Detailed Reaction Mechanism Research Articles

Experimental Studies on Parametric Effects and Reaction Mechanisms in Electrolytic Decomposition and Ignition of HAN Solutions.

The green propellant hydroxylammonium nitrate (HAN) is a good alternative to the conventional propellants in space propulsion applications because of its low toxicity and high energy density. Electrolytic decomposition and ignition of HAN solution, an ionic liquid, is a promising approach. In this work, comprehensive experimental studies were conducted to examine effects of different electrolytic voltages, electrode surface areas, and HAN concentrations on the decomposition process. In the test cases, an optimum electrolytic voltage appears to exist, which leads to the fastest decomposition process. As the voltage increases, a larger electrode surface area on the anode side should be used to overcome an anodic inhibition phenomenon and accelerate the electrolytic process. A high concentration of HAN solution is preferred for its decomposition and ignition. Results also reveal that the electrolytic process of a HAN solution could eventually trigger thermal decomposition reactions, raising the maximum temperature to around 550 K at the final stage. A detailed chemical reaction mechanism was proposed, based on the experimental data and FTIR spectra analyses. Results obtained herein would provide fundamental understandings on the complex electrochemical and physical processes and should be helpful for future applications of the electrolytic decomposition and ignition technology.

(Digital Presentation) High-Dose Ion-Implanted Photoresist Stripping Technology Employing High Temperature Single-Wafer SPM System

We found that the high-dose ion-implanted photoresist can be removed with high efficiency without residue by using SPM heated to 250 °C. We evaluated the reaction mechanism in detail, and proposed a model: a heat consumption by vaporization of H2O, a heat gain by decomposition of H2O2, and a character change of SPM itself interact, the high-dose ion-implanted photoresist along with dopants is removed.

Combustion characteristics of a reverse-cross-flow combustor

The effect of fuel-to-air jet momentum flux ratios (varied from 0.1 to 5.1) in a 6.25 kW Reverse-Cross-Flow (RCF) combustor is investigated at a maximum thermal intensity of 40 MW/m3-atm using methane fuel. Reaction zone is characterised by imaging OH radicals using planar laser-induced fluorescence (OH-PLIF) technique. Reynolds-averaged Navier-Stokes (RANS) simulations are performed at an equivalence ratio of 0.8 using Eddy Dissipation Concept (EDC) model for turbulence-chemistry interactions with detailed reaction mechanism (GRI-Mech 3.0). Numerical results show a qualitative match with the experimental results for averaged OH intensity distribution and NOx and CO emissions. Air jet is observed to deflect more with increase in fuel-to-air jet momentum flux ratio. Flame-front is observed to be located at the periphery of the air jet due to mixing of reactants and hot burned products in the shear layer. Instantaneous OH-PLIF data suggest that the flame-front location changes considerably with time. Both numerical and experimental results show increase in CO emissions and reduction in NOx emissions with increase in fuel-to-air jet momentum flux ratio. This may be linked to unfavorable residence time distribution, despite better mixing at high fuel injection momentum.

Water coordinated on Cu(I)-based catalysts is the oxygen source in CO2 reduction to CO

Catalytic reduction of CO2 over Cu-based catalysts can produce various carbon-based products such as the critical intermediate CO, yet significant challenges remain in shedding light on the underlying mechanisms. Here, we develop a modified triple-stage quadrupole mass spectrometer to monitor the reduction of CO2 to CO in the gas phase online. Our experimental observations reveal that the coordinated H2O on Cu(I)-based catalysts promotes CO2 adsorption and reduction to CO, and the resulting efficiencies are two orders of magnitude higher than those without H2O. Isotope-labeling studies render compelling evidence that the O atom in produced CO originates from the coordinated H2O on catalysts, rather than CO2 itself. Combining experimental observations and computational calculations with density functional theory, we propose a detailed reaction mechanism of CO2 reduction to CO over Cu(I)-based catalysts with coordinated H2O. This study offers an effective method to reveal the vital roles of H2O in promoting metal catalysts to CO2 reduction.

