High N-doped hierarchical porous carbon networks with expanded interlayers for efficient sodium storage

Sodium-ion batteries (SIBs) have been attracting considerable attention as a promising candidate for large-scale energy storage because of the abundance and low-cost of sodium resources. However, lack of appropriate anode materials impedes further applications. Herein, a novel self-template strategy is designed to synthesize uniform flowerlike N-doped hierarchical porous carbon networks (NHPCN) with high content of N (15.31 at.%) assembled by ultrathin nanosheets via a self-synthesized single precursor and subsequent thermal annealing. Relying on the synergetic coordination of benzimidazole and 2-methylimidazole with metal ions to produce a flowerlike network, a self-formed single precursor can be harvested. Due to the structural and compositional advantages, including the high N doping, the expanded interlayer spacing, the ultrathin two-dimensional nano-sized subunits, and the three-dimensional porous network structure, these unique NHPCN flowers deliver ultrahigh reversible capacities of 453.7 mAh·g⁻¹ at 0.1 A·g⁻¹ and 242.5 mAh·g⁻¹ at 1 A·g⁻¹ for 2,500 cycles with exceptional rate capability of 5 A·g⁻¹ with reversible capacities of 201.2 mAh·g⁻¹. The greatly improved sodium storage performance of NHPCN confirms the importance of reasonable engineering and synthesis of hierarchical carbon with unique structures.

     

Dandelion-Like Bi2S3/rGO hierarchical microspheres as high-performance anodes for potassium-ion and half/full sodium-ion batteries

Sodium-ion batteries (SIBs) and potassium-ion batteries (PIBs) have been considered as attractive alternatives for next-generation battery systems, which have promising application potential due to their earth abundance of potassium and sodium, high capacity and suitable working potential, however, the design and application of bi-functional high-performance anode still remain a great challenge up to date. Bismuth sulfide is suitable as anode owing to its unique laminar structure with relatively large interlayer distance to accommodate larger radius ions, high theoretical capacity and high volumetric capacity etc. In this study, dandelion-like Bi₂S₃/rGO hierarchical microspheres as anode material for PIBs displayed reversible capacity, and 206.91 mAh·g⁻¹ could be remained after 1,200 cycles at a current density of 100 mA·g⁻¹. When applied as anode materials for SIBs, 300 mAh·g⁻¹ could be retained after 300 cycles at 2 A·g⁻¹ and its initial Coulombic efficiency is as high as 97.43%. Even at high current density of 10 A·g⁻¹, 120.3 mAh·g⁻¹ could be preserved after 3,400 cycles. The Na₃V₂(PO₄)₃@rGO//Bi₂S₃/rGO sodium ion full cells were successfully assembled which displays stable performance after 60 cycles at 100 mA·g⁻¹. The above results demonstrate that Bi₂S₃/rGO has application potential as high performance bi-functional anode for PIBs and SIBs.

     

2D interspace confined growth of ultrathin MoS2-intercalated graphite hetero-layers for high-rate Li/K storage

Herein,a two-dimensional(2D)interspace-confined synthetic strategy is developed for producing MoS₂intercalated graphite(G-MoS₂)hetero-layers composite through sulfuring the pre-synthesized stage-1 MoCI5-graphite intercalation compound(M0 CI5-GIC).The in situ grown MoS₂nanosheets(3-7 layers)are evenly encapsulated in graphite layers with intimate interface thus forming layer-by-layer MoS₂-intercalated graphite composite.In this structure,the unique merits of MoS₂and graphite components are integrated,such as high capacity contribution of MoS₂and the flexibility of graphite layers.Besides,the tight interfacial interaction between hetero-layers optimizes the potential of conductive graphite layers as matrix for MoS₂.As a result,the G-MoS₂exhibits a high reversible Li+storage of 344 mAh·g^-1even at 10 A·g^-1and a capacity of 539.9 mAh·g^-1after 1,500 cycles at 5 A·g^-1.As for potassium ion battery,G-MoS₂delivers a reversible capacity of 377.0 mAh·g^-1at 0.1 A·g^-1and 141.2 mAh·g^-1even at 2 A·g^-1.Detailed experiments and density functional theory calculation demonstrate the existence of hetero-layers enhances the diffusion rates of Li⁺and K⁺.This graphite interspace-confined synthetic methodology would provide new ideas for preparing function-integrated materials in energy storage and conversion,catalysis or other fields.     

