Waste to Wealth: Exhausted Nitrogen-doped Mesoporous Carbon

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Energy, Environmental, and Catalysis Applications

Waste to Wealth: Exhausted Nitrogen-doped Mesoporous Carbon/MgO Desulfurizers Turned to High-sulfurloading Composite Cathodes for Li-S Batteries Guoyu Ding, Yahui Li, Ying Zhang, Chunming Huang, Xurui Yao, Kaixi Lin, Kelin Shen, Wei Yan, Fugen Sun, and Lang Zhou ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.9b02844 • Publication Date (Web): 10 May 2019 Downloaded from http://pubs.acs.org on May 11, 2019

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ACS Applied Materials & Interfaces

Waste

to

Wealth:

Exhausted

Nitrogen-doped

Mesoporous Carbon/MgO Desulfurizers Turned to High-sulfur-loading Composite Cathodes for Li-S Batteries Guoyu Ding, Yahui Li, Ying Zhang, Chunming Huang, Xurui Yao, Kaixi Lin, Kelin Shen, Wei Yan, Fugen Sun* and Lang Zhou

Institute of Photovoltaics, Nanchang University, 999 Qianhu Road, Nanchang 330031, China * Corresponding author. E-mail: [email protected]

KEYWORDS: lithium-sulfur battery, high sulfur loading, mesoporous carbon, sulfur/carbon composites, H2S removal

ABSTRACT: We demonstrate a sustainable and cost-effective route to fabricate high-sulfurloading cathode materials with the cooperative interfaces of “sulfiphilic” and “lithiophilic” sites from the removal industry of the pollutant H2S gas. The MgO-impregnated and nitrogen-doped mesoporous carbon composite desulfurizers (NMC/MgO), acting as effective catalysts and large

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storehouses, could catalytically oxidize H2S into elemental S with high catalytic selectivity and sulfur capacity. The obtained by-product NMC/MgO/S-CO composites possess high sulfur loading (73.8 wt.%) and significant structure advantages for practical application in Li-S batteries. Firstly, the uniform distribution of S in the NMC/MgO frameworks via the in situ catalytic oxidation approach, could offer large interface area for charge transport and Li+ reaction. Then, the cooperative effects of the “sulfiphilic” MgO nanoparticles and the “lithiophilic” nitrogen dopants in the NMC/MgO, could effectively suppress the polysulfide shuttling. Under the further assistance of physical confinement of the mesoporous NMC/MgO, the NMC/MgO/S-CO composites present excellent electrochemical performances with a high reversible capacity of 772 mAh g-1 and a Coulombic efficiency of 93.6% at the 100th cycle at 0.2 C. These encouraging results not only develop a sustainable way to turn waste into wealth, but also provide a promising strategy to product high-sulfur-loading cathode materials with uniform distribution of S through the in-situ catalytic strategy for high-performance Li-S batteries.

INTRODUCTION Efficient energy storage in a sustainable and eco-friendly way has become a great challenge for a large range of practical applications.1-6 The lithium-sulfur battery has been considered to be one of the most promising energy storage systems, owing to their unparalleled theoretical energy density and environmental benignancy.7-9 Nevertheless, the commercial application of Li-S batteries is hindered by several issues, mainly including poor conductivity of both S and the discharge end product Li2S, and dissolution of high-order lithium polysulfides (Li2Sx, 4 ≤ x ≤ 8) in the electrolytes.10-12 To date, exciting progress has been made through combining elemental S with carbon materials, such as carbon nanotubes,13 graphene14 and porous carbons15 via the melt


