Fast Ion Diffusion Research Articles

Assembly of Defect-Free Microgel Nanomembranes for CO2 Separation.

The development of robust and thin CO2 separation membranes that allow fast and selective permeation of CO2 will be crucial for rebalancing the global carbon cycle. Hydrogels are attractive membrane materials because of their tunable chemical properties and exceptionally high diffusion coefficients for solutes. However, their fragility prevents the fabrication of thin defect-free membranes suitable for gas separation. Here, we report the assembly of defect-free hydrogel nanomembranes for CO2 separation. Such membranes can be prepared by coating an aqueous suspension of colloidal hydrogel microparticles (microgels) onto a flat, rough, or micropatterned porous support as long as the pores are hydrophilic and the pore size is smaller than the diameter of the microgels. The deformability of the microgel particles enables the autonomous assembly of defect-free 30-50 nm-thick membrane layers from deformed ∼15 nm-thick discoidal particles. Microscopic analysis established that the penetration of water into the pores driven by capillary force assists the assembly of a defect-free dense hydrogel layer on the pores. Although the dried films did not show significant CO2 permeance even in the presence of amine groups, the permeance dramatically increased when the membranes are adequately hydrated to form a hydrogel. This result indicated the importance of free water in the membranes to achieve fast diffusion of bicarbonate ions. The hydrogel nanomembranes consisting of amine-containing microgel particles show selective CO2 permeation (850 GPU, αCO2/N2 = 25) against post-combustion gases. Acid-containing microgel membranes doped with amines show highly selective CO2 permeation against post-combustion gases (1010 GPU, αCO2/N2 = 216) and direct air capture (1270 GPU, αCO2/N2 = 2380). The membrane formation mechanism reported in this paper will provide insights into the self-assembly of soft matters. Furthermore, the versatile strategy of fabricating hydrogel nanomembranes by the autonomous assembly of deformable microgels will enable the large-scale manufacturing of high-performance separation membranes, allowing low-cost carbon capture from post-combustion gases and atmospheric air.

N-Enriched Porous Carbon/SiO2 Composites Derived from Biomass Rice Husks for Boosting Li-Ion Storage: Insight into the Effect of N-Doping.

A N-enriched porous carbon/SiO2 (SiO2 /NC) composite from rice husks was prepared by ball milling and tested as a stable anode for lithium ion batteries (LIBs), in which the homogeneous dispersion of SiO2 nanoparticles and carbon matrix, and high level of N-doping can be realized simultaneously. The influence of N-doping on a series of SiO2 /NCs was systematically studied; this proved that the porosity, N-doping content, and electronic conductivity of SiO2 /NC can be controlled by adjusting common nitrogen sources (urea and melamine) and doping routes, including dry and wet milling, to reach a desirable balance of high capacity, long-term cyclability, and rate property. The optimized SiO2 /NC composite delivers a stably reversible capacity of 581 mA h g-1 at the high current load of 1.0 A g-1 at the 1000th cycle. The novel Li-storage mechanism of active silica in a composite was first proposed after observation of the N-doping effect that the redox reaction between SiO2 and Li+ is accelerated to transform into an alloying reaction of generated Si and Li+ , thus enhancing the reversible capacity. Moreover, kinetics analysis confirms that there is a combined Li-storage mechanism of battery-capacitive pattern in composite that contributes to fast charge transfer and ion diffusion during cycle.

Copper diffusion rates and hopping pathways in superionic Cu2Se

The ultra-low thermal conductivity of Cu2Se is well established, but so far there is no consensus on the underlying mechanism. One proposal is that the fast-ionic diffusion of copper suppresses the acoustic phonons. The diffusion coefficients reported previously, however, differ by two orders of magnitude between the various studies and it remains unclear whether the diffusion is fast enough to impact the heat-bearing phonons. Here, a two-fold approach is used to accurately re-determine the diffusion rates. Ab-initio molecular dynamics simulations, incorporating landmark analysis techniques, were closely compared with experimental quasielastic/inelastic neutron scattering. Reasonable agreement was found between these approaches, consistent with a diffusion coefficient of 3.1 ± 1.3× 10−5 cm2.s−1 at 675 K and an activation barrier of 140 ± 60 meV. The hopping mechanism includes short 2 Å hops between tetrahedral and interstitial octahedral sites. This process forms dynamic Frenkel defects. Despite the latter processes, there is no major loss of the phonon mode intensity in the superionic state, and there is no strong correlation between the phonon spectra and the increased diffusion rates. Instead, intrinsic anharmonic phonon interactions appear to dictate the thermal conductivity above and below the superionic transition, and there is only subtle mode broadening associated with the monoclinic-cubic structural transition point, with the phonon density-of-states remaining almost constant at higher temperatures.

