Expanded Interlayer Spacing Research Articles

Short-Range Graphitic Nanodomains in Hypocrystalline Carbon Nanotubes Realize Fast Potassium Ion Migration and Multidirection Stress Release.

Defect-rich carbon materials are considered as one of the most promising anodes for potassium-ion batteries due to their enormous adsorption sites of K+ , while the realization of both rate capability and cycling stability is still greatly limited by unstable electrochemical kinetics and inevitable structure degradation. Herein, an Fe3+ -induced hydrothermal-pyrolysis strategy is reported to construct well-tailored hybrid carbon nanotubes network architecture (PP-CNT), in which the short-range graphitic nanodomains are in-situ localized in the pea pod shape hypocrystalline carbon. The N,O codoped hypocrystalline carbon region contributes to abundant defect sites for potassium ion storage, ensuring high reversible capacity. Meanwhile, the short-range graphitic nanodomains with expanded interlayer spacing facilitate stable K+ migration and fast electron transfer. Furthermore, the finite element analysis confirms the volume expansion caused by K+ intercalation can be availably buffered due to the multidirection stress release effect of the unique porous pea pod shape, endowing carbon nanotubes with superior structural integrity. Consequently, the PP-CNT anode exhibits superior potassium-storage performance, including high reversible capacity, exceptional rate capability, and ultralong cycling stability. This work opens a new avenue for the fabrication of advanced carbon materials for achieving durable and fast potassium storage.

3D porous MnCo2S4 network decorated nitrogen-doped monolayer Ti3C2 based supercapacitors with superior energy density

The development of supercapacitors generally suffers from the used anodes with insufficient energy density. In this paper, nitrogen-doped monolayered Ti3C2 (N-Ti3C2) is synthesized via a facile urea assisted solvothermal route and then abundant MnCo2S4 curved nanosheets are directly in-situ grown on their surface to form a novel 3D porous anode material (N-Ti3C2/MnCo2S4). The expanded interlayer spacing of nitrogen-doped Ti3C2 can effectively facilitate ion diffusion as well as regulate the growth of MnCo2S4 nanosheets. Subsequently, the highly conductive 3D MnCo2S4 porous network further gives a rapid pathway for ions and electrolyte transfer. Hence, N-Ti3C2/MnCo2S4 electrode delivers an ultra-high mass capacitance of 1243.1 Fg−1 at 5 mVs−1. Furthermore, the asymmetric supercapacitors (ASCs) based on N-Ti3C2/MnCo2S4 not only acquires a higher energy density of 162.8 Whkg−1 at the power density of 2700.0 Wkg−1 under a wide potential window of 0–1.5 V, but also exhibits an outstanding cycling durability with a minor loss of 6.20 % after 10,000 charge and discharge cycles.

Oxygen Defect Engineering toward Zero-Strain V2O2.8@Porous Reticular Carbon for Ultrastable Potassium Storage.

Potassium-ion batteries (KIBs) are promising candidates for large-scale energy storage devices due to their high energy density and low cost. However, the large potassium-ion radius leads to its sluggish diffusion kinetics during intercalation into the lattice of the electrode material, resulting in electrode pulverization and poor cycle stability. Herein, vanadium trioxide anodes with different oxygen vacancy concentrations (V2O2.9, V2O2.8, and V2O2.7 determined by the neutron diffraction) are developed for KIBs. The V2O2.8 anode is optimal and exhibits excellent potassium storage performance due to the realization of expanded interlayer spacing and efficient ion/electron transport. In situ X-ray diffraction indicates that V2O2.8 is a zero-strain anode with a volumetric strain of 0.28% during the charge/discharge process. Density functional theory calculations show that the impacts of oxygen defects are embodied in reducing the band gap, increasing electron transfer ability, and lowering the diffusion energy barriers for potassium ions. As a result, the electrode of nanosized V2O2.8 embedded in porous reticular carbon (V2O2.8@PRC) delivers high reversible capacity (362 mAh g-1 at 0.05 A g-1), ultralong cycling stability (98.8% capacity retention after 3000 cycles at 2 A g-1), and superior pouch-type full-cell performance (221 mAh g-1 at 0.05 A g-1). This work presents an oxygen defect engineering strategy for ultrastable KIBs.

