H2S-containing Atmosphere Research Articles

Promotion of mixed protonic–electronic transport in La5.4WO11.1−δ membranes under H2S atmospheres

S ions are incorporated in the LWO lattice when treated under H2S-containing atmospheres. Electronic conductivity increases by the coupled S incorporation and W reduction and, subsequently, H2 permeation is boosted at moderate temperatures.

NiFe]-(Oxy)Sulfides Derived from NiFe2O4 for the Alkaline Hydrogen Evolution Reaction

The development of noble-metal-free electrocatalysts is regarded as a key factor for realizing industrial-scale hydrogen production powered by renewable energy sources. Inspired by nature, which uses Fe- and Ni-containing enzymes for efficient hydrogen generation, Fe/Ni-containing chalcogenides, such as oxides and sulfides, received increasing attention as promising electrocatalysts to produce hydrogen. We herein present a novel synthetic procedure for mixed Fe/Ni (oxy)sulfide materials by the controlled (partial) sulfidation of NiFe2O4 (NFO) nanoparticles in H2S-containing atmospheres. The variation in H2S concentration and the temperature allows for a precise control of stoichiometry and phase composition. The obtained sulfidized materials (NFS) catalyze the hydrogen evolution reaction (HER) with increased activity in comparison to NFO, up to −10 and −100 mA cm−2 at an overpotential of approx. 250 and 450 mV, respectively.

Hydrogen permeability and stability of palladium films in a high pressure reactor

Palladium (Pd) thin films were fabricated by colloidal spray deposition (CSD) on substrates of porous yttrium-stabilized zirconium oxide (YSZ). The films were sintered at 1140–1160 °C for 2–3 h in argon and had thickness of 5–11 µm. The hydrogen (H2) permeation flux for the Pd film was measured with simulated feed gases (90% H2/He, syn-gas/steam, or syn-gas/steam with H2S) flowing on the film side and sweep gas (Ar) flowing on the substrate side. The hydrogen flux with the Pd film was obtained by adjusting the flow rate and pressure of the gas. Hydrogen flux values of 121–173 cm3 min−1 cm−2 were measured at 388–596 °C (feed: 90% H2/He at 200 mL min−1; sweep: Ar at 1400 mL min−1; and ΔP = ~170 psi), and the permeability was calculated and compared with literature values. Because Pd is known to be sensitive to some gases, the stability of Pd films was evaluated by examining the microstructures of samples after their exposure to gas mixtures containing CO, CO2, H2O, and H2S. From the results of stability tests in H2S-containing atmospheres, the Pd/Pd4S phase boundary was determined, and this measured boundary was compared to the Pd/Pd4S boundary calculated from the thermodynamic data in the literature.

Sb2Se3 films fabricated by thermal evaporation and post annealing

Herein, Sb2Se3-related thin films were prepared by thermal evaporation at room-temperature and post annealing at high temperature. The Sb2Se3 film performance was studied as a function of annealing atmosphere: an inert Ar atmosphere, a H2S-containing atmosphere or a H2Se-containing atmosphere. The phase structure and microscopic morphology were mainly investigated as a function of temperature and annealing atmosphere. The results show that all films possess the orthorhombic Sb2Se3 phase regardless of the annealing atmosphere. Furthermore, the preferred epitaxial growth of the films annealed under the H2S-containing and H2Se-containing atmospheres is along (020) and (120) planes; while the preferred epitaxial growth of the films annealed under an inert Ar atmosphere is along (211) and (221) planes. When subjecting the films to annealing temperatures >450 °C, the film thickness was observed to reduce when annealing under Ar and H2Se-containing atmospheres, which may be ascribed to the volatilization of the films at high temperatures.

Sulfur-tolerant Fe-doped La0·3Sr0·7TiO3 perovskite as anode of direct carbon solid oxide fuel cells

Fe-doped La0·3Sr0·7TiO3 (LSFT) is synthesized and systematically characterized towards application as an anode material for direct carbon solid oxide fuel cells (DC-SOFCs). The structural, electrical and electrochemical properties of LSFT under the operation conditions of DC-SOFCs have been evaluated. High structural stability, improved ionic conductivity, electrocatalytic activity, and electrochemical performance are demonstrated. Electrolyte-supported DC-SOFC with LSFT anode provides a maximum power density of 292 mW cm−2 at 850 °C, which is comparable to those state-of-the-art Ni-YSZ anode for DC-SOFC. In addition, it shows excellent long-term operational stability (over 110 h) in H2S-containing CO atmosphere. It thus promises as a novel anode candidate for DC-SOFCs with whole-solid-state configuration.