CFD modelling of the off-gas system of HIsarna iron making process. Part 1: model development using detailed reaction mechanism for post-combustion of CO–H2 mixture and carbon particles

ABSTRACT The HIsarna process is a new and breakthrough smelting reduction process for hot metal (liquid iron) production from iron ores and coal directly fed into the reactor. The flue gas from the main reactor enters the off-gas system containing small amounts of H2, CO and carbon particles which need to be removed before further treatment by post combustion oxygen injection. A three-dimensional Computational Fluid Dynamics (CFD) simulation of the HIsarna off-gas system is performed and validated using a detailed reaction mechanism and kinetic data for post-combustion of a CO–H2 mixture and carbon particles. Using the validated model, a series of simulations were performed to investigate the effect of water quenching and post combustion oxygen injection. It was found that water quenching can significantly reduce the off-gas temperature. It is also possible to reduce oxygen injection during operations where inlet CO content of the off-gas system is low.

A synergistic study on the synthesis of juglone via photooxidation in a UV–Vis LED based photomicroreactor

Photochemical transformations are mobilized by traceless photons of narrow or broad visible light wavelength and have been proven as a green and sustainable synthesis route for organic compounds. However, most of such investigations were restricted to only parametric studies, lacking in examining a synergistic involvement of actinometric, kinetics and mass transfer mechanisms on product yield. To address this vital issue, we executed the synthesis of natural product juglone via the photooxidation of 1,5-dihydroxynapthalene (DHN) mediated through singlet oxygen, which was produced by triplet–triplet energy transfer from three porphyrin-based photosensitizers to triplet oxygen upon irradiation from UV–Vis LED. Compared to the other two photosensitizers, m-TcPP (meso-tetracarboxyphenylporphyrine) showed a higher molar extinction coefficient and remarkable energy transfer, resulting in higher DHN conversion and juglone yield. Full DHN conversion and 82% yield were obtained at the m-TcPP loading of 2.0 mol% and the residence time of 22.1 min. Actinometric investigation showed that the photon flux was significantly improved by rising m-TcPP and DHN concentrations. The maximum radiant power absorbed by the DHN photooxidation could reach 17.3% of the total input power of UV–Vis LED strip. The detailed reaction mechanism of the DHN photooxygenation was discussed through the Jablonski diagram and rate constants of intermediate steps were determined. A positive relationship between the photon flux and the apparent rate constant was found by rising m-TcPP concentration from 0.01 to 0.05 mM, while the rise in DHN concentration from 5.0 to 10.0 mM resulted in a negative correlation between these parameters. Consequently, a synergistic improvement of photon flux and apparent rate constant was necessitated to attain complete DHN conversion and high juglone yield.

Effects of number of air holes on flame and heat transfer characteristics in a multihole baffled combustor combined with micro-thermophotovoltaic and micro-thermoelectric systems

• A multihole baffled micro combustor combined with micro-thermoelectric generators is proposed as a micro power generator. • The optimal number of air holes related to the combustion efficiency and the preheating effect is obtained. • The good features for micro-thermophotovoltaic(TPV) and micro-thermoelectric(TEG) systems is linked to wavy and lobed flames. • The emitter efficiency for TPV applications is comparable to the swirling flow combustor. • A high conversion efficiency of 3.58% is obtained for the multihole baffled micro combustor. Currently, micro power generators have been widely drawing attention for various applications. In this study, the H 2 –air micro combustor (MC) with a multihole baffle plate was combined with two power generators based on micro-thermophotovoltaic and micro-thermoelectric systems. The reacting flow and conjugate heat transfer including the MC wall were analyzed by the detailed reaction mechanism and the outer wall condition of convection and radiation. From the resulting thermal fields, the characteristics of heat emission and electrical potential were examined. Eight baffles with different numbers of air holes (N a ) and three global equivalence ratios were selected, and a baffle with N a = ∞ was adopted to compare the multihole and annular air flows. The combustion characteristics depending on N a were explored by analyzing the changes in the reaction zone, the flammable range, reaction rate, and wall heat transfer rate. The N a effect on wall and center recirculation zones was comparable to the variation due to other geometrical variables of the baffle plate. As N a increased, the combustion efficiency increased to 20% of the N a = ∞ case. The combustion efficiency equivalent to the swirl MC was obtained for N a = 5–8, having enhanced preheating effects and large center recirculation zones. Compared to N a = ∞, the mean temperature of the multihole baffled MC increased by 6.4%–19.2% depending on N a . The emitter efficiency related a TPV system was comparable to the swirling flow MC. For a thermoelectric generator, the conversion efficiency of N a = ∞ was similar to that of a Swiss-roll MC, and the multihole baffled MC showed a high conversion efficiency of 1.55%–3.58% depending on N a and the global equivalence ratio.