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diffusion or wet impregnation methods. In this way, the sulfur is constrained within the channels of conductive carbon frameworks through the capillary force and acquires fast electron transfer. At the same time, the physical adsorption effect of the porous carbons and the kinetic suppression abilities towards diffusion in their channels are favorable to entrap the Li2Sx.16,17 However, only carbon hosts fail to settle the poor cyclic issue of the Li-S batteries, owing to that the weak interactions of the non-polar carbons with the ionic polysulfides greatly limit their confining ability towards these soluble polysulfides. From this aspect, the hybrid of the conductive carbon with the polar metal compounds, should act as a very promising host for resolving the dissolution problem of Li2Sx in Li-S batteries.18,19 Our previous research has discovered that ultrafine La2O3 decorated into the mesoporous carbon hosts could greatly improve the voltage output and cycling stability.20 Analogously, other metal compounds such as MnO2,21 Ni2O5,22 MoS2,23 and VN,24 have been integrated with porous carbons to act as multifunctional hosts for enhancing the electrochemical performances of Li-S batteries. The strong chemical binding between the polysulfides and these polar metal compounds, working together with the physical adsorption effects of porous carbons, synergistically suppress the polysulfides shuttling.25-27 All of these encouraging results reveal that the realm of the high-performance sulfur cathodes has been significantly expanded, benefiting from the delicate integration of the conductive carbons, polar metal compounds and active sulfur.28-30 However, how to explore stronger encapsulation hosts and to make more costeffective and uniform sulfur cathodes to enable Li-S batteries for future practical applications, is still a very meaningful and challenging work. Hydrogen sulfide (H2S), as one of the most common sulfur-containing compound, is an extremely corrosive and toxic pollutant gas, which is emitted from several industrial processes,


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such as coal gasifiers, petrochemical plants and natural gas processing.31,32 Among the established technologies for H2S removal, the use of a solid catalyst to directly oxidize H2S into elemental S is one of the best methods for the diluted H2S-containing air streams, due to its low cost, green and high efficiency.33,34 This technology thus has been widely used, which also means that an abundant of exhausted desulfurizers will be discarded. Therefore, it is imperative that H2S should be removed and sulfur should be reused since Li-S batteries require a large amount of sulfur. Indeed, our previous work has found that the nitrogen-doped mesoporous carbons can catalytically oxidize H2S to fabricate the S/C composite (S content: 59.1 wt.%) as a by-product which is available for Li-S batteries.35 Subsequently, Zhang et. al.36 also recovered S in H2S by a redox reaction between H2S and graphene oxide to obtain graphene/S composites (S content: ~ 40 wt.%) for use in Li-S batteries. However, although these obtained S/C by-products from H2S removal have presented high reversible capacity, the improvement on cycle stability is still limited probably due to the above-mentioned poor polar nature of carbon materials. Additionally, the low sulfur loading of these S/C composites greatly offsets their advantage in high energy density of Li-S batteries, which could not have any significant value for applications. Herein, based on the concept of “waste to wealth”, we demonstrate a sustainable and costeffective route for producing high-sulfur-loading cathode materials from H2S removal via the catalytic oxidation of H2S over MgO-impregnated and nitrogen-doped mesoporous carbon composite desulfurizers (NMC/MgO). Besides the doped nitrogen in the NMCs, the impregnated MgO could further improve the catalytic performance of the NMCs which catalytically oxidize H2S into S through the reaction H2S + 1/2O2 → S + H2O. Resultantly, unprecedented sulfur capacity has been obtained for the NMC/MgO, which not only makes them on the edge of being


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employed in H2S removal for industrial application, but also enables their by-product NMC/MgO/S-CO composites (The notation CO indicates the catalytic oxidation approach) into high-sulfur-loading cathode materials (S content: 73.8 wt.%) for Li-S batteries. And moreover, the intrinsic structural benefits of the NMC/MgO/S-CO are also favorable for boosting the electrochemical performances of sulfur cathodes. Firstly, the uniform dispersion of sulfur in the NMC/MgO frameworks via the in situ catalytic oxidation approach, which is hard to achieved using other methods, provide high interface area for electron transfer and Li+ reaction. Then, the strong chemical interaction of the hydrophilic MgO with the ionic Li2Sx effectively suppress the polysulfide shuttling. Furthermore, with the further assistance of physical confinement of the mesoporous NMC/MgO, the NMC/MgO/S-CO composites present excellent capacity retention after long-time cycling.

