rGO Cathodes Research Articles

Expediting Polysulfide Anchoring by Fe3O4/Reduced Graphene Oxide Composite for High‐Performance Lithium‐Sulfur Batteries

AbstractThe inherent low conductivity of sulfur, sluggish redox kinetics, and the challenge of maximizing active material utilization are the bottlenecks for practical implementation in lithium‐sulfur (Li−S) battery technology. Herein, a low‐cost Fe3O4‐rGO that serves as both a sulfur host matrix and an electrocatalytic interlayer in a Li−S battery has been synthesized. With the merit of high specific surface area, Fe3O4‐rGO offers high sulfur loading (80 wt. %) and sufficient space to accommodate sulfur volume expansion during the redox reaction. The symmetric cell experiment demonstrated that Fe3O4 in the rGO structure promotes the lithium polysulfide (LPS) redox conversion. The Li−S battery is constructed using the Fe3O4‐rGO@S as the cathode and Fe3O4‐rGO as the interlayer, demonstrating an impressive specific capacity of 1258 mAh g−1 at 0.1 C and the battery retained 76 % of its capacity after 400 cycles at 0.5 C. This study also explores the confinement of LPS on the Fe3O4‐rGO@S_Fe3O4‐rGO cathode and interfacial redox kinetics by dynamic electrochemical impedance spectroscopy. This work presents a cost‐effective method for improving the catalytic conversion of lithium polysulfides, which can contribute to the development of high‐performance lithium‐sulfur batteries.

Three-dimensional N,P co-doped graphene hydrogel cathode for zinc-ion hybrid capacitor with high specific capacitance and excellent rate performance

Zinc-ion hybrid capacitor (ZHSC) is recognized as a favorable energy storage device due to the combined advantages of battery-type anode and capacitor-type cathode. However, it still remains a huge challenge to achieve a high-specific-capacitance cathode without compromising the rate capability for high-performance ZHSC. Here, a three-dimensional hierarchical nitrogen and phosphorus co-doped reduced graphene oxide hydrogel (NPGH) is synthesized with small-sized graphene oxide precursors via one-step hydrothermal reduction and in-situ doping, which is firstly used as cathode for ZHSC without adding extra conductive additives and binders. In this case, small-sized graphene sheets can increase and shorten ions diffusion channels for the efficient utilization of active surface compared with commonly-used large-sized counterparts. Moreover, nitrogen and phosphorus co-doping can synergistically enhance the conductivity, provide additional active sites, and promote the adsorption of zinc ions, which is well demonstrated by electrochemical analysis, ex situ characterization and DFT theoretical calculation. Attributed to the synergy, NPGH-based ZHSC displays large specific capacitance (251.3 F g−1, 0.5 A g−1), outstanding rate performance (79 %, 50 A g−1) and excellent cycle stability. This work proposes a novel strategy of tailoring rGO cathode by simultaneous size effect and doping engineering, which shows a great promise of constructing high-performance rGO based ZHSC.

Dual-function hollow MoS2 nanocages decorated on graphene sheets as efficient sulfur hosts for advanced lithium-sulfur batteries

Due to the presence of polysulfitabde shuttling, serious electrode expansion, and the low electrical conductivity of sulfur materials at room temperature, the commercialization of Li-S batteries is still not feasible. In this study, we have synthesized unique hollow molybdenum disulfide nanocages/reduced graphene oxide (H-MoS2/rGO) composites to be employed as highly effective cathodes for Li-S batteries. In this well-designed structure, the hollow MoS2 nanocages are tightly bound by C-O-Mo bonds and uniformly distributed across the graphene sheets. The dual-function MoS2 nanocages can adsorb polysulfides by Mo-S bond and accelerate the conversion reaction of S8 and Li2S. Moreover, the 3D rGO network with abundant pores effectively reduces the diffusion path and enhances the rapid transport of electrons and ions. The hybrid H-MoS2/rGO cathodes with these advantages exhibit a remarkable initial discharge capacity of 801.7 mAh g−1 at 1 C, as well as a high specific discharge capacity of 533.2 mAh g−1 is remained over 500 cycles.

