Mo2C Surface Research Articles

Contrasting Metallic (Rh0) and Carbidic (2D-Mo2C MXene) Surfaces in Olefin Hydrogenation Provides Insights on the Origin of the Pairwise Hydrogen Addition.

Kinetic studies are vital for gathering mechanistic insights into heterogeneously catalyzed hydrogenation of unsaturated organic compounds (olefins), where the Horiuti-Polanyi mechanism is ubiquitous on metal catalysts. While this mechanism envisions nonpairwise H2 addition due to the rapid scrambling of surface hydride (H*) species, a pairwise H2 addition is experimentally encountered, rationalized here based on density functional theory (DFT) simulations for the ethene (C2H4) hydrogenation catalyzed by two-dimensional (2D) MXene Mo2C(0001) surface and compared to Rh(111) surface. Results show that ethyl (C2H5*) hydrogenation is the rate-determining step (RDS) on Mo2C(0001), yet C2H5* formation is the RDS on Rh(111), which features a higher reaction rate and contribution from pairwise H2 addition compared to 2D-Mo2C(0001). This qualitatively agrees with the experimental results for propene hydrogenation with parahydrogen over 2D-Mo2C1-x MXene and Rh/TiO2. However, DFT results imply that pairwise selectivity should be negligible owing to the facile H* diffusion on both surfaces, not affected by H* nor C2H4* coverages. DFT results also rule out the Eley-Rideal mechanism appreciably contributing to pairwise addition. The measurable contribution of the pairwise hydrogenation pathway operating concurrently with the dominant nonpairwise one is proposed to be due to the dynamic site blocking at higher adsorbate coverages or another mechanism that would drastically limit the diffusion of H* adatoms.

Pulsed laser induced plasma and thermal effects on molybdenum carbide for dry reforming of methane

Dry reforming of methane (DRM) is a highly endothermic process, with its development hindered by the harsh thermocatalytic conditions required. We propose an innovative DRM approach utilizing a 16 W pulsed laser in combination with a cost-effective Mo2C catalyst, enabling DRM under milder conditions. The pulsed laser serves a dual function by inducing localized high temperatures and generating *CH plasma on the Mo2C surface. This activates CH4 and CO2, significantly accelerating the DRM reaction. Notably, the laser directly generates *CH plasma from CH4 through thermionic emission and cascade ionization, bypassing the traditional step-by-step dehydrogenation process and eliminating the rate-limiting step of methane cracking. This method maintains a carbon-oxygen balanced environment, thus preventing the deactivation of the Mo2C catalyst due to CO2 oxidation. The laser-catalytic DRM achieves high yields of H2 (14300.8 mmol h−1 g−1) and CO (14949.9 mmol h−1 g−1) with satisfactory energy efficiency (0.98 mmol kJ−1), providing a promising alternative for high-energy-consuming catalytic systems.

Effect of loading different transition metals W, Pt and Pd monolayers on quinoline hydrogenation and C–N bond cleavage over Mo2C(001)

Nitrogen-containing compounds such as quinoline in coal-based crude oils cause environmental pollution in the course of application. Consequently, dealing with the nitrogen-containing compounds from coal-based crude oil is of paramount importance. The hydrogenation and CN bond cleavage mechanisms of quinoline on the active Mo-terminated over Mo2C(001) surface, as well as on surfaces doped with W, Pt and Pd monolayers, were examined employing the density functional theory (DFT) method. The Pd and Pt-doped catalysts exhibited higher hydrogenation activity. The catalytic efficiency is enhanced by the loading of different metals, particularly with d-band center further away from the Fermi energy level. Additionally, a novel CN bond cleavage mechanism for quinoline has been proposed. The new proposed mechanism is more conducive for the CN bond cleavage. After a thorough comparison, the Pd-loaded catalyst was identified as the most effective for quinoline hydrogenation and CN bond cleavage.

