Slow Reaction Kinetics Research Articles

Synergistic Catalytic Effects of CeCuO3 @ Vulcan Carbon Composites on the Oxygen Reduction Reaction

AbstractThe reduction of molecular oxygen is considered to be a key reaction for electrochemical energy conversion in direct methanol fuel cells (DMFCs). The slow kinetics of oxygen reduction reaction along with the high cost of Pt catalyst hampers the application of fuel cells. In this study, we have reported for the first time oxygen reduction reaction (ORR) activity on rare earth cerium containing perovskite oxides composite with vulcan carbon (VC) in alkaline media. The study has demonstrated the synergistic role of vulcan carbon in cerium perovskite nanomaterials‐VC composite for improving ORR activity. The 60 % CeCuO3‐VC perovskite oxide composite with surface areas of 180 m2/g showed better oxygen reduction capability as compared to that of bare cerium perovskite. On optimization, among all the prepared catalysts 60 % CeCuO3‐VC showed the highest ORR activity with low onset potential and high current density. Further, the optimized 60 % CeCuO3‐VC followed the 4e− pathway with 95 % methanol tolerance properties and high stability i.e 76 %. This study on cerium‐based perovskite with vulcan carbon will provide an opportunity for the study of rare earth cerium perovskite electrocatalysts for electrochemical energy conversion.

Fe-doping-induced cation substitution and anion vacancies promoting Co3O4 hexagonal nanosheets for efficient overall water splitting

Water electrolysis is a green technology for hydrogen fuel production, but greatly hampered by the slow kinetics of the anodic oxygen evolution reaction (OER) and the cathodic hydrogen evolution reaction (HER). In this work, we report an efficient strategy to simultaneously promote OER and HER performance on Co3O4 hexagonal nanosheets via Fe-doping-induced cation substitution and anion vacancies. Benefiting from the integrated advantages of well-defined ultrathin nanosheets, abundant vacancies, and unique three-dimensional electrode configuration, the optimized Fe-doped Co3O4 hexagonal nanosheets/nickel foam (Fe0.4Co2.6O4 HNSs/NF) can achieve overpotentials of 328 mV at 100 mA cm−2 for OER and 315 mV at 500 mA cm−2 for HER, respectively, which is comparable to those of the benchmark noble electrocatalysts. More importantly, the Fe0.4Co2.6O4 HNSs/NF-assembled electrolyzer for overall water splitting can deliver a current density of 100 mA cm−2 at a cell voltage as low as 1.66 V and work steadily at 50 mA cm−2 with a negligible fading up to 140 h.

Tunable Electronic Properties of Graphene Quantum Dots Guide the CO2-to-Formate Conversion Efficiency on SnO2 Nanosheet

SnO2 has been proved to be a promising catalyst for the electrochemical conversion of CO2 to formate. However, slow interfacial charge transfer and the unoptimized binding of intermediates to active sites result in large barriers and slow reaction kinetics for formate formation. Herein, SnO2 was selected as a model catalyst and decorated with graphene quantum dots (GQDs) embedding different functional groups (SnO2/R-GQD, with “R” being −NH2, −OH, or −SO3) to systematically explore the variation of interfacial effect on the behavior of intermediates adsorption and CO2 reduction reaction (CO2RR) activity. Experimental results show that the CO2RR performance was dependent on the electron-donating property of functional groups on GQDs. The SnO2/NH2-GQD composite can selectively convert CO2 to formate with a Faraday efficiency (FEformate) as high as 92.9% at −1.3 V vs RHE and a partial electric current density (jformate) as high as 16.2 mA cm–2. Experimental results and density functional theory (DFT) calculations indicate that the performance of CO2RR depends on the electron-donating properties of the functional groups on the GQDs. The strong electron-donating effect of −NH2 optimizes the adsorption free energy of the key intermediate and accelerates the desorption of *HCOOH, thus improving the catalyst activity. This study not only shows a series of advanced CO2RR electrocatalysts but also provides a feasible strategy for the rational design of catalysts for other proton-coupled electron-transfer reactions.

