Reduced graphene oxide doping flower-like Fe7S8 nanosheets for high performance potassium ion storage

Finding easy-to-operate strategy to obtain anode material with well-designed structure and excellent electrochemical performance is necessary to promote the development of the future potassium-ion batteries(PIBs).In this work,we synthesized reduced graphene oxide doping flower-like Fe₇S₈ nanosheets electrode materials using one-step hydrothermal strategy.The rGO@Fe₇S₈ composite is composed of homogeneous Fe₇S₈ and reduced graphene oxide thin nanosheets.This unique structure not only promotes the penetration of electrolyte and increases the conductive of the pure Fe₇S₈ electrode materials,but also relieves the volume expansion of K⁺ during charge/discharge process.When applied this interesting anode electrode for PIBs,the rGO@Fe₇S₈ exhibits excellent electrochemical performance.It delivers a high reversible specific capacity of 445 mAh g^-1 at 50 mA g^-1,excellent rate performance(284 mAhg^-1at 500 mA g^-1 and 237 mAh g^-1 at 1000 mA g^-1),and a high cycling stability at 100 mA g^-1(maintained 355 mAh g^-1 after 300 cycles).     

β-MnO2 with proton conversion mechanism in rechargeable zinc ion battery

Rechargeable aqueous zinc ion battery(RAZIB)is a promising energy storage system due to its high safety,and high capacity.Among them,manganese oxides with low cost and low toxicity have drawn much attention.However,the under-debate proton reaction mechanism and unsatisfactory electrochemical performance limit their applications.Nanorod b-MnO₂ synthesized by hydrothermal method is used to investigate the reaction mechanism.As cathode materials for RAZIB,the Zn//b-MnO₂ delivers 355 mA h g^-1(based on cathode mass)at0.1 A g^-1,and retain 110 mA h g^-1 after 1000 cycles at 0.2 A g^-1.Different from conventional zinc ion insertion/extraction mechanism,the proton conversion and Mn ion dissolution/deposition mechanism of b-MnO₂ is proposed by analyzing the evolution of phase,structure,morphology,and element of b-MnO₂ electrode,the pH change of electrolyte and the determination of intermediate phase MnO OH.Zinc ion,as a kind of Lewis acid,also provides protons through the formation of ZHS in the proton reaction process.This study of reaction mechanism provides a new perspective for the development of Zn//MnO₂ battery chemistry.     

Flexible asymmetric supercapacitor based on MnO2 honeycomb structure

By controlling the electroplating time of solution containing Mn(Ac)₂, the MnO₂ nanosheets were self-assembled to the honeycomb structure and showed an excellent electrochemical performance in 1 mol/L Na₂SO₄ electrolyte. Via pairing with activated carbon as negative electrode, the capacitor could deliver a maximum energy density of 43.84 Wh/kg and a maximum power density of 6.62 kW/kg.     

High-capacity Bi2O3 anode for 2.4 V neutral aqueous sodium-ion battery-supercapacitor hybrid device through phase conversion mechanism

Aqueous battery-supercapacitor hybrid devices(BSHs)are of great importance to enrich electrochemical energy storage systems with both high energy and power densities.However,further improvement of BSHs in aqueous electrolytes is greatly hampered by operating voltage and capacity limits.Different from the conventional intercalation/de-intercalation mechanism,Bi₂O₃ implements charge storage by a reversible phase conversion mechanism.Herein,taking Bi₂O₃ electrode with wide potential window(from-1.2 to 1 V vs.saturated calomel electrode)and high capacity as battery-type anode,we propose that the overall performance of aqueous BSHs can be greatly upgraded under neutral condition.By paring with stable layer-structuredδ-MnO₂ cathode,a sodium-ion Bi₂O₃//MnO₂ BSH with an ultrahigh voltage of 2.4 V in neutral sodium sulfate electrolyte is developed for the first time.This hybrid device exhibits high capacity(~215 C g^-1 at 1 mA cm^-2),relatively long lifespan(~77.2%capacity retention after 1500 cycles),remarkable energy density(71.7 Wh kg^-1@400.5 W kg^-1)and power density(3204.3 W kg^-1@18.8 Wh kg^-1).Electrochemical measurements combining a set of spectroscopic techniques reveal the reversible phase conversion between bismuth oxide and metallic bismuth(Bi₂O₃?Bi0)through Bi²⁺ transition phase in neutral sodium sulfate solution,which can deliver multielectron transfer up to 6,leading to the high-energy BSHs.Our work sheds light on the feasibility of using Bi₂O₃ electrode under neutral condition to address the issue of narrow voltage and low capacity for aqueous BSHs.     