Interlayer-expanded and carbon-coated VS2 nanosheets self-assembled on 3D CNTs cross-linked network skeleton for ultrastable lithium-ion storage

Layered VS2 has high theoretical capacity and is considered a promising anode material for lithium-ion batteries. However, its poor cycle stability seriously affects its commercial application. The smart design of anode material microstructure is a crucial point to optimize the stability of batteries. Herein, a hierarchical composite of VS2/CNTs/C was successfully fabricated via a simple one-step solvothermal method, in which few-layer VS2 nanosheets were in situ self-assembled on a 3D CNTs cross-linked network skeleton and coated with a thin carbon layer. The interlayer spacing of (001) planes of VS2 nanosheets was expanded from 0.58 nm to 0.89 nm due to NH4+ intercalation during the solvothermal reaction. Density functional theory (DFT) calculations demonstrated that expanded interlayer spacing of VS2 can enhance the electron conductivity and significantly reduce the diffusion barrier of Li+. More importantly, the 3D CNTs skeleton could prevent the aggregation of VS2 nanosheets, provide a fast ionic/electronic migration channel, and ensure a large specific surface area and an extra buffer space. In addition, the carbon coating could further increase the conductivity and stabilize the connection between the VS2 nanosheets and CNTs skeleton. Benefiting from their synergistic effects, the VS2/CNTs/C electrode exhibited an enormous Li+ diffusion coefficient and favorable capacitive kinetics, and delivered excellent lithium storage performance, such as a large reversible specific capacity of 1075 mAh g−1 at 0.1 A g−1, a high rate performance of 592 mAh g−1 at 2 A g−1, and a remarkable cycling stability with a specific capacity of 629 mAh g−1 after 900 cycles at 1 A g−1. This work may guide the design of other similar anode materials and help to understand their energy storage mechanism.

Dynamic Electronic and Ionic Transport Actuated by Cobalt-Doped MoSe2 /rGO for Superior Potassium-Ion Batteries.

Molybdenum selenium (MoSe2 ) has tremendous potential in potassium-ion batteries (PIBs) due to its large interlayer distance, favorable bandgap, and high theoretical specific capacity. However, the poor conductivity and large K+ insertion/extraction in MoSe2 inevitably leads to sluggish reaction kinetics and poor structural stability. Herein, Coinduced engineering is employed to illuminate high-conductivity electron pathway and mobile ion diffusion of MoSe2 nanosheets anchored on reduced graphene oxide substrate (Co-MoSe2 /rGO). Benefiting from the activated electronic conductivity and ion diffusion kinetics, and an expanded interlayer spacing resulting from Co doping, combined with the interface coupling with highly conductive reduced graphene oxide (rGO) substrate through Mo-C bonding, the Co-MoSe2 /rGO anode demonstrates remarkable reversible capacity, superior rate capability, and stable long-term cyclability for potassium storage, as well as superior energy density and high power density for potassium-ion capacitors. Systematic performance measurement, dynamic analysis, in-situ/ex-situ measurements, and density functional theory (DFT) calculations elucidate the performance-enhancing mechanism of Co-MoSe2 /rGO in view of the electronic and ionic transport kinetics. This work offers deep atomic insights into the fundamental factors of electrodes for potassium-ion batteries/capacitors with superior electrochemical performance.

Polyvinylpyrrolidone-Intercalated Mn0.07 VOx toward High Rate and Long-Life Aqueous Zinc-Ion Batteries.