Enhanced electrocatalytic performance for oxygen evolution reaction via active interfaces of Co3O4 arrays@FeO x /Carbon cloth heterostructure by plasma-enhanced atomic layer deposition

Oxygen evolution reaction (OER) is a necessary procedure in various devices including water splitting and rechargeable metal-air batteries but required a higher potential to improve oxygen evolution efficiency due to its slow reaction kinetics. In order to solve this problem, a heterostructured electrocatalyst (Co3O4@FeO x /CC) is synthesized by deposition of iron oxides (FeO x ) on carbon cloth (CC) via plasma-enhanced atomic layer deposition, then growth of the cobalt oxide (Co3O4) nanosheet arrays. The deposition cycle of FeO x on the CC strongly influences the in situ growth and distribution of Co3O4 nanosheets and electronic conductivity of the electrocatalyst. Owing to the high accessible and electroactive areas and improved electrical conductivity, the free-standing electrode of Co3O4@FeO x /CC with 100 deposition cycles of FeO x exhibits excellent electrocatalytic performance for OER with a low overpotential of 314.0 mV at 10 mA cm−2 and a small Tafel slope of 29.2 mV dec−1 in alkaline solution, which is much better than that of Co3O4/CC (448 mV), and even commercial RuO2 (380 mV). This design and optimization strategy shows a promising way to synthesize ideally designed catalytic architectures for application in energy storage and conversion.

Gold-Promoted Electrodeposition of Metal Sulfides on Silicon Nanowire Photocathodes To Enhance Solar-Driven Hydrogen Evolution.

Constructing composite structures is the key to breaking the dilemma of slow reaction kinetics and easy oxidation on the surface of lightly doped p-type silicon nanowire (SiNW) array photocathodes. Electrodeposition is a convenient and fast technique to prepare composite photocathodes. However, the low conductivity of SiNWs limits the application of the electrodeposition technique in constructing composite structures. Herein, SiNWs were loaded with Au nanoparticles by chemical deposition to decrease the interfacial charge transfer resistance and increase active sites for the electrodeposition. Subsequently, co-catalysts CoS, MoS2, and Ni3S2 with excellent hydrogen evolution activity were successfully composited by electrodeposition on the surface of SiNWs/Au. The obtained core-shell structures exhibited excellent photoelectrochemical hydrogen evolution activity, which was contributed by the plasma property of Au and the abundant hydrogen evolution active sites of the co-catalysts. This work provided a simple and efficient solution for the preparation of lightly doped SiNW-based composite structures by electrodeposition.

Metallic nickel anchored on amorphous nickel cobalt oxide nanorods as efficient electrocatalysts toward oxygen evolution reaction

Developing high-activity and capital-saving electrocatalysts for the slow kinetics of the oxygen evolution reaction (OER) is important to improve the efficiency of water splitting. Herein, a facile reduction approach is employed to prepare metallic Ni-decorated amorphous nickel cobalt oxide (NiCoOx) nanoarray electrocatalysts, with three-dimensional nickel foam (Ni/NiCoOx/NF) as substrate. Benefiting from abundant oxygen vacancies and preferred electron transport between metallic Ni and the NiCoOx substrate，the Ni/NiCoOx/NF delivers a current density of 50 mA cm−2 at an overpotential of 348 mV in 1.0 M KOH toward OER, comparable with that of commercial RuO2 (320 mV). Moreover, Ni/NiCoOx/NF is further served as an anodic material to assemble a two-electrode overall water splitting system (commercial Pt/C as the cathode), which achieves a current density of 10 mA cm−2 at a low voltage of 1.589 V and displays reliable durability over at least 50 h (around 30 mA cm−2). This research offers an efficient way for generating catalysts with multi components via reduction of polymetallic oxides for electrocatalytic conversion of small molecules.

Constructing an active and stable oxygen electrode surface for reversible protonic ceramic electrochemical cells

The reversible protonic ceramic electrochemical cells (R-PCECs) can efficiently and cost-effectively store and convert energy at low-intermediate temperatures (400-700 oC). Their widespread commercialization is mainly limited by the challenges of oxygen electrodes due to the slow oxygen reaction kinetics and poor durability. In this study, we first enhance the reaction activity and surface stability of a double-perovskite PrBaCo2O5+δ (PBC) oxygen electrode by employing a fluorite-based Pr0.1Ce0.9O2+δ (PCO) catalyst coating. The PCO-coated PBC (PCO-PBC) oxygen electrode shows a much-reduced area-specific resistance of 0.096 Ωcm2 and good performance on a fuel-electrode supported single cell at 650 oC, displaying a typical peak power density of 1.21 Wcm-2 (in fuel cell mode) and a typical current density of 2.69 Acm-2 at 1.3 V (in electrolysis mode) with reasonable faradaic efficiencies and durability. PCO coating has significantly improved the surface exchange process, facilitated ion diffusion, and suppressed the Ba-segregation of PBC, as confirmed by the analyses of electrochemical performance and TEM.

