Surface Sulfur Research Articles

Effect of sulfur on α-Al2O3-supported iron catalyst for Fischer–Tropsch synthesis

The effects of sulfur modification (S/Fe=0.001∼0.05, molar ratio) on the α-Al2O3-supported iron catalysts for the Fischer–Tropsch synthesis (FTS) were investigated. It was found that the presence of sulfur promoted the reduction of FeO to metallic Fe during the H2 reduction process, but decreased the rates of reduction, carburization and carbon deposition of the catalysts when CO is used as the reducing agent. Both the sulfide (S2−) and sulfate species (SO42-) are found in the SxFe/α-Al2O3 catalysts after H2 reduction and FTS reaction. The sulfide species in the H2-reduced SxFe/α-Al2O3 catalysts are located on the surface of metallic Fe particles. The intensity of H2 desorption peak around 500K is enhanced by a small amount of sulfur, while an excess of sulfur suppresses the H2 adsorption. The dissociative adsorption of CO on H2-reduced catalysts was also found to be inhibited by the presence of sulfur. The activity of the Fe/α-Al2O3 catalyst can be decreased significantly by the addition of sulfur due to the inhibition of CO dissociation and thus reduce the formation of iron carbide phases under FTS reaction conditions. Resistance to sulfur poisoning of the Fe/α-Al2O3 catalyst was found to improve with increasing the reaction temperature. The presence of sulfur also suppressed the formation of C5+ hydrocarbons and shifted the products to C2–C4 hydrocarbons. At the same time, the olefin to paraffin (O/P) ratio of the C2–C4 hydrocarbons decreased with increasing S/Fe molar ratio. These may have resulted from the increasing of the H/C ratio on the surface of sulfur modified catalyst under FTS conditions.

Preparation of un-promoted molybdenum HDS catalysts supported on titania by equilibrium deposition filtration: Optimization of the preparative parameters and investigation of the promoting action of titania

The present work deals with un-promoted molybdenum hydrodesulphurization (HDS) catalysts supported on titania (anatase) which have been prepared by “Equilibrium Deposition Filtration” (EDF). The catalysts were characterized using various techniques (XRD, N2 adsoption–desorption isotherms, TPR, DRS and XPS) and evaluated at various temperatures and atmospheric pressure in a fixed bed differential reactor, using the HDS of thiophene as a probe reaction.The calcination of the carrier before its usage has been optimized. The adjustment of the impregnation parameters allowed regulating the Mo loading in the monolayer region and thus optimizing the catalytic performance. A linear decrease of the intrinsic activity with the Mo surface density and a concomitant volcano trend for the specific activity have been found.Monomer, monopodal Mo species are deposited on the anatase surface in the pH range 7.0–4.5 and polymer Mo species at pH 2. The former are transformed into tripodal ones after calcination. Thus, the monolayer capacity of the anatase surface is decreased leading to a partial association of these species into oligomer ones where the mean number of TiOMo bridges per Mo atom is lower than three. The extent of this transformation increased with the Mo surface density. The DRS, XPS and TPR results suggested that electron transfer takes place through the TiOMo bridges from the anatase surface oxygen to the Mo4d orbitals.The monomer tripodal Mo species are transformed into relatively small Mo sulphided edge clusters in tilted or perpendicular configuration bonded on the anatase surface by TiOMo and/or TiSMo bridges. The aforementioned transfer in the electronic density from the surface oxygens, and likewise from the surface sulfur, to Mo4d orbitals weakens the MoS bonds of the clusters and stabilizes S-deficient structures creating coordinative unsaturated active sites. This explains the very high intrinsic activity of these small Mo sulphided clusters.The oligomer Mo species, on the other hand, are transformed into relatively larger Mo S-deficient sulphided clusters, also with tilted or perpendicular configuration with respect to the anatase surface. The number the MoOTi and MoSTi bridges per Mo atom is smaller than that in the small Mo sulphided clusters, resulting to less coordinative unsaturated active sites per Mo atom. The above explained the aforementioned trends for the intrinsic and specific activities.