Binder free cobalt Manganese layered double hydroxide anode conjugated with bioderived rGO cathode for sustainable, high-performance asymmetric supercapacitors

Metal-organic frameworks (MOFs) possessmultifunctional characteristicssuch as tuneable pore structure and high specific surface area and are being designed with great interest to enhance the electrochemical properties of current energy storage devices. In this aspect, MOFs-derived layered double hydroxides (LDHs) are important candidates for advanced supercapacitors due to their high electrochemical activity and electric conductivity. Herein, we report synthesis of Cobalt Manganese layered double hydroxides (CoMn LDH) utilising Co MOF as a precursor via ion exchange method, while optimising the dosage of Mn to achieve the best possible structural outcome. The unique structure of CoMn LDH expressed high electrochemical parameters possessing specific capacitance of 1305F/g at 1 A/g. Afterwards, an asymmetric supercapacitor device was fabricated employing CoMn LDH as cathode and coffee grounds derived rGO (reduced graphene oxide) as anode. The as-prepared asymmetric supercapacitor device demonstrated a maximum working potential window of 1.2 V with energy and power density of 23.8 Wh/kg and 0.30 kW/Kg respectively. The device also exhibits superiorcoulombic efficiency and capacitance retention of 71.11 % and 82.7 % respectively over 3010 charge–discharge cycles that represents an effectiveapproach towards sustainable and effectiveenergy storage devices. In a nutshell, our study centred on adjusting composition, engineering structures, and assembling devices.

Hybrid Ascharite/Reduced Graphene Oxide with Polysulfide Adsorption Host for Advanced Lithium-Sulfur Batteries.

Balancing the adsorption of lithium-polysulfide intermediates on polar host material surfaces and the effect of their electronic conductivity in the subsequent oxidation and reduction kinetics of electrochemical reactions is necessary and remains a challenge. Herein, we have evaluated the role of polarity and conductivity in preparing a series of ascharite/reduced graphene oxide (RGO) aerogels by dispersing strong polar ascharite nanowires of varying mass into the conductive RGO matrix. When severed as Li-S battery cathodes, the optimized S@ascharite/RGO cathode with a sulfur content of 73.8 wt % demonstrates excellent rate performance and cycle stability accompanied by a high-capacity retention for 500 cycles at 1.0 C. Interesting advantages including the enhanced adsorption ability by the formation of the Mg-S and Li bonds, the continuous and quick electron/ion transportations assembled conductive RGO framework, and the effective deposition of Li2S are combined in the ascharite/RGO aerogel hosts. The electrochemical results further demonstrate that the polarity of ascharite components for the S cathode plays a dominant role in the improvement of electrochemical performance, but the absence of a conductive substrate leads to serious capacity attenuation, especially the rate performance. The balanced design protocol provides a universal method for the synthesis of multiple S hosts for high-performance LSBs.

Fe-doped α-MnO2/rGO cathode material for zinc ion batteries with long lifespan and high areal capacity

The Fe-doped α-MnO2/rGO nanocomposite possesses 72.2 mA h g−1 after 10 000 cycles, and exhibits power density 734.1 mW cm−2 which can drive commercial portable fans (4.5 W).

A magnetically induced self-assembly of Ru@Fe3O4/rGO cathode for diclofenac degradation in electro-Fenton process

In this study, a novel magnetic nanocomposite of Ru@Fe3O4/rGO was successfully synthesized by a simple hydro-thermal method. The Ru@Fe3O4/rGO particles were assembled and immobilized for innovative magnetically assembled electrode (MAE) without any binder, and the electrode was further applied in heterogeneous electro-Fenton (hetero-EF) process for the degradation of diclofenac (DCF). The results showed that rGO could remarkably enhance the conductivity and catalyze the two-electron oxygen reduction, which greatly improved the generation of H2O2. In addition, the mixture valence of Fe and Ru species might provide rich reaction sites and enhance electron transfer by synergy. Thus, the Ru@Fe3O4/rGO MAE exhibited a stable and high electrocatalytic activity in the hetero-EF process for DCF degradation over a wide pH range from 2 to 9 owing to the higher electroactive surface area (EASA) and lower charge/mass-transfer resistance. The DCF degradation efficiency could reach about 100% within 90 min under pH 5 and current 40 mA, and the Ru@Fe3O4/rGO MAE showed high stability and reusability after five cycles. Theoretically, 1O2 and •OH were the main reactive oxygen species (ROS) participating in DCF degradation in the Ru@Fe3O4/rGO MAE hetero-EF process. Furthermore, according to the LC-MS/MS intermediates, the possible DCF degradation pathway was deduced including dechlorination, hydroxylation and ring opening attacked by ROS. Eleven intermediates were detected during DCF degradation in the MAE hetero-EF process, and the ecological risk of DCF degradation in Ru@Fe3O4/rGO MAE hetero-EF process was significantly reduced. This study provides new insights into the magnetically assembled electrode of Ru@Fe3O4/rGO and displays a new practical application prospect of the materials for high-efficient removal and degradation of DCF from wastewater.

