Nano-Au-decorated hierarchical porous cobalt sulfide derived from ZIF-67 toward optimized oxygen evolution catalysis:Important roles of microstructures and electronic modulation

Enhancing both the number of active sites available and the intrinsic activity of Co-based electrocatalysts simultaneously is a desirable goal.Herein,a ZIF-67-derived hierarchical porous cobalt sulfide decorated by Au nanoparticles(NPs)(denoted as HP-Au@CoxSy@ZIF-67)hybrid is synthesized by low-temperature sulfuration treatment.The well-defined macroporous-mesoporous-microporous structure is obtained based on the combination of polystyrene spheres,as-formed CoxSy nanosheets,and ZIF-67 frameworks.This novel three-dimensional hierarchical structure significantly enlarges the three-phase interfaces,accelerating the mass transfer and exposing the active centers for oxygen evolution reaction.The electronic structure of Co is modulated by Au through charge transfer,and a series of experiments,together with theoretical analysis,is performed to ascertain the electronic modulation of Co by Au.Meanwhile,HP-Au@CoxSy@ZIF-67 catalysts with different amounts of Au were synthesized,wherein Au and NaBH4 reductant result in an interesting“competition effect”to regulate the relative ratio of Co^(2+)/Co^(3+),and moderate Au assists the electrochemical performance to reach the highest value.Consequently,the optimized HP-Au@CoxSy@ZIF-67 exhibits a low overpotential of 340 mV at 10 mA cm^(-2)and a Tafel slope of 42 mV dec-1 for OER in 0.1 M aqueous KOH,enabling efficient water splitting and Zn-air battery performance.The work here highlights the pivotal roles of both microstructural and electronic modulation in enhancing electrocatalytic activity and presents a feasible strategy for designing and optimizing advanced electrocatalysts.

Insights into Formation and Li-Storage Mechanisms of Hierarchical Accordion-Shape Orthorhombic CuNb_(2)O_(6) toward Lithium-Ion Capacitors as an Anode-Active Material

The orthorhombic CuNb_(2)O_(6)(O-CNO)is established as a competitive anode for lithium-ion capacitors(LICs)owing to its attractive compositional/structural merits.However,the high-temperature synthesis(>900℃)and controversial charge-storage mechanism always limit its applications.Herein,we develop a low-temperature strategy to fabricate a nano-blocks-constructed hierarchical accordional O-CNO framework by employing multilayered Nb_(2)CT_(x)as the niobium source.The intrinsic stress-induced formation/transformation mechanism of the monoclinic CuNb_(2)O_(6)to O-CNO is tentatively put forward.Furthermore,the integrated phase conversion and solid solution lithium-storage mechanism is reasonably unveiled with comprehensive in(ex)situ characterizations.Thanks to its unique structural merits and lithium-storage process,the resulted O-CNO anode is endowed with a large capacity of 150.3 mAh g^(-1)at 2.0 A g^(-1),along with long-duration cycling behaviors.Furthermore,the constructed O-CNO-based LICs exhibit a high energy(138.9 Wh kg^(-1))and power(4.0 kW kg^(-1))densities with a modest cycling stability(15.8%capacity degradation after 3000 consecutive cycles).More meaningfully,the in-depth insights into the formation and charge-storage process here can promote the extensive development of binary metal Nb-based oxides for advanced LICs.

Sub-nanoscale Engineering of MoO_(2) Clusters for Enhanced Sodium Storage

Smart construction of battery-type anodes with high rate and good mechanical properties is significant for advanced sodium ion capacitors(SICs).Herein,a flexible film consisting of MoO_(2) subnanoclusters encapsulated in nitrogen-doped carbon nanofibers(MoO_(2) SCs@N-CNFs)is designed and synthesized via electrospinning toward SICs as anodes.The strong N-Mo interaction guarantees the stable yet uniform dispersion of high loading MoO_(2) SCs(≈40 wt.%)in the flexible carbonaceous substrate.The sub-nanoscale effect of SCs restrains electrode pulverization and improves the Na+diffusion kinetics,rendering better pseudocapacitance-dominated Na+-storage properties than the nanocrystal counterpart.The MoO_(2) SCs@N-CNFs paper with mass loadings of 2.2–10.1 mg cm^(−2) can be directly used as free-standing anode for SICs,which exhibit high reversible gravimetric/areal capacities both in liquid and quasi-solid-state electrolytes.The assembled flexible SICs competitively exhibit exceptional energy density and cycling stability.More significantly,the sub-nanoscale engineering strategy here is promisingly generalized to future electrode design for other electrochemical energy-related applications and beyond.