VO2·0.2H2O nanocuboids anchored onto graphene sheets as the cathode material for ultrahigh capacity aqueous zinc ion batteries

Aqueous Zinc-ion batteries (ZIBs), using zinc negative electrode and aqueous electrolyte, have attracted great attention in energy storage field due to the reliable safety and low-cost. A composite material comprised of VO₂·0.2H₂O nanocuboids anchored on graphene sheets (VOG) is synthesized through a facile and efficient microwave-assisted solvothermal strategy and is used as aqueous ZIBs cathode material. Owing to the synergistic effects between the high conductivity of graphene sheets and the desirable structural features of VO₂·0.2H₂O nanocuboids, the VOG electrode has excellent electronic and ionic transport ability, resulting in superior Zn ions storage performance. The Zn/VOG system delivers ultrahigh specific capacity of 423 mAh·g⁻¹ at 0.25 A·g⁻¹ and exhibits good cycling stability of up to 1,000 cycles at 8 A·g⁻¹ with 87% capacity retention. Systematical structural and elemental characterizations confirm that the interlayer space of VO₂·0.2H₂O nanocuboids can adapt to the reversible Zn ions insertion/extraction. The as-prepared VOG composite is a promising cathode material with remarkable electrochemical performance for low-cost and safe aqueous rechargeable ZIBs.

     

Flower-like NiCo2S4 nanosheets with high electrochemical performance for sodium-ion batteries

A three-dimensional flower-like NiCo₂S₄ formed by two-dimensional nanosheets is synthesized by a facile hydrothermal method and utilized as the anode for sodium-ion batteries. Studies have shown that materials can achieve the best performance under the ether-based electrolyte system with voltage ranging from 0.3 to 3 V, which could effectively avoid the dissolution of polysulfides and over-discharge of the material. Here, sodium storage mechanism and charge compensation behaviors of this ternary metal sulfide are comprehensively investigated by ex situ X-ray diffraction. Moreover, ex situ Raman spectra, ex situ X-ray photoelectron spectroscopy and transmission electron microscopy measurements are used to related tests for the first time. Additionally, quantitative kinetic analysis unravels that sodium storage partially depends on the pseudocapacitance mechanism, resulting in good specific capacity and excellent rate performance. The initial discharge capacity is as high as 748 mAh·g⁻¹ at a current density of 0.1 A·g⁻¹ with the initial coulomb efficiency of 94%, and the capacity can still maintain at 580 mAh·g⁻¹ with the Coulomb efficiency close to 100% after following 50 cycles. Moreover, by the long cycle test at a high current density of 2 A·g⁻¹, the capacity can still reach at 376 mAh·g⁻¹ after over 500 cycles.

     

High power and stable P-doped yolk-shell structured Si@C anode simultaneously enhancing conductivity and Li+diffusion kinetics

Silicon is a low price and high capacity ancxje material for lithium-ion batteries.The yolk-shell structure can effectively accommodate Si expansion to improve stability.However,the limited rate performance of Si anodes can't meet people's growing demand for high power density.Herein,the phosphorus-doped yolk-shell Si@C materials(P-doped Si@C)were prepared through carbon coating on P-doped Si/SiO_xmatrix to obtain high power and stable devices.Therefore,the as-prepared P-doped Si@C electrodes delivered a rapid increase in Coulombic efficiency from 74.4%to 99.6%after only 6 cycles,high capacity retention of-95%over 800 cycles at 4 A·g^-1,and great rate capability(510 mAh·g^-1at 35 A·g^-1).As a result,P-doped Si@C anodes paired with commercial activated carbon and LiFePO₄cathode to assemble lithium-ion capacitor(high power density of?61,080 W·kg^-1at 20 A·g^-1)and lithium-ion full cell(good rate performance with 68.3 mAh·g^-1at 5 C),respectively.This work can provide an effective way tofurther improve power density and stability for energy storage devices.     