EXPERIMENTAL SECTION Synthesis of nitrogen-doped mesoporous carbon/MgO nanocomposites The nitrogen-doped mesoporous carbons (NMCs) were synthesized based on a conventional colloidal silica nanocasting method, employing phenol, formaldehyde and melamine as carbon precursors and commercial silica sol as templates, as reported in our pervious work.37 The nitrogen-doped mesoporous carbon/MgO (NMC/MgO) nanocomposites were synthesized via a simple wetness impregnation approach. Typically, 0.6 g NMCs were added into 10 mL Mg(NO3)2 aqueous solution (0.4 g Mg(NO3)2) and then dispersed with ultrasound. The mixtures were heated at 60 oC with continuous stirring, and then dried at 100 oC, finally calcinated under N2 at 400 oC for 3 h. Synthesis of NMC/MgO/S-CO nanocomposites The NMC/MgO/S-CO nanocomposites were synthesized through the catalytic oxidation of H2S


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over the NMC/MgO, similar with that employed in our previous works.31,33 The catalytic oxidation reaction was performed in a fixed-bed reactor at room temperature under atmospheric pressure. The simulated mixtures of H2S, N2 and O2 (Flow rate: 150 mL min-1) sequentially pass through the humidifier and the column of NMC/MgO. The NMC/MgO/S-CO composites were obtained after catalytic oxidation reaction of H2S for 5 days and subsequently drying under vacuum at 60 oC for 1 day. In addition, the NMC/MgO/S-MI samples were synthesized via the conventional melt-diffusion method for comparison.37 Material characterization The surface chemistry of the NMCs and NMC/MgO/S-CO were determined by the X-ray photoelectron spectroscopy (Axis-Ultra DLD). The Shirley-type backgrounds and mixed Lorentzian-Gaussian curves were employed to fit the XPS signals. The transmission electron microscopy (TEM, JEOL 2100F) and scanning electron microscopy (SEM, JEOL 7100F) observation were conducted to investigate the morphology of the NMCs, NMC/MgO, NMC/MgO/S-MI and NMC/MgO/S-CO. The scanning electron microscopy (SEM, FEI Q-300) was used for the elemental mapping of the NMC/MgO/S-CO. The Rigaku D/max 2550 diffractometer was employed to record the X-ray diffraction (XRD) pattern of the NMCs, NMC/MgO, NMC/MgO/S-MI and NMC/MgO/S-CO. The thermogravimetric analysis of the NMCs, NMC/MgO, NMC/MgO/S-MI and NMC/MgO/S-CO were performed on a TA Instrument Q600 analyzer (Heating rate: 10 °C min−1). The Quadrasorb SI analyser was employed to measure the N2 adsorption/desorption isotherms of the NMCs, NMC/MgO, NMC/MgO/S-MI and NMC/MgO/S-CO at 77 K. The Barrett-Joyner-Halenda (BJH) model was used to calculate the pore size distributions from the desorption branch. The specific surface area was calculated based on the Brunauer-Emmett-Teller (BET) method.


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Electrochemical tests The sulfur composite cathodes were prepared through the slurry-casting method on an aluminium current collector. In a typical procedure, the NMC/MgO/S-CO, super-P carbon and PVDF binder with the mass ratio of 80:10:10 were added into the NMP solvent and mixed homogeneously. The obtained slurries were uniformly coated onto the aluminium foils and then dried under

vacuum at 60 oC for 12 h. The CR2032-type coin cells were assembled, using the

NMC/MgO/S-CO cathodes, Celgard 2400 microporous separators and lithium metal anodes. The electrolyte solution consisting of 1M LiTFSI salt in the mixture of DOL and DME (1:1 by volume) was injected into the coin cells. The diameter of the electrodes was 1.4 cm and the areal mass loadings of sulfur range from 2.4 to 2.7 mg cm-2, with the electrolyte volume of around 60 μL. The Arbin battery cycler BT2000 was used to conduct the cyclic voltammetry measurements and charge-discharge tests. The electrochemical working station Gamry PCI4/300 was used to investigate the electrochemical impedance spectroscopy with the frequency range from 0.1 MHz to 0.01 Hz.

