Sulfur Trap Research Articles

Metal-organic-framework derived NiS2/C hollow structures for enhanced polysulfide redox kinetics in lithium-sulfur batteries.

To cope with the shuttling of soluble lithium polysulfides in lithium-sulfur batteries, confinement tactics, such as trapping of sulfur within porous carbon structures, have been extensively studied. Although performance has improved a bit, the slow polysulfide conversion inducing fast capacity decay remains a big challenge. Herein, a NiS2/carbon (NiS2/C) composite with NiS2 nanoparticles embedded in a thin layer of carbon over the surface of micro-sized hollow structures has been prepared from Ni-metal-organic frameworks. These unique structures can physically entrap sulfur species and also influence their redox conversion kinetics. By improving the reaction kinetics of polysulfides, the NiS2/carbon@sulfur (NiS2/C@S) composite cathode with a suppressed shuttle effect shows a high columbic efficiency and decent rate performance. An initial capacity of 900 mAh g-1 at the rate of 1 C (1 C = 1675 mA g-1) and a low-capacity decline rate of 0.132% per cycle after 500 cycles are obtained, suggesting that this work provides a rational design of a sulfur cathode.

The thermal instability of hydrogen-substituted graphdiyne and its role in lithium-sulfur batteries.

This study reveals the role of thermal instability in hydrogen-substituted graphdiyne (HsGDY) and its impact on lithium-sulfur (Li-S) battery performance. HsGDY undergoes significant chemical and physical transformations when subjected to thermal heating, both in the presence and absence of sulfur. Our findings suggest that the structural transformation of HsGDY into a graphene-like structure is primarily responsible for enhancing sulfur trapping and reducing the polysulfide shuttle effect, rather than the previously hypothesized alkyne-sulfur chemical interactions.

Design of High Specific Power Solid Oxide Fuel Cells

Fuel-Cell Electric-Vehicle demonstrated by PCI was fueled with military-spec F-24/JP-8 and does not require on-board hydrogen storage. An onboard fuel reformer with integrated sulfur trap was used for processing these fuels. The 10-kW electric generator included a SOFC and balance of plant components. It was hybridized with a rechargeable battery for startup, peak loads, and load following. The power produced was sufficient for vehicle propulsion and export power. Both 28-32 VDC and 110 VAC for charging batteries and supporting external load demands were available onboard. Initial off-road demonstrations were successfully conducted at PCI and customer sites. This prototype unit showed the feasibility of utilizing hydrocarbon fuels with on-board reforming and SOFC stack to generate power suitable for mobile applications while the system weight and start-up time still need to be improved. To reduce the system weight and start-up time, we are separately investigating advanced SOFC’s that show potential to address the known limitations of the state-of-the-art technology. These advanced SOFC’s demonstrated potential for fast start-up and high-power density on the cell level at 750-800°C of operating temperatures. By optimizing the configuration and design, the system performance is expected to be further improved.

Covalent organic framework-based core-shell sulfur cathode design for enhanced polysulfide immobilization and redox kinetics in lithium-sulfur batteries

The industrialization of lithium-sulfur (Li-S) batteries is largely hindered by the low cycle performance stemming from the polysulfide shuttle effect and slow reaction kinetics. In order to address these problems, an advanced design strategy for multifunctional sulfur cathode with core-shell structure is proposed by embedding transition metal-based porous carbon composites derived from metal-organic framework (MOF) within covalent organic framework (COF). The inner carbon/metal core within the composite serves both as sulfur trapping and catalyst for promoting sulfur reaction kinetics. The COF shell, rich in micropores and polar functional groups, further mitigates lithium polysulfide (LiPS) shuttling through its sieving effect. This strategy is demonstrated by fabricating Co-decorated MIL-125-NH2-derived Co/Ti-NC composite coated with a layer of TpPa-1 COF. Based on these advantages, the S/Co/Ti-NC@TpPa cathode delivers an outstanding cycling performance. The battery shows a high initial specific capacity of 1135 mAh g−1 at 0.2 C, and the capacity decay rate is 0.05% per cycle at 1 C after 500 cycles. The area capacity of the cell reaches 3.6 mAh cm−2 at a high sulfur loading of 4.46 mg cm−2. The MOF in COF core-shell design provides a promising strategy for developing practical sulfur cathode.