Interlayer-expanded MoS2 assemblies for enhanced electrochemical storage of potassium ions

Potassium-ion batteries are regarded as the low-cost alternative to lithium-ion batteries. However, their development is hampered by the lack of suitable electrode materials. In this work, we demonstrate that MoS₂ with expanded interlayers represents a promising candidate for the electrochemical storage of potassium ions. Hierarchical interlayer-expanded MoS₂ assemblies supported on carbon nanotubes are prepared via a straightforward solution method. The increased interlayer spacing not only enables the better accommodation of foreign ions, but also lowers the diffusion energy barrier and improves diffusion kinetics of ions. When investigated as the anode material of potassium ion batteries, our interlayer-expanded MoS₂ assemblies exhibit an excellent electrochemical performance with large capacity (up to ∼ 520 mAhg⁻¹), good rate capability (∼ 310 mAhg⁻¹ at 1,000 mAg⁻¹) and impressive cycling stability, superior to most competitors.

     

Graphitic nanorings for super-long lifespan lithium-ion capacitors

Porous graphitic carbon nanorings (PGCNs) are proposed by smart catalytic graphitization of nano-sized graphene quantum dots (GQDs). The as-prepared PGCNs show unique ring-like morphology with diameter around 10 nm, and demonstrate extraordinary mesoporous structure, controllable graphitization degree and highly defective nature. The mechanism from GQDs to PGCNs is proven to be a dissolution-precipitation process, undergoing the procedure of amorphous carbon, intermediate phase, graphitic carbon nanorings and graphitic carbon nanosheets. Further, the relationship between particles size of GQDs precursor and graphitization degree of PGCNs products is revealed. The unique microstructure implies PGCNs a broad prospect for energy storage application. When applied as negative electrode materials in dual-carbon lithium-ion capacitors, high energy density (77.6 Wh·kg⁻¹) and super long lifespan (89.5% retention after 40,000 cycles at 5.0 A·g⁻¹) are obtained. The energy density still maintains at 24.5 Wh·kg⁻¹ even at the power density of 14.1 kW·kg⁻¹, demonstrating excellent rate capability. The distinct microstructure of PGCNs together with the strategy for catalytic conversion from nanocarbon precursors to carbon nanorings opens a new window for carbon materials in electrochemical energy storage.

     

Improved Na storage and Coulombic efficiency in TiP2O7@C microflowers for sodium ion batteries

Ti-based anode materials in sodium ion batteries have attracted extensive interests due to its abundant resources,low toxicity,easy synthesis and long cycle life.However,low Coulombic efficiency and limited specific capacity affect their applications.Here,cubic-phase TiP₂O₇is examined as anode materials,using in-situ/ex-situ characterization techniques.It is concluded that the redox reactions of Ti4⁺/Ti³⁺and Ti³⁺/Ti⁰consecutively occur during the discharge/charge processes,both of which are highly reversible.These reactions make the specific capacity of TiP₂O₇even higher than the case of TiO2 that only contains a simple anion,0^2-.Interestingly,Ti species participate only one of the redox reactions,due to the remarkable difference in local structures related to the sodiation process.The stable discharge/charge products in TiP₂O₇reduce the side reactions and improve the Coulombic efficiency as compared to T i02.These features make it a promising Ti-based anode for sodium ion batteries.Therefore,TiP₂O₇@C microflowers exhibit excellent electrochemical performances,?109 mAh·g^-1after 10,000 cycles at 2 A·g^-1,or 95.2 mAh·g^-1at 10 A·g^-1.The results demonstrate new opportunities for advanced Ti-based anodes in sodium ion batteries.     