Hydrogen transport through Mo2C/PdCu composite membranes

First-principle calculations have been adopted to systematically investigate the adsorption and dissociation of H2 on Mo2C (100) and (001) surfaces, as well as the fluxes of hydrogen dissociative adsorption on the Mo2C surfaces and the hydrogen across the Mo2C(100)/PdCu(110) and Mo2C(001)/PdCu(110) interfaces. It is observed that the adsorption and dissociation of H2 as well as the hydrogen flux on the Mo2C (100) surfaces are energetically more favorable than on the Mo2C (001) surfaces. Calculations also reveal that the hydrogen flux across the Mo2C(100)/PdCu(110) and Mo2C(001)/PdCu(110) interfaces is one and six order of magnitude greater than the hydrogen desorption flux on the permeation side of PdCu, respectively. In other words, the hydrogen diffusion in BCC PdCu bulk and hydrogen desorption are the dominant steps of hydrogen transport through Mo2C/PdCu composite membranes, rather than the hydrogen diffusion across the Mo2C/PdCu interfaces. The calculational findings are consistent with the similar experimental observations in the literature, and provide a profound understanding regarding the hydrogen transport across Mo2C-coated PdCu membrane.

Functional ladder-like heterojunctions of Mo2C layers inside carbon sheaths for efficient CO2 fixation

The development of two-dimensional heterogeneous catalysts with highly exposed active site areas for heterogeneous catalytic systems is highly promising for achieving the green transformation of small molecules. 2D transition metal carbides (TMCs) show great promise for catalysis and carbon capture but suffer from heavy aggregation and autooxidation. Mass transfer barrier is also a standard problem of lamellar TMCs caused by slight aggregation of layers. Here, we successfully developed a method to prepare “ladder-like” heterojunctions of Mo2C layers confined inside nitrogen-rich carbon sheaths (2D-Mo2C@NC) via an effective oxygen-diffusion etching strategy, acting as efficient catalysts for CO2 fixation. The enhanced electron enrichment of the as-integrated 2D-Mo2C subunits induced by the Schottky barrier could further keep the exposed Mo2C surface from possible autooxidation and aggregation confronted by conventional 2D TMCs. The experimental results and density functional theory (DFT) calculation further demonstrate that electron-rich Mo2C could boost the adsorption and activation of CO2 for universal carbonylation of various diamines, providing a turnover frequency value (TOF) of 10.2 h−1 to produce benzimidazolone, which is 5.2 times of that of the state-of-the-art catalyst in the literature under even critical conditions.

Mo2C coated with Ni nanoparticles as the cathode catalyst towards efficient hydrogen evolution reaction: an experimental and computational investigation.

Although Mo2C and earth-abundant 3d transition metals are regarded as potential catalysts to replace noble metal catalysts for effective hydrogen evolution reaction, their large-scale application is still inhibited by their own defects. Here, a facile thermal treatment method for nonprecious metal catalysts is developed to prepare a porous Ni/Mo2C composite catalyst. The loading density of Ni nanoparticles on the Mo2C surface has an important effect on the activity of the catalyst. By optimizing the Ni doping ratio, the Ni-40/Mo2C-17 sample exhibits the lowest onset overpotential and lowest overpotential at 10 mA cm-2 in both acidic and alkaline electrolytes, compared to other reported Ni- and Mo2C-based catalysts. In addition, theoretical calculations have also confirmed the synergistic effect between Ni nanoparticles and Mo2C, which can balance the thermodynamics between H adsorption and desorption of H2. This work provides an avenue for designing high-performance water-splitting catalytic materials using low-cost species, which exhibit excellent HER activity in a wide pH range.

Mo2C catalyst leads to highly efficient hydrogen transfer of alcohols and amines to synthesize N-alkylamines.

We found that molybdenum carbide (Mo2C) can be applied as a novel and efficient heterogeneous catalyst for hydrogen transfer of anilines and alcohols to synthesize N-alkylamines. The results of experiments and DFT calculations demonstrate that Mo2C surface can reduce the energy barrier of the key step of alcohol dehydrogenation and generate a hydrogen spillover effect, thereby exhibiting outstanding catalytic performance.