Paper-based all-solid-state flexible asymmetric micro-supercapacitors fabricated by a simple pencil drawing methodology

A simple and novel methodology was developed for manufacturing interdigitated asymmetric all-solid-state flexible micro-supercapacitors (MSCs) by a facile pencil drawing process followed by electrodepositing MnO₂ on one of the as-drawn graphite electrode as anode and the other as cathode.     

Highly active Fe_7S_8 encapsulated in N-doped hollow carbon nanofibers for high-rate sodium-ion batteries

Nanostructured iron sulfides are regarded as a potential anode material for sodium-ion batteries in virtue of the rich natural abundance and remarkable theoretical capacity.However,poor rate performance and inferior cycling stability caused by sluggish kinetics and volume swelling represent two main obstacles at present. The previous research mainly focuses on nanostructure design and/or hybridizing with conductive materials.Further boosting the property by adjusting Fe/S atomic ratio in iron sulfides is rarely reported.In this work,Fe_7 S_8 and FeS_2 encapsulated in N-doped hollow carbon fibers(NHCFs/Fe_7 S_8 and NHCFs/FeS_2) are constructed by a combined chemical bath deposition and subsequent sulfidation treatment.The well-designed NHCFs/Fe₇ S₈ electrode displays a remarkable capacity of 517 mAh g^-1 at 2 A g^-1after 1000 cycles and a superb rate capability with a capability of 444 mAh g^-1 even at 20 A g^-1 in etherbased electrolyte.Additionally,the rate capability of NHCFs/Fe₇ S₈ is superior to that of the contrast NHCFs/FeS₂ electrode and also much better than the values of the most previously reported iron sulfide-based anodes.The in-depth mechanism explanation is explained by further experimental analysis and theoretical calculation,revealing Fe₇ S₈ displays improved intrinsic electronic conductivity and faster Na⁺ diffusion coefficient as well as higher reaction reversibility.     

Nb2O5-carbon core-shell nanocomposite as anode material for lithium ion battery

Mb₂O₅ -carbon nanocomposite is synthesized through a facile one-step hydrothermal reaction from sucrose as the carbon source,and studied as an anode material for high-performance lithium ion battery.The structural characterizations reveal that the nanocomposite possesses a core-shell structure with a thin layer of carbon shell homogeneously coated on the Nb₂O₅ nanocrystals.Such a unique structure enables the composite electrode with a long cycle life by preventing the Nb₂O₅ from volume change and pulverization during the charge-discharge process. In addition,the carbon shell efficiently improves the rate capability.Even at a current density of 500 mA·g^-1,the composite electrode still exhibits a specific capacity of～100 mAh·g^-1.These results suggest the possibility to utilize the Nb₂O₅-carbon core-shell composite as a high performance anode material in the practical application of lithium ion battery.     

MnO2 cathode materials with the improved stability via nitrogen doping for aqueous zinc-ion batteries

The research and exploration of manganese-based aqueous zinc-ion batteries have been controversial of cycle stability and mechanism investigation,thus improving the stability and exploring storage mechanism are still the most main issue.Defect engineering has become an effective method to improve cycle stability.Herein,a nitrogen-doped ε-MnO₂(MnO₂@N)has been prepared using electrochemical deposition and heat treatment under nitrogen atmosphere.As the cathode for zinc-ion batteries,the capacity retention rate of MnO₂@N cathode is close to 100%after 500 cycles at 0.5 A g^-1,while the capacity retention rate for the initial MnO₂ cathode is 62%.At 5 A g^-1,the capacity retention rate of MnO₂@N cathode is 83%after 1000 cycles,which is much higher than the 27%capacity retention rate for the original MnO₂ cathode.And it can be found that the oxygen vacancies increase after nitrogen doping,which can improve the conductivity of the MnO₂@N cathode.Also,there is Mn-N bond in MnO₂@N,which can enhance the electrochemical stability of MnO₂@N cathode.In addition,the electrochemical mechanism of MnO₂@N cathode has been explored by the CV,GCD and GITT tests.It is found that nitrogen doping promotes the intercalation of H⁺ and the corresponding capacity contribution.Compared with the original MnO₂ cathode,the diffusion coefficient of H⁺ and Zn²⁺ in MnO₂@N cathode increases.Also,the reactions during the charging and discharging process are explored through the ex-situ XRD test.And this work may provide some new ideas for improving the stability of manganese-based zinc-ion batteries.     