Rational Design of High-Performance Electrodes Based on Ferric Oxide Nanosheets Deposited on Reduced Graphene Oxide for Advanced Hybrid Supercapacitors.

The core strategy for constructing ultra-high-performance hybrid supercapacitors is the design of reasonable and effective electrode materials. Herein, a facile solvothermal-calcination strategy is developed to deposit the phosphate-functionalized Fe2O3 (P-Fe2O3) nanosheets on the reduced graphene oxide (rGO) framework. Benefiting from the superior conductivity of rGO and the high conductivity and fast charge storage dynamics of phosphate ions, the synthesized P-Fe2O3/rGO anode exhibits remarkable electrochemical performance with a high capacitance of 586.6Fg-1 at 1Ag-1 and only 4.0% capacitance loss within 10000 cycles. In addition, the FeMoO4/Fe2O3/rGO nanosheets are fabricated by utilizing Fe2O3/rGO as the precursor. The introduction of molybdates successfully constructs open ion channels between rGO layers and provides abundant active sites, enabling the excellent electrochemical features of FeMoO4/Fe2O3/rGO cathode with a splendid capacity of 475.4C g-1 at 1Ag-1. By matching P-Fe2O3/rGO with FeMoO4/Fe2O3/rGO, the constructed hybrid supercapacitor presents an admirable energy density of 82.0Whkg-1 and an extremely long working life of 95.0% after 20000 cycles. Furthermore, the continuous operation of the red light-emitting diode for up to 30min demonstrates the excellent energy storage properties of FeMoO4/Fe2O3/rGO//P-Fe2O3/rGO, which provides multiple possibilities for the follow-up energy storage applications of the iron-based composites.

Two-birds with one stone: Improving both cathode and anode electrochemical performances via two-dimensional Te-CoTe2/rGO ultrathin nanosheets as sulfur hosts in lithium-sulfur batteries

A Te-doped CoTe2 film could be grown in situ on reduced graphene oxide (rGO) to develop a Te-CoTe2/rGO composite with an ultrathin layered structure, which has multiple protective effects on both the sulfur positive electrode and lithium negative electrode in lithium sulfur (Li-S) batteries. The Te-CoTe2/rGO composite as a sulfur host not only shows a strong adsorbing ability for lithium polysulfides (LiPSs) but can also accelerate the conversion reaction of active material sulfur during the charging/discharging process. More importantly, this host can turn the shuttle effect from an unfavorable factor to a favorable factor, which could improve the electrochemical performance of the lithium anode with uniform lithium plating/stripping resulting from the intermediate polytellurosulfide species (Li2TexSy), which could be generated on the cathode surface via Te reacting with soluble Li2Sn (4 ≤ n ≤ 8). As a result, the S@Te-CoTe2/rGO cathode shows a discharge capacity of 970.0 mA h g−1 in the first cycle at 1 C and retains a high capacity of 545.5 mA h g−1 after 1000 cycles, corresponding to a low capacity decay rate of only 0.043% per cycle. In addition, in situ X-ray diffraction (XRD) and in situ Raman were used to explore the sulfur conversion process. This study not only demonstrates that a two-dimensional (2D) ultrathin Te-CoTe2/rGO composite is successfully developed with multiple effects on Li-S batteries but also opens a new pathway for designing unique sulfur hosts to promote the electrochemical performance of Li-S batteries.