RESULTS AND DISCUSSION The nitrogen-doped mesoporous carbon/MgO composite desulfurizers (NMC/MgO) were synthesized via a facile wetness impregnation approach, which is well-known for fabricating the heterogeneous catalyst, as shown in Figure 1a. The NMCs, which were prepared based on a conventional colloidal silica nanocasting method, have a highly developed mesoporous structure (more detailed characterizations of porous structure and surface composition of the NMCs are given in Figure S1-S3). The decoration of 15 wt.% MgO nanoparticles in NMCs (determined by TG result in Figure S4) does not significantly change the morphology of the pristine NMCs. SEM image in Figure 1b shows that the NMC/MgO samples still maintain the similar open


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honeycomb structures with 3D interconnected mesopores as that of the NMCs. The 3D mesoporosity of the NMC/MgO samples could ensure the quick diffusion of reactants during the catalytic oxidation process of H2S, while their high pore volume could offer large room for storing the product S. Furthermore, TEM images in Figure 1c-d reveal that the MgO nanoparticles with the particle size of about 6 nm, are uniformly loaded in the NMCs frameworks. Considering that hydrophilic MgO will offer monolayer chemical sorption, these MgO nanoparticles with the high ratio of surface to volume should be very suitable, not only for catalyzing H2S oxidation in H2S removal, but also for on-site entrapping Li2Sx in Li-S batteries.


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Figure 1. (a) Schematic illustration of the uniform deposition of MgO within the NMCs matrix. (b) SEM, (c) TEM and (d) HRTEM images of the NMC/MgO.

Figure 2. (a) The “waste to wealth” concept that the exhausted NMC/MgO desulfurizers from H2S removal industry into NMC/MgO/S-CO composite cathodes for energy storage. (b) Schematic representation of the catalytic oxidation process of H2S over the NMC/MgO. (c) SEM and (d) elemental mapping images of the NMC/MgO/S-CO. The catalytic oxidation of H2S over the NMC/MgO catalyst was performed in a fixed-bed reactor at room temperature. In general, the catalytic oxidation process of H2S over the caustic catalysts has been widely accepted to follow the vapor-liquid-solid mechanism,38,39 which


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proposes that the humidified H2S is dissociated firstly into HS- ions in the film of adsorbed water in the mesopores of catalysts. The subsequent oxidation of HS- ions by the oxygen radicals (O*) which are preferentially adsorbed on the active sites results in the formation of the elemental S at room temperature. These formed elemental S would be reserved as a condensed phase in the mesopores, leading to the slow deactivation of the catalysts through the continuous occlusion of catalytic active site by the product S. The dissociation of H2S into HS- ions was considered to be the rate determining step.40 Our previous work has reported that the nitrogen functional groups could serve as Lewis basic sites in the NMCs and increase the local basicity of the water film, thus facilitating the formation of HS-.33 On the basis of this, the basic MgO nanoparticles with slight solubility loaded in the NMCs could permanently release the OH- ions and thus promote the dissociation of H2S into HS- for a certain long time, which endow them with improved H2S removal capacity (Figure 2b). Therefore, with the synergetic effects of the well-developed porous carbon structures, the doped nitrogen atoms and the impregnated MgO nanoparticles in the desulfurizer frameworks, the obtained NMC/MgO/S-CO by-product should have high sulfur loading and homogenous dispersion, which is difficult to achieved using other approaches. SEM image of the NMC/MgO/S-CO shows that the NMC/MgO framework is uniformly coated by the product S, and no distinct agglomerations of sulfur are observed on the surface of the NMC/MgO (Figure 2c). Figure 2d displays the SEM elemental mapping of the NMC/MgO/S-CO and reveals that the spatial distribution of C, Mg and S match well, further suggesting the homogenous dispersion of S in the NMC/MgO framework. The uniform NMC/MgO/S-CO composites should promise much improved electrochemical performance, thus enabling the waste product in H2S removal to be used as a high-value cathode material for Li-S batteries, as shown in the concept representation of waste to wealth (Figure 2a).