Efficient hydrogen evolution enabled by in-situ synthesis of biphasic Mo2C/Mo16N7 nitrogen-doped carbon nanorods as catalysts

Molybdenum carbide (Mo2C) has gained significant recognition as a cutting-edge, non-precious transition metal catalysts for efficiently driving the hydrogen evolution reaction (HER). However, the desorption of Mo-H bonds on the pristine Mo2C surface are difficult, resulting in a slow Heyrovsky/Tafel step. Herein, biphasic Mo2C/Mo16N7 nitrogen doped carbon nanorods (Mo2C/Mo16N7@NRs) is synthesized as the high-performance HER electrocatalyst by using a one-step in-situ pyrolysis growth method. It is found that a suitable pyrolysis temperature can simultaneously tune the morphology of the catalyst and form abundant heterointerface. Benefit from abundant porous nanostructure and more electron-rich Mo active sites at the Mo2C-Mo16N7 interfaces, the optimized Mo2C/Mo16N7@NRs demonstrates exceptional catalytic activity. It achieves low overpotentials (η10) of 63.62 and 117.43 mV at 10 mA cm−2, accompanied by Tafel scopes of 49.73 and 64.44 mV dec−1 in both alkaline and acidic electrolytes. Also, Mo2C/Mo16N7@NRs shows long-lasting stability for 24 h in the different electrolytes. The experimental and theoretical findings explain the synergistic effects of unique morphology control and interface engineering on electrocatalyst activity. The one-step in-situ pyrolysis growth method is expected to produce non-precious metal catalysts with distinct morphology and heterointerfaces.

Catalyst for polysulfide conversion by Mo2C/MoO3 hybrids modified separator in lithium-sulfur batteries

The lithium-sulfur (Li–S) batteries have achieved important developments, but still suffer from some main intrinsic disadvantages, such as the dissolution and diffusion of the lithium polysulfides (LiPSs). In response, here we develop a Mo2C/MoO3 heterostructure as the interlayer to restrain the leakage and migration of LiPSs. Owing to its good conductivity and excellent electronic transport, this heterostructure can perform excellently as an ideal carrier for providing reduction reaction sites of LiPSs conversion, thus greatly improving the electrochemical properties of Mo2C/MoO3 for Li–S batteries. The resultant Mo2C/MoO3 electrodes can deliver a high specific capacity of 1346 mAh g−1 at 0.1C and long-term cycling stability (660 mAh g−1 after 800 cycles at 2C) with a low capacity decay rate of 0.05% per cycle, indicating high sulfur utilization and fast kinetic conversion of LiPSs and Li2S. When the sulfur loading is increased to 4.34 mg cm−2, the initial discharge capacity and areal capacity of the Mo2C/MoO3 electrode at 0.1C is still up to 1405 mAh g−1 and 6.1 mAh cm−2 with a coulombic efficiency of 99% in the first cycle, indicating faster LiPSs conversion. First-principle calculations reveal that the as-synthesized LiPSs species are selectively adsorbed on the MoO3 (001) and Mo2C (001) surface. This work provides an alternative strategy toward high-performance Li–S battery with high sulfur loading.

Comparative DFT study of methanol decomposition on Mo2C(001) and Mo2C(101) surfaces

Comparative DFT study of methanol decomposition on Mo2C(001) and Mo2C(101) surfaces

Changes in fundamental and catalytic properties of β-molybdenum carbide decorated by a single atom of Fe, Co, Ni and Cu

The interaction of single Fe, Co, Ni, and Cu atoms with polar terminations of orthorhombic Mo2C(001) surface has been investigated at low surface coverage by using density functional theory. Calculations indicate high stability of all considered adsorbates, regardless the surface termination. The presence of a single foreign atom has a localized impact on the properties of the surface, causing charge redistribution in the adsorbate/surface interface. As the result lowering of the work function is observed for both Mo2C(001) terminations. Another effect is shifting the position of d-band center further away from the Fermi level for surface Mo atoms of metal-terminated carbide, while no changes are seen for carbon’s near-Fermi level electronic states in the case of C-terminated modified surface. Results demonstrate a short-range effect on the stability of atomic hydrogen caused by the foreign adatom on both terminations. Specifically, the observed adsorption energy weakening would entail an enhancement in the catalytic activity of Mo2C toward hydrogen evolution reaction according to the Sabatier principle. Results evidence that molybdenum carbide modified by cobalt and iron is expected to be more active toward hydrogen evolution reaction than Mo2C modified by nickel and copper or than unmodified carbide.