A combination of hierarchical pore and buffering layer construction for ultrastable nanocluster Si/SiOx anode

Porous Si can be synthesized from diverse silica (SiO₂) via magnesiothermic reduction technology and widely employed as potential anode material in lithium ion batteries. However, concerns regarding the influence of residual silicon oxide (SiO_x) component on resulted Si anode after reduction are still lacked. In this work, we intentionally fabricate a cauliflower-like silicon/silicon oxide (CF-Si/SiO_x) particles from highly porous SiO₂ spheres through insufficient magnesiothermic reduction, where residual SiO_x component and internal space play an important role in preventing the structural deformation of secondary bulk and restraining the expansion of Si phase. Moreover, the hierarchically structured CF-Si/SiO_x exhibits uniformly-dispersed channels, which can improve ion transport and accommodate large volume expansion, simultaneously. As a result, the CF-Si/SiO_x-700 anode shows excellent electrochemical performance with a specific capacity of ~1,400 mA·h·g⁻¹ and a capacity retention of 98% after 100 cycles at the current of 0.2 A·g⁻¹.

     

Electrocatalytic N2 reduction to NH3 with high Faradaic efficiency enabled by vanadium phosphide nanoparticle on V foil

To develop highly efficient electrochemical catalysts for N₂ fixation is important to sustainable ambient NH₃ production through the N₂ reduction reaction (NRR). Herein, we demonstrate the development of vanadium phosphide nanoparticle on V foil as a high-efficiency and stable catalyst for ambient NH₃ production with excellent selectivity. The high Faradaic efficiency of 22% with a large NH₃ yield of 8.35 × 10⁻¹¹ mol·s⁻¹·cm⁻² was obtained at 0 V vs. the reversible hydrogen electrode in acid solution, superior to all previously studied V-based NRR catalysts. Density functional theory calculations are also utilized to have an insight into the catalytic mechanism.

     

Ultrasonication-assisted and gram-scale synthesis of Co-LDH nanosheet aggregates for oxygen evolution reaction

Electrochemical water splitting (EWS) is a highly clean and efficient method for high-purity hydrogen production. Unfortunately, EWS suffers from the sluggish and complex oxygen evolution reaction (OER) kinetics at anode. At present, the efficient, stable, and low-cost non-precious metal based OER electrocatalyst is still a great and long-term challenge for the future industrial application of EWS technology. Herein, we develop a simple and fast approach for gram-scale synthesis of flower-like cobalt-based layered double hydroxides nanosheet aggregates by ultrasonic synthesis, which show outstanding electrocatalytic performance for the oxygen evolution reaction in alkaline media, such as preeminent stability, small overpotential of 300 mV at 10 mA·cm⁻² and small Tafel slope of 110 mV·dec⁻¹.

     

Exploiting oleic acid to prepare two-dimensional assembly of Si@graphitic carbon yolk-shell nanoparticles for lithium-ion battery anodes

Carbon coating has been a routine strategy for improving the performance of Si-based anode materials for lithium-ion batteries. The ability to tailor the thickness, homogeneity and graphitization degree of carbon-coating layers is essential for addressing issues that hamper the real applications of Si anodes. Herein, we report the construction of two-dimensional (2D) assemblies of interconnected Si@graphitic carbon yolk-shell nanoparticles (2D-Si@gC) from commercial Si powders by exploiting oleic acid (OA). The OA molecules act as both the surface-coating ligands for facilitating 2D nanoparticle assembly and the precursor for forming uniform and conformal graphitic shells as thin as 4 nm. The as-prepared 2D-Si@gC with rationally designed void space exhibits excellent rate capability and cycling stability when used as anode materials for lithium-ion batteries, delivering a capacity of 1,150 mAh·g⁻¹ at an ultrahigh current density of 10 A·g⁻¹ and maintaining a stabilized capacity of 1,275 mAh·g⁻¹ after 200 cycles at 4 A·g⁻¹. The formation of yolk-shell nanoparticles confines the deposition of solid electrolyte interphase (SEI) onto the outer carbon shell, while simultaneously providing sufficient space for volumetric expansion of Si nanoparticles. These attributes effectively mitigate the thickness variations of the entire electrode during repeated lithiation and delithiation, which combined with the unique 2D architecture and interconnected graphitic carbon shells of 2D-Si@gC contributes to its superior rate capability and cycling performance.