Mesh-like vertical structures enable both high areal capacity and excellent rate capability

In order to balance electrochemical kinetics with loading level for achieving efficient energy storage with high areal capacity and good rate capability simultaneously for wearable electronics,herein,2 D meshlike vertical structures(NiCo_2 S_4@Ni(OH)_2) with a high mass loading of 2.17 mg cm^-2 and combined merits of both 1 D nanowires and 2 D nanosheets are designed for fabricating flexible hybrid supercapacitors.Particularly,the seamlessly interconnected NiCo_2 S_4 core not only provides high capacity of 287.5 μAh cm^-2 but also functions as conductive skeleton for fast electron transport;Ni(OH)_2 sheath occupying the voids in NiCo_2 S_4 meshes contributes extra capacity of 248.4 μAh cm^-2;the holey features guarantee rapid ion diffusion along and across NiCO_2 S_4@Ni(OH)_2 meshes.The resultant flexible electrode exhibits a high areal capacity of 535.9 μAh cm^-2(246.9 mAh g^-1) at 3 mA cm^-2 and outstanding rate performance with 84.7% retention at 30 mA cm^-2,suggesting efficient utilization of both NiCo_2 S_4 and Ni(OH)_2 with specific capacities approaching to their theoretical values.The flexible solid-state hybrid device based on NiCo_2 S_4@Ni(OH)_2 cathode and Fe_2 O_3 anode delivers a high energy density of 315 μWh cm^-2 at the power density of 2.14 mW cm^-2 with excellent electrochemical cycling stability.     

Highly efficient photocatalytic NO removal and in situ DRIFTS investigation on SrSn（OH）6

A novel SrSn（OH）₆ photocatalyst with large plate and particle size were synthesized via a facile chemical precipitation method.The photocatalytic activity of the SrSn（OH）₆ was evaluated by the removal of NO at ppb level under UV light irradiation.Based on the ESR measurements,SrSn（OH）₆ photocatalyst was found to have the ability to generate the main active species of O₂^·-,^·OH and ¹ O₂ during the photocatalyti...     

KAl（SO4）2·12H2O catalyzed efficient synthesis of 3,4,6-trisubstituted 2-pyridone in water

An efficient green protocol for the preparation 3,4,6-trisubstituted 2-pyridone of employing a condensation reaction of cyanoacetamide and acetylacetone in the presence of KAl（SO₄）₂·12H₂O in water has been described.The present procedure offers advantage such as shorter reaction time,simple workup,and excellent yields.     

A new 28-Ni-added poly(polyoxometalate) with B atoms: synthesis,structure and catalysis for Knoevenagel condensation

The synergistic effect of trivacant B-α-Ge W₉O₃₄fragments as structure-directing agents and inorganic B-O segments as intramolecular decoration afforded an unprecedented 28-Ni-added huge cluster K₂Na₁₄H₁₀[{Ni₆(OH)₃(H₂O)₆(Ge W₉O₃₄)}{Ni₈-(μ₆-O)(OH)₃(H₂O)(BO(OH)₂)(B₂O₃(OH)₂)(Ge W₉O<...     

Tuning electronic structure ofδ-MnO2 by the alkali-ion(K,Na,Li)associated manganese vacancies for high-rate supercapacitors

Cation vacancies can bring numerous surprising characters due to its multifarious electron and orbit distribution.In this work,d-MnO₂ with alkali-ion(K,Na,Li)associated manganese(Mn)vacancies is fabricated by a simple hydrothermal reaction,and the correlation between their electronic structure and pseudocapacitance are systematically investigated.FESEM/TEM images have shown that the morphology of MnO₂ is obviously changed after the introducing of cation vacancies.The position of alkali-ion in MnO₂ structure can be controlled by adjusting the ion concentration.XRD patterns and Raman spectra demonstrate that the alkali-ion is embedded in Mn vacancies at low concentration,while entered the interlayer of MnO₂ at high concentration.The existence of Mn vacancies will resulting in the distortion of neighboring atoms,leading to the electronic delocalization,and thus enhancing the conductivity,pseudocapacitance and rate capability of MnO₂.Accordingly,the specific capacitances of optimized 0.4 KMO,0.4 NaMO and 0.4 LiMO samples are enhanced about 1.9,1.6 and 1.6 times compared to pure MnO₂.Meanwhile,the rate performance has also been improved about 76%,46%and 42%,respectively.Theoretical calculations further confirm that the Mn vacancies can generate additional occupancy states and cause an increase in carrier concentration,which will improve the conductivity and further boost the pseudocapacitance of MnO₂.This result open up a promising approach to explore active and durable electrode materials.     