DFT study on the electrochemical synthesis of ammonia over Mo2C(121) with N-doping

The electrocatalytic nitrogen reduction reaction (eNRR) is a green and sustainable approach for ammonia (NH3) production. Mo2C, a commonly used catalyst for the hydrogen evolution reaction (HER), has been confirmed to have good eNRR performance experimentally, and N-doping is reported to be beneficial to the activation of N2. But the theoretical understanding on eNRR over N-doped Mo2C is rather limited. In this work, the eNRR over the N-doped Mo2C(121) (xN@Mo2C, x = 1-6) are investigated by using density functional theory (DFT), and compared with Mo2C(121) surface. The N2 adsorption, electronic structure of catalyst, mechanism of eNRR, and the effect of N-doping on the activity and selectivity of eNRR are systematically calculated. The results reveal that with the increase of the N content, the d-band center of Mo atom moves away from the Fermi level, which makes the N2 adsorption strength gradually weaken. And on the 6@Mo2C(121) surface, the adsorption of N2 is the weakest than Mo2C(121) and the xN@Mo2C(121) (x = 1-5). On the Mo2C(121) and the xN@Mo2C(121) (x = 2-5) surfaces (except for 1N@Mo2C(121)), the Gibbs free energy barrier of potential-determining step (ΔGPDS) of the enzymatic pathway is significantly lower than those of the alternating and distal pathways, which indicates that enzymatic pathway is the dominant pathway of eNRR. N-doping is beneficial to reduce the ΔGPDS of eNRR in xN@Mo2C(121), and 6N@Mo2C(121) surface presents the lowest ΔGPDS (0.32 eV). Further, compared the ΔGPDS with the main side reaction, HER, it shows that the 4N@Mo2C(121), 5N@Mo2C(121) and 6N@Mo2C(121) surfaces can effectively inhibit the occurrence of HER. Overall, 6N@Mo2C(121) is identified to be the most promising catalyst for eNRR among the caculated xN@Mo2C(121). This work uncovers the theoretical information of N-doped Mo2C(121) for eNRR and provides theoretical guidance for the construction and design of the efficient eNRR catalysts deriving from the HER catalysts.

Unveiling the Origin of Alkali Metal (Na, K, Rb, and Cs) Promotion in CO2 Dissociation over Mo2C Catalysts.

Molybdenum carbide (Mo2C) is a promising and low-cost catalyst for the reverse water−gas shift (RWGS) reaction. Doping the Mo2C surface with alkali metals can improve the activity of CO2 conversion, but the effect of these metals on CO2 conversion to CO remains poorly understood. In this study, the energies of CO2 dissociation and CO desorption on the Mo2C surface in the presence of different alkali metals (Na, K, Rb, and Cs) are calculated using density functional theory (DFT). Alkali metal doping results in increasing electron density on the Mo atoms and promotes the adsorption and activation of CO2 on Mo2C; the dissociation barrier of CO2 is decreased from 12.51 on Mo2C surfaces to 9.51–11.21 Kcal/mol on alkali metal-modified Mo2C surfaces. Energetic and electronic analyses reveal that although the alkali metals directly bond with oxygen atoms of the oxides, the reduction in the energy of CO2 dissociation can be attributed to the increased interaction between CO/O fragments and Mo in the transition states. The abilities of four alkali metals (Na, K, Rb, and Cs) to promote CO2 dissociation increase in the order Na (11.21 Kcal/mol) < Rb (10.54 Kcal/mol) < Cs (10.41 Kcal/mol) < K (9.51 Kcal/mol). Through electronic analysis, it is found that the increased electron density on the Mo atoms is a result of the alkali metal, and a greater negative charge on Mo results in a lower energy barrier for CO2 dissociation.

Mo2C-MoO2 Heterostructure Quantum Dots for Enhanced Electrocatalytic Nitrogen Reduction to Ammonia.

The electrocatalytic nitrogen reduction reaction (NRR) has been regarded as a promising strategy for producing ammonia (NH3) at ambient conditions. However, the development of the NRR is severely hindered by the difficult adsorption and activation of N2 on the catalyst surface and the competitive hydrogen evolution reaction (HER) due to the lack of efficient NRR electrocatalysts. Herein, Mo2C-MoO2 heterostructure quantum dots embedded in reduced graphene oxide (RGO) are proposed as efficient catalysts for the electrocatalytic NRR. The ultrasmall size of the quantum dot is beneficial for exposing the active sites for the NRR, and the synergetic effect of Mo2C and MoO2 can promote N2 adsorption and activation and suppress the competitive HER simultaneously. As a result, a well-balanced NRR performance is achieved with a high NH3 yield rate of 13.94 ± 0.39 μg h-1 mg-1 at -0.15 V vs RHE and a high Faradaic efficiency of 12.72 ± 0.58% at -0.1 V vs RHE. Density functional theory (DFT) calculations reveal that the Mo2C (001) surface has a strong N2 adsorption energy of -1.47 eV with the side-on configuration, and the N≡N bond length is elongated to 1.254 Å, indicating the enhanced N2 adsorption and activation on the Mo2C surface. On the other hand, the low ΔGH* for HER over the MoO2 (-111) surface demonstrates the impeded HER process for MoO2. This work may provide effective catalyst-design strategies for enhancing the electrocatalytic NRR performance of Mo-based materials.

