the effect of different nitrogen species on theirORRactivity on basis of experimental analysis and theoretical calculations. The formation mechanism is clearly revealed, including low-pressure vapor superassembly of thin zeolitic imidazolate framework(ZIF-8) shell on ZnO templates,in situ carbonization and template removal. The obtained NC-800 displays better ORR activity compared with other NC-700 and NC-900 samples. Our results indicate that the superior ORR activity of NC-800 is mainly attributed to its content balance of three nitrogen species. The graphitic N and pyrrolic N sites are responsible for lowering the working function, while the pyridinic N and pyrrolic N sites as possible active sites are beneficial for increasing the density of states.

Bismuth based photoelectrodes for solar water splitting

Photoelectrochemical water splitting is a sustainable path to generate valuable hydrogen using sunlight and water as the only inputs.Despite significant efforts to date,it is still a challenge to achieve photoelectrode with superior performance and long-term stability.Many bismuth-based semiconductor materials have demonstrated excellent visible light harvesting capability and suitable band edge for water splitting.Herein,we summarized the latest studies conducted on bismuth-based photoelectrodes for photoelectrochemical water splitting.Specifically,photoelectrochemical properties of copper bismuth oxide(CuBi_(2)O_(4)),bismuth ferrites(BiFeO_(3),Bi_(2)Fe_(4)O_(9)),bismuth vanadate(BiVO_(4)),bismuth tungstate(Bi_(2)WO_(6)),bismuth molybdate(Bi_(2)MoO_(6))and bismuth oxyhalids(BiOX,X=I,Cl,Br)are presented.Strategies to achieve high stability and photolectrochemical performance were discussed in the aspects of nanostructure formation,heterostructure assembly,practical defect engineering,preferential facet growth and oxygen evolution catalyst incorporation.

All-Climate Aluminum-Ion Batteries Based on Binder-Free MOF-Derived FeS_(2)@C/CNT Cathode

Aluminum-ion batteries(AIBs)are promising next-generation batteries systems because of their features of low cost and abundant aluminum resource.However,the inferior rate capacity and poor all-climate performance,especially the decayed capacity under low temperature,are still critical challenges toward high-specific-capacity AIBs.Herein,we report a binder-free and freestanding metal-organic framework-derived FeS_(2)@C/carbon nanotube(FeS_(2)@C/CNT)as a novel all-climate cathode in AIBs working under a wide temperature window between−25 and 50℃ with exceptional flexibility.The resultant cathode not only drastically suppresses the side reaction and volu-metric expansion with high capacity and long-term stability but also greatly enhances the kinetic process in AIBs with remarkable rate capacity(above 151 mAh g^(−1) at 2 A g^(−1))at room temperature.More importantly,to break the bottleneck of the inherently low capacity in graphitic material-based all-climate AIBs,the new hierarchical conductive composite FeS_(2)@C/CNT highly promotes the all-climate performance and delivers as high as 117 mAh g^(−1) capacity even under−25°C.The well-designed metal sulfide electrode with remarkable performance paves a new way toward all-climate and flexible AIBs.

Custom Molecular Design of Ligands for Perovskite Photovoltaics

CONSPECTUS:Perovskite photovoltaics have witnessed overwhelming success owing to their high power conversion efficiency,low voltage deficit,sensitive photoelectric response and good operational stability.However,solution-processed,polycrystalline perovskite films inevitably contain a high density of crystallographic defects,such as uncoordinated ions and dangling bonds at the surfaces and grain boundaries,which can result in charge recombination,thus causing energy loss and impaired device performance.These intrinsic imperfections can be remedied through a chemically induced intermarriage between halide perovskites of soft crystallographic nature and judiciously designed exotic ligand molecules.Utilizing rational molecular design of the component moieties,i.e.,the core and tail functional groups,the ligand molecules can be endowed with both more comprehensive and salient advantages to further boost device performance,thus setting perovskite photovoltaics on course for a more prosperous future.