In-situ construction of conducting alloy interphase towards modulating Li-ion storage kinetics

Interface engineering strategy shows great promise in promoting the reaction kinetic and cycling performance in the field of electrochemical energy storage application.In this work,an in-situ interface growth strategy is proposed to introduce a robust and conducting MoGe₂ alloy interphase between the electrochemical active Ge nanoparticle and flexible MoS₂ nanosheets to modulate their Li-ion storage kinetics.The structural evolution processes of the Ge@MoGe₂@MoS₂ composite are unraveled,during which the initially-generated Ge metals serve as a crucial reduction mediator in the formation of MoGe₂ species bridging the Ge and MoS₂.The as-generated MoGe₂ interface,chemically bonding with both Ge and MoS₂,possesses multi-fold merits,including the maintaining stable framework of electrochemically inactive Mo matrix to buffer the strain-stress effect and the"welding spot"effects to facilitate the efficient Li⁺/e^-conduction.As well,the introduction of MoGe₂ interface leads to a unique sequential lithiation/de^-lithiation process,namely in the order of the electrochemically active MoS₂-MoGe₂-Ge during lithiation and vice versa,during which the electrode strain could be more effectively released.Benefited from the robust and rigid MoGe₂ interface,the delicately designed Ge@MoGe₂@MoS₂ composite exhibits an improved charge/discharge performances(866.7 mAh g^-1 at 5.0 A g^-1 and 838.5 mAh g^-1 after 400 cycles)while showing a high tap density of 1.23 g cm^-3.The as-proposed in-situ interface growth strategy paves a new avenue for designing novel high-performance electrochemical energy storage materials.     

Metal-organic framework as a multi-component sensor for detection of Fe3+, ascorbic acid and acid phosphatase

In this research,a hydroxyl group functionalized metal-organic framework(MOF),UiO-66-(OH)₂,was synthesized as a "on-off-on" fluore scent switching nanoprobe for highly sensitive and selective detection of Fe³⁺,ascorbic acid(AA) and acid phosphatase(ACP).UiO-66-(OH)₂ emits yellow-green light under ultraviolet light,when Fe³⁺ was added,Fe³⁺ was chelated with hydroxyl group,the electrons in the excited state S_1 of the MOF transferred to the half-filled 3 d orbits of Fe³⁺,resulting in fluorescence quenching because of the nonradiative electron/hole recombination annihilation.AA could reduce Fe³⁺ to Fe²⁺,which can destroy the electron transfer between UiO-66-(OH)₂ and Fe³⁺ after AA adding,resulted in nonoccurrence of the nonradiative electron transfer,leading to the recovery of UiO-66-(OH)₂ fluorescence intensity.The probe can also be used to detect ACP based on the enzymolysis of 2-phospho-L-ascorbic acid(AAP) to produce AA.Benefitting from the hydroxyl group and the characteristics of UiO-66,including the high porosity and large surface area,the developed UiO-66-(OH)₂ showed extensive advantages as a fluorescent probe for detection of multi-component,such as high sensitivity and selectivity,colorimetric detection,fast response kinetics and easy to operate,economical and secure.This is the first time to use active group functionalized MOFs as a multicomponent sensor for these three substances detection.     

Monodispersed SWNTs Assembled Coating Layer as an Alterna-tive to Graphene with Enhanced Alkali-ion Storage Performance

Graphene coating is commonly used to improve the performance of electrode materials,while its steric hindrance effect hampers fast ion transport with compromised rate capability.Herein,a unique single-walled carbon nanotubes(SWNTs)coating layer,as an alternative to graphene,has been developed to improve the battery behavior of iron-based anodes.Benefiting from the structure merits of mesoporous SWNTs layer for fast electron/ion transport and hollow Fe₃O₄ for volume accommodation,as-prepared Fe₃O₄@SWNTs exhibited excellent lithium storage performance.It delivers a high capacity,excellent rate capability,and long lifespan with capacities of 582 mA·h·g^-1 at 5 A·g^-1 and 408 mA·h·g^-1 at 8 A·g^-1 remained after 1000 cycles.Such performance is better than graphene-coated Fe₃O₄ and other SWNT-Fe₃O₄ architectures.Besides,SWNTs coating is also used to improve the sodium and potassium storage performance of FeSe₂.The kinetics analysis and ex-situ experiment further reveal the effect of SWNTs coating for fast electron/ion transfer kinetics and good structure stability,thus leading to the superior performance of SWNTs-coated composites.     