Nanofabrication of selenium/reduced graphene oxide composite with sulfur doping via solution co-impregnation for enhanced lithium-selenium batteries

Lithium-selenium batteries are still plagued by polyselenides dissolution and low utilization of active material. In the present work, sulfur-doped selenium/reduced graphene oxide composite (Se68-S9/rGO) was successfully designed and prepared by solution co-impregnation of selenium and sulfur within the rGO matrix, and further used as cathode materials in lithium-selenium batteries. The introduction of sulfur could form the CS chemical bond and the stable chemical bond between selenium and sulfur, which effectively limit the leaching of higher order soluble polyselenides intermediate as well as immobilizing Se, further enhancing the rate performance and the cycling stability of the Se68-S9/rGO cathode. With high selenium and sulfur content of ca. 80%, the Se68-S9/rGO cathode can achieve a capacity of 538 mA h g−1 after 200 cycles at a current density of 0.5 C, and a capacity of 473 mA h g−1 after 200 cycles at a current density of 1 C, exhibiting superior cycling performance.

Three-dimensional printed Li4Ti5O12@VSe2 composites as high-performance anode material in full 3D-printed lithium-ion batteries with three-dimensional -printed LiFePO4@AC/rGO cathode

Currently, the development of high-performance lithium-ion batteries (LIBs) with improved areal capacity is still challenging. The common strategy to improve areal capacity is to increase the thickness of electrode materials. However, the application of thick electrodes remains challenge due to poor mechanical properties, slow charge and ion transport, and poor electrolyte infiltration. In this study, thick electrodes are constructed by 3D printing a Li4Ti5O12@VSe2-based ink. The highly electrical conductor VSe2 on the Li4Ti5O12 surface improves the ion and charge transport and eases the internal resistance of the 3D-printed electrode during charge and discharge. As a result, LIBs employing these thick electrodes show a high-rate capability of 128.9 mAh/g at 10 C, improved areal capacities up to 6.2 mAh/cm2, and ultrastable cycling capability (84.5% of capacity retention after 1700 cycles). Moreover, full cells utilizing 3D-Li4Ti5O12@VSe2 as the anode and 3D-LiFePO4@AC/rGO as the cathode with 1.81 V potential yield a high specific capacity of 152.5 mAh/g at 0.1C, a high specific energy density of 276.025 Wh/kg, and a power density of 30.5 W/kg at 0.1C. This work paves the way to designing thick electrodes for high-performance LIBs.

Enhancing the Catalytic Activity of Layered Double Hydroxide Supported on Graphene for Lithium–Sulfur Redox Reactions

The lithium–sulfur battery is one of the next-generation rechargeable battery candidates due to its high theoretical energy density and low cost. However, the sluggish conversion kinetics of soluble lithium polysulfides into insoluble Li2S2/Li2S leads to low sulfur utilization, retarded rate responses, and rapid capacity decay. Here, we enhance the sulfur reduction kinetics by designing and synthesizing a lamellar-structured NiFeLDH and reduced graphene oxide (rGO) composite. The assembly of a two-dimensional NiFeLDH with rGO, which has high conductivity and electrocatalytic activity, significantly enhances the electrochemical steps of sulfur reduction. The S@NiFeLDH/rGO cathode delivers an initial discharge capacity of 1014 mAh g−1 at 0.2 C and a capacity of 930 mAh g−1 after 100 cycles at 0.2 C. Even at a high current density of 1 C, the S@NiFeLDH/rGO could maintain a high capacity of 554 mAh g−1 after 400 cycles.

Active Sulfur-Host Material VS4 with Surface Defect Engineering: Intercalation-Conversion Hybrid Cathode Boosting Electrochemical Performance of Li-S Batteries.