A COF-coated MOF framework polysulfide barrier design for enhanced performance in lithium-sulfur batteries

The shuttle effect of lithium polysulfide (LiPS) and slow sulfur reaction kinetics is a key problem hindering the application of lithium-sulfur (Li-S) batteries. To address these problems, herein, a novel multifunctional sulfur cathode design strategy of coating microsporous covalent organic framework (COF) onto metal organic framework (MOF)-derived carbon/transition metal composite is developed. This strategy is proofed by coating a TpPa-1 COFs layer on the UIO-66-NH2-derived N-doped Co/Zr-NC, forming core-shell structured Co/Zr-NC@TpPa composite. The Co/Zr-NC core consists of Co nanoparticles and ZrO2 that offers effective sulfur trapping and catalysis effect for sulfur redox reaction, whereas the microsporous COF shell with polar functional groups further reduces the shuttling of LiPS. The S/Co/Zr-NC@TpPa cathode achieves an initial capacity of 792 mAh g−l at 1 C with 76.4% capacity retention after 500 cycles. More importantly, under the high sulfur loading of 5.10 mg cm−2, it has a high specific surface area capacity of 4.15 mAh cm−2 at 0.2 C. This study provides a promising alternative design strategy for the development of efficient sulfur host in Li-S batteries.

Development of an online sulfur trapping system for graphitization of cremated bones with automated graphitization system AGE-3

The graphitization of cremated bones by an online Carbonate Handling System (CHS) coupled to Automated Graphitization Equipment (AGE-3) can be complicated due to the presence of impurities in the samples. An online sulfur trap was created for the purification of CO2 during graphitization of cremated bones with the CHS-AGE-3 system for radiocarbon measurements with an accelerator mass spectrometer. High graphitization efficiency was obtained starting from 100 °C and further increase of temperature to 600 °C resulted in graphitization yield improvement of 4–6%. Based on graphitization yield and 14C analyses, our proposed CO2 purification line was successful in removing sulfur impurities and did not contaminate samples due to the continuous flushing of the trap with helium. The expected chronology of most burials was the 5th–6th centuries AD, referring to the grave goods. Sometimes, the radiocarbon dating confirmed that of archaeological typology, while some radiocarbon dates proved older or younger than presumed.

Performance and Regeneration of Methane Oxidation Catalyst for LNG Ships

Liquefied natural gas (LNG) use as marine fuel is increasing. Switching diesel to LNG in ships significantly reduces air pollutants but the methane slip from gas engines can in the worst case outweigh the CO2 decrease with an unintended effect on climate. In this study, a methane oxidation catalyst (MOC) is investigated with engine experiments in lean-burn conditions. Since the highly efficient catalyst needed to oxidize methane is very sensitive to sulfur poisoning a regeneration using stoichiometric conditions was studied to reactivate the catalyst. In addition, the effect of a special sulfur trap to protect the MOC and ensure long-term performance for methane oxidation was studied. MOC was found to decrease the methane emission up to 70–80% at the exhaust temperature of 550 degrees. This efficiency decreased within time, but the regeneration done once a day was found to recover the efficiency. Moreover, the sulfur trap studied with MOC was shown to protect the MOC against sulfur poisoning to some extent. These results give indication of the possible use of MOC in LNG ships to control methane slip emissions.

Hierarchically porous, ultrathin N–doped carbon nanosheets embedded with highly dispersed cobalt nanoparticles as efficient sulfur host for stable lithium–sulfur batteries

The sluggish redox kinetics and shuttle effect of soluble polysulfides intermediate primarily restrict the electrochemical performance of lithium–sulfur (Li–S) batteries. To address this issue, rational design of high–efficiency sulfur host is increasingly demanded to accelerate the polysulfides conversion during charge/discharge process. Herein, we propose a macro–mesoporous sulfur host ([email protected]), which comprises highly dispersed cobalt nanoparticles embedding in N–doped ultrathin carbon nanosheets. [email protected] is simply synthesized via a carbon nitride–derived pyrolysis approach. Owing to the highly conductive graphene–like matrix and well defined porous structure, the designed multifunctional [email protected] host enables rapid electron/ion transport, electrolyte penetration and effective sulfur trapping. More significantly, N heteroatoms and homogeneous Co nanocatalysts in the graphitic carbon nanosheets could serve as chemisorption sites as well as electrocatalytic centers for sulfur species. These Co–N active sites can synergistically facilitate the redox conversion kinetics and mitigate the shuttling of polysulfides, thus leading to improved electrochemical cycling performance of Li–S batteries. As a consequence, the S/[email protected] cathode demonstrates high initial specific capacity (1505 mA h g−1 at 0.1 C) and excellent cycling stability at 1 C over 300 cycles, giving rise to a capacity retention of 91.7% and an average capacity decline of 0.03% cycle−1.