Binary molten salt in situ synthesis of sandwich-structure hybrids of hollowβ-Mo2C nanotubes and N-doped carbon nanosheets for hydrogen evolution reaction

Focused exploration of earth-abundant and cost-efficient non-noble metal electrocatalysts with superior hydrogen evolution reaction(HER)performance is very important for large-scale and efficient electrolysis of water.Herein,a sandwich composite structure(designed as MS-Mo2C@NCNS)ofβ-Mo2C hollow nanotubes(HNT)and N-doped carbon nanosheets(NCNS)is designed and prepared using a binary NaCl–KCl molten salt(MS)strategy for HER.The temperature-dominant Kirkendall formation mechanism is tentatively proposed for such a three-dimensional hierarchical framework.Due to its attractive structure and componential synergism,MS-Mo2C@NCNS exposes more effective active sites,confers robust structural stability,and shows significant electrocatalytic activity/stability in HER,with a current density of 10 mA cm-2 and an overpotential of only 98 mV in 1 M KOH.Density functional theory calculations point to the synergistic effect of Mo2C HNT and NCNS,leading to enhanced electronic transport and suitable adsorption free energies of H*(ΔGH*)on the surface of electroactive Mo2C.More significantly,the MS-assisted synthetic methodology here provides an enormous perspective for the commercial development of highly active non-noble metal electrocatalysts toward efficient hydrogen evolution.

Conductive metal-organic frameworks: Recent advances in electrochemical energy-related applications and perspectives

Metal-organic frameworks(MOFs),typically constructed with metallic nodes and organic linkers,have influenced the development of modular solid materials.Their adjustable molecular structure provides a remarkable variety of MOF-based solid-state structures towards diverse applications.However,the low conductivity of traditional MOFs extremely hinders their applications in electronic and electrochemical devices.The emerging conductive MOFs,generally possessing twodimensional layered structures,are endowed with both the structural merits of common MOFs and exceptional electronic/ionic conductivities.Besides,the selection and optimization of ligands and metal centers,as well as synthetic methods enormously affects the intrinsic conductivity of conductive MOFs.The distinctive crystal structures and superb conductivity promise their appealing applications in electrochemical energy-related fields.In the review,we mainly summarize representative crystal features,conducting mechanisms and recent advances in rational design and synthesis of conductive MOFs,along with their versatile applications as electrodes for electrochemical capacitors and rechargeable batteries,and as catalysts towards electrocatalysis.Finally,the involved challenges and future trends/prospects of the conductive MOFs for electrochemical energyrelated applications are further proposed.

Boosting sodium-storage properties of hierarchical Na_(3)V_(2)(PO_(4))_(3)@C micro-flower cathodes by tiny Cr doping:The effect of“four ounces moving a thousand pounds”

Na_(3)V_(2)(PO_(4))_(3)(NVP),as a great potential cathode candidate for Na-ion batteries(NIBs),has attracted enormous interest due to its three-dimensional(3D)large open framework for convenient Na+transport,yet its practical application is still limited by its inferior electron conductivity and sluggish Na+diffusion kinetics.Herein,the tiny Cr doped hierarchical NVP micro-flower cathodes(i.e.,Na_(3)V_(2-x)Crx(PO_(4))_(3)@C,x≤0.1),which are self-assembled with single-crystal nanoflake subunits in-situ coated with carbon nano-shell,are designed and fabricated via a scalable avenue.The optimized cathode,i.e.,Na_(3)V_(1.94)Cr_(0.06)(PO_(4))_(3)@C(NVCP-6),was endowed with more electro-active Na(2)sites and higher electronic/ionic conductivity for efficient sodium storage.Benefiting from these competitive merits,the NVCP-6,when evaluated as a cathode towards NIBs,exhibits an ultrahigh-rate capability of 99.8 mAh·g^(-1)at 200 C and superior stability of 82.2%over 7300 cycles at 50 C.Furthermore,the NVCP-6 based full NIBs display remarkable electrochemical properties in terms of both high-rate capacities and long-duration cycling properties at different temperatures(-20–50°C).The contribution,i.e.,the design of“four ounces can move a thousand pounds”,here will promote the practical industrial application of NVP towards advanced NIBs.