Transition-metal sulfides as late-model electrocatalysts usually remain inactive in lithium-sulfur (Li-S) batteries in spite of their advantages to accelerate the rapid conversion of lithium polysulfides (LiPSs). Herein, a series of cobalt-doped vanadium tetrasulfide/reduced graphene oxide (x%Co-VS4/rGO) composites with an ultrathin layered structure as an active sulfur-host material are prepared by a one-pot hydrothermal method. The well-designed two-dimensional ultrathin 3%Co-VS4/rGO with heteroatom architecture defects (defect of Co-doping and defect of S-vacancies) can significantly improve the adsorption ability on LiPSs, the electrocatalytic activity in the Li2S potentiostatic deposition, and the active sulfur reduction/oxidation conversion reactions and greatly boost the electrochemical performances of Li-S batteries. On the one hand, the ultrathin 3%Co-VS4/rGO possesses good conductivity inheriting from rGO which contributes to the capacity of internal redox reactions on lithiation from VS4. On the other hand, the hybrid architectures provide strong adsorption and excellent electrocatalytic ability on LiPSs, which benefit from the surface defects caused by heteroatom doping. The S@3%Co-VS4/rGO cathode displays a high specific capacity of 1332.6 mA h g-1 at 0.2 C and a low-capacity decay of only 0.05% per cycle over 1000 cycles at 3 C with a primary capacity of 633.1 mA h g-1. Furthermore, when the sulfur loading (single-side coating) reaches 4.48 mg cm-2, it still can deliver 756.2 mA h g-1 after the 100th cycle at 0.2 C with 89.5% capacity retention. In addition, the in situ X-ray diffraction test reveals that the sulfur conversion mechanism is the processes of α-S8 → Li2S → β-S8 (first cycle) and then β-S8 ↔ Li2S during the subsequent cycles. The designing strategy with heteroatom doping and self-intercalation capacity adopted in this work would provide novel inspiration for fabricating advanced sulfur-host materials to achieve excellent electrochemical capability in Li-S batteries.

A lignin-derived flexible porous carbon material for highly efficient polyselenide and sodium regulation.

Low-cost and sustainable sodium-selenium (Na-Se) batteries are promising energy storage media for the advancement of electromobility and large-scale energy storage. However, the sluggish kinetics of Se cathodes and the unpredictable metal electrodeposition of Na at the anode remain critical challenges. In this work, we reveal the catalytic effect of atomic Fe on the conversion of polyselenides (SPSs) to Na2Se by density functional theory (DFT) calculations. Then, we prepare a lignin-derived flexible porous carbon matrix loaded with atomic Fe (Fe-BC/rGO, BC: lignin-derived porous carbon material; rGO: reduced graphene oxide) as a Se host to further verify the DFT calculation results. Due to the encapsulation of Se into the porous carbon matrix, the catalytic effect of atomic Fe on the conversion of SPSs to Na2Se and the continuous electron/ion transportation path, the prepared Se@Fe-BC/rGO cathode can deliver a high reversible capacity of 213 mA h g-1 at 2 A g-1, which is much better than the electrochemical performance of a Se cathode without atomic Fe loading (Se@BC/rGO). In addition, we further reveal the advantageous effect of the presence of the Fe-BC/rGO film in regulating the interfacial Na electrodeposition at the anode. Due to the porous structure and the catalytic effect of atomic Fe, a very low nucleation overpotential of 15.3 mV is achieved at a current density of 1 mA cm-2, which is much lower than that of the BC/rGO film. Therefore, this work provides a low-cost and sustainable strategy for simultaneously solving the challenges of the Se cathode and the Na metal anode for future Na-Se batteries.

Aqueous Aluminum‐Carbon Rechargeable Batteries

AbstractCarbon cathodes have shown excellent electrochemical behavior in aluminum batteries based on non‐aqueous electrolytes. By contrast, their use in Al systems operating in a salt‐water medium is plagued by poor and unstable performance. Herein, it is sustained that a successful C cathode for rechargeable aqueous Al batteries requires surface customization to enable hydrophilicity and grafting of charged Al molecules. Employing a freeze‐dried reduced graphene oxide (rGO) as the active electrode material, an aqueous Al‐C battery is assembled with a high energy density (136 Wh kg−1 per cathode mass) and one of the best capacity retentions reported (≈60% across a range of current densities and constant Coulombic efficiencies close to unit). Furthermore, the rGO cathode more than doubles the benchmark for life cycles (to ≈200 cycles) and can be charged rapidly (<5 min). To explain this response, a charge storage mechanism is proposed wherein the [Al(H2O)6]3+ ions do not get desolvated when inserted into the cathode. The guest Al ions (surface adsorbed or intercalated) act as proton donors and may get anchored on the oxygen moieties of the rGO, further promoting the formation of an electrochemical double layer. A mixed charge‐storage regime follows that stabilizes the carbon cathode and enables an unprecedented response.