Zr-MOF/NiS2 hybrids on nickel foam as advanced electrocatalysts for efficient hydrogen evolution

As a typical transition-metal sulfides (TMS), nickel disulfide (NiS2) has attracted great attention in terms of hydrogen evolution reaction (HER). Howbeit, owing to the poor conductivity, slow reaction kinetics and instability of NiS2, its HER activity is still necessary to be improved. In this work, we designed hybrid structures consisting of the nickel foam (NF) as a self-supporting electrode, NiS2 derived from the sulfuration of NF and Zr-MOF grown on the surface of NiS2@NF (Zr-MOF/NiS2@NF). Due to the synergistic effect between the different constituents, the obtained Zr-MOF/NiS2@NF demonstrates ideal electrochemical hydrogen evolution ability in acidic and alkalescent environment, reaching a standard current density of 10 mA cm−2 at overpotentials of 110 and 72 mV in 0.5 M H2SO4 and 1 M KOH electrolytes, respectively. What is more, it also maintains excellent electrocatalytic durability for 10 h in both electrolytes. This work could provide a useful guidance on effectively combining metal sulfide with MOF for high-performance HER electrocatalysts.

In Situ Transformation of LDH into NiCo2S4-NiS2 Nano-heterostructures on Hollow Carbon Boxes to Promote Sulfur Electrochemistry for High-Performance Lithium–Sulfur Batteries

The practical application of lithium–sulfur batteries is hindered by slow redox reaction kinetics and serious lithium polysulfide (LiPS) migration, especially in the scene of high sulfur loading and a lean electrolyte. A strategy has been proposed to catalyze the liquid–solid conversion of lithium polysulfides in “sealed” nanoboxes with the NiCo2S4-NiS2 nano-heterostructures, in which both LiPS migration and retardation reaction kinetics can be handled simultaneously. The design of hollow carbon boxes can alleviate the volume expansion during the cyclic process. Meanwhile, the NiCo2S4-NiS2 nano- heterostructures on hollow carbon boxes can effectively adsorb LiPS and catalyze their quick conversion, which have a synergistic enhancement effect on inhibiting the shuttle effect. Ultimately, this design achieves decent battery performance with a high specific capacity of 1207 mAh g–1 at 0.2C and long-term cyclability with a capacity retention of 60.23% after 450 cycles at 1C as well as a high initial areal capacity of 6.09 mAh cm–2 with a loading of 5 mg cm–2 under an electrolyte/sulfur ratio of 8.0 mL g–1.

Rapid and stable calcium-looping solar thermochemical energy storage via co-doping binary sulfate and Al–Mn–Fe oxides

Solar thermochemical energy storage based on calcium looping (CaL) process is a promising technology for next-generation concentrated solar power (CSP) systems. However, conventional calcium carbonate (CaCO3) pellets suffer from slow reaction kinetics, poor stability, and low solar absorptance. Here, we successfully realized high power density and highly stable solar thermochemical energy storage/release by synergistically accelerating energy storage/release via binary sulfate and promoting cycle stability, mechanical strength, and solar absorptance via Al–Mn–Fe oxides. The energy storage density of proposed CaCO3 pellets is still as high as 1455 kJ kg−1 with only a slight decay rate of 4.91% over 100 cycles, which is higher than that of state-of-the-art pellets in the literature, in stark contrast to 69.9% of pure CaCO3 pellets over 35 cycles. Compared with pure CaCO3, the energy storage power density or decomposition rate is improved by 120% due to lower activation energy and promotion of Ca2+ diffusion by binary sulfate. The energy release or carbonation rate rises by 10% because of high O2− transport ability of molten binary sulfate. Benefiting from fast energy storage/release rate and high solar absorptance, thermochemical energy storage efficiency is enhanced by more than 50% under direct solar irradiation. This work paves the way for application of direct solar thermochemical energy storage techniques via achieving fast energy storage/release rate, high energy density, good cyclic stability, and high solar absorptance simultaneously.