Lithiophilic Sn sites on 3D Cu current collector induced uniform lithium plating/stripping

With continuously surging high-energy–density demand in lithium rechargeable batteries, soaring efforts have been spotlighted on lithium metal anode. However, its practical implementation is hindered by the uncontrolled growth of Li dendrites. Herein, 3D Cu current collector with lithiophilic Sn sites (3D Cu@Sn), fabricated by magnetron sputtering technique, was applied to enhance the electron conduction and lithium-ion diffusion and guide uniform Li growth. The channel in 3D Cu@Sn increases the specific surface area and the three-dimensional structure reduces the local current density. Moreover, the homogeneous lithiophilic Sn sites possess superior affinity with Li, which constructs as a fast electron conduction and ion diffusion network. Phase-field simulation and operando optical microscopy results demonstrate dendrite suppression and outstanding reversibility of Li. An ultralong lifespan over 3000 h was achieved at a current density of 1 mA cm−2 in Li-plated 3D Cu@Sn symmetric cell, which exhibits an excellent cycling performance. Furthermore, the full cell with LiCoO2 cathode displays excellent cycling performances and improved capacity retention by pairing with Li-plated 3D Cu@Sn anode.

Exploration of fast ion diffusion kinetics in graphene nanoscrolls encapsulated CoSe2 as advanced anode for high-rate sodium-ion batteries

Sodium-ion batteries (SIBs) have drawn much attention due to the abundance and low cost of sodium. However, electrode materials of SIBs displayed sluggish Na+ diffusivity and fatal volume expansion, owing to the larger ionic radius of Na+ ions than Li+ ions. In this work, we built the CoSe2 nanoparticles embedded in graphene nanoscrolls (GNS) as advanced anodes for high-rate SIBs. The CoSe2/C@GNS anodes exhibited a high reversible capacity of 545 mA h g−1 at 0.2 A g−1. Moreover, they showed an outstanding cycling stability of 455 mA h g−1 after 5000 cycles at 1 A g−1, with a capacity retention of 92% calculated from 10th cycle. The CoSe2/C@GNS anode also demonstrate ultrahigh rate capabilities (212.5 mAh g−1 at 50 A g−1). In addition, with a high mass loading (6 mg cm−2), the electrode still displayed a stable capacity (412 mA h g−1 1 A g−1). The fast electron transfer and Na+ ion diffusion kinetics creates the excellent electrochemical properties, on account of the uniform arrangement of nanoparticles and unique reticular crosslinking structure of CoSe2/C@GNS. This strategy could also be constructed other electrode materials, which provides more probabilities for the development of SIBs.

Layer‐by‐Layer 2D Ultrathin Conductive Cu3(HHTP)2 Film for High‐Performance Flexible Transparent Supercapacitors

Abstract2D conductive metal–organic frameworks (2D c‐MOFs) naturally possess high active sites, large specific surface areas, and fast ion transport for energy‐storage devices. However, the intelligent exploration of 2D c‐MOFs for the emerging flexible transparent supercapacitors (FTSCs) with excellent photoelectric property and electrochemical activity is rarely implemented. Herein, 2D conductive ultrathin Cu3(HHTP)2 (HHTP = 2,3,6,7,10,11‐hexahydroxytriphenylene) film is synthesized on the indium tin oxide/polyethylene terephthalate (ITO/PET) substrate for flexible transparent conductive electrodes (FTCEs) through the layer‐by‐layer assembly method. The interconnected conductive frameworks possess the cooperative superiority of low internal resistance, fast electrolyte ion diffusion, and quick electron transfer. Cu3(HHTP)2‐15/ITO/PET FTCEs show high photoelectric property of T550 nm = 82.2% and Rs = 49.1 Ω sq−1, and high areal capacitance (CA) of 1700 µF cm−2. The corresponding symmetrical FTSCs (T550 nm = 62.1%) exhibit excellent CA of 939.2 µF cm−2 at the current density of 7 µA cm−2, superior rate capability (63.9% at 150 µA cm−2), long‐term cycling stability (85% after 3000 cycles), and mechanical flexibility under different bending angles. This work provides key insights into the design and synthesis of 2D c‐MOF films for flexible transparent energy‐storage devices.