Confining ultrafine tin monophosphide in Ti_(3)C_(2)T_(x)interlayers for rapid and stable sodium ion storage

Phase separation in conversion/alloying-based anodes easily causes crystal disintegration and leads to bad cycling performance.Tin monophosphide(SnP)is an excellent anode material for sodium ion battery due to its unique three-dimensional crystallographic layered structure.In this work,we report the in situ growth of ultrafine SnP nanocrystals within Ti_(3)C_(2)T_(x)MXene interlayers.The MXene framework is used as a conductive matrix to provide high ionic/electrical transfer paths and reduce the Na^(+)diffusion barrier in the electrode.In situ and ex situ measurements reveal that the synergy between small SnP crystal domains and the confinement provided by the MXene host prevents mechanical disintegration and major phase separation during the sodiation and desodiation cycles.The resultant electrode exhibits fast Na^(+)storage kinetics and excellent cycling stability for over 1000 cycles.A full cell assembled with this new SnP-based anode and a Na_(3)V_(2)(PO_(4))_(3)cathode delivers a high energy density of 265.4 Wh kg^(-1)and a power density of 3252.4 W kg^(-1),outperforming most sodium-ion batteries reported to date.

Revisiting solar hydrogen production through photovoltaicelectrocatalytic and photoelectrochemical water splitting

Photoelectrochemical(PEC)water splitting is regarded as a promising way for solar hydrogen production,while the fast development of photovoltaic-electrolysis(PV-EC)has pushed PEC research into an embarrassed situation.In this paper,a comparison of PEC and PV-EC in terms of efficiency,cost,and stability is conducted and briefly discussed.It is suggested that the PEC should target on high solar-to-hydrogen efficiency based on cheap semiconductors in order to maintain its role in the technological race of sustainable hydrogen production.

The role of tungsten-related elements for improving the electrochemical performances of cathode materials in lithium ion batteries

Lithium ion batteries using Ni-Co-Mn ternary oxide materials(NCMs)and Ni-Co-Al materials(NCAs)as the cathode materials are dominantly employed to power the electric vehicles(EVs).Increasing the driving range of EVs necessitates an increase of Ni content to improve the energy densities,which,however,degrades the cycle stability.Here we review the doping/coating of tungsten and related elements to improve the electrochemical performance of these cathodes especially the cycle stability.The selection of tungsten and related elements is based on their special properties including the high valence state,strong bonding with oxygen and the large ionic radius.The improvement of cycle stability mainly results from two features:(1)the enhancement of bulk structure stability upon doping(Mo,W,Ta,Nb)and(2)the resistance of side reactions of electrode/electrolyte by the surficial layer induced by direct coating(V,W,Nb)or bulk doping.For the recent high Ni materials,the formation of Ni2+and its migration to the Li layer induced by these doped/coated tungsten-related elements,and the presence of spinel or rock-salt phase before cycling contributes to improving the cycle stability.The key challenges are the selection of an optimized additive concentration and the fundamental understanding of the reaction mechanism,which will provide insightful guidance for maximizing the electrochemical performance of the state-of-the-art lithium-ion batteries at minimal additional process costs.

Enhanced CH4 selectivity in CO2 photocatalytic reduction over carbon quantum dots decorated and oxygen doping g-C3N4

Graphitic carbon nitride(g-C3N4,CN)exhibits inefficient charge separation,deficient CO2 adsorption and activation sites,and sluggish surface reaction kinetics,which have been recognized as the main barriers to its application in CO2 photocatalytic reduction.In this work,carbon quantum dot(CQD)decoration and oxygen atom doping were applied to CN by a facile one-step hydrothermal method.The incorporated CQDs not only facilitate charge transfer and separation,but also provide alternative CO2 adsorption and activation sites.Further,the oxygen-atom-doped CN(OCN),in which oxygen doping is accompanied by the formation of nitrogen defects,proves to be a sustainable H^+ provider by facilitating the water dissociation and oxidation half-reactions.Because of the synergistic effect of the hybridized binary CQDs/OCN addressing the three challenging issues of the CN based materials,the performance of CO2 photocatalytic conversion to CH4 over CQDs/OCN-x(x represents the volume ratio of laboratory-used H2O2(30 wt.%)in the mixed solution)is dramatically improved by 11 times at least.The hybrid photocatalyst design and mechanism proposed in this work could inspire more rational design and fabrication of effective photocatalysts for CO2 photocatalytic conversion with a high CH4 selectivity.