Stabilizing agents assisted construction of monometallic self-supporting Palladium NCs with ultrafine nanostructures and rich surface area for highly efficient direct ethanol fuel cell

Design and construct nanoparticles to develop highly efficient electrocatalysts for energy-associated fuel cells remains a significant challenge. High cost, slow reaction kinetics, and poor durability of catalysts are also essential challenges toward the commercialization of DEFCs. Hence, the optimizationof highly structuredPalladium nanocatalysts (Pd-NCs) with suitable nanostructure, rich surface area, and excellent electrochemical performance is a hot area to explore. Herein, we have successfully developed monometallic Pd-NCs with different nanostructures (nonporous, nanoshere, cubes, and unspecified shapes) via altering the varieties of stabilizing agents (PVA, PVP, AA, CTAB, and SOA) for direct ethanol fuel cells (DEFCs) in alkaline medium. The morphological characterization findings indicate that the monometallic Pd-NCs have ultrafine morphologies with small particle size and large surface areas, indicating the role of stabilizing agents in regulating structures. The obtained CTAB-Pd NCs exhibited promising electrocatalytic activity (5429 mAmgPd-1) toward ethanol oxidation in alkaline medium, which is outperforms SF-Pd NCs (917 mAmgPd-1), PVA-Pd NCs (3458 mAmgPd-1), PVP-Pd NCs (3678 mAmgPd-1), AA-Pd NCs (5126 mAmgPd-1), and SOA-Pd NCs (2196 mAmgPd-1). More impressively, the as-prepared CTAB-Pd NCs demonstrated greater EOR durability and a strong ability to remove CO poisoning to accelerate the overall DEFC system. Therefore, our prepared catalysts represents outstanding EOR performance than most of resent reported catalysts, due to their distinct structures and huge ECSA. This work provides more insight into the structure-regulated nanocatalysts, which will contribute to the rational development of highly-efficient Pd-based electrocatalysts for practical application of DEFCs.

In Situ Fabrication of Mn-Doped NiMoO4 Rod-like Arrays as High Performance OER Electrocatalyst

The slow kinetics of the oxygen evolution reaction (OER) is one of the significant reasons limiting the development of electrochemical hydrolysis. Doping metallic elements and building layered structures have been considered effective strategies for improving the electrocatalytic performance of the materials. Herein, we report flower-like nanosheet arrays of Mn-doped-NiMoO4/NF (where NF is nickel foam) on nickel foam by a two-step hydrothermal method and a one-step calcination method. The doping manganese metal ion not only modulated the morphologies of the nickel nanosheet but also altered the electronic structure of the nickel center, which could be the result of superior electrocatalytic performance. The Mn-doped-NiMoO4/NF electrocatalysts obtained at the optimum reaction time and the optimum Mn doping showed excellent OER activity, requiring overpotentials of 236 mV and 309 mV to drive 10 mA cm-2 (62 mV lower than the pure NiMoO4/NF) and 50 mA cm-2 current densities, respectively. Furthermore, the high catalytic activity was maintained after continuous operation at a current density of 10 mA cm-2 of 76 h in 1 M KOH. This work provides a new method to construct a high-efficiency, low-cost, stable transition metal electrocatalyst for OER electrocatalysts by using a heteroatom doping strategy.

Mechanistically Novel Frontal‐Inspired In Situ Photopolymerization: An Efficient Electrode|Electrolyte Interface Engineering Method for High Energy Lithium Metal Polymer Batteries

The solvent‐free in situ polymerization technique has the potential to tailor‐make conformal interfaces that are essential for developing durable and safe lithium metal polymer batteries (LMPBs). Hence, much attention has been given to the eco‐friendly and rapid ultraviolet (UV)‐induced in situ photopolymerization process to prepare solid‐state polymer electrolytes. In this respect, an innovative method is proposed here to overcome the challenges of UV‐induced photopolymerization (UV‐curing) in the zones where UV‐light cannot penetrate, especially in LMPBs where thick electrodes are used. The proposed frontal‐inspired photopolymerization (FIPP) process is a diverged frontal‐based technique that uses two classes (dual) of initiators to improve the slow reaction kinetics of allyl‐based monomers/oligomers by at least 50% compared with the conventional UV‐curing process. The possible reaction mechanism occurring in FIPP is demonstrated using density functional theory calculations and spectroscopic investigations. Indeed, the initiation mechanism identified for the FIPP relies on a photochemical pathway rather than an exothermic propagating front forms during the UV‐irradiation step as the case with the classical frontal photopolymerization technique. Besides, the FIPP‐based in situ cell fabrication using dual initiators is advantageous over both the sandwich cell assembly and conventional in situ photopolymerization in overcoming the limitations of mass transport and active material utilization in high energy and high power LMPBs that use thick electrodes. Furthermore, the LMPB cells fabricated using the in situ‐FIPP process with high mass loading LiFePO4 electrodes (5.2 mg cm‐2) demonstrate higher rate capability, and a 50% increase in specific capacity against a sandwich cell encouraging the use of this innovative process in large‐scale solid‐state battery production.