Aqueous zinc-ion batteries (AZIBs) are expected to be an attractive alternative in advanced energy storage devices due to large abundance and dependable security. Nevertheless, the undesirable energy density and operating voltage still hinder the development of AZIBs, which is intimately associated with the fundamental properties of the cathode. In this work, polyvinylpyrrolidone (PVP) intercalated Mn0.07 VOx (PVP-MnVO) with a large interlayer spacing of 13.5 Å (against 12.5 Å for MnVO) synthesized by a facile hydrothermal method is adopted for the cathode in AZIBs. The experimental results demonstrate that PVP-MnVO with expanded interlayer spacing provides beneficial channels for the rapid diffusion of Zn2+ , resulting in a high discharge capacity of 402 mAh g-1 at 0.1 A g-1 , superior to that of MnVO (275 mAh g-1 at 0.1 A g-1 ). Meanwhile, the PVP molecule remains in the layer structure as a binder/pillar, which can maintain its structural integrity well during the charging/discharging process. Consequently, PVP-MnVO cathode exhibits superior rate capability and cycling stability (89% retention after 4300 cycles at 10 A g-1 ) compared to that of MnVO (≈51% retention over 500 cycles at 2 A g-1 ). This work proposes a new approach to optimize the performance of vanadium-based electrode materials in AZIBs.

Sulphur- and nitrogen-codoped layered double hydroxides with expanded interlayer distance for enhanced overall water splitting

Developing highly active, durable, and non-noble electrocatalysts for water-splitting is critical for efficient renewable energy conversion. Nickel-iron layered double-hydroxide (NiFe-LDH) materials show potential in achieving good catalytic performance, however, which was restricted by the scarce active sites and poor conductivity. Herein, we report a series of NiFe-LDH-based materials of expanded interlayer spacing constructed through S/N co-doping with rich active sites, used as a high-efficient bifunctional electrocatalyst for the oxygen and hydrogen evolution reactions (OER and HER). The experimental results indicate that the intercalation/decoration on the interlayer structure of NiFe-LDH can efficiently reduce the energy barrier and accelerate reaction kinetics. Combining with the structural advantages, including the expanded lattice spacing and exposed active surface sites, the resulting S-N/NiFe-LDH anchored in nickel foam (NF) drives an alkaline electrolyzer with a cell voltage of 1.67 V at a current density of 100 mA cm−2, as well as robust stability over 100 h, which is much superior to the state-of-the-art Pt/C-RuO2 electrocatalysts.

Dual Effects of Metal and Organic Ions Co‐Intercalation Boosting the Kinetics and Stability of Hydrated Vanadate Cathodes for Aqueous Zinc‐Ion Batteries

AbstractFor the development of aqueous zinc‐ion batteries, exploiting vanadium‐based cathode materials with quick kinetics and acceptable cycling stability is crucial. Herein, to achieve these goals, transition metal ions (Zn2+) and organic ions (C5H14ON+ and Ch+) are introduced into layered hydrated V2O5. The intrinsic high conductivity of Ch+ and the oxygen vacancies generated through ion pre‐intercalation accelerate the electrical mobility by optimizing the electronic structure. The Zn2+ stabilizes the layered structure and the expanded interlayer spacing improves the ionic diffusivity. The synergistic effect of pre‐intercalated Zn2+ and Ch+ results in the (Zn0.1, Ch0.1)V2O4.92·0.56H2O cathode exhibiting a discharge capacity of 473 mAh g−1 at 0.1 A g−1 with a high energy efficiency of 88% and excellent cycling stability with 91% retention after 2000 cycles at 4 A g−1. Ex situ characterizations and density functional theory calculations reveal a reversible intercalation mechanism of Zn2+, and the improved electrochemical kinetics are attributed to the altered electronic conductivity and the reduced binding energy between Zn2+ and host O2−.

Edge-Enriched Molybdenum Disulfide Ultrathin Nanosheets with a Widened Interlayer Spacing for Highly Efficient Gaseous Elemental Mercury Capture.