UBIAD1 effectively alleviated myocardial ischemia reperfusion injury by activating SIRT1/PGC1α.

Myocardial ischemia-reperfusion injury (MIRI) threatens global health and lowers people's sense of happiness. Till now, the mechanism of MIRI has not been well-understood. Therefore, this study was designed to explore the role of UBIAD1 in MIRI as well as its detailed reaction mechanism. The mRNA and protein expressions of UBIAD1 before or after transfection were measured using RT-qPCR and western blot. Western blot was also adopted to measure the expressions of signaling pathway-, mitochondrial damage- and apoptosis-related proteins. Moreover, mitochondrial membrane potential and ATP level were verified by JC-1 immunofluorescence and ATP kits, respectively. With the application of CCK-8, LDH and CK-MB assays, the cell viability, LDH and CK-MB levels were evaluated, respectively. In addition, the cell apoptosis was detected using TUNEL. Finally, the expressions of ROS, SOD, MDA and CAT were measured using DCFH-DA, SOD, MDA and CAT assays, respectively. In the present study, we found that UBIAD1 was downregulated in hypoxia-reoxygenation (H/R) -induced H9C2 cells and its upregulation could activate SIRT1/PGC1α signaling pathway. It was also found that UBIAD1 regulated mitochondrial membrane potential and ATP level via activating SIRT1/PGC1α signaling pathway. In addition, the injury of H/R-induced H9C2 cells could be relieved by UBIAD1 through the activation of SIRT1/PGC1α signaling pathway. Moreover, UBIAD1 exhibited inhibitory effects on apoptosis and oxidative stress of H/R-induced H9C2 cells through activating SIRT1/PGC1α signaling pathway. To sum up, UBIAD1 could alleviate apoptosis, oxidative stress and H9C2 cell injury by activating SIRT1/PGC1α, which laid experimental foundation for the clinical treatment of MIRI.

Growth of MoS2 and metal back electrode-dependent performance of MoS2/Si heterojunction solar cells

In this work, MoS2 thin films were successfully synthesized by chemical vapor deposition (CVD) using MoO3 and sulfur powders as precursor sources. The effect of the MoO3 dosage and heating temperature on the quality of the synthesized MoS2 films are investigated and a detailed reaction mechanism is proposed to interpret the obtained experimental result. Furthermore, we have studied the influence of different metal back electrodes (including Ag and Au) on the photovoltaic performance of the fabricated MoS2/Si heterojunction solar cell. It is shown that, in comparison with the solar cell using Au as a metal back electrode, the solar cell using Ag as a metal back electrode has poor photovoltaic performance with the appearance of the S-type shape in the measured current density-voltage curve. Finally, numerical simulation based on AFORS-HET software has been carried out to investigate the photovoltaic performance of the [Formula: see text]-MoS2/[Formula: see text]-Si heterojunction solar cell under different work functions of the metal back electrode. The result of numerical simulation is consistent with our experiential result in the trend. This work is highly relevant to the development of transition metal dichalcogenides in the application of solar cells.

Structural Enzymology of the Cysteine Tryptophylquinone (CTQ) Enzyme GoxA

GoxA from Pseudoalteromonas luteoviolaceae belongs to a recently identified family of enzymes (the LodA‐like proteins) that utilize a post‐translationally derived cysteine tryptophylquinone (CTQ) cofactor for catalysis. In contrast to other tryptophylquinone enzymes, GoxA acts as an oxidase rather than a dehydrogenase, using molecular oxygen to catalyze the oxidative deamination of glycine to produce ammonia, glyoxylate and hydrogen peroxide. The crystal structure of this enzyme revealed a homotetramer with a novel alpha helical domain and extensive inter‐subunit interactions, which account for the positive cooperativity observed toward its substrate by steady‐state kinetics. Soaking GoxA crystals in glycine results in a dramatic color change from yellow to blue, indicating the formation of an unusual intermediate at the CTQ site that was also detected in solution. The structure of this intermediate reveals a Schiff‐base formed between the substrate and CTQ that is stabilized by numerous hydrogen bond contacts with residues both in the active site and from a neighboring protomer. The kinetics and structures of active site mutants reveal the roles of specific residues in substrate binding, cooperativity, and catalysis, and allowed for the detection of another intermediate in the GoxA reaction pathway. This combination of kinetics, spectroscopy and X‐ray crystallography has allowed for the construction of a detailed reaction mechanism for this unusual enzyme with high‐resolution structures now available for key intermediates.