A p‐n WO3/SnSe2 Heterojunction for Efficient Photo‐assisted Electrocatalysis of the Oxygen Evolution Reaction

Water splitting is important to the conversion and storage of renewable energy, but slow kinetics of the oxygen evolution reaction (OER) greatly limits its utility. Here, under visible light illumination, the p‐n WO3/SnSe2 (WS) heterojunction significantly activates OER catalysis of CoFe‐layered double hydroxide (CF)/carbon nanotubes (CNTs). Specifically, the catalyst achieves an overpotential of 224 mV at 10 mA cm−2 and a small Tafel slope of 47 mV dec−1, superior to RuO2 and most previously reported transition metal‐based OER catalysts. The p‐n WS heterojunction shows strong light absorption to produce photogenerated carriers. The photogenerated holes are trapped by CF to suppresses the charge recombination and facilitate charge transfer, which accelerates OER kinetics and boost the activity for the OER. This work highlights the possibility of using heterojunctions to activate OER catalysis and advances the design of energy‐efficient catalysts for water oxidation systems using solar energy.

Understanding the influence of strain-modified oxygen vacancies and surface chemistry on the oxygen reduction reaction of epitaxial La0.8Sr0.2CoO3-δ thin films

One of the key challenges in developing high-performance electrochemical energy devices is the slow kinetics of the oxygen reduction reaction (ORR). Implementing epitaxial strain induced by a lattice mismatch between a film and a substrate has shown great potential for enhancing the ORR by increasing the concentration of oxygen vacancies. However, strain also influences the surface chemistry which also impacts the ORR. Here, we show the role of strain in concurrent changes of oxygen vacancies and surface chemistry, which in turn significantly influence the ORR activity by employing epitaxial La0.8Sr0.2Co3-δ (LSC) thin films with three different strain states. Tensile strained LSC films dramatically enhanced ORR activity up to two orders of magnitude compared to compressively strained LSC films. Among the tensile strained films, moderately tensile strained LSC films show the highest ORR activity, which is attributed to both increased concentration of oxygen vacancies and suppressed Sr segregation. Our study provides a new design strategy to enhance the ORR activity by controlling the strain state to tune the Sr segregation, oxygen vacancies, and oxygen surface exchange kinetics.

Polyaniline-Coated Porous Vanadium Nitride Microrods for Enhanced Performance of a Lithium–Sulfur Battery

To solve the slow kinetics of polysulfide conversion reaction in Li-S battery, many transition metal nitrides were developed for sulfur hosts. Herein, novel polyaniline-coated porous vanadium nitride (VN) microrods were synthesized via a calcination, washing and polyaniline-coating process, which served as sulfur host for Li-S battery exhibited high electrochemical performance. The porous VN microrods with high specific surface area provided enough interspace to overcome the volume change of the cathode. The outer layer of polyaniline as a conductive shell enhanced the cathode conductivity, effectively blocked the shuttle effect of polysulfides, thus improving the cycling capacity of Li-S battery. The cathode exhibited an initial capacity of 1007 mAh g-1 at 0.5 A g-1, and the reversible capacity remained at 735 mAh g-1 over 150 cycles.

Bifunctional carbon nanofibrous interlayer embedded with cobalt single atoms for polysulfides trapping and catalysis in lithium-sulfur batteries

Lithium-sulfur (Li-S) batteries are in the spotlight as one of the most promising energy storage systems, specifically suitable for electric vehicles and intelligent electronic devices. However, Li-S batteries still suffer from the shuttle effect of intermediate polysulfides, inducing the loss of active materials and slow redox reaction kinetics. Herein, a freestanding functional nanofibrous membrane with cobalt single atoms supported by porous carbon nanofiber skeletons is fabricated using a one-step carbonization process. The flexible nanofiber structure can provide the characteristics of good conductivity and lightweight, helping the polysulfides trapped in the porous structure of the fibrous skeleton. Moreover, the results of electrocatalytic characterization and theoretical calculation demonstrate the existence of the metal coordinate center Co-Nx sites, and their functions of reducing polarization voltage and accelerating polysulfide conversion. Using this functional nanofiber membrane as an interlayer with the Co-Nx coordination structure (Co@N-PCNFs), the assembled Li-S batteries exhibit a high initial specific capacity (1522 mAh·g−1 at 0.1C) and outstanding rate performance (905 mAh·g−1 at 2C). Especially, the specific capacity of the Li-S batteries can achieve 786 mAh·g−1 at 0.5C with a sulfur loading of 4 mg·cm−2 after 100 cycles. This effective method of fabricating nanofibrous interlayers can effectively promote the development of advanced Li-S batteries and the application of electrospun materials in energy storage fields.