Coordination polymer nanowires/reduced graphene oxide paper as flexible anode for sodium-ion batteries

构建基于有机材料的高性能柔性储钠电极面临诸多挑战.本工作通过可控组装及还原的方式,实现了铁基配位聚合物纳米线/还原氧化石墨烯柔性薄膜的构筑.多维复合薄膜可直接用作钠离子电池自支撑负极,且具有较高的储钠容量(200 mA g^−1电流密度下可逆容量为319 mA h g^−1)和优异的倍率性能(3000 mA g^−1大电流密度下比容量可保持在∼120 mA h g^−1).研究表明有机配体(氨三乙酸)中的羧基及氨基为储钠活性位点,而配位金属离子(Fe^2+)不参与电化学反应.

Interconnected N/P co-doped carbon nanocage as high capacitance electrode material for energy storage devices

Heteroatom doping carbon materials exhibit a huge application potential for energy storage devices(ESDs).Herein,interconnected N/P co-doped carbon nanocage(NP-CNC)was synthesized from pyrene molecules by using nano-MgO as template and melamine-phytic acid supramolecular aggregate as dopant coupled with KOH activation.The as-prepared NP-CNC possesses interconnected nanocages for electron transportation and abundant micropores for ion adsorption.Moreover,co-doped N/P species in NP-CNC provide active sites and additional pseudocapacitance.Consequently,NP-CNC as electrode material for symmetric supercapacitor exhibits a high gravimetric capacitance of 435 F·g^(-1) at 0.05 A·g^(-1),high volumetric capacitance of 274 F·cm^(-3) at 0.032 A·cm^(-3),and long cycle lifespan with 96.1%capacitance retention after 50,000 cycles.Furthermore,NP-CNC as cathode for zinc-ion hybrid supercapacitor delivers satisfactory energy and power densities of 130.6 Wh·kg^(-1)(82.3 Wh·L^(-1))and 14.4 kW·kg^(-1)(9.1 kWL^(-1)).This work paves a promising approach to the preparation of high capacitance NP-CNC for ESDs.

Laser irradiation construction of nanomaterials toward electrochemical energy storage and conversion:Ongoing progresses and challenges

The emerging use of laser irradiation in synthesis smartly bridges“nanotech-nology”and“light”,and has attracted enormous attention as an efficient syn-thetic methodology for versatile nanomaterials toward electrochemical energy storage and conversion devices(ESCDs).In this review,recent contributions and progress regarding the laser-induced nanomaterials for ESCDs are com-prehensively summarized,with a special focus on their practical utilization in rechargeable batteries,supercapacitors and electrocatalysis.The laser-induced synthesis strategies and corresponding mechanisms involved in nano-architecture generation/regulation,including pulsed laser deposition and laser irradiation in liquid,are also discussed in detail.With the in-depth insights into the mechanisms and revolutionary advancements of laser irradiation tech-nology,the comprehensive performances of ESCDs have been strikingly opti-mized.Finally,the existing challenges and future directions in this booming research field are outlined.This review will exert the significant guidance for future design and purposeful fabrication of advanced laser-induced nano-materials with appealing properties for advanced ESCDs and beyond.