Formic acid reduction and CO2 activation at Mo2C: The important role of surface oxide

AbstractSmall organic acids, such as formic or acetic acid, which are well‐known products of the electrochemical CO2 reduction reaction, are often not further reduceable to their respective alcohols. Alcohols are well‐desired chemicals and useful as fuels, since they can be easily purified and provide a high energy density. Here, we present a combined electrochemical, differential electrochemical mass spectrometry (DEMS), and nuclear magnetic resonance spectroscopy (NMR) study, providing insight in the electro‐reduction of formic acid on Mo2C electrodes, and the corresponding formation of notable amounts of methanol, with a Faraday efficiency of ∼27 % at a high steady state current density of –0.3 mA/cm2 compared to other formic acid electroreduction catalysts, such as Pb or Sn. Intriguingly, we find that formic and acetic acid readily form on native oxide covered Mo2C surfaces in air and especially in humid CO2 atmosphere. We realize that the thin native oxide layer that is ubiquitously present on these electrodes is the key factor for the activation of CO2 and the corresponding formation of formic and acetic acid at the solid/gas interface. Subsequent electrochemical reduction of these two acids at the solid/liquid interface proceeds through direct formation of their respective alcohols. The activity toward organic acid reduction on Mo2C catalysts can therefore be enhanced by their adsorption properties at the surface and not necessarily through inhibition of the HER, which is exceptional and points to a general strength of compound catalysts for organic acid reduction and CO2 activation.

Adsorption of CO, H2, H2O, and CO2 on Fe-, Co-, Ni-, Cu-, Pd-, and Pt-Doped Mo2C(101) Surfaces

Adsorption of CO, H₂, H₂O, and CO₂ on Fe-, Co-, Ni-, Cu-, Pd-, and Pt-Doped Mo₂C(101) Surfaces

Structural Evolution and Underlying Mechanism of Single-Atom Centers on Mo2C(100) Support during Oxygen Reduction Reaction.

The single-metal atoms coordinating with the surface atoms of the support constitute the active centers of as-prepared single-atom catalysts (SACs). However, under hash electrochemical conditions, (1) supports' surfaces may experience structural change, which turn to be distinct from those at ambient conditions; (2) during catalysis, the dynamic responses of a single atom to the attack of reaction intermediates likely change the coordination environment of a single atom. These factors could alter the performance of SACs. Herein, we investigate these issues using Mo2C(100)-supported single transition-metal (TM) atoms as model SACs toward catalyzing the oxygen reduction reaction (ORR). It is found that the Mo2C(100) surface is oxidized under ORR turnover conditions, resulting in significantly weakened bonding between single TM atoms and the Mo2C(100) surface (TM@Mo2C(100)_O* term for SAC). While the intermediate in 2 e- ORR does not change the local structures of the active centers in these SACs, the O* intermediate emerging in 4 e- ORR can damage Rh@ and Cu@Mo2C(100)_O*. Furthermore, on the basis of these findings, we propose Pt@Mo2C(100)_O* as a qualified ORR catalyst, which exhibits extraordinary 4 e- ORR activity with an overpotential of only 0.33 V, surpassing the state-of-the-art Pt(111), and thus being identified as a promising alternative to the commercial Pt/C catalyst.

Emerging Hexagonal Mo2C Nanosheet with (002) Facet Exposure and Cu Incorporation for Peroxymonosulfate Activation Toward Antibiotic Degradation.