     

Phosphorus-doping activates carbon nanotubes for efficient electroreduction of nitrogen to ammonia

The electrochemical nitrogen reduction reaction (NRR) as an energy-efficient approach for ammonia synthesis is hampered by the low ammonia yield and ambiguous reaction mechanism. Herein, phosphorus-doped carbon nanotube (P-CNTs) is developed as an efficient metal-free electrocatalyst for NRR with a remarkable NH₃ yield of 24.4 μg·h⁻¹·mg⁻¹_cat. and partial current density of 0.61 mA·cm⁻². Such superior activity is found to be from P doping and highly conjugated CNTs substrate. Experimental and theoretical investigations discover that the electron-deficient phosphorus sites with Lewis acidity should be genuine active sites and NRR on P-CNTs follows the distal pathway. These findings provide insightful understanding on NRR processes on P-CNTs, opening up opportunities for the rational design of highly-active cost-effective metal-free catalysts for electrochemical ammonia synthesis.

     

A phenazine anode for high-performance aqueous rechargeable batteries in a wide temperature range

Aqueous rechargeable batteries are a possible strategy for large-scale energy storage systems. However, limited choices of anode materials restrict their further application. Here we report phenazine (PNZ) as stable anode materials in different alkali-ion (Li⁺, Na⁺, K⁺) electrolyte. A novel full cell is assembled by phenazine anode, Na_0.44MnO₂ cathode and 10 M NaOH electrolyte to further explore the electrochemical performance of phenazine anode. This battery is able to achieve high capacity (176.7 mAh·g^?1 at 4 C (1.2·Ag^?1)), ultralong cycling life (capacity retention of 80% after 13,000 cycles at 4 C), and excellent rate capacity (92 mAh·g^?1 at 100 C (30 A·g^?1)). The reaction mechanism of PNZ during charge—discharge process is demonstrated by in situ Raman spectroscopy, in situ Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and density functional theory (DFT) calculations. Furthermore, the system is able to successfully operate at wide temperature range from ?20 to 70 °C and achieves remarkable electrochemical performance.

     

Ultra-stable K metal anode enabled by oxygen-rich carbon cloth

The K metal batteries are emerged as promising alternatives beyond commercialized Li-ion batteries. However, suppressing uncontrolled dendrite is crucial to the accomplishment of K metal batteries. Herein, an oxygen-rich treated carbon cloth (TCC) has been designed as the K plating host to guide K homogeneous nucleation and suppress the dendrite growth. Both density function theory calculations and experimental results demonstrate that abundant oxygen functional groups as K-philic sites on TCC can guide K nucleation and deposition homogeneously. As a result, the TCC electrode exhibits an ultra-long-life over 800 cycles at high current density of 3.0 mA·cm⁻² for 3.0 mA·h·cm⁻². Furthermore, the symmetrical cells can run stably for 2,000 h with low over-potential less than 20 mV at 1.0 mA·cm⁻² for 1.0 mA·h·cm⁻². Even at a higher current of 5.0 mA·cm⁻², the TCC electrode can still stably cycle for 1,400 h.