CFD modelling of the off-gas system HIsarna iron making process part 2: reflux chamber geometry modification and effects on flow behaviour

ABSTRACT A three-dimensional computational fluid dynamics (CFD) model for the HIsarna off-gas system is set up and validated by real plant data. In the model detailed reaction mechanism and kinetic data for post-combustion of CO-H2 mixture and carbon particles are incorporated. The results are presented and discussed in another study (Part 1) by the same authors. In the present paper, the focus will be on geometry modification of the off-gas system and the effects on the operating parameters. The effect of this modification on heat loss, temperature profile, carbon conversion and gaseous phase composition across the off-gas system is investigated. It is shown that the modified geometry leads to a higher heat loss through the reflux chamber walls which can change the temperature profile and consequently species composition. The modified geometry also offers possibility of higher CO-H2 mixture and carbon particles conversion rate and reduce unwanted emission from the reflux chamber.

Reaction Mechanisms of Histidine and Carnosine with Hypochlorous Acid Along with Chlorination Reactivity of N-Chlorinated Intermediates: A Computational Study.

Hypochlorous acid (HOCl) released from activated leukocytes not only plays a significant role in the human immune system but is also implicated in numerous diseases including atherosclerosis and some cancers due to its inappropriate production. Histidine (His) and carnosine (Car), as a respective mediator and protective agent of HOCl damage, have attracted considerable attention; however, their detailed reaction mechanisms are still unclear. In this study, using a His residue with two peptide bond groups (HisRes) as a model, the reaction mechanisms of HisRes and Car including NεH and NδH tautomers with HOCl along with the chlorination reactivity of N-chlorinated intermediates were investigated by quantum chemical methods. The obtained results indicate that in the imidazole side chain, the pyridine-like N is the most reactive site rather than the pyrrole-like N, and the kinetic order of all of the possible reaction sites in HisRes follows pyridine-like N > imidazole Cδ ≫ imidazole Cε > pyrrole-like N, while that in Car is pyridine-like N ≫ imidazole Cδ ≫ amide N. As for N-chlorinated intermediates at imidazole, although the unprotonated form has a low chlorination reactivity as expected, it can still chlorinate tyrosine. Especially, the protonated form exhibits similar ability to HOCl, causing secondary damage in vivo. N-Chlorinated Car features higher internal chlorine migration ability than its intermolecular transchlorination, preventing further HOCl-induced damage. Additionally, a generally overlooked nucleophilic Cl- shift is also found in N-chlorinated Car/HisRes, indicating that nucleophilic sites in biomolecules also need to be considered. The outcomes of this study are expected to expand our understanding of secondary damage and protective mechanisms involved in HOCl in humans.

Experimental and numerical study on the laminar burning velocities of n-decane/toluene/air mixtures at elevated temperatures

The laminar burning velocities (LBVs) of n-decane/toluene/air mixtures were measured at elevated temperatures using externally heated diverging channel (EHDC) method. The effects of initial temperature (up to 650 K), toluene blending ratio (RC7H8 = 0 to 1.0 by liquid volume) and equivalence ratio (ϕ = 0.6 to 1.4) on the LBVs of n-decane/toluene/air mixtures have been investigated. Numerical computation with a detailed reaction mechanism was used to further analyze the effects of potential interactions between n-decane and toluene. It was observed that the LBVs of n-decane/toluene/air mixtures increase with the increase of initial temperature, while the LBVs decrease with the increase of toluene blending ratio. The effects of toluene on the LBVs through chemical reactions, heat and mass transfer were analyzed in detail. Moreover, the temperature compensation method, which separates the effect of adiabatic flame temperature and contribution from chemical and disunion, was used in analysis. The effects of the toluene blending on the LBV is mainly attributed to chemical term, and the thermal effect have a second order importance. The reaction pathways and sensitivity analysis show that the LBVs of stoichiometric mixtures is less sensitive to kinetic coupling. The distinct flame propagation properties of the n-decane/toluene blended fuels are determined by the distributions of reaction rates of the crucial intermediate species and radicals.

Photodeprotection Reaction Mechanisms of Caged Species Utilizing a Photochromism Function.