Nitrogen-doped carbon encapsulated in mesoporous TiO_2 nanotubes for fast capacitive sodium storage

Controllable synthesis of insertion-type anode materials with beneficial micro-and nanostructures is a promising approach for the synthesis of sodium-ion storage devices with high-reactivity and excellent electrochemical performance.In this study,we developed a sacrificial-templating route to synthesize TiO₂@N-doped carbon nanotubes(TiO₂@NC-NTs)with excellent electrochemical performance.The asprepared mesoporous TiO₂@NC-NTs with tiny nanocrystals of anatase TiO₂ wrapped in N-doped carbon layers showed a well-defined tube structure with a large specific surface area of 198 m² g^-1 and a large pore size of~5 nm.The TiO₂@NC-NTs delivered high reversible capacities of 158 m A h g^-1 at 2 C(1 C=335 m A g^-1)for 2200 cycles and 146 m A h g^-1 at 5 C for 4000 cycles,as well as an ultrahigh rate capability of up to 40 C with a capacity of 98 m A h g^-1.Even at a high current density of 10 C,a capacity of 138 m A h g^-1 could be delivered over 10,000 cycles.Thus,the synthesis of mesoporous TiO₂@NC-NTs was demonstrated to be an efficient approach for developing electrode materials with high sodium storage and long cycle life.     

Halogen chlorine triggered oxygen vacancy-rich Ni(OH)2 with enhanced reaction kinetics for pseudocapacitive energy storage

Two-dimensional(2D) Ni(OH)2nanosheets can theoretically expose their active sites of 100%. Whereas,their intrinsic easy accumulation and low conductivity lead to weak and unsustainable reaction kinetics.Herein, we propose a novel halogen chlorine-triggered electrochemical etching strategy to controllably manage the reaction kinetics of 2D Ni(OH)₂nanosheets(EE/Cl-Ni(OH)₂). It is found that halogen chlorine doping can adjust the interlamellar spacing flexibly and promote the ...     

Tin phosphide-carbon composite as a high-performance anode active material for sodium-ion batteries with high energy density

Tin phosphide(Sn₄P₃)is a promising anode material for sodium-ion batteries because of its relatively large theoretical capacity,appropriate Na⁺ alloying potential,and good cyclic stability.Herein,the Sn₄P₃ embedded into a carbon matrix with good rate performance and long cycle life is reported.The Sn₄P₃-C composite exhibits excellent rate performance(540 mAh g^-1 at 5 A g^-1)and the highest reversible capacity(844 mAh g^-1 at 0.5 A ^g-1)among Sn4P3-based anodes reported so far.Its reversible capacity is as high as 705 mAh g^-1 even after 100 cycles at 0.5 A g^-1.Besides,its initial Coulomb efficiency can reach 85.6%,with the average Coulomb efficiency exceeding 99.75%from the 3rd to 100th cycles.Na₂C₆O₆ is firstly used as a cathode when Sn₄P₃ acts as anode,and the Na-Sn₄P₃-C//Na₂C₆O₆ full cell shows excellent electrochemical performance.These results demonstrate that the Sn₄P₃-C composite prepared in this work displays high-rate capability and superior cyclic performance,and thus is a potential anode for sodium ion batteries.     

LiNi0.6Co0.2Mn0.2O2单晶的简易制备及其电化学性能

以Ni_0.6Co_0.2Mn_0.2(OH)₂和LiOH·H₂O为前驱体,在LiOH·H₂O不过量的条件下,采用简单的固相焙烧法,在910℃下制备出单晶LiNi_0.6Co_0.2Mn_0.2O₂(NCM622)。所得材料无需水洗、烘干、退火等处理,可直接用于电极浆料的制备。电化学测试表明,所得NCM622单晶具有较高的比容量和优异的循环稳定性。在0.1C电流下的首次放电比容量达到181.2 mAh·g^-1,0.3C下的首次放电比容量为174.4 m Ah·g^-1。在0.3C的电流密度下,经过300次循环,放电比容量为150.7 mAh·g^-1,容量保持率为86.4%,经500次循环后,放电比容量仍有141.2 mAh·g^-1,容量保持率为81.0%。该电化学性能优于850℃下焙烧的多晶NCM...