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Figure 3. (a) XPS survey, high-resolution (c) S2p, (b) N1s and (d) Mg1s spectras of the NMC/MgO/S-CO. The chemical natures of the NMC/MgO/S-CO composites were further studied through XPS analysis. In the XPS survey scans, only C, N, O, Mg and S peaks are observed, which excludes the existence of other impurities in the NMC/MgO/S-CO (Figure 3a). The high resolution S2p XPS spectra in Figure 3b reveals the S in the NMC/MgO/S-CO exists as the dominated form of elemental S (S2p1/2 and S2p3/2, BE=165.4 and 164.2 eV). The presence of a little amount of sulfate by-products (BE=169.7 eV) should be due to the weak side-reactions involving the deep oxidation of H2S to SO3, further confirming the high catalytic selectivity toward sulfur over the NMC/MgO catalyst. The high resolution N1s XPS spectra (Figure 3c) shows that the N-bonding configuration of NMC/MgO/S-CO can be divided into the graphitic N, pyrrolic N and pyridinic


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N (BE=401.6, 400.5 and 398.5 eV, respectively), which is very similar with that of the pristine NMCs (Figure S3). Furthermore, the high resolution Mg1s XPS spectra (Figure 3d) suggests that the MgO nanoparticles still exist in the exhausted NMC/MgO after catalytic oxidation reaction, accompanying with a little amount of Mg(OH)2 and MgSO3 which should be due to the slight dissolution and neutralization of basic MgO with acid SO3 during the catalytic oxidation reaction. It has been reported that N dopants in carbons could chemically bind Li2Sx through Li-N bonds, exhibiting a “lithiophilic” affinity;41 and the exposed Mg metal sites in MgO could chemically bind to terminal S atoms via Mg-S bonds, illustrating a “sulfiphilic” affinity.42 Therefore, the coexistence of N dopants and MgO nanoparticles in the NMC/MgO/S-CO should enable them have a cooperative interface with both desirable “lithiophilicity” and “sulfiphilicity”, which provide bifunctional chemical binding toward terminal Li and S (Figure S5) and thus enhance the retention of polysulfides for Li-S batteries.

Figure 4. (a) TGA and DTG curves of the NMC/MgO/S-CO. (b) XRD patterns, (c) N2


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adsorption-desorption isotherms and (d) BJH pore size distributions of the NMCs, NMC/MgO and NMC/MgO/S-CO.

The high sulfur loading in the NMC/MgO/S-CO is further evidenced by TGA in N2 flow. The NMC/MgO/S-CO sample exhibits a large weight loss of 73.8 wt.% between 150 and 500 °C (Figure 4a), attributed to the heat evaporation of the elemental S in the NMC/MgO/S-CO. The sulfur loading of the NMC/MgO/S-CO composite is much higher than that of our previously reported NMC/S-CO composite which are obtained from catalytic oxidation of H2S over the NMCs desulfurizer without MgO loading (S content in the NMC/S-CO: 59.1 wt.%)35, further confirming better catalytic performance of the NMC/MgO desulfurizer. XRD patterns in Figure 4b display that the XRD peaks assigned to MgO crystals are not present in the NMC/MgO and NMC/MgO/S-CO composites, further confirming the existence form of ultra-fine nanoparticles of the well-dispersed MgO. Moreover, except for the presence of two very weak diffraction peaks corresponding to the Fddd orthorhombic sulfur in the NMC/MgO/S-CO composite, there is almost no distinct difference between the NMC/MgO and NMC/MgO/S-CO, even with such high content of elemental S condensed in the mesopores of the NMC/MgO. These results indicate that most of the elemental S could be tightly confined in the very internal structures of the NMC/MgO framework and thus hard to crystallize into large size during the catalytic oxidation process. The N2 sorption results reveal that the NMC/MgO composite could well retain the mesoporous structure of the pristine NMCs (Figure 4c-d), except with slight decrease in the BET specific surface area (714 m2 g-1) and total pore volume (2.2 cm3 g-1). After the filling of such high content of sulfur, the BET specific surface area and pore volume of the NMC/MgO/SCO reduce significantly to 234 m2 g-1 and 0.6 cm3 g-1, respectively, but still much higher than that of the NMC/MgO/S-MI composite (The notation MI represents the melt-impregnation