Synthesis of nitrogen and sulfur co-doped reduced graphene oxide by hydrothermal method for fabrication of cathodes in dye-sensitized solar cells

Carbon-based materials have been known as non-metal electrocatalysts with both high performance and low cost for the reduction at the cathode of dye-sensitized solar cells (DSSCs). In this work, nitrogen and sulfur co-doped reduced graphene oxide (NSG) materials were synthesized via using graphene oxide (GO) as a precursor with reducing agent thiourea as the source of providing heteroatoms. Furthermore, NSG materials were extensively prepared via hydrothermal treatment with the investigation of different mass ratios of GO to thiourea. To study the impact of the quantity of reductant on the properties of NSG, reduced graphene oxide (rGO) was prepared by reducing GO with ascorbic acid as a reference sample. Moreover, NSG and rGO cathodes were both prepared by drop-casting method, while platinum (Pt) cathodes were fabricated using commercial Pt paste by screen-printing method. The DSSCs based on NSG cathodes with ratio of GO to thiourea of 1:10 exhibited an efficiency of 7.21 %, which was similar to commercial DSSCs Pt (7.44 %), proving that the judicious heteroatom doping of GO might introduce a potential candidate for increasing performance of DSSCs.

Enhancement of the electrochemical performance of free-standing graphene electrodes with manganese dioxide and ruthenium nanocatalysts for lithium-oxygen batteries

Hybrid ternary Graphene/Ruthenium/α-MnO2 (rGO/Ru/α-MnO2) flexible nanocomposite cathodes were fabricated via controlling both reduction and vacuum filtration processes without using a binder and conductive carbon additives for flexible Li-air battery system. To compare the electrochemical performance of the Graphene/Ruthenium/α-MnO2 cathodes, bare rGO and rGO/Ru free-standing cathodes were also manufactured. rGO cathodes with well-dispersed α-MnO2 nanowires and ruthenium nanoparticles were successfully synthesized and shown to dramatically increase (decrease) oxygen reduction (evolution) reactions. The enhancement on the electrochemical performance of the synthesized cathodes was attributed not only to catalysis effect of ruthenium and α-MnO2 but also well-stacked morphology of the nanocomposite architecture which enables increased oxygen flow between the layers and, hence boosted reaction kinetics.Physical characterization of the cathodes was carried out using FESEM, EDS, TEM, XRD, XPS and Raman spectroscopy. The discharge product of the cathodes was also evaluated using TEM and XPS. Electrochemical performances of the cathodes were evaluated by means of CV, EIS, galvanostatic charge-discharge and electrochemical cycling tests. Thanks to the synergetic effect of Ruthenium and α-MnO2 catalysts, our ternary rGO/Ru/α-MnO2 cathodes were shown to serve full discharge capacity of 2225 mAh/g while rGO/Ru can deliver only 1670 mAh/g. Besides, the cycling stability of the ternary rGO/Ru/α-MnO2 cathodes was shown for 50 cycles at 650 mAh/g capacity limited tests in assembled Li–O2 batteries.

Pd–SnO2 heterojunction catalysts anchored on graphene sheets for enhanced oxygen reduction

Palladium (Pd) has received extensive attention as the substitute for platinum to work as efficient catalyst towards the oxygen reduction reaction (ORR) owing to its high intrinsic activity. However, the Pd catalyst usually performs inferior catalytic stability in the practical electrochemical test. Here, we report a novel design of constructing efficient ORR catalyst with Pd/SnO2 heterojunctions uniformly loaded on the reduced graphene oxide sheets (Pd@SnO2/rGO). The highly conductive rGO sheets are beneficial to increase the electron transfers during the ORR process and the SnO2 support can induce tensile-strain and electron-rich features for Pd nanocrystals in the Pd/SnO2 heterojunctions. The electrochemical results illustrate that the Pd@SnO2/rGO catalyst has higher ORR activity compared to commercial Pd/C and shows remarkable catalytic stability with 1 mV of negative shift in half-wave potential over 20000 cycles of accelerated durability tests. Moreover, the Zn-air battery assembled with Pd@SnO2/rGO cathode exhibits a 2.8-fold higher specific capacity than that with Pd/C cathode.