Adsorption Kinetics and Surface Characterization of Microorganisms Grown under Different Conditions

The adsorption of bacteria onto minerals is the premise for bioleaching and plays an important role in minerals oxidation. Understanding of the adsorption kinetics onto the surface will give information on the effectiveness of bioleaching. Three kinds of mixed bacteria (Acidithiobacillus ferrooxidans, Leptospirillum ferrooxidans, Sulfobacillus) were cultured in different substrates - copper concentrate, elemental sulfur and ferrous iron and adsorbed onto different solid surface of elemental sulfur, silica and copper concentrate. Adsorption kinetics was examined and surface properties were investigated by Zeta-potential and FT-IR spectroscopy. Bacterial adsorption equilibrium data for bacteria grown on three different substrates were well fitted to Freundlich isotherms, indicating inhomogeneous and selective adsorption. Microorganisms grown on copper concentrate and S0 showed similar adsorption kinetics whereby cell adsorptions proceeded rapidly and reached equilibrium within 30 mins of interaction. With the average KF value of 46.2, most copper concentrate-grown cells were strongly adsorbed to three solid surfaces. Microorganisms grown on copper concentrate and S0 also showed higher hydrophobicity and higher isoelectric point (IEP) (pH 3.4-3.8) as compared to the soluble Fe2+-grown cells (pH 2.1), indicating higher amount of EPS and proteins on the surfaces. The FT-IR spectra indicated the presence of COOH, NH2, OH and PO4 groups on all cell surfaces. However, more proteinaceous compounds were found on cells grown on copper concentrate and S0 substrates.

Arsenopyrite weathering under conditions of simulated calcareous soil.

Mining activities release arsenopyrite into calcareous soils where it undergoes weathering generating toxic compounds. The research evaluates the environmental impacts of these processes under semi-alkaline carbonated conditions. Electrochemical (cyclic voltammetry, chronoamperometry, EIS), spectroscopic (Raman, XPS), and microscopic (SEM, AFM, TEM) techniques are combined along with chemical analyses of leachates collected from simulated arsenopyrite weathering to comprehensively examine the interfacial mechanisms. Early oxidation stages enhance mineral reactivity through the formation of surface sulfur phases (e.g., S n (2-)/S(0)) with semiconductor properties, leading to oscillatory mineral reactivity. Subsequent steps entail the generation of intermediate siderite (FeCO3)-like, followed by the formation of low-compact mass sub-micro ferric oxyhydroxides (α, γ-FeOOH) with adsorbed arsenic (mainly As(III), and lower amounts of As(V)). In addition, weathering reactions can be influenced by accessible arsenic resulting in the formation of a symplesite (Fe3(AsO4)3)-like compound which is dependent on the amount of accessible arsenic in the system. It is proposed that arsenic release occurs via diffusion across secondary α, γ-FeOOH structures during arsenopyrite weathering. We suggest weathering mechanisms of arsenopyrite in calcareous soil and environmental implications based on experimental data.

Direct Synthesis of Highly Conductive tert-Butylthiol-Capped CuInS2 Nanocrystals.

tert-butylthiol (tBuSH) is used as the sulfur source, surface ligand and co-solvent in the synthesis of CuInS2 nanocrystals (NCs). The presented method gives direct access to short-ligand-capped NCs without post-synthetic ligand exchange. The obtained 5 nm CuInS2 NCs crystallize in the cubic sphalerite phase with space group F-43m and a lattice parameter a=5.65 Å. Their comparably large optical and electrochemical band gap of 2.6-2.7 eV is attributed to iodine incorporation into the crystal structure as reflected by the composition Cu1.04 In0.96 S1.84 I0.62 determined by EDX. Conductivity measurements on thin films of the tBuSH-capped NCs result in a value of 2.5(.) 10(-2) S m(-1) , which represents an increase by a factor of 400 compared to established dodecanethiol-capped CuInS2 NCs.