Acetoxy-1,2,2-tri(aryl)ethanone (1) is a novel and visual release-and-report system that contains the photochromic diarylethylene function attached to the photocage dimethoxybenzoin platform. However, the mechanism of 1 cyclization and a subsequent deprotection remains unclear. Here, we use femtosecond and nanosecond transient absorption spectroscopies in combination with density functional theory computations to study the detailed reaction mechanism. The photodeprotection proceeds with competition between pathways initiated by two different configurations of the singlet excited state of 1 (labeled as 11LE and 11CT); the stepwise elimination after cyclization of 11LE constitutes the predominant pathway, whereas the concerted removal of acetic acid after cyclization of 11CT is the minor pathway. These results contribute to a detailed photodeprotection mechanism of 1 and provide new insights into the effect of geometric configurations of intermediates on the photodeprotection pathways. This new information can help in the further development of this type of the photolabile protecting group (PPG) for the protection of biorelevant molecules and in the design of an improved and versatile release-and-report PPG.

Modulation of wall turbulence by propagating flame of premixed hydrogen–air combustion

The mechanism of modulation of turbulent structures in the vicinity of a combustion engine wall is not yet clarified. Thus, we conducted direct numerical simulations of wall turbulence based on premixed hydrogen–air combustion using a detailed chemical reaction mechanism to clarify the mechanism of modulation of turbulence structures such as quasi-streamwise vortices by a flame propagating toward a wall. In particular, the turbulence modulation can alter the momentum and heat fluxes through the wall surface. In the simulations, we solved the fundamental equations for the compressible flow of multiple chemical species under combustion. The flame propagation speed was affected by the turbulence and was 2.04 times larger than that of the laminar flame. Moreover, upon examining the variation in the flow field, we determined that the turbulence kinetic energy in the flow field increased temporarily owing to the newly produced vortices along the flame surface including the existing turbulence vortices. In contrast, the turbulence vortices along the wall were suppressed as the flame approached the wall, and the turbulent flow tended to become laminar. In terms of vorticity transport equation, the suppression of the turbulence vortices was caused by the thermal expansion of the combustion rather than the increased viscosity. Furthermore, we determined that the vortex structure slightly influenced the chemical reaction process, but it strongly influenced the heat release rate distribution and concentration distribution of the chemical species. The current findings on the stated mechanism will aid in improving the accuracy of practical prediction and control methods for wall turbulence with combustion.

NiH-catalysed proximal-selective hydroalkylation of unactivated alkenes and the ligand effects on regioselectivity

Alkene hydrocarbonation reactions have been developed to supplement traditional electrophile-nucleophile cross-coupling reactions. The branch-selective hydroalkylation method applied to a broad range of unactivated alkenes remains challenging. Herein, we report a NiH-catalysed proximal-selective hydroalkylation of unactivated alkenes to access β- or γ-branched alkyl carboxylic acids and β-, γ- or δ-branched alkyl amines. A broad range of alkyl iodides and bromides with different functional groups can be installed with excellent regiocontrol and availability for site-selective late-stage functionalization of biorelevant molecules. Under modified reaction conditions with NiCl2(PPh3)2 as the catalyst, migratory hydroalkylation takes place to provide β- (rather than γ-) branched products. The keys to success are the use of aminoquinoline and picolinamide as suitable directing groups and combined experimental and computational studies of ligand effects on the regioselectivity and detailed reaction mechanisms.

인공신경망을 이용한 반응유동 수치해석의 반응기구 대체 연구

Reducing the computational cost of chemical kinetics is essential to implement detailed reaction mechanisms into realistic numerical simulations. The present study introduces an artificial neural network (ANN) that can predict the chemical source terms of each species for the given species mass fractions and temperature, replacing the conventional chemical terms based on Arrhenius rate equations. The ANN was trained using numerical solutions of opposed-flow flames that can cover a wide range of combustion problems. The OPPDIF code and a detailed reaction mechanism for hydrogen and air with 9 species and 19 reactions were used to generate a training dataset comprised of species mass fractions, temperature, chemical source terms. A physics-guided loss function that considers mass conservation of elemental species was employed. Using the trained ANN, a modified OPPDIF, named OPPDIF-ANN, was prepared by replacing the CKWYP with CKWYP-ANN evaluating the chemical sources via the trained ANN. For multiple global strain rate conditions, the solutions using ANN-based source terms were proven to be identical to those using Arrhenius source terms.