Water/acetonitrile hybrid electrolyte enables using smaller ions for achieving superior energy density in carbon-based supercapacitors

There is a big push toward developing low-cost and safe supercapacitors with high energy to meet increasing demands for grid-scale applications. Activated carbons have reached their capacitance limit because of their limited accessible surface area in organic electrolytes, commonly used in commercial supercapacitors. Herein, we reveal that a shift from organic electrolytes to polar hybrid electrolytes allows switching to smaller ions without a penalty on solubility and ionic conductivity, which in turn allows for smaller pores and higher capacitance. We show that elevated storage capability can be realized by matching the porosity of a hierarchically porous carbon to a water/acetonitrile hybrid electrolyte with sodium perchlorate. Leveraging the small size of ions along with good wetting by the hybrid electrolyte ensures fast ion diffusion and enhanced accessibility of ions to carbon pores. Using the hybrid electrolyte for our model coal-derived activated carbon, we fabricated a high-rate supercapacitor with the best capacitance and energy density reported to date for activated carbons (hybrid or organic electrolytes), including 41.2 F/g (18.3 F/cm3) and 35.0 Wh/Kg at 1 A/g. A commercial carbon with a higher surface area delivers comparable gravimetric capacitance but lower volumetric capacitance due to much lower density than our carbon (7.4 F/cm3).

Sulfur-Doped Graphdiyne as a High-Capacity Anode Material for Lithium-Ion Batteries.

Heteroatom doping is regarded as a promising approach to enhance the electrochemical performance of carbon materials, while the poor controllability of heteroatoms remains the main challenge. In this context, sulfur-doped graphdiyne (S-GDY) was successfully synthesized on the surface of copper foil using a sulfur-containing multi-acetylene monomer to form a uniform film. The S-GDY film possesses a porous structure and abundant sulfur atoms decorated homogeneously in the carbon skeleton, which facilitate the fast diffusion and storage of lithium ions. The lithium-ion batteries (LIBs) fabricated with S-GDY as anode exhibit excellent performance, including the high specific capacity of 920 mA h g−1 and superior rate performances. The LIBs also show long-term cycling stability under the high current density. This result could potentially provide a modular design principle for the construction of high-performance anode materials for lithium-ion batteries.

Aqueous MXene/PH1000 Hybrid Inks for Inkjet‐Printing Micro‐Supercapacitors with Unprecedented Volumetric Capacitance and Modular Self‐Powered Microelectronics

AbstractDespite intense development of inkjet printing for scalable and customizable fabrication of power sources, one major shortcoming is the lack of eco‐friendly aqueous inks free of additives (e.g., toxic solvents, surfactants). Here, an aqueous printable MXene/poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonic acid) (MP) hybrid ink is demonstrated that has an adjustable viscosity to directly inkjet‐print micro‐supercapacitors (MP‐MSCs) with excellent performance, seamless integration, and desirable customization, which is crucial for scalable industrialization of self‐powered integrated systems. The MP‐MSCs deliver an unprecedented volumetric capacitance of 754 F cm−3 and a remarkable energy density of 9.4 mWh cm−3, superior to previously reported inkjet‐printed MSCs. Such outstanding performance is partly attributed to highly conductive PH1000 that prevents restacking of MXene nanosheets, enabling fast electron and ion diffusion throughout the microelectrodes. Moreover, MP‐MSCs present exceptional miniaturization and superior modularization featuring high voltage output up to 36 V from 60 serially connected cells and impressive areal voltage of 5.4 V cm−2 connected in tandem. Further, a printable temperature sensor integrated with the MP‐MSC and a flexible solar cell exhibits an exceptional response of 2% and mechanical flexibility without any bias voltage input. Therefore, the MXene inks are expected to create various opportunities for miniaturization and innovative construction of flexible, self‐sustaining, energy harvesting–storing–consuming microsystems for printable electronics.