Non-blinking (Zn)CuInS/ZnS Quantum Dots Prepared by In Situ Interfacial Alloying Approach.

Semiconductor quantum dots (QDs) are very important optical nanomaterials with a wide range of potential applications. However, blinking behavior of single QD is an intrinsic drawback for some biological and photoelectric applications based on single-particle emission. Herein we present a rational strategy for fabrication of non-blinking (Zn)CuInS/ZnS QDs in organic phase through in situ interfacial alloying approach. This new strategy includes three steps: synthesis of CuInS QDs, eliminating the interior traps of QDs by forming graded (Zn)CuInS alloyed QDs, modifying the surface traps of QDs by introducing ZnS shells onto (Zn)CuInS QDs using alkylthiols as sulfur source and surface ligands. The suppressed blinking mechanism was mainly attributed to modifying QDs traps from interior to exterior via a step-by-step modification. Non-blinking QDs show high quantum yield, symmetric emission spectra and excellent crystallinity, and will enable applications from biology to optoelectronics that were previously hindered by blinking behavior of traditional QDs.

Improved interface properties of atomic-layer-deposited HfO2 film on InP using interface sulfur passivation with H2S pre-deposition annealing

Surface sulfur (S) passivation on InP substrate was performed using a dry process – rapid thermal annealing under H2S atmosphere for III–V compound-semiconductor-based devices. The electrical properties of metal-oxide-semiconductor capacitor fabricated with atomic-layer-deposited HfO2 film as a gate insulator were examined, and were compared with the similar devices with S passivation using a wet process – (NH4)2S solution treatment. The H2S annealing provided solid S passivation with the strong resistance against oxidation compared with the (NH4)2S solution treatment, although S profiles at the interface of HfO2/InP were similar. The decrease in electrical thickness of the gate insulator by S passivation was similar for both methods. However, the H2S annealing was more effective to suppress interface state density near the valence band edge, because thermal energy during the annealing resulted in stronger S bonding and InP surface reconstruction. Moreover, the flatband voltage shift by constant voltage stress was lower for the device with H2S annealing.

Effects of Additives on Sulfur Transformation, Crystallite Structure and Properties of Coke during Coking of High-sulfur Coal

High-sulfur coal, as an alternative coal source, has a relatively high proportion in coal reserves. However, the feature of high sulfur content, which can cause environmental pollution and poor quality of molten iron, restrains its utilization in coking industry. Coking experiments of high-sulfur coal with Fe2O3, La2O3 and CaO as additives were carried out in order to fix the sulfur in coke. The effects of additives on sulfur distribution, crystallite structure, surface morphology and properties of coke were investigated. The results indicate that CaO can be used as sulfur-fixing agent in coking process, and CaS is the main mineralogical phase of the sulfur-contained mineral constituents in coke. Fe2O3 and La2O3 facilitate the conversion of CaO to CaS. The additives mainly influence the crystallite height and the average interlayer spacing d002 of coke. The addition of La2O3 increases the value of the crystallite height while the addition of CaO and Fe2O3 decreases it. CaO leads the pores of coke to increase with its physical action and agglomerating characteristic. Fe2O3 and C can form (Fe,C), resulting in the pulverization and erosion of the pore wall. La2O3 makes the coke surface become more compact and thinner. The reactivity of coke increases with the decrease of crystallite height and crystallite layer number.