Transition metal sulfides have exhibited remarkable advantages in gaseous elemental mercury (Hg0) capture under high SO2 atmosphere, whereas the weak thermal stability significantly inhibits their practical application. Herein, a novel N,N-dimethylformamide (DMF) insertion strategy via crystal growth engineering was developed to successfully enhance the Hg0 capture ability of MoS2 at an elevated temperature for the first time. The DMF-inserted MoS2 possesses an edge-enriched structure and an expanded interlayer spacing (9.8 Å) and can maintain structural stability at a temperature as high as 272 °C. The saturated Hg0 adsorption capacities of the DMF-inserted MoS2 were measured to be 46.91 mg·g-1 at 80 °C and 27.40 mg·g-1 at 160 °C under high SO2 atmosphere. The inserted DMF molecules chemically bond with MoS2, which prevents possible structural collapse at a high temperature. The strong interaction of DMF with MoS2 nanosheets facilitates the growth of abundant defects and edge sites and enhances the formation of Mo5+/Mo6+ and S22- species, thereby improving the Hg0 capture activity at a wide temperature range. Particularly, Mo atoms on the (100) plane represent the strongest active sites for Hg0 oxidation and adsorption. The molecule insertion strategy developed in this work provides new insights into the engineering of advanced environmental materials.

Hierarchical 3D Porous Hydrogen-Substituted Graphdiyne for High-Performance Electrochemical Lithium-Ion Storage.

Graphdiyne (GDY) has realized significant achievements in lithium-ion batteries (LIBs) because of its unique π-conjugated skeleton with sp- and sp2-hybridized carbon atoms. Enriching the accessible surface areas and diffusion pathways of Li ions can realize more storage sites and rapid transport dynamics. Herein, three-dimensional porous hydrogen-substituted GDY (HsGDY) is developed for high-performance Li-ion storage. HsGDY, fabricated via a versatile interface-assisted synthesis strategy, exhibits a large specific surface area (667.9 m2 g-1), a hierarchical porous structure, and an expanded interlayer space, which accelerate Li-ion accessibility and lithiation/delithiation. Owing to this high π-conjugated, conductive, and porous framework, HsGDY exhibits a large reversible capacity (930 mA h g-1 after 100 cycles at 1 A g-1), superior cycle (720 mA h g-1 after 300 cycles at 1 A g-1), and rate (490 mA h g-1 at 5 A g-1) performances. Density functional theory calculations of the low diffusion barrier in the lamination and vertical directions further reveal the fast Li-ion transport kinetics of HsGDY. Additionally, a LiCoO2-HsGDY full cell is constructed, which exhibits a good practical charge/discharge capacity of 128 mA h g-1 and stable cycling behavior. This study highlights the advanced design of next-generation LIBs to sustainably develop the new energy industry.

Carbon Nitride Pillared Vanadate Via Chemical Pre-Intercalation Towards High-Performance Aqueous Zinc-Ion Batteries.

Vanadium based compounds are promising cathode materials for aqueous zinc (Zn)-ion batteries (AZIBs) due to their high specific capacity. However, the narrow interlayer spacing, low intrinsic conductivity and the vanadium dissolution still restrict their further application. Herein, we present an oxygen-deficient vanadate pillared by carbon nitride (C3 N4 ) as the cathode for AZIBs through a facile self-engaged hydrothermal strategy. Of note, C3 N4 nanosheets can act as both the nitrogen source and pre-intercalation species to transform the orthorhombic V2 O5 into layered NH4 V4 O10 with expanded interlayer spacing. Owing to the pillared structure and abundant oxygen vacancies, both the Zn2+ ion (de)intercalation kinetics and the ionic conductivity in the NH4 V4 O10 cathode are promoted. As a result, the NH4 V4 O10 cathode delivers exceptional Zn-ion storage ability with a high specific capacity of about 370 mAh g-1 at 0.5 A g-1 , a high-rate capability of 194.7 mAh g-1 at 20 A g-1 and a stable cycling performance of 10 000 cycles.