Facile preparation of N-doped porous carbon nanosheets derived from potassium citrate/melamine for high-performance supercapacitors

Nitrogen (N)-doped porous carbon nanosheets have attracted research attention owing to their effective structure for fast ion diffusion and pseudocapacitive properties in supercapacitors. However, to synthesize N-doped porous carbon nanosheets while maintaining their original shape requires complicated multistep processes such as plasma and arc-discharge methods. Herein, we propose a facile and effective method for N-doping into interconnected porous carbon nanosheets that preserves their original structure with a stepwise thermal annealing using melamine as N-doping source. The stepwise thermal annealing is advantageous to improve N-doping efficiency into the carbon matrix compared to direct thermal annealing method owing to the condensation of melamine. As-synthesized N-doped carbon nanosheets with interconnected and porous structure exhibits high specific surface area and N-doping contents, which favorable for the fast ion movement, adsorption, and increasing the wettability of the electrolyte. The electrochemical performance shows a maximum specific capacitance of 350F g−1 at 1 A g−1 in a three-electrode test. Moreover, a fabricated symmetric full-cell device using an optimized N-doped carbon electrode demonstrates a long-term durability over 10,000 cycles and a maximum energy density of 16.1 Wh kg−1.

Defect modulation of ZnMn2O4 nanotube arrays as high-rate and durable cathode for flexible quasi-solid-state zinc ion battery

• A novel N-ZMO NTAs is developed as advanced cathode for ZIBs. • The N-ZMO NTAs have high electrical conductivity and stable architecture. • The flexible quasi-solid-state ZIBs show decent energy/power density with long-term stability. The exploration of a stable and high-rate cathode is very important for rechargeable Zn ion batteries (ZIBs). With unique merits of rich abundance, low price, and environmental friendliness, spinel ZnMn 2 O 4 (ZMO) hold great promise as a cathode material for ZIBs. However, its inherent low electronic conductivity and large volume variation in the process of charge/discharge severely restrict the rate capability and durability. Herein, the novel N-doping coupled oxygen vacancies modulated ZMO nanotube arrays (NTAs) (N-ZMO NTAs) are fabricated as high-performance cathode for rechargeable ZIBs. Taking advantages of high electrical conductivity, fast ion diffusion, high surface area, sufficient active sites, and stable hollow nanotubular architecture, the N-ZMO NTAs show an admirable capacity (223 mA h g −1 at 0.1 A g −1 ), decent rate capability (133.3 mA h g −1 at 4 A g −1 ) and distinguished long-term durability (92.1% after 1500 cycles). Furthermore, a flexible quasi-solid-state ZIBs is fabricated with N-ZMO NTAs cathode, which achieves favorable energy density (214.6 W h kg −1 ), superb power density (4 kW kg −1 ), and impressive long-term stability (88.6% after 1500 cycles), outperforming most state-of-the-art ZIBs. This study may shed light on designing advanced cathodes for advanced ZIBs.

Interior design of hierarchical micro/nanostructures for enhancing energy storage ability of polyanilines through frozen interfacial polymerization