Typomorphism of pyrite of the Sukhoi Log deposit (East Siberia)

The typomorphic features of pyrite of the Sukhoi Log deposit were studied by a set of volumetric and surface methods: electron probe microanalysis, scanning electron and probe microscopy, powder X-ray diffraction, X-ray photoelectron and Auger electron spectroscopy, atomic-absorption spectrometry in the SSADSC (method of statistical sample of analytical data for single crystals) version, and atomic-emission spectrometry. Pyrite from the Sukhoi Log deposit has the following distinctive features: permanent presence of sulfite ion, which often dominates over other surface sulfur anions; weakly determined size dependence of the content of uniformly distributed Au owing to the presence of an internal concentrator of gold—dispersed carbonaceous material—in pyrite from ore zones; cell sculptures of the crystal faces, which appeared owing to the nanofragmentation of the growth surface; micro- and nanoinclusions of carbonaceous phases within crystals, associated with defects in their structure; and thin films enriched in O and C on the surface of and within the crystals. It has been shown that gold-sulfide mineralization at the Sukhoi Log deposit formed in a single ore-generating hydrothermal system, in which gold, sulfur, and carbon belonged to a microparagenesis. Some features (composition of surface, characteristics of submicroscopic structure, and elemental composition) evidence that the conditions of crystallization of pyrite in inter-ore space were different from the conditions of its genesis in the ore zones, which suggests the presence of at least two genetic types of pyrite. Carbonaceous micro- and nanoparticles and O- and C-containing films can favor an increase in the adsorption of gold from cyanide solutions on pyrite. To reduce this effect during gold recovery, a technique for surface modification should be elaborated. The ways for solving the most complicated problems dealt with the source of noble metals (NM) and the ore specialization of the deposit have been outlined. For this purpose, a detailed analysis of the main ore minerals for trace-element speciation is required. In the case of the magmatic source of NM, correlation between the contents of Au and PGE structural forms should exist. On the other hand, there is no correlation between the structural forms of Au or Pt and elements whose contents in fluid are determined by the host rock rather than the magmatic source.

Evaluation of Polycrystalline Platinum and Rhodium Surfaces for the Electro-Oxidation of Aqueous Sulfur Dioxide

Polycrystalline Rh and Pt were studied to ascertain their electrocatalytic activity for the electro-oxidation of SO2, an important reaction in sulfur dioxide depolarized electrolyzers used to produce hydrogen. Cyclic voltammetry and linear polarization methods were employed to evaluate the catalytic activity of these surfaces. Rh exhibited 25-fold lower catalytic activity than Pt and was more susceptible to poisoning by adsorbed intermediate sulfur species. Koutecky-Levich analysis indicated a two-electron transfer reaction on the Pt surface, which corresponded to the most commonly accepted SO2 electro-oxidation reaction mechanism. The Tafel slopes in the low potential region (near the onset potential), in conjunction with an analysis of well-known reaction mechanisms, suggested that the step leading to the oxidation of water to form adsorbed hydroxyl species was the rate-determining step (RDS). This mechanistic model predicts a decrease in Tafel slope with increasing coverage of catalyst active surface sites by adsorbed sulfur species. For Pt, we estimate a surface sulfur coverage of 4 % based on the experimentally measured Tafel slope. In the case of Rh, the sulfur coverage was calculated to be approximately 1 %. The Tafel slopes obtained changed from 106 mV decade−1 for Rh and 80 mV decade−1 for Pt at potentials below 0.7 V vs. standard hydrogen electrode (SHE) to 210 mV decade−1 for Rh and 162 mV decade−1 for Pt at potentials above 0.7 V vs. SHE, suggesting a change in the reaction mechanism corresponding to a change in the surface of the electrocatalyst.

Approaching the Hole Mobility Limit of GaSb Nanowires.