Carbon Nitride Pillared Vanadate Via Chemical Pre‐Intercalation Towards High‐Performance Aqueous Zinc‐Ion Batteries

AbstractVanadium based compounds are promising cathode materials for aqueous zinc (Zn)‐ion batteries (AZIBs) due to their high specific capacity. However, the narrow interlayer spacing, low intrinsic conductivity and the vanadium dissolution still restrict their further application. Herein, we present an oxygen‐deficient vanadate pillared by carbon nitride (C3N4) as the cathode for AZIBs through a facile self‐engaged hydrothermal strategy. Of note, C3N4 nanosheets can act as both the nitrogen source and pre‐intercalation species to transform the orthorhombic V2O5 into layered NH4V4O10 with expanded interlayer spacing. Owing to the pillared structure and abundant oxygen vacancies, both the Zn2+ ion (de)intercalation kinetics and the ionic conductivity in the NH4V4O10 cathode are promoted. As a result, the NH4V4O10 cathode delivers exceptional Zn‐ion storage ability with a high specific capacity of about 370 mAh g−1 at 0.5 A g−1, a high‐rate capability of 194.7 mAh g−1 at 20 A g−1 and a stable cycling performance of 10 000 cycles.

Bifunctional covalent triazine frameworks based on Ti-ON bonds for micropollutants removal: Effects of 3D extended structure and electron transport bridges

Adsorption-photocatalysis technology enables the enrichment of pollutants and the regeneration of materials, which is expected to control long-lasting organic micropollutants (OMPs) in water. In particular, taking the comprehensive advantages of composites to simultaneously improve the adsorption and photocatalytic performance is currently worth considering. Therefore, a kind of Ti/MDCTF composite with specific and strong chemical bonds (Ti-ON bonds) was synthesized by a facile approach. Compared with pristine MDCTF, 30 %-Ti/MDCTF showed an increased saturated adsorption capacity (440.56 μmol/g) and a 5.6-fold increase in photocatalytic degradation kinetic (0.315 h−1). It was comfirmed by homogenous surface diffusion model (HSDM) that the adsorption kinetics were controlled by the intra-particle diffusion. Additionally, 30 %-Ti/MDCTF exhibited a high photocatalytic regeneration efficiency (91.7 %) after 7 rounds of degradation cycles in the natural water matrix. Experimental results and theoretical analysis collaboratively showed that the porous 3D extended structure with expanded interlayer spacing promoted the mass transfer and adsorption of OMPs. Furthermore, the Ti-ON bonds acting as electron transport bridges could promote the generation of photogenerated electrons from CTF and directional movement of them to TiO2 for efficient utilization. These findings reinforce the understanding of the adsorption-promoted 3D structure and site-specific regulation of directed electron-feeding, providing a feasible and convenient solution for the removal of OMPs in water.

Phosphorous-doped carbon nanotube/reduced graphene oxide aerogel cathode enabled by pseudocapacitance for high energy and power zinc-ion hybrid capacitors

The design and development of energy storage device with high energy/power density has become a research hotspot. Zinc-ion hybrid capacitors (ZHCs) are considered as one of the most promising candidates. However, the application of ZHCs is hindered by their low energy density at high power density due to the unsatisfactory cathode material. In this study, a novel 3D phosphorus-doped carbon nanotube/reduced graphene oxide (P-CNT/rGO) aerogel cathode is synthesized through a synergistic modification strategy of CNT insertion and P doping modification combined with 3D porous design. The as-obtained P-CNT/rGO aerogel cathode manifests significantly increased surface aera, expanded interlayer spacing, and enhanced pseudocapacitance behavior, thus leading to significantly enhanced specific capacitance and superb ions transport performance. The as-assembled ZHC based on P-CNT/rGO cathode delivers a superior energy density of 42.2 Wh/kg at an extreme-high power density of 80 kW/kg and excellent cycle life. In-depth kinetic analyses are undertaken to prove the enhanced pseudocapacitance behavior and exceptional power output capability of ZHCs. Furthermore, the reaction mechanism of physical and chemical adsorption/desorption of electrolyte ions on the P-CNT/rGO cathode is revealed by systematic ex-situ characterizations. This work can provide a valuable reference for developing advanced graphene-based cathode for high energy/power density ZHCs.