The catalyst with a special exposed active facet and multivalent element synergism is much desired for advanced oxidation progress (AOP) reaction. Herein, an emerging substrate, Cu-incorporated Mo2C, with an active (002) facet exposed was developed by one-step calcination to activate peroxymonosulfate (PMS) toward antibiotic degradation. Combining the multivalent Cu-Mo synergistic effect and Cu complexing interaction, Cu was incorporated onto the Mo2C surface to further enhance its antibiotic removal through PMS activation. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) measurements indicated the 5% Cu-Mo2C exhibited in the hexagonal nanosheet with Cu uniformly dispersed on the surface. Moreover, 5% Cu-Mo2C displayed excellent PMS activation which could fully degrade the tetracycline (TC) within 20 min, and the degradation rate was found to be at least 20 times higher than those of pure Mo2C, classical Fe2O3 and Co3O4, and Fenton reaction of 5% Cu-Mo2C. The results were found to be ascribed to enhanced electrical conductivity, multivalent Cu-Mo synergism, and increased generation of active radicals which contributed in the sequence SO4•- > •OH > O2•-. Surface chemical analysis combined with density functional theory (DFT) calculations confirmed that both Cu2+/Cu+ and Mo6+/Mo4+/Mo2+ redox cycles occurred on the (002) plane of Mo2C, which dominated more free electrons and mainly accounted for facilitating PMS activation. Meanwhile, systematically conditional experiments uncovered that the 5% Cu-Mo2C exhibited superb catalysis even under a wide pH and temperature, various natural polluted waters and coexisting ions, and long-time recycle. In addition, the as-prepared catalyst presented excellent adaptability for the degradation of different organic effluents originated from medical, dyeing, and beneficiation wastewaters. Considering its great performance, stability, and applicability, 5% Cu-Mo2C would be a capable candidate for PMS activation toward large-scale practical application in environmental remediation.

Mechanism-of-Action Elucidation of Reversible Li-CO2 Batteries Using the Water-in-Salt Electrolyte.

Li-CO2 batteries have attracted worldwide attention because of their dual characteristics of high energy density and effective CO2 capture. However, the basic electrochemistry mechanism involved has been unclear, which is mainly confused by the complicated decomposition of organic electrolytes. Herein, water-in-salt (WIS, LiTFSI/H2O 21.0 mol/1 kg) has been explored as a suitable electrolyte for the first time to investigate the reaction mechanism of Li-CO2 batteries with different cathodes (carbon nanotube (CNT) and Mo2C/CNT, respectively). An Mo2C-based Li-CO2 battery with WIS delivers a higher energy efficiency of 83% and a superior cyclability, compared to those of the CNT-based counterpart cell. Through various ex/in situ qualitative/quantitative characterizations, the Mo2C-based Li-CO2 battery with WIS can operate on the reversible conversion of CO2-to-Li2C2O4 ((e-/CO2)ideal = 1) at lower discharge/charge overpotentials, while the CNT-based counterpart cell is based on the formation/decomposition of Li2CO3 ((e-/CO2)ideal ≈ 1.33) at high overpotentials. Such a difference in CO2 reduction products stems from the stronger interaction between Mo2C(101) and Li2C2O4 than that of the CNT and Li2C2O4 based on the density functional theory calculations, resulting in the selective stabilization of the intermediate product Li2C2O4 on the Mo2C surface.

Immobilization and kinetic promotion of polysulfides by molybdenum carbide in lithium-sulfur batteries

The shuttle effect of lithium polysulfides (LiPSs) intermediates is mainly responsible for the poor cycling stability of lithium sulfur (Li-S) batteries. Accelerating the reaction kinetics of the LiPSs conversion is proved to be effective in suppressing the migration of LiPSs. Herein, we propose an effective KB/Mo2C-modified separator for enabling stable Li-S batteries. The Mo2C shows both favorable anchoring capability and catalysis activity for LiPSs conversion due to its strong chemical affinity with LiPSs. The reaction kinetics of LiPSs reduction are facilitated on the Mo2C surface, and the activation potential of lithium sulfide (Li2S) oxidation is reduced. The battery using the modified separator shows high active material utilization and long-term cycling stability with a low decay rate of 0.076% per cycle up to 600 cycles at 1C. Moreover, when the sulfur loading increases to 6.5 mg cm−2, a high areal capacity of 5.2 mAh cm−2 can be maintained after 60 cycles with a capacity retention of 87%, demonstrating the feasibility for practical applications in Li-S batteries.