CO2 Methanation in Microstructured Reactors – Catalyst Development and Process Design

AbstractThe sulfur tolerance of mono‐ and bimetallic ruthenium catalysts for CO2 hydrogenation was investigated in microchannel reactors. H2S was selected as a model compound. It was found that a Ru/CeO2 catalyst deactivates rapidly. Ni was a much better additive to improve the catalyst stability compared to Rh and serves as a sulfur trap. The influence of the support was evaluated showing that a SiO2‐supported catalyst has a higher stability and better selectivity compared to CeO2 and TiO2. A plant concept was developed comprising two‐step methanation with a first adiabatic reactor stage followed by a plate heat‐exchanger reactor with integrated cooling which allows more than 97 % CO2 conversion. A pilot plant will be put into operation in connection with a biogas plant and an electrolyser of 50 kW power consumption.

In situ and downstream sulfidation reactivity of PbO and ZnO during pyrolysis and hydrogenation of a high–sulfur lignite

Economical valorization of low quality, high sulfur feedstocks is an important challenge. Most of the valorization processes start from pyrolysis, with a significant amount of evolution of sulfur containing compounds. This study addresses in situ and downstream sulfur capture ability of lead oxide (PbO) in comparison to zinc oxide (ZnO) during the pyrolysis of high–sulfur Tuncbilek lignite. In order to assess the role of hydrogen in sulfur capture, hydrogenation experiments were also performed. Sulfidation reaction thermodynamics of PbO and ZnO was compared to most commonly used metal oxides for sulfur capture i.e., FeO, MnO, and CaO. The equilibrium conversions indicated superior performance of PbO and ZnO towards sulfidation reactions at high temperatures. Thermodynamic superiority of PbO sulfidation encouraged us to investigate the PbO as a new sulfur sorbent for hot gas desulfurization. The experimental verification of the high temperature sulfidation ability of PbO and ZnO was performed using high–sulfur Tuncbilek lignite under semibatch conditions. The final compounds formed after each process were observed by X-ray diffractometer (XRD) and Diffuse Reflectance Infrared Fourier Transformation Spectroscopy (DRIFTS). Experiments revealed that PbO can be promising candidate as hot gas sulfur trap during pyrolysis and hydrogenation processes, while ZnO can hold up sulfur only in the presence of hydrogen. Furthermore, both PbO and ZnO show the superior sulfur capture performance in the presence of hydrogen when they were used as adsorbents located after the reactor (downstream) at ambient conditions.

A polypyrrole hollow nanosphere with ultra-thin wrinkled shell: Synergistic trapping of sulfur in Lithium-Sulfur batteries with excellent elasticity and buffer capability

To suppress the shuttle effect, reduce the capacity fade, and improve coulombic efficiency of Lithium-Sulfur (Li-S) battery, a polypyrrole hollow nanosphere (PHNS) with an ultra-thin wrinkled shell, which is expected to synergistically trap sulfur (S) with excellent elasticity and buffer capability, is fabricated by an in situ polymerization method. When S is encapsulated in PHNS (S@PHNS) with an optimum shell structure and used as the cathode, surprisingly, a specific capacity as high as 1500.5 mA h·g-1 in the first discharge at a current rate of 0.1 C with high coulombic efficiency as well as excellent rate performance is achieved. Also, a reversible capacity as high as 536.5 mA h·g-1 is obtained even at a high current rate of 5 C. Such a PHNS with the ultra-thin wrinkled shell has good conductivity, short ion and electron transport channel, and fast kinetics characteristics and especially during the charge-discharge cycles, it is conducive to the access of electrolyte and effective accommodation of the volume change. This PHNS should be a promising alternative cathode material for lithium-Sulfur batteries.

Oxidation of a [Cu2S] complex by N2O and CO2: insights into a role of tetranuclearity in the CuZ site of nitrous oxide reductase.

Oxidation of a [Cu2(μ-S)] complex by N2O or CO2 generated a [Cu2(μ-SO4)] product. In the presence of a sulfur trap, a [Cu2(μ-O)] species also formed from N2O. A [Cu2(μ-CS3)] species derived from CS2 modeled initial reaction intermediates. These observations indicate that one role of tetranuclearity in the CuZ catalytic site of nitrous oxide reductase is to protect the crucial S2- ligand from oxidation.

Confined Sulfur in 3 D MXene/Reduced Graphene Oxide Hybrid Nanosheets for Lithium-Sulfur Battery.