In recent years, high-mobility GaSb nanowires have received tremendous attention for high-performance p-type transistors; however, due to the difficulty in achieving thin and uniform nanowires (NWs), there is limited report until now addressing their diameter-dependent properties and their hole mobility limit in this important one-dimensional material system, where all these are essential information for the deployment of GaSb NWs in various applications. Here, by employing the newly developed surfactant-assisted chemical vapor deposition, high-quality and uniform GaSb NWs with controllable diameters, spanning from 16 to 70 nm, are successfully prepared, enabling the direct assessment of their growth orientation and hole mobility as a function of diameter while elucidating the role of sulfur surfactant and the interplay between surface and interface energies of NWs on their electrical properties. The sulfur passivation is found to efficiently stabilize the high-energy NW sidewalls of (111) and (311) in order to yield the thin NWs (i.e., <40 nm in diameters) with the dominant growth orientations of ⟨211⟩ and ⟨110⟩, whereas the thick NWs (i.e., >40 nm in diameters) would grow along the most energy-favorable close-packed planes with the orientation of ⟨111⟩, supported by the approximate atomic models. Importantly, through the reliable control of sulfur passivation, growth orientation and surface roughness, GaSb NWs with the peak hole mobility of ∼400 cm(2)V s(-1) for the diameter of 48 nm, approaching the theoretical limit under the hole concentration of ∼2.2 × 10(18) cm(-3), can be achieved for the first time. All these indicate their promising potency for utilizations in different technological domains.

Dynamic Covalent Polymers via Inverse Vulcanization of Elemental Sulfur for Healable Infrared Optical Materials.

We report on dynamic covalent polymers derived from elemental sulfur that can be used as thermally healable optical polymers for mid-IR thermal imaging applications. By accessing dynamic S-S bonds in these sulfur copolymers, surface scratches and defects of free-standing films of poly(sulfur-random-1,3-diisopropenylbenzene) (poly(S-r-DIB) can be thermally healed, which enables damaged lenses and windows from these materials to be reprocessed to recover their IR imaging performance. Correlation of the mechanical properties of these sulfur copolymers with different curing methods provided insights to reprocess damaged samples of these materials. Mid-IR thermal imaging experiments with windows before and after healing of surface defects demonstrated successful application of these materials to create a new class of "scratch and heal" optical polymers. The use of dynamic covalent polymers as healable materials for IR applications offers a unique advantage over the current state of the art (e.g., germanium or chalcogenide glasses) due to both the dynamic character and useful optical properties of S-S bonds.

Alkane reforming on partially sulfided CeO2 (1 1 1) surfaces

Cleanup of biomass gasification effluent requires a catalyst that can reform methane and larger hydrocarbons while tolerating the presence of H2S or, ideally, that can act as a sulfur sorbent while reforming hydrocarbons. We utilize density functional theory (DFT) methods to examine the impact of oxide sulfidation on the reforming of methane and the initial steps of propane reforming, using M-doped CeO2 catalysts. On a ceria oxy-sulfide surface, surface oxygen atoms remain active for CH bond activation via hydride abstraction whereas surface sulfur atoms are significantly less active. Methyl adsorption is slightly favored at a surface sulfur site, and though subsequent dehydrogenation steps remain viable, the final steps of methane decomposition may lead to carbon buildup on the surface. However, surface sulfur sites will be less active globally for the initial rate limiting H abstraction step, and these sites can nucleate carbon buildup. Doping CeO2 with Mn accelerates CH bond activation, aids eventual CO product desorption, and may induce sulfur tolerance by motivating CHx intermediates to bind to surface O atoms rather than surface S atoms. This work represents an initial step in the development of S-tolerant oxide catalysts for hydrocarbon reforming.

Hydrogen Activation on the Promoted and Unpromoted ReS2 (001) Surfaces under the Sulfidation Conditions: A First-Principles Study

Hydrogen activation on the promoted and promoter-free ReS2(001) surfaces under the sulfidation conditions is studied by means of periodic density function theory (DFT) calculations within the generalized gradient approximation. First, surface-phase diagrams are investigated by plotting the surface free energy as a function of the chemical potential of S (μS) on the unpromoted and promoted ReS2 (001) surfaces with different loadings of nickel, cobalt, tungsten, and tantalum. The results show that on the unpromoted surface sulfur coverage of 25% and on the promoted surfaces sulfur coverage of 25% as well as 25% promoter modification are the most stable conditions, respectively, under hydrodesulfurization (HDS) reaction conditions. Second, hydrogen adsorption and dissociation are explored on these preferred surfaces. It is found that hydrogen adsorbs weakly on all the surfaces studied. The physical adsorption character makes its diffusion favorable, resulting in various adsorption sites and dissociation path...