Efficient and selective removal of Hg(II) from water using recyclable hierarchical MoS2/Fe3O4 nanocomposites

Developing practical and cost-effective adsorbents with satisfactory mercury (Hg) remediation capability is indispensable for aquatic environment safety and public health. Herein, a recyclable hierarchical MoS2/Fe3O4 nanocomposite (by in-situ growth of MoS2 nanosheets on the surface of Fe3O4 nanospheres) is presented for the selective removal of Hg(II) from aquatic samples. It exhibited high adsorption capacity (∼1923.5 mg g −1), fast kinetics (k2 ∼ 0.56 mg g −1 min−1), broad working pH range (2–11), excellent selectivity (Kd > 1.0 × 107 mL g −1), and great reusability (removal efficiency > 90% after 20 cycles). In particular, removal efficiencies of up to ∼97% for different Hg(II) concentrations (10–1000 μg L −1) in natural water and industrial effluents confirmed the practicability of MoS2/Fe3O4. The possible mechanism for effective Hg(II) removal was discussed by a series of characterization analyses, which was attributed to the alteration of the MoS2 structure and the surface coordination of Hg-S. The accessibility of surface sulfur sites and the diffusion of Hg(II) in the solid-liquid system were enhanced due to the advantage of the expanded interlayer spacing (0.96 nm) and the hierarchical structure. This study suggests that MoS2/Fe3O4 is a promising material for Hg(II) removal in actual scenarios and provides a feasible approach by rationally constructing hierarchical structures to promote the practical applications of MoS2 in sustainable water treatments.

Studies on the intercalation of calcium–aluminium layered double hydroxide-MCPA and its controlled release mechanism as a potential green herbicide

Abstract The intercalation of 2-methyl-4-chlorophenoxyacetic acid (MCPA) herbicide into the interlayer matrix of calcium–aluminium layered double hydroxide (CaAl LDH) host has been successfully done via the co-precipitation method to form CaAl-MCPA nanocomposite, proposing an eco-friendly alternative with an adjusted delivery system for herbicide application. The intercalation process is supported by powder X-ray diffraction analysis with an expanded interlayer spacing from 8.6 to 19.6 Å for nanocomposite pH 13, which is due to the inclusion of larger size anion in the interlayer. Next, the absence of a nitrate peak at 1,326 cm−1 and the presence of a newly formed peak at 1,416 cm−1 in the Fourier transformed infrared spectroscopy analysis also confirmed the process of the intercalation. The significant decrease in nitrogen content to 0.50% indicates the intercalation of MCPA using the carbon, hydrogen, nitrogen, sulphur analyser. The release rate of the MCPA anion in the aqueous solutions is initially rapid, followed by the slow release in the order of phosphate > carbonate > chloride and followed the pseudo-second-order kinetic model. Hence, the conducted studies exhibit the successful intercalation of the MCPA herbicide anion and its controlled release mechanism as a potential hybrid green herbicide.

Sustainable Regeneration of Spent Graphite as a Cathode Material for a High-Performance Dual-Ion Battery

A resource-efficient and energy-saving recycling process is vital for establishing a sustainable circular economy of lithium-ion batteries (LIBs). Herein, we propose and use a one-step water-based recycling process to recycle and regenerate the graphite anode materials from spent LIBs. This process can not only successfully regenerate graphite from a solid electrolyte interface, dead lithium, and residual electrolyte and maintain its long-range-ordered layer graphite structure but also enlarge the interlayer distance and introduce abundant oxygen-containing functional groups to the as-regenerated graphite. Our electrochemical characterization and density functional theory (DFT) calculations reveal that expanded interlayer spacing and the oxygen-containing moieties make the regenerated graphite more suitable for storing PF6– rather than Li+. As such, the as-regenerated graphite facilitates resultant graphite dual-ion batteries (GDIBs) with impressive rate performance and stability, for example, an 85.3% capacity retention even after 500 cycles at 1 A g–1. Such a simple waste-to-resource strategy proposed in this work is expected to provide a low-cost and inspiring recycling pathway for spent LIBs and enable the sustainable manufacturing of GDIBs.

NaGaSe2: A Water-Loving Multifunctional Non-van der Waals Layered Selenogallate.