Large specific surface area and hierarchically porous structure play critical roles in the preparation of high–performance electrodes for supercapacitor that strongly depended on the morphologies of electroactive materials. To impart large specific surface area and high ionic permeability, three kinds of hierarchical micro/nanostructures, i.e. sea urchin–like, flower–like and carpenterworm–like nanostructures, of polyaniline (PANI) products were constructed through simple frozen interfacial polymerization without any templates, special chemical regents or organic solvents. The formation of hierarchical micro/nanostructured PANIs were significantly affected by the interfacial area between aniline and oxidant ice layers and the adding order of aniline and oxidant, more detailedly, the number of the nanofibrous seeds formed at the early stage of polymerization and their ambient aniline concentration as well as the release rates of aniline and oxidant. Furthermore, the PANI with sea urchin–like micro/nanostructure exhibited the highest charge storage ability among all the electrode materials, more clearly, the specific capacitance of 716.8 F g–1 at a current density of 1 A g–1, rate retention of 96.9% from 1 to 20 A g–1, and cycling retention of 73.6% after 2000 cycles. The remarkable electrochemical performance can be ascribed to unique self–assembly of highly ordered nanofibers, making it possible to give full play to the advantages of PANI nanofibers including large electrode/electrolyte contact area, high charge transport along the nanofibers, accommodate volume changes extending in every direction during cycling, and fast electron transport and ion diffusion through porous structure. It is believed that such interior design and eco–friendly fabrication can offer an effective strategy to promote the electroactive properties of the PANI, and further development in the sensor– and energy–related fields.

Metal–Organic Framework (MOF)-Assisted Construction of Core–Shell Nanoflower-like CuO/CF@NiCoMn–OH for High-Performance Supercapacitor

Urgent requests for environmentally friendly clean energy and the development of modern electronic products have resulted in fervent research on novel energy storage technologies, particularly for supercapacitors. But supercapacitors suffer from low energy densities, restricting their development. In order to obtain high performance supercapacitors with a high energy density and power density, the indispensable factor is designing electrode materials with excellent capacitive performance. We have successfully prepared innovative materials and unique structures to apply in high-performance supercapacitors. The nanowire is good for making close contact with the electrolyte for fast ion diffusion, and the nanoflower sheet enables shortening the electron convey route and provides a number of reaction active sites. Herein, we use copper foam (CF) as the substrate, and binder-free core–shell nanoflower-like CuO/CF@NiCoMn–OH is designed as a battery-style positive electrode. Benefiting from the advantages of a metal–organic framework (MOF)-assisted growth strategy and simple hydrothermal dynamics, the prepared optimizing electrode structure delivers a distinguished specific capacity of 26.8 F cm–² at 8 mA cm–² (3356 F g–¹ at 1 A g–¹). The assembled CuO/CF@NiCoMn–OH//AC exhibits a high energy density of 37.28 W h kg–¹ and a power density of 170 W kg–¹, under a potential window of 1.5 V. This work implies that MOF-assisted construction of core–shell nanoflower-like CuO/CF@NiCoMn–OH has broad application prospects in high-performance energy storage equipment.

Proton-assisted calcium-ion storage in aromatic organic molecular crystal with coplanar stacked structure

Rechargeable calcium-ion batteries are intriguing alternatives for use as post-lithium-ion batteries. However, the high charge density of divalent Ca2+ establishes a strong electrostatic interaction with the hosting lattice, which results in low-capacity Ca-ion storage. The ionic radius of Ca2+ further leads to sluggish ionic diffusion, hindering high-rate capability performances. Here, we report 5,7,12,14-pentacenetetrone (PT) as an organic crystal electrode active material for aqueous Ca-ion storage. The weak π-π stacked layers of the PT molecules render a flexible and robust structure suitable for Ca-ion storage. In addition, the channels within the PT crystal provide efficient pathways for fast ionic diffusion. The PT anode exhibits large specific capacity (150.5 mAh g-1 at 5 A g-1), high-rate capability (86.1 mAh g-1 at 100 A g-1) and favorable low-temperature performances. A mechanistic study identifies proton-assisted uptake/removal of Ca2+ in PT during cycling. First principle calculations suggest that the Ca ions tend to stay in the interstitial space of the PT channels and are stabilized by carbonyls from adjacent PT molecules. Finally, pairing with a high-voltage positive electrode, a full aqueous Ca-ion cell is assembled and tested.