Lifetime and Performance Prediction of SOFC Anodes Operated with Trace Amounts of Hydrogen Sulfide

Chemical degradation of Solid Oxide Fuel Cell (SOFC) anodes can be caused by various types of impurities present in practical fuels, as e.g. sulfur, chlorine, phosphorus and siloxane. To allow for a deeper understanding of the processes leading to sulfur poisoning, this study presents a modeling work of SOFC operating on H2/H2O and CH4/H2/H2O gas mixtures with different hydrogen sulfide (H2S) concentrations. In order to interpret experimental measurements, an elementary kinetic model is developed comprising a detailed multi‐step reaction mechanism of sulfur formation and oxidation at Ni/YSZ anodes coupled with channel gas-flow, porous-media transport and elementary charge-transfer chemistry. A thermodynamic and kinetic data set of sulfur formation and oxidation is derived based upon various literature sources including a coverage-dependent description of the enthalpy of surface-adsorbed sulfur. Firstly, the developed model is validated against literature-based sulfur chemisorption isobars, and subsequently against electrochemical button-cell experiments displaying a significant influence of operation temperature and applied potential on cell performance and degradation. It is shown that sulfur surface coverage increases with increasing current density indicating a low sulfur oxidation rate. In order to gain for an advanced fundamental understanding of sulfur poisoning, sensitivity analyses towards total anode resistance and sulfur coverage for different operating conditions will be presented. Furthermore, the identified elementary sulfur poisoning reactions are used to extend an existing reaction mechanism for methane steam reforming which is then validated based upon a variety of electrochemical experiments. It is shown that atomically adsorbed sulfur significantly influences heterogeneous reforming chemistry, causing a substantial decrease in OCV. Under polarization, at constant current densities the cell voltage decreases in a non-linear way. After the removal of hydrogen sulfide from the feed gas the cell shows a faster recovery than in H2/H2O mixtures. In addition, numerical impedance simulations over a wide range of operating conditions were performed, which allows a physically-based assignment of observed gas concentration, heterogeneous chemistry and electrochemical processes.

Surface trace gases at a rural site between the megacities of Beijing and Tianjin

The North China Plain (NCP) has recently faced serious air quality problems as a result of enhanced gas pollutant emissions due to the process of urbanization and rapid economic growth. To explore regional air pollu- tion in the NCP, measurements of surface ozone (O3), nitrogen oxides (NOx), and sulfur dioxide (SO2) were car- ried out from May to November 2013 at a rural site (Xianghe) between the twin megacities of Beijing and Tianjin. The highest hourly ozone average was close to 240 ppbv in May, followed by around 160 ppbv in June and July. High ozone episodes were more notable than in 2005 and were mainly associated with air parcels from the city cluster in the hinterland of the polluted NCP to the southwest of the site. For NOx, an important ozone precur- sor, the concentrations ranged from several ppbv to nearly 180 ppbv in the summer and over 400 ppbv in the fall. The occurrence of high NOx concentrations under calm condi- tions indicated that local emissions were dominant in Xianghe. The double-peak diurnal pattern found in NOx concentrations and NO/NOx ratios was probably shaped by local emissions, photochemical removal, and dilution re- sulting from diurnal variations of surface wind speed and the boundary layer height. A pronounced SO2 daytime peak was noted and attributed to downward mixing from an SO2-rich layer above, while the SO2-polluted air mass transported from possible emission sources, which differed between the non-heating (September and October) and heating (November) periods, was thought to be responsible

Monitoring the temporal variations of PM2.5 and gases close to the highway in Sohar, Oman