Three-dimensional metal carbide MXene/reduced graphene oxide hybrid nanosheets are prepared and applied as a cathode host material for lithium-sulfur batteries. The composite cathodes are obtained through a facile and effective two-step liquid-phase impregnation method. Owing to the unique 3 D layer structure and functional 2 D surfaces of MXene and reduced graphene oxide nanosheets for effective trapping of sulfur and lithium polysulfides, the MXene/reduced graphene oxide/sulfur composite cathodes deliver a high initial capacity of 1144.2 mAh g-1 at 0.5 C and a high level of capacity retention of 878.4 mAh g-1 after 300 cycles. It is demonstrated that hybrid metal carbide MXene/reduced graphene oxide nanosheets could be a promising cathode host material for lithium-sulfur batteries.

Mechanical reinforcement in magadiite/styrene‐butadiene rubber composites

ABSTRACTThis work investigates mechanical properties of styrene‐butadiene rubber (SBR) composites incorporating magadiite (MGD), a synthetic layered silicate (Na2Si14O29·9H2O) with surface chemistry similar to precipitated silica used in tire tread formulations. Treatment with cetyltrimethylammonium (CTA+) expands the MGD layers and makes the interlayer face surfaces accessible to sulfur‐functional silane TESPT (Si69) and SBR, primarily during batch mixing. DMA and tensile testing of cured CMGD/SBR composites show that CTA‐treated MGD (CMGD) provides substantially higher levels of mechanical reinforcement than equivalent amounts of silica. However, CMGD/SBR composites exhibit larger loss tangent values above Tg, probably due to lower SBR‐SBR crosslink density resulting from interlayer trapping of sulfur released by Si69 during vulcanization. DMA and tensile testing also demonstrate Si69′s critical role in forming MGD‐SBR graft sites essential to mechanical reinforcement. Replacing silica with CMGD reduces composite weight without sacrificing tensile modulus, suggesting that use of CMGD in tire rubber formulations could improve vehicle energy efficiency. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44763.

Chemical Bonding and Physical Trapping of Sulfur in Mesoporous Magnéli Ti4O7 Microspheres for High‐Performance Li–S Battery

Various host materials have been investigated to address the intrinsic drawbacks of lithium sulfur batteries, such as the low electronic conductivity of sulfur and inevitable decay in capacity during cycling. Besides the widely investigated carbonaceous materials, metal oxides have drawn much attention because they form strong chemical bonds with the soluble lithium polysulfides. Here, mesoporous Magnéli Ti4O7 microspheres are prepared via an in situ carbothermal reduction that exhibit interconnected mesopores (20.4 nm), large pore volume (0.39 cm3 g−1), and high surface area (197.2 m2 g−1). When the sulfur cathode is embedded in a matrix of mesoporous Magnéli Ti4O7 microspheres, it exhibits a superior reversible capacity of 1317.6 mA h g−1 at moderate current (C/10) and a low decay in capacity of 12% after 400 cycles at C/5. Strong chemical bonding of the lithium polysulfides to Ti4O7, as well as effective physical trapping in the mesopores and voids in the matrix are considered responsible for the improved electrochemical performance. A mechanism of the physical and chemical interactions between mesoporous Magnéli Ti4O7 microspheres and sulfur is proposed based on systematic investigations.

Hybrid nanostructured microporous carbon-mesoporous carbon doped titanium dioxide/sulfur composite positive electrode materials for rechargeable lithium-sulfur batteries

Herein, we design hybrid nanostructured microporous carbon-mesoporous carbon doped titanium dioxide/sulfur composite (MC-Meso C-doped TiO2/S) as a positive electrode material for lithium-sulfur batteries. The hybrid MC-Meso C-doped TiO2 host material is produced by a low-cost, hydrothermal and annealing process. The resulting conductive material shows dual microporous and mesoporous behavior which enhances the effective trapping of sulfur and polysulfides. The hybrid MC-Meso C-doped TiO2/S composite material possesses rutile TiO2 nanotube structure with successful carbon doping while sulfur is uniformly distributed in the hybrid MC-Meso C-doped TiO2 composite materials after the melt-infusion process. The electrochemical measurement of the hybrid material also shows improved cycle stability and rate performance with high sulfur loading (61.04%). The material delivers an initial discharge capacity of 802 mAh g−1 and maintains it at 578 mAh g−1 with a columbic efficiency greater than 97.1% after 140 cycles at 0.1 C. This improvement is thought to be attributed to the unique hybrid nanostructure of the MC-Meso C-doped TiO2 host and the good dispersion of sulfur in the narrow pores of the MC spheres and the mesoporous C-doped TiO2 support.