Oxygen incorporated in 1T/2H hybrid MoS2 nanoflowers prepared from molybdenum blue solution for asymmetric supercapacitor applications

Molybdenum disulfide (MoS2) has shown potential as a supercapacitor electrode material, owing to its high theoretical specific capacitance and wide negative potential window, especially in neutral electrolytes. However, its practical application is hindered by low inherent electrical conductivity and narrow interlayer spacing. In this study, oxygen-incorporated MoS2 nanoflowers with 1T/2H hybrid phase were fabricated on a graphite foil substrate (1T/2H-O-MoS2@GF) from molybdenum blue solution via a facile hydrothermal process. Dispersible Mo-blue clusters, composed of polymerized structures containing numerous MoOx-type building units combined with NH4+ cations, were formed by introducing ammonium persulfate before hydrothermal synthesis; they were subsequently used as precursors of MoS2. Mo-blue clusters lead to the formation of metallic 1T-phase dominant heterostructure and incorporation of oxygens in MoS2 during the hydrothermal reaction. The 1T/2H hybrid phase formed by using Mo-blue clusters provided MoS2 with excellent stability in the 2H-phase and high electrical conductivity in the 1T-phase, simultaneously. The incorporated oxygens induced a wide interlayer spacing (9.8 Å) and improved the surface hydrophilicity of MoS2, thereby facilitating the fast diffusion of electrolyte ions. As a result, the 1T/2H-O-MoS2@GF electrode exhibited a high specific capacitance of 280 F g−1 at 1.0 A g−1 and 88% capacitance retention after 10,000 cycles at 10 A g−1. The asymmetric supercapacitor device, assembled using a 1T/2H-O-MoS2@GF negative electrode and MnO2@GF positive electrode, demonstrated superior power and energy densities of 450–18000 W kg−1 and 39.7–5.46 Wh kg−1 in a working window of 1.8 V.

A High‐Rate and Ultrastable Aqueous Zinc‐Ion Battery with a Novel MgV2O6·1.7H2O Nanobelt Cathode

High-safety and low-cost aqueous Zn-ion batteries have triggered an astounding investigation surge in the last 5years and are becoming competitive alternatives for grid-scale energy storage. However, the implementation of this promising technology is still plagued by the lack of effective and affordable cathode materials that can enable high energy densities and an exceptional cycling stability. Herein, a novel vanadium-based oxide cathode based on MgV2 O6 ·1.7H2 O nanobelts, which delivers a high capacity (425.7mAhg-1 at 0.2Ag-1 ), a robust rate capability (182.1mAhg-1 at 10Ag-1 ), and an ultrastable cycle without any visible deterioration, as well as an adequate energy density (331.6Whkg-1 ), is developed. Such excellent electrochemical Zn-ion storage performance is believed to result from the fast ion-diffusion kinetics boosted by a stable layered structure and an ultrahigh intercalation pseudocapacitance reaction, which are also benefited by a typical H+ /Zn2+ co-insertion mechanism, accompanied by an atypical Zn2+ intercalation chemistry with a partial but irreversible Mg2+ -Zn2+ ion-exchange reaction during the initial discharge. These results provide key and enlightening insights into the design of high-performance vanadium oxide cathode materials.

Novel Lamellar Tetrapotassium Pyromellitic Organic for Robust High‐Capacity Potassium Storage

AbstractRedox‐active organics are investigation hotspots for metal ion storage due to their structural diversity and redox reversibility. However, they are plagued by limited storage capacity, sluggish ion diffusion kinetics, and weak structural stability, especially for K+ ion storage. Herein, we firstly reported the lamellar tetrapotassium pyromellitic (K4PM) with four active sites and large interlayer distance for K+ ion storage based on a design strategy, where organics are constructed with the small molecular mass, multiple active sites, fast ion diffusion channels, and rigid conjugated π bonds. The K4PM electrode delivers a high capacity up to 292 mAh g−1 at 50 mA g−1, among the best reported organics for K+ ion storage. Especially, it achieves an excellent rate capacity and long‐term cycling stability with a capacity retention of ≈83 % after 1000 cycles. Incorporating in situ and ex‐situ techniques, the K+ ion storage mechanism is revealed, where conjugated carboxyls are reversibly rearranged into enolates to stably store K+ ions. This work sheds light on the rational design and optimization of organic electrodes for efficient metal ion storage.

Novel Lamellar Tetrapotassium Pyromellitic Organic for Robust High-Capacity Potassium Storage.