Modeling of the Branching Point Distribution During the Polymerization of N‐Vinylpyrrolidone

AbstractTo gain insights into the microstructure of polyvinylpyrrolidone (PVP), a detailed reaction mechanism is developed, which characterizes the polymer along the property coordinate chain length, terminal double bonds (TDB), and branching points. For practical purposes, calculations with three property coordinates are unfeasible, and model reduction is needed. Here, a reduced model with only one single property coordinate without significant loss of accuracy is derived. In the first step, the coordinate TDBs are reduced by a linear relationship between TDBs and chain length. As the parameters of this relation are state dependent, they are dynamically adjusted from a parallel calculated 0D model. In a second step, the pseudodistribution approach is used to reduce the 2D distribution to chain length as the only property coordinate and calculate moments of branching points as a function of chain length. A 2D class model is set up for validation. To demonstrate the benefits of the model, the chain length distribution and moments of branching points are calculated for different average residence times and monomer concentrations in a stirred tank reactor. In a future publication, the model will be validated by experimental data in terms of chain length distribution and branching points.

Simulation of the Air Quality in Southern California, USA in July and October of the Year 2018

A numerical investigation of the air quality in Southern California, USA in the year 2018 is presented using the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem). In July, a heat wave occurred, and in October, Santa Ana conditions prevailed; these conditions and their impact on air quality are the scope of the present numerical study.The high spatial resolution in the simulation includes two nested domains of 1 km and 3 km, respectively. Local climate zones land use categories are combined with the complex urban model building effect parameterization coupled with the building energy model (BEP+BEM) and the detailed MOZCART-T1 chemical reaction mechanism, which is the MOZART-T1 mechanism for trace gases with GOCART aerosols. Thus, the model is suitable to compare simulation results to in situ and satellite measurements of O3, NO2, CH4, and CO. The meteorology is captured well by the model. Comparison of simulation results with observations shows a good agreement of NO2 and ozone, whereas CO mixing ratios are generally underestimated. This hints at missing emissions in the 2017 National Emissions Inventory (NEI) dataset. Both the heat wave and the Santa Ana winds increase the air pollution with gas-phase species in Los Angeles. In both cases, nighttime boundary layer heights are small, which causes emissions to reside near the ground. During Santa Ana winds, NOx removal on aerosols is reduced. Methane mixing ratios are modeled very well at most stations in Los Angeles, but predictions of low emissions near the University of California cause inaccuracies at that location. Modeled and observed PM2.5 agree well on low-pollution days, but high-pollution events are generally missed by the model. During the heat wave, both modeled and observed PM2.5 concentrations exceed the recommended NAAQS National Ambient Air Quality Standards value of 12.5 g/m3. The present modeling approach serves as a base for the study and prediction of special weather events and their impact on air pollution.

Interconnected Microporous and Mesoporous Carbon Derived from Pitch for Lithium–Sulfur Batteries

Lithium–sulfur (Li–S) batteries receive great attention due to their high theoretical energy density and low cost. However, the sulfur–carbon cathode suffers from the polysulfide dissolution during cycling, and the severe shuttle effect limits the practical application of Li–S batteries. In this work, a carbon material (XU76 carbon) derived from industry-residual petroleum was synthesized with a simple and low-cost method. Nitrogen adsorption, small-angle neutron scattering (SANS), adsorption kinetics, and UV–vis spectroscopy results show that the interconnected micromesopores in XU76 could act as a reservoir and trap polysulfide intermediates efficiently. The XU76 carbon with high surface area (∼1005 m2 g–1), good electric conductivity, good ion transport, and optimized distribution of interconnected micromesopores is used as the sulfur host for trapping polysulfide intermediates and advancing sulfur redox kinetics. The Li–S battery with the sulfur–XU76 carbon cathode gives an initial discharge capacity of ∼1200 mAh g–1 in the initial cycle and reversible capacity of ∼700 mAh g–1 after 100 cycles at a C rate of 0.1 C while the Li–S battery with the sulfur–KB carbon cathode only delivers a discharge capacity of 400 mAh g–1 after 100 cycles. Also, a discharge capacity of 462 mAh g–1 is obtained after 200 cycles at a high C rate (1 C). The detailed reaction mechanism of sulfur–carbon cathodes is systematically studied at high C rates using operando Raman and S K-edge X-ray absorption spectroscopy.