Built‐in Carbon Nanotube Network inside a Biomass‐Derived Hierarchically Porous Carbon to Enhance the Performance of the Sulfur Cathode in a Li‐S Battery

AbstractThe practical application of lithium‐sulfur batteries is usually hindered by the unstable discharge intermediates and the low conductivity of the sulfur cathode. Herein, we propose to improve the performance of the sulfur cathode by introducing a built‐in carbon nanotube network inside a biomass‐derived hierarchically porous carbon for the subsequent sulfur loading. This balanced structural design of the carbon substrate enables effective trapping of active sulfur within the cathode and provides a highly efficient pathway for electron transmission, contributing to an increased conductivity and structural integrity of the cathode. By using a potentiostatic process at the end of charge, the reversibility of the electrode reaction of sulfur is improved. The sulfur cathode delivers an initial discharge capacity of 1739 mA h g−1 and reaches a high initial Columbic efficiency of 87.6 %, and maintains its efficiency to >97.5 % from the 2nd cycle. It also shows admirable cycling and rate performance.

Sulfur encapsulated in a TiO2-anchored hollow carbon nanofiber hybrid nanostructure for lithium-sulfur batteries.

A hollow carbon nanofiber hybrid nanostructure anchored with titanium dioxide (HCNF@TiO2) was prepared as a matrix for effective trapping of sulfur and polysulfides as a cathode material for Li-S batteries. The synthesized composites were characterized and examined by X-ray diffraction, nitrogen adsorption-desorption measurements, field-emission scanning electron microscopy, scanning transmission electron microscopy, and electrochemical methods such as galvanostatic charge/discharge, rate performance, and electrochemical impedance spectroscopy tests. The obtained HCNF@TiO2-S composite showed a clear core-shell structure with TiO2 nanoparticles coating the surface of the HCNF and sulfur homogeneously distributed in the coating layer. The HCNF@TiO2-S composite exhibited much better electrochemical performance than the HCNF-S composite, which delivered an initial discharge capacity of 1040 mA h g(-1) and maintained 650 mAh g(-1) after 200 cycles at a 0.5 C rate. The improvements of electrochemical performances might be attributed to the unique hybrid nanostructure of HCNF@TiO2 and good dispersion of sulfur in the HCNF@TiO2-S composite.

Micro-nano structure composite cathode material with high sulfur loading for advanced lithium–sulfur batteries

ABSTRACT A micro-nano structure based on polydopamine-grafted hollow carbon nanofiber–sulfur composite (HCNF@PDA–S) is designed as a cathode material for effective trapping of sulfur and polysulfides for lithium–sulfur batteries. Hollow carbon nanofiber@polydopamine (HCNF@PDA) micro-nano structure hybrid is first prepared by an in-situ polymerization dopamine monomer decorating on the surface of HCNFs and then elemental sulfur is infiltrated into the HCNF@PDA hybrid nanostructure by thermal treatment. The obtained HCNF@PDA–S composite shows the micro-nano structure based on the micron-sized hollow carbon nanofiber in length and nano-sized polydopamine grafted on the outer surfaces of the HCNFs with homogeneously distribution of sulfur. Compared with the HCNF–S composite, HCNF@PDA–S composite with a high sulfur content of approximately 80 wt% exhibits better electrochemical performance, which delivers initial discharge capacity of 800 mAh g−1 and maintains 530 mAh g−1 after 200 cycles at 0.5 C rate. The enhancements of electrochemical performances may be attributed to the unique micro-nano hybrid structure based on HCNFs and PDA coating layer, in which the micro-sized HCNFs offer the electronic conductivity and provide a firm porous network of the cathode tolerating the volume expansion of sulfur cathode, and nano-sized PDA layers effectively prevent the dissolution of the polysulfides into the electrolyte.

Hollow fiber membranes with polyimide matrix for sulfur-free hydrogen source

Sulfur-free hydrogen production is significant for sustainable energy such as fuel cell to avoid poisoning catalysts. The hollow fiber membrane is proposed as sulfur trapper for the hydrocarbon fuels. Hollow fiber membranes with polyimide (PI) matrix and adsorptive zeolites fillers are fabricated by dry–wet spinning with subsequent imidization process. By detailed investigation of FT-IR, thermal degradation cures, morphology and sulfur trapping performance, the molecular structure, thermostability and adsorption channels of membranes have been analyzed. The hollow fiber membranes have abundant pores, and the zeolites particles are incorporated in the three-dimension polymer matrix. The inlet fuel can be desulfurized to below 0.1 mg L−1, which means that the outlet fuel can be used as sulfur-free hydrogen source for fuel cell applications. Excellent sustainability of the system with hollow fiber configuration show attractive on-board application potential.