Boosting polysulfide confinement and redox kinetics via ZnSe/NC@rGO as separator modifier for high-performance lithium-sulfur batteries

Although lithium-sulfur (Li-S) batteries have an unparalleled specific capacity, the notorious shuttle effect, and slow reaction kinetics severely inhibit their development. Herein, a composite composed of ZnSe nanoparticles with a nitrogen-doped (N-doped) carbon shell uniformly dispersed in reduced graphene oxide (ZnSe/NC@rGO) is designed as a separator modifier for Li-S batteries. The underlying mechanism of the ZnSe/NC@rGO modified separator is confirmed by both systemic electrochemical characterization and density functional theory (DFT) calculations. Graphene as a highly conductive skeleton promotes electrical conductivity, while N-doping provides additional adsorption sites for the immobilization of lithium polysulfides (LiPSs). Moreover, the polar ZnSe has good chemical adsorption capabilities for LiPSs and could lower the decomposition energy barrier of Li2S, which effectively facilitates the catalytic conversion of polysulfides. In addition, the separator modifier is beneficial to the uniform deposition of lithium. Thus, the delicate catalyst can effectively suppress the shuttle effect and accelerate the redox reaction kinetics during the charging and discharging processes. When used as a separator modifier of Li-S batteries, ZnSe/NC@rGO delivers enhanced electrochemical performance, including a high capacity (1057 mAh g–1 at 0.2 C after 100 cycles) and excellent rate performance of 685 mAh g–1 at 3 C. The negligible capacity decay per cycle within 900 cycles at 1 C is as low as 0.043%. These findings not only provide a feasible method for boosting the electrochemical performance of Li-S batteries but also reveal that transition metal selenides have potential in energy storage as electrocatalysts.

Transformation of Graphitic Carbon Nitride by Reactive Chlorine Species: "Weak" Oxidants Are the Main Players.

Graphitic carbon nitride (g-C3N4) nanomaterials hold great promise in diverse applications; however, their stability in engineering systems and transformation in nature are largely underexplored. We evaluated the stability, aging, and environmental impact of g-C3N4 nanosheets under the attack of free chlorine and reactive chlorine species (RCS), a widely used oxidant/disinfectant and a class of ubiquitous radical species, respectively. g-C3N4 nanosheets were slowly oxidized by free chlorine even at a high concentration of 200-1200 mg L-1, but they decomposed rapidly when ClO· and/or Cl2•- were the key oxidants. Though Cl2•- and ClO· are considered weaker oxidants in previous studies due to their lower reduction potentials and slower reaction kinetics than ·OH and Cl·, our study highlighted that their electrophilic attack efficacy on g-C3N4 nanosheets was on par with ·OH and much higher than Cl·. A trace level of covalently bonded Cl (0.28-0.55 at%) was introduced to g-C3N4 nanosheets after free chlorine and RCS oxidation. Our study elucidates the environmental fate and transformation of g-C3N4 nanosheets, particularly under the oxidation of chlorine-containing species, and it also provides guidelines for designing reactive, robust, and safe nanomaterials for engineering applications.

Multiple Effects of High Surface Area Hollow Nanospheres Assembled by Nickel Cobaltate Nanosheets on Soluble Lithium Polysulfides

Inhibiting the shuttle effect of soluble polysulfides and improving slow reaction kinetics are key factors for the future development of Li-S batteries. Herein, edelweiss shaped NiCo2O4 hollow nanospheres with a high surface area were prepared by a simple template method to modify the separator to realize multiple physical constraints and strong chemical anchoring on the polysulfides. On one hand, the good electrolyte wettability of NiCo2O4 promoted the migration of Li-ions and greatly improved the dynamics. On the other hand, mesoporous NiCo2O4 nanomaterials provided many strong chemical binding sites for loading sulfur species. The hollow structure also provided a physical barrier to mitigate the sulfur species diffusion. Therefore, the modified separator realized multiple physical constraints and strong chemical anchoring on sulfur species. As a result, the sulfur cathode based on this composite separator showed significantly enhanced electrochemical performance. Even at 4 C, a high capacity of 505 mAh g-1 was obtained, and about 80.6% could be retained after 300 cycles.