Redox-active organics are investigation hotspots for metal ion storage due to their structural diversity and redox reversibility. However, they are plagued by limited storage capacity, sluggish ion diffusion kinetics, and weak structural stability, especially for K+ ion storage. Herein, we firstly reported the lamellar tetrapotassium pyromellitic (K4 PM) with four active sites and large interlayer distance for K+ ion storage based on a design strategy, where organics are constructed with the small molecular mass, multiple active sites, fast ion diffusion channels, and rigid conjugated π bonds. The K4 PM electrode delivers a high capacity up to 292 mAh g-1 at 50 mA g-1 , among the best reported organics for K+ ion storage. Especially, it achieves an excellent rate capacity and long-term cycling stability with a capacity retention of ≈83 % after 1000 cycles. Incorporating in situ and ex-situ techniques, the K+ ion storage mechanism is revealed, where conjugated carboxyls are reversibly rearranged into enolates to stably store K+ ions. This work sheds light on the rational design and optimization of organic electrodes for efficient metal ion storage.

A facile in-situ coating strategy for Ni-rich cathode materials with improved electrochemical performance

A facile in-situ hydrolytic coating strategy has been suggested to architecture LiAlSiO4 (LASO)-coated LiNi0.8Co0.1Mn0.1O2 (LNCM) cathode material for lithium-ion batteries. Homogeneous LASO coating layer, as an one-dimensional lithium ion conductor, on the surface of LNCM is observed clearly and ascertained jointly by several testing methods. The effects of LASO coating layer on physicochemical properties, electrochemical properties and electrochemical kinetics of LNCM cathode material have been rigorously investigated by various tests. The cycling stability, rate capability and Li+ ion diffusion rate are enhanced evidently after LASO coating. Moreover, the polarization, impedance increase and particles cracking after cycles under the high cut-off voltage are greatly improved. These effective and obvious improvements are ascribed to the LASO coating layer, which could effectively inhibit the occurrence of side reactions and HF erosion and provide a fast ion diffusion channel for lithium ions on the surface of LNCM.

Incorporating ultra-small N-doped Mo2C nanoparticles onto 3D N-doped flower-like carbon nanospheres for robust electrocatalytic hydrogen evolution

Developing highly-efficient and stable hydrogen evolution reaction (HER) electrocatalysts plays a crucial role in realizing the hydrogen production from electrocatalytic water splitting. Herein, ultra-small and nitrogen-doped molybdenum carbide (N-Mo 2 C) nanoparticles with oxidized surfaces are facilely synthesized with the assistance of cationic surfactants and simultaneously anchored onto three-dimensional nitrogen-doped flower-like carbon nanospheres (NFCNS), and the N-Mo 2 C/NFCNS composites are further investigated as HER electrocatalysts. Analysis results reveal that nitrogen atoms are doped into both the lattice and the carbon framework of Mo 2 C, resulting in low desorption energy of Mo-H bond for the easy evolution of hydrogen gas. Moreover, the high specific area of NFCNS enables enrichment of N-Mo 2 C nanoparticles, and its open framework facilitates fast ion diffusion. As a result, the N-Mo 2 C/NFCNS composites exhibit impressive HER activities with low overpotential, small Tafel slope, and excellent durability in both acidic and alkaline media, which outperform most of the reported Mo-based HER catalysts and are also highly comparable to the commercial Pt/C catalyst. Not limited to HER electrocatalysts, this work should open a new avenue for tailoring highly-efficient carbon/metal compounds-based electrocatalysts for oxygen reduction reaction, oxygen evolution reaction, nitrogen reduction reaction, etc. A simple strategy to downsize and stabilize Mo 2 C nanoparticles within 3D N-doped flower-like carbon nanospheres has been developed by using cationic surfactant as linker between carbon and molybdenum sources. The nitrogen doping in Mo 2 C leads to superior hydrogen evolution activities and excellent durability in both acidic and alkaline media, which outperform most of the current Mo-based electrocatalysts. • A simple protocol is introduced to downsize and stabilize molybdenum carbide electrocatalysts. • Nitrogen-doped molybdenum carbide electrocatalysts are developed for hydrogen evolution. • Three-dimensional nitrogen-doped flower-like carbon nanospheres are designed as supports. • Lowering Mo-H desorption energy owing to nitrogen doping facilitates hydrogen evolution.