Effect of Sulfur on the Reduction of Ilmenite by Syngas in Chemical Looping Combustion

The reactivity of ilmenite as an oxygen carrier (OC) in the presence of H2S was studied. A simulated syngas (66% CO, 34% H2) was used as the fuel. H2S concentrations were set to 4700 and 6580 ppm. The effect of the presence of CO2 was also investigated. The experiments were carried out using a thermogravimetric analyzer (TGA) at atmospheric pressure, with temperatures varying from 1073 to 1223 K. The results showed that the presence of H2S had no effect on the reduction kinetics of ilmenite. With the presence of only CO2 in the syngas, deposition on ilmenite samples was not observed. In the presence of H2S, deposition was observed regardless of the presence of CO2. Higher H2S concentration led to more pronounced deposition. It was shown that deposition only occurred after the ilmenite sample was sufficiently reduced. For ilmenite oxidation, the mass change curves display a distinct peak followed by a valley when the sample was previously reduced in the presence of H2S, indicating reactions between the sulfur deposit and air. The amount of the sulfur deposit could be calculated using the oxidation curves. Scanning electron microscope-energy dispersive X-ray (SEM-EDX) and X-ray diffraction (XRD) analyses were conducted to examine the surface of the reduced samples and the results from these analyses confirmed the presence of the sulfur deposit on the surface of the samples that were reduced in H2S-containing atmospheres.

Structural evolution of BaCe0.65Zr0.20Y0.15O3-δ-Ce0.85Gd0.15O2-δ composite MPEC membrane by in-situ synchrotron XRD analyses

Nowadays, dense ceramic membranes based on mixed ionic and electronic conductors are considered very promising materials for H2 separation at T > 600 °C. Among these, BaCe0.65Zr0.2Y0.15O3-δ-Ce0.85Gd0.15O2-δ (BCZ20Y15-GDC15) composite combine an acceptable H2 flux and good chemical stability under CO2- and H2S-containing atmospheres. However, a clear understanding of its crystal structure, phase stability and mechanical stability under real working conditions could not yet be obtained. In this work, its structural evolution was investigated from room temperature to 800 °C by in-situ synchrotron XRD analyses under dry and wet H2. No chemical interaction between the BCZ20Y15 and GDC15 phases occurred in the composite, thus demontrating its excellent chemical stability under operating conditions. However, some phase transitions were observed for the BCZ20Y15 phase, under both dry and wet H2: i.e., it showed an orthorhombic Imma structure from room temperature to 100 °C, trigonal R-3c up to 700 °C and cubic Pm-3m up to 800 °C. On the other hand, the GDC15 phase did not display any phase transition, remaining in a cubic Fm-3m structure under all tested conditions. Moreover, a synergistic effect of the BCZ20Y15 and GDC15 phases in the volume expansion of the composite was revealed: indeed, BCZ20Y15 and GDC15 lattice expansion rates tend to approach each other in the composite under reducing conditions. This synergistic effect is very important for the mechanical performances of BCZ20Y15-GDC15 composite. The similar expansion rate observed for BCZ20Y15 and GDC15 may reduce the strain and prevent failure of this ceramic membrane under operating conditions.

Influences of sulfurization on performances of Cu(In,Ga)(Se,S)2 cells fabricated based on the method of sputtering CIGSe quaternary target

The sequential processes of sputtering quaternary CIGSe ceramic targets and annealing in sulfur-containing atmosphere were applied to prepare Cu(In,Ga)(Se,S)2 (CIGSeS) absorbers. Solar cell devices were fabricated with CIGSeS absorbers annealed in H2S-containing atmosphere with different H2S concentrations. Composition and microstructure of absorbers and performances of cells were investigated. Gallium tends to diffuse towards CIGSeS absorber surface as H2S concentration increases, furthermore leading to a Ga-rich layer at the surface. The Ga gradient and the incorporation of S at surface result in the enlarged band gap (Eg) in the space charge region (SCR). In this work, the conversion efficiency of CIGSeS solar cells could be promoted with the highest efficiency of 13.3%, with a VOC of 566 mV. The increasing Eg gradient towards surface enhances the suppress of deep level recombination, and the best device performance was achieved with the improvement of band gap structure as the annealing H2S concentration reached 15 vol%.

A novel study of sulfur-resistance for CO2 separation through asymmetric ceramic-carbonate dual-phase membrane at high temperature

Sulfur compounds present in high-temperature gases from various industrial sources have a negative influence on the permeability of different kinds of membranes. In this study, we present a general and efficient strategy to design and prepare two asymmetric membranes for CO2 separation that are resistant to H2S. The asymmetric membranes, mainly composed of one adsorbed layer for H2S consumption and one dense ceramic-carbonate layer for CO2 separation, show not only high CO2 permeation flux but also remarkably stable permeation behavior under an H2S-containing atmosphere. The sulfur-resistant stability times of the asymmetric membranes are approximately 10–12 times higher than the single ceramic-carbonate dual-phase membrane. The adsorbed layer of the asymmetric membranes can react with H2S to form Ce-O-S phases, gradually causing deactivation of the adsorbed layer. However, the adsorbed layer can be regenerated in the oxygen-containing gas stream above 850 °C, which can effectively remove the sulfur content from the adsorbed layer, making recycle of the membrane possible. Sulfur accumulated in the adsorbed layer of the membrane as a Ce2O2S phase, can be oxidized into SO2 under air stream and elemental sulfur (S) under a 2.5% O2/He gas stream. These asymmetric membranes thus possess high permeation stability in the H2S-containing atmosphere with good regenerability and also have potential in collection and removal of sulfur impurities from gas streams.