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method) obtained by melt-impregnation of a similar 73 wt.% sulfur loading into the NMC/MgO (The detail structure characterizations of the NMC/MgO/S-MI are shown in Figure S6-S8). These results further confirm that the catalytic oxidation strategy could produce very uniform NMC/MgO/S-CO cathode materials with highly-developed mesoporous structures, which could offer quick Li+ transfer channels during the charge/discharge processes and thus result in the possibility of high electrochemical performance.

Figure 5. (a) Cyclic voltammogram and (b) the initial charge-discharge curves of the NMC/MgO/S-CO and NMC/MgO/S-MI.

To demonstrate the structure benefits of the NMC/MgO/S-CO, the electrochemical performance of the NMC/MgO/S-CO and NMC/MgO/S-MI composites were evaluated. As shown in the CV curves of the composites, the two reduction peaks, located at 2.33 V and 2.02 V, should be responding to the reduction of elemental S into high-order Li2Sx (4≤x≤8) and Li2Sx into solid Li2S, respectively, while the one broad oxidation peak could be assigned to the oxidation of Li2S into elemental S through the conversion of the Li2Sx intermediates (Figure 5a). Except for the difference on the peak intensity of these CV curves, almost no other distinct differences are present between these composites, providing unequivocal proof for the existence of elemental S in the NMC/MgO/S-CO composites. Figure 5b shows the initial galvanostatic


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charge/discharge curves of the NMC/MgO/S-CO and NMC/MgO/S-MI composites at 0.2 C. Two voltage plateaus are present for both the NMC/MgO/S-CO and NMC/MgO/S-MI during the discharge process, which are the typical features of the sulfur-based composite cathode materials. The first discharge and charge capacities of the NMC/MgO/S-MI are 987 and 1088 mAh g-1, respectively, corresponding to a overcharge capacity of 101 mAh g-1. This implies that only melt-impregnation of S in the NMC/MgO cannot completely suppress the shuttling of the Li2Sx. Interestingly, the NMC/MgO/S-CO composites deliver a higher discharge capacity of 1110 mAh g-1 than the NMC/MgO/S-MI, accompanying with a negligible overcharge capacity even at such high sulfur loading. Therefore, the homogeneous distribution of elemental S via the catalytic oxidation route, in cooperation with the “sulfiphilic” MgO nanoparticles and the “lithiophilic” nitrogen dopants could effectively prevent the diffusion of Li2Sx into the electrolytes.


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Figure 6. (a) Cycling performance and coulombic efficiency of the NMC/MgO/S-CO and NMC/MgO/S-MI at 0.2 C. (b) Rate performances of the NMC/MgO/S-CO and NMC/MgO/S-MI at different current rates. (c) Cycling stability of the NMC/MgO/S-CO for 300 cycles at 0.5 C. Inset in (c) show the cooperative interface with both the lithiophilic nitrogen dopant and the sulfiphilic MgO nanoparticle.