     

Multi-redox phenazine/non-oxidized graphene/cellulose nanohybrids as ultrathick cathodes for high-energy organic batteries

Various redox-active organic molecules can serve as ideal electrode materials to realize sustainable energy storage systems. Yet, to be more appropriate for practical use, considerable architectural engineering of an ultrathick, high-loaded organic electrode with reliable electrochemical performance is of crucial importance. Here, by utilizing the synergetic effect of the non-covalent functionalization of highly conductive non-oxidized graphene flakes (NOGFs) and introduction of mechanically robust cellulose nanofiber (CNF)-intermingled structure, a very thick (≈ 1 mm), freestanding organic nanohybrid electrode which ensures the superiority in cycle stability and areal capacity is reported. The well-developed ion/electron pathways throughout the entire thickness and the enhanced kinetics of electrochemical reactions in the ultrathick 5,10-dihydro-5,10-dimethylphenazine/NOGF/CNF (DMPZ-NC) cathodes lead to the high areal energy of 9.4 mWh·cm?2 (= 864 Wh·kg?1 at 158 W·kg?1). This novel ultrathick electrode architecture provides a general platform for the development of the high-performance organic battery electrodes.     

Theory-guided construction of electron-deficient sites via removal of lattice oxygen for the boosted electrocatalytic synthesis of ammonia

Rational design of catalytic sites to activate the inert N≡N bond is of paramount importance to advance N2 electroreduction. Here, guided by the theoretical predictions, we construct a NiFe layered double hydroxide (NiFe-LDH) nanosheet catalyst with a high density of electron-deficient sites, which were achieved by introducing oxygen vacancies in NiFe-LDH. Density functional theory calculations indicate that the electron-deficient sites show a much lower energy barrier (0.76 eV) for the potential determining step compared with that of the pristine NiFe-LDH (2.02 eV). Benefiting from this, the NiFe-LDH with oxygen vacancies exhibits the greatly improved electrocatalytic activity, presenting a high NH3 yield rate of 19.44 μg·h?1·mgcat?1, Faradaic efficiency of 19.41% at ?0.20 V vs. reversible hydrogen electrode (RHE) in 0.1 M KOH electrolyte, as well as the outstanding stability. The present work not only provides an active electrocatalyst toward N2 reduction but also offers a facile strategy to boost the N2 reduction.     

Nanovilli electrode boosts hydrogen evolution:A surface with superaerophobicity and superhydrophilicity

Although tremendous efforts have been paid on electrocatalysts toward efficient electrochemical hydrogen generation,breakthrough is still highly needed in the design and synthesis of wonderful non-precious-metal electrocatalyst.Herein,a nanovilli Ni2P electrode,which with superaerophobic and superhydropholic can significantly facilitate the mass and electron transfer was constructed via a facial morphology control strategy.Meanwhile,the substitution of sluggish oxygen evolution with urea oxidation,lowering the two-electrode cell voltage to only 1.48 volts to achieve a current density of 10 mA·cm^-2.Thus,the as-constructed electrode achieves the operation of hydrogen generation by an AA battery.This work sheds new light on the exploration of other high-efficient electrocatalysts for hydrogen generation by using intermittent clean energy.     

Gold-vapor-assisted chemical vapor deposition of aligned monolayer WSe2 with large domain size and fast growth rate

Orientation-controlled growth of two-dimensional (2D) transition metal dichalcogenides (TMDCs) may enable many new electronic and optical applications. However, previous studies reporting aligned growth of WSe₂ usually yielded very small domain sizes. Herein, we introduced gold vapor into the chemical vapor deposition (CVD) process as a catalyst to assist the growth of WSe₂ and successfully achieved highly aligned monolayer WSe₂ triangular flakes grown on c-plane sapphire with large domain sizes (130 µm) and fast growth rate (4.3 µm·s⁻¹). When the aligned WSe₂ domains merged together, a continuous monolayer WSe₂ was formed with good uniformity. After transferring to Si/SiO₂ substrates, field effect transistors were fabricated on the continuous monolayer WSe₂, and an average mobility of 12 cm²·V⁻¹·s⁻¹ was achieved, demonstrating the good quality of the material. This report paves the way to study the effect of catalytic metal vapor in the CVD process of TMDCs and contributes a novel approach to realize the growth of aligned TMDC flakes.