A missing member of well-known ternary chalcometallates, a sodium selenogallate, NaGaSe2, has been synthesized by employing a polyselenide flux and stoichiometric reaction. Crystal structure analysis using X-ray diffraction techniques reveals that it contains supertetrahedral adamantane-type Ga4Se10 secondary building units. These Ga4Se10 secondary building units are further connected via corners to form two-dimensional (2D) [GaSe2]∞- layers stacked along the c-axis of the unit cell, and the Na ions reside in the interlayer space. The compound has an unusual ability to absorb water molecules from the atmosphere or a nonanhydrous solvent to form distinct hydrated phases, NaGaSe2·xH2O (where x can be 1 and 2), with an expanded interlayer space, as verified by X-ray diffraction (XRD), thermogravimetric-differential scanning calorimetry (TG-DSC), desorption, and Fourier transform infrared spectroscopy (FT-IR) studies. The in situ thermodiffractogram indicates the emergence of an anhydrous phase before 300 °C with the decrease of interlayer spacings and reverting to the hydrated phase within a minute of re-exposure to the environment, supporting the reversibility of such a process. Structural transformation induced through water absorption results in an increase of Na ionic conductivity by 2 orders of magnitude compared to that of the pristine anhydrous phase, as verified by impedance spectroscopy. Na ions from NaGaSe2 can be exchanged in the solid-state route with other alkali and alkaline earth metals in a topotactic or nontopotactic way, leading to 2D isostructural and three-dimensional networks, respectively. Optical band gap measurements show a band gap of ∼3 eV for the hydrated phase, NaGaSe2·xH2O, which is in good agreement with the calculated band gap using a density functional theory (DFT)-based method. Sorption studies further confirm the selective absorption of water over MeOH, EtOH, and CH3CN with a maximum water uptake of 6 molecules/formula unit at a relative pressure, P/P0, of 0.9.

Sulfur-grafted hard carbon with expanded interlayer spacing and increased defects for high stability potassium-ion batteries

Carbon materials have been proven to be an effective anode for potassium-ion batteries (PIBs) due to their high safety, low cost, and environmental benignity. However, the repeated insertion/extraction of K-ions with a larger size into/from electrode at low voltage region will inevitably cause obvious volume expansion, easily resulting in poor cycle stability. Hence, we synthesize S-doped hard carbon material (NSHCM2) using biomass as carbon and thiourea as S sources. Various characterizations demonstrate that the introduced S-heteroatom not only expands the distance between carbon layers, but also creates more defects. The former ensures the free intercalation/deintercalation of K-ions without structure deformation, while the latter can provide numerous active sites to adsorb K-ions, all these together contribute to structure stability and reversible capacity. As a result, the optimized NSHCM2 electrode delivers a high capacity of 294 mAh g−1 at 200 mA g−1 and an ultra-long cycling stability by achieving 220 mAh g−1 at 2000 mA g−1 over 5000 cycles. This simple and high effective synthesis route makes durable and fast potassium storage possible.

Disorder and hydrogenation in graphene nanopowder revealed by complementary X-ray and neutron scattering

Functionalization of graphene's two-dimensional sheets can be used to modify the physical properties of graphene, such as changing its conductivity or inducing ferromagnetism, which is of broad interest for a myriad of applications. However, functionalized graphene can possess significant structural disorder that is often overlooked and is difficult to characterize quantitatively. Here we investigate hydrogenated graphene nanopowder (H-Gr) produced by Birch reduction of graphene oxide. By combining complementary x-ray and neutron diffraction, we show how to quantitatively characterize the H-Gr nanostructure, including the hydrogen content. We show that the majority of the H-Gr consists of highly disordered molecular-scale carbon while a small portion of the sample contains few-layered graphene having an expanded interlayer spacing. Modeling the coherent diffuse scattering for both x-ray and neutron diffraction, and comparing it with the incoherent neutron scattering, the hydrogen to carbon ratio was measured and it was determined that most of the hydrogen resides within the disordered carbon rather than in the graphene. Evidence is presented for hydrogen clustering as well as for hydrogen bonded perpendicular to the plane of molecular-carbon bonds. Our quantitative approach to characterizing carbon nanopowders has broad relevance to understanding disorder and bonding of hydrogen in graphitic carbons and other nanomaterials.