The aim of this study was to identify the relationship between the concentrations of PM2.5 (particulate matter less than 2.5 μm) and the temporal variation of the monitored gases at Sohar highway, Oman, from November 2014 to February 2015. The hourly concentrations of surface ozone (O3), nitric dioxide (NO2) and sulphur dioxide (SO2) were measured by an open-path differential optical absorption spectroscopy instrument installed across Sohar highway. Additionally, the same gases and the meteorological parameters were measured in the same location of the PM2.5 analyser. The findings of this study show that on the hourly time scale, PM2.5 and O3 were very weakly and negatively correlated. In contrast, on the daily time scale, PM2.5 and O3 were positively rather weakly correlated. Stronger correlation coefficient was found between 24 h averages of PM2.5 and daily maximum O3 concentrations. A policy implication of these findings could be that reducing the emissions of O3 precursors reduces the levels of PM2.5 as well.

Modulating Electrical Properties of InAs Nanowires via Molecular Monolayers.

In recent years, InAs nanowires have been demonstrated with the excellent electron mobility as well as highly efficient near-infrared and visible photoresponse at room temperature. However, due to the presence of a large amount of surface states that originate from the unstable native oxide, the fabricated nanowire transistors are always operated in the depletion mode with degraded electron mobility, which is not energy-efficient. In this work, instead of the conventional inorganic sulfur or alkanethiol surface passivation, we employ aromatic thiolate (ArS(-))-based molecular monolayers with controllable molecular design and electron density for the surface modification of InAs nanowires (i.e., device channels) by simple wet chemistry. More importantly, besides reliably improving the device performances by enhancing the electron mobility and the current on-off ratio through surface state passivation, the device threshold voltage (VTh) can also be modulated by varying the para-substituent of the monolayers such that the molecule bearing electron-withdrawing groups would significantly shift the VTh towards the positive region for the enhancement mode device operation, in which the effect has been quantified by density functional theory calculations. These findings reveal explicitly the efficient modulation of the InAs nanowires' electronic transport properties via ArS(-)-based molecular monolayers, which further elucidates the technological potency of this ArS(-) surface treatment for future nanoelectronic device fabrication and circuit integration.

Nitrogen and Sulfur Co-doped Graphene Supported Cobalt Sulfide Nanoparticles as an Efficient Air Cathode for Zinc-air Battery

Zinc-air battery is considered as one of the promising energy storage devices due to their low cost, eco-friendly and safe. Here, we present a simple approach to the preparation of cobalt sulfide nanoparticles supported on a nitrogen and sulfur co-doped graphene oxide surface. Cobalt sulfide nanoparticles dispersed on graphene oxide hybrid was successfully prepared by solid state thermolysis approach at 400 °C, using cobalt thiourea and graphene oxide. X-ray diffraction study revealed that hybrid electrode prepared at 400 °C results in pure CoS2 phase. The hybrid CoS2(400)/N,S-GO electrode exhibits low over-potential gap about 0.78 V vs. Zn after 70 cycles with remarkable and robust charge and discharge profile. And also the CoS2(400)/N,S-GO showing deep discharge behavior with stability up to 7.5 h.

Lifetime and Performance Prediction of SOFC Anodes Operated with Trace Amounts of Hydrogen Sulfide

An elementary kinetic model is developed to predict the influence of sulfur on Ni/YSZ anodes of solid oxide fuel cells (SOFC) performance. A multi-step reaction mechanism describing the formation and oxidation of sulfur on the Ni surface is coupled with gas transport in the channel and porous phase, and charge-transfer processes. A thermodynamic and kinetic data set of sulfur formation and oxidation is derived based upon various literature sources including a coverage-dependent description of the enthalpy of surface-adsorbed sulfur. The validity of the model is demonstrated on two SOFC operation modes, namely H2/H2O/H2S and CH4/H2/H2O/H2S fuel mixtures, at different operating conditions using various electrochemical literature experiments. The first concern is the influence of adsorbed sulfur on charge-transfer processes and the second concern is the effect of adsorbed sulfur on complex methane reforming chemistry. The results reveal that sulfur surface coverage increases with current density demonstrating a low sulfur oxidation rate.