The cycling performances of the NMC/MgO/S-CO composites were further investigated in Figure 6. Due to their intrinsic structure benefits of the exhausted NMC/MgO desulfurizers, the NMC/MgO/S-CO composites experience excellent capacity retention after long-time cycling. As shown in Figure 6a, the NMC/MgO/S-CO could retain a much higher reversible capacity of 772 mAh g-1 and a much higher Coulombic efficiency of 93.6% than the NMC/MgO/S-MI composite (585 mAh g-1 and 86.2%) after 100 cycles at 0.2 C. The NMC/MgO/S-CO composite also presents higher capacity value based on the total mass of the composite than our previously reported NMC/S-CO composite35 which are obtained from catalytic oxidation of H2S over the NMCs desulfurizer without MgO loading (Figure S9). Moreover, the NMC/MgO/S-CO exhibits better cycling responses to the continuously varied current rates (Figure 6b). At the current rate of 0.5, 1, 3 and 5 C, the reversible capacities of 866, 720, 554 and 391 mAh g-1 are respectively maintained for the NMC/MgO/S-CO, which are much higher than those of the NMC/MgO/S-MI. After extended cycling for 300 cycles at the current rate of 0.5 C, the NMC/MgO/S-CO sample also presents a high reversible capacity of 405 mAh g-1 (Figure 6c). Such excellent kinetic behaviors of the NMC/MgO/S-CO composites are further confirmed by the EIS result which indicates the much lower charge transfer resistances of the NMC/MgO/S-CO than those of the NMC/MgO/S-MI (Figure S10). These results further demonstrate that the exhausted NMC/MgO desulfurizers from H2S removal industry could indeed realize the sustainable and cost-effective route to recycle and reuse S for the high performance Li-S batteries.


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CONCLUSION In conclusion, a sustainable and high-sulfur-loading cathode material for Li-S batteries was successfully fabricated from the removal industry of the pollutant H2S gas over MgOimpregnated and nitrogen-doped mesoporous carbon composite desulfurizers (NMC/MgO). The well-developed mesoporosity and high pore volume of the NMC/MgO could offer large room for storing the product S. Additionally, the synergy effect of nitrogen dopants and MgO impregnants could also greatly improve the catalytic performance for catalytic oxidation of H2S to S with high catalytic selectivity and sulfur capacity. While elevated as cathode materials, the by-product NMC/MgO/S-CO composites with high sulfur loading present a high reversible capacity, improved cycle stability and excellent rate performance. Such superior electrochemical performance of NMC/MgO/S-CO should be due to the homogenous dispersion of sulfur via the in situ catalytic oxidation route, the cooperative effect of the “sulfiphilic” MgO nanoparticles and the “lithiophilic” nitrogen dopants, and the mesopore confinement of the NMC/MgO hosts. More significantly, instead of the cost for fabricating sulfur composite cathodes, the NMC/MgO/S-CO could achieve the economic value of the waste product from the removal industry of the pollutant H2S, and boost the electrochemical performances of high-sulfur-loading cathodes in LiS batteries for practical applications.

ASSOCIATED CONTENT Supporting Information: More results including TEM image, N2 sorption, XPS and TGA results and electrochemical performances. This material is available free of charge via the


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Internet at http://pubs.acs.org.

AUTHOR INFORMATION Corresponding Author * Corresponding Author: Fugen Sun E-mail: [email protected] Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT This work was financially supported by Natural Science Foundation of Jiangxi Province (Grant Nos. 20181BAB206006 and 20171BAB216007), National Natural Science Foundation of China (Grant No. 51502090), and Innovation Fund Designated for Graduate Students of Nanchang University (Grant No. CX2017005).

REFERENCES (1) Chu H.; Noh H.; Kim Y.; Yuk S.; Lee J.; Lee J.; Kwack H.; Kim Y.; Yang D.; Kim H., Achieving Three-Dimension Lithium Sulfide Growth in Lithium-Sulfur Batteries Using High-Donor-Number Anions, Nat. Commun. 2019, 188, 10. (2) Chen W.; Lei T.; Lv W.; Hu Y.; Yan Y.; Jiao Y.; He W.; Li Z.; Yan C.; Xiong J., Atomic Interlamellar Ion Path in High Sulfur Content Lithium-Montmorillonite Host Enables High-Rate and Stable Lithium-Sulfur Battery, Adv. Mater. 2018, 30, 1804084.


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Waste to Wealth: Exhausted Nitrogen-doped Mesoporous Carbon

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