Insights into the sandwich-like ultrathin Ni-doped MoS2/rGO hybrid as effective sulfur hosts with excellent adsorption and electrocatalysis effects for lithium-sulfur batteries

Dual redox mediator based on a novel ultrathin sandwich-type Ni-doped MoS 2 /rGO with rich MoS 2 -defect accelerate the electrochemical kinetics for high performance lithium-sulfur batteries. • The sandwich-type Ni-MoS 2 /rGO is developed as sulfur host via hydrothermal method. • The rich MoS 2 -defect plays key role in adsorption and redox kinetics of LiPSs. • Adsorption-electrocatalysis synergy enhances the electrochemical properties. • The S@Ni-MoS 2 /rGO cathode has high specific capacity and long cycle stability. The design of sulfur hosts with high conductivity, large specific surface area, strong adsorption and electrocatalytic ability is crucial to advance high performance lithium-sulfur batteries. Herein, a novel ultrathin sandwich-type Ni-doped MoS 2 /reduced graphene oxide (denote as Ni-doped MoS 2 /rGO) hybrid is developed as a sulfur host through a simple one-step hydrothermal route. The two-dimensional layered structure Ni-doped MoS 2 /rGO hybrid with heterostructure and heteroatom architecture defects not only plays a key role in adsorption of lithium polysulfide but also catalyzes on redox kinetics of sulfur and polysulfide species. Meanwhile, it can contribute to the large specific surface area for Li 2 S/S 8 deposition, fast Li-ion and electron transportation, thus enhancing the electrocatalytic properties, as confirmed firstly by cyclic voltammetry (CV) results. Due to the adsorption-catalytic synergistic effect, the Ni-doped MoS 2 /rGO cathode exhibits high specific capacity (1343.6 mA h g −1 at 0.2 C, 921.6 mA h g −1 at 1 C), high coulombic efficiency and an outstanding cycle stability (with the low attenuation rate of 0.077% per cycle over 140 cycles at 0.5 C and 0.11% per cycle over 400 cycles at 1 C, respectively). This work proposes some inspiration for exploring the construction of advanced lithium-sulfur batteries through the rational design defects of atomic structure and electronic states of MoS 2 as sulfur host.

Simultaneous defect-engineered and thiol modified of MoO2 for improved catalytic activity in lithium-sulfur batteries: A study of synergistic polysulfide adsorption-conversion function

Rational design of nanostructure and proper interfacial engineering is of significant in pursuing high performance Li-S batteries. Here we report a strategy to fabricate reduced graphene oxide coated MoO2 with defect engineered and thiol modified nanotubes (H-S@MoO2/rGO) as highly stable host material for cathode in Li-S batteries. Thiourea was used as sulfur source and etching agent to construct the hollow architecture and realize thiol modification of MoO2 with the aid of ethanol. The modifying H-S@MoO2/rGO nanotubes offer improved affinity with LiPSs and accelerating the conversion kinetics from LiPSs to final Li2S. Oxygen vacancy remarkably reduce energy barrier and facilitating charge transfer, improving catalytic activity, regulating the deposition of Li2S on electrode surface. Furthermore, H-S@MoO2/rGO nanotubes offer enough interior capacity for high sulfur loading of 84 wt% (donate as S-S@MoO2/rGO), effectively confine sulfur through confinement effect. The simultaneous defect-engineered and thiol modified of MoO2 effectively cooperate the adsorption, diffusion and conversion of LiPSs in sulfur redox process, synergistically enable host material effective adsorption-conversion function for polysulfide. The developed S-S@MoO2/rGO cathodes exhibit excellent rate performance and superior reliability with a high specific capacity of 927 mAh g−1 and small capacity fading rate of 0.042% per cycle over 500 cycles at 0.1 Ag−1. This work shows a feasible and effective method to analyze the systematic kinetic and in-depth mechanism explanation of functional groups modifying metal oxide to guide the design of effective catalysts for practical application in lithium-sulfur batteries.