A Review of Metal Silicides for Lithium-Ion Battery Anode Application

Lithium batteries(LIBs) with low capacity graphite anode(~372 mAh g-1) cannot meet the ever-growing demand for new energy electric vehicles and renewable energy storage.It is essential to replace graphite anode with higher capacity anode materials for high-energy density LIBs.Silicon(Si) is well known to be a possible alternative for graphite anode due to its highest capacity(~4200 mAh g-1).Unfortunately,large volume change during lithiation and delithiation has prevented the Si anode from being commercialized.Metal silicides are a promising type of anode materials which can improve cycling stability via the accommodation of volume change by dispersing Si in the metal inactive/active matrix,while maintain greater capacity than graphite.Here,we present a classification of Si alloying with metals in periodic table of elements,review the available literature on metal silicide anodes to outline the progress in improving and understanding the electrochemical performance of various metal silicides,analyze the challenges that remain in using metal silicides,and offer perspectives regarding their future research and development as anode materials for commercial LIBs application.

Template-Free Synthesis of Ordered Mesoporous NiO/Poly (Sodium-4-Styrene Sulfonate) Functionalized Carbon Nanotubes Composite for Electrochemical Capacitors

We report the first example of a practical and efficient template-free strategy for synthesizing ordered mesoporous NiO/poly(sodium-4-styrene sulfonate)(PSS)functionalized carbon nanotubes(FCNTs)composites by calcining a Ni(OH)_(2)/FCNTs precursor prepared by refl uxing an alkaline solution of Ni(NH_(3))x^(2)+and FCNTs at 97 oC for 1 h.The morphology and structure were characterized by X-ray diffraction,scanning electron microscopy,and transmission electron microscopy.Thermal decomposition of the precursor results in the formation of ordered mesoporous NiO/FCNTs composite(ca.48 wt%NiO)with large specifi c surface area.Due to its enhanced electronic conductivity and hierarchical(meso-and macro-)porosity,composite simultaneously meets the three requirements for energy storage in electrochemical capacitors at high rate,namely,good electron conductivity,highly accessibleelectrochemical surface areas owing to the existence of mesopores,and efficient mass transport from the macropores.Electrochemical data demonstrated that the ordered mesoporous NiO/FCNTs composite is capable of delivering a specifi c capacitance(SC)of 526 F/g at 1 A/g and a SC of 439 F/g even at 6 A/g,and show a degradation of only ca.6%in SC after 2000 continuous charge/discharge cycles.

In-situ growth of hybrid NaTi8O13/NaTiO2 nanoribbons on layered MXene Ti3C2 as a competitive anode for high-performance sodium-ion batteries

In the work,we successfully explore a two-step hydrothermal method for scalable synthesis of the hybrid sodium titanate(NaTi8O13/NaTiO2) nanoribbons well in-situ formed on the multi-layered MXene Ti3C2(designed as NTO/Ti3C2).Benefiting from the inherent structural and componential superiorities,the resulted NTO/Ti3C2 composite exhibits long-duration cycling stability and superior rate behaviors when evaluated as a hybrid anode for advanced SIBs,which delivers a reversible and stable capacity of^82 mAh/g even after 1900 cycles at 2000 mA/g for SIBs.

Solid-state template-free fabrication of uniform Mo2C microflowers with lithium storage towards Li-ion batteries

Herein,we first report one-step synthesis of uniform Mo2 C microflowers(MCMFs)from low-cost precursors via industrialized solid-state strategy.With fine optimization in precursor ratio and pyrolysis temperatures,the as-fabricated MCMFs are assembled well with interconnected single-crystalline nanosheet subunits.More encouragingly,the resultant MCMFs are further highlighted as a competitive anode with robust and long-duration lithium-storage behaviors towards high-performance Li-ion batteries.

Facile hydrothermal construction of Nb2CTx/Nb2O5 as a hybrid anode material for high-performance Li-ion batteries

Herein,a simple yet efficient hydrothermal strategy is developed to in-situ convert multi-layered niobium-based MXene(Nb2 CTx)to hierarchical Nb2 CTx/Nb2O5 composite.In the hybrid,the Nb2O5 nanorods are well dispersed in and/or on the Nb2 CTx.Thanks to the synergetic contributions from the high capacity of Nb2O5 and superb electrical conductivity of the two-dimensional Nb2 CTx itself,the resultant Nb2 CTx/Nb2O5 hybrid exhibits excellent rate behaviors and stable long-term cycling behaviors,when evaluated as anodes for Li-ion batteries.