Enhanced sulfur tolerance of BaCe0.65Zr0.20Y0.15O3-δ-Ce0.85Gd0.15O2-δ composite for hydrogen separation membranes

Thanks to its high hydrogen permeability and good chemical stability in moist CO2 environments, BaCe0.65Zr0.20Y0.15O3-δ-Ce0.85Gd0.15O2-δ mixed conducting material is considered one of the most promising candidates for hydrogen separation ceramic membranes. In this work, its chemical stability under H2S-rich atmosphere was systematically investigated by in-situ electrochemical characterizations and ex-situ structural, chemical and morphological analyses. A performance degradation of the total conductivity depending on the H2S content was observed: at 700 °C and under 1500 and 700 ppm of H2S the conductivity drop was 15% and 2% respectively. The complementary information gathered by morphological and chemical analyses showed that the changes responsible for the total conductivity degradation are mainly confined to the surface of the membrane. Indeed, after the exposure to the H2S-containing atmosphere, some traces of sulfur-related compounds were detected only on the top of the membrane while the bulk preserved a fully dense structure with well-defined grain boundaries and no evidence of cracks. However, no evidence of S-based compounds were revealed by structural investigations, probably due to the detection limit of these techniques and/or to the low crystallinity of the secondary phases. Contrary to Pd-based membranes that are severely deteriorated by a few ppm of sulfur, this material shows an acceptable stability even under 700 ppm of H2S and could be attractive for tailored applications such as, for example, operations related to steam reforming of methane often containing 10–300 ppm of H2S.

Comparison of the high-temperature chloride-induced corrosion between duplex steel and Ni based alloy in presence of H2S

Duplex steel 1.4462 and Ni-based alloy Centralloy ET45 micro were tested in HCl- and H2S-containing atmospheres at 680 °C for 24, 72 and 240 h. Corroded samples were investigated by metallography, SEM/EDX and XRD. Corrosion products on the surface consisted of Cr2O3 and chromium sulfides. Beneath this surface layer, iron and chromium chloride were found. A depletion of iron was observed due to formation of volatile iron chloride. Both materials displayed a selective attack of the existing phases. The ferrite phase of the Duplex steel was attacked, while the Ni-based alloy showed the selective attack of chromium carbides.

Effect of Hot-Dip Aluminizing on High-Temperature Corrosion of Fe-Cr Steels

Hot-dip aluminizing is a simple, cost-effective diffusion coating technique that can coat aluminum on diverse substrates with complicated shapes. It is carried out by dipping the substrate into molten Al bath for a certain period, and pulling out of the bath into the air. The employed substrates were mostly carbon steels, low alloyed steels, Fe-(Si, Cr) alloys. During hot-dipping, inter-diffusion between the steel substrate and molten Al occurs to produces the Al-rich topcoat, the outer FeAl3 layer, and the inner Fe2Al5 layer. The property of these aluminized layers depends on various hot-dipping parameters such as bath composition, time, temperature, and substrate. In this study, hot-dipping was performed on Fe-Cr alloys, and the corrosion behavior of aluminized Fe-Cr alloys at high temperatures was studied. The corrosion tests were performed in air, SO2-containing atmospheres, and H2S-containing atmospheres. Hot-dip aluminizing was found as an effective coating technique, which could form protective α-Al2O3 scales not only in air but also in (SO2, H2S)-containing aggressive corrosive environments due to high thermodynamic stability of Al2O3. ACKNOWLEDGEMENT. This work was supported by the project “Development of the High-Efficiency Low-Emission Future Energy Production Technology (EO15580)” of National Research Council of Science & Technology (NST) grant by the Korea government (MSIP) (No. CRC-15-07-KIER).

Corrosion of Fe<sub>3</sub>Al-4Cr Alloys at 1000°C in N<sub>2</sub>-0.1%H<sub>2</sub>S Gas

Pure Fe3Al and Fe3Al+4%Cr alloys were corroded at 1000 °C for up to 200 h in N2-0.1%H2S-mixed gas in order to study their corrosion behavior in H2S-containing atmosphere. The formed scales consisted primarily of α-Al2O3, FeAl2O4, and Fe2O3. In these oxide scales, hydrogen and sulfur dissolved according to the reaction; H2S→2H+S. Corrosion products of Cr were not identified in the scales from the XRD analysis, indicating that Cr dissolved in the oxide scales. Fe3Al+4%Cr alloy displayed poorer corrosion resistance than Fe3Al alloy, indicating that chromium accelerated the corrosion rates of Fe3Al alloys.

Pentlandite-MoS2 as sulfur tolerant anode materials for solid oxide fuel cells

(Co, Ni)9S8 pentlandite was prepared via the hydrothermal method and applied with MoS2 as the sulfur tolerant anode materials for solid oxide fuel cells (SOFCs). XRD patterns showed that (Co, Ni)9S8 was converted from (Co, Ni)3S4 at temperature higher than 600 °C. The performance of the single cell with (Co, Ni)9S8 -MoS2-YSZ (8% yttria stabilized zirconia) anode was 104.5 mWcm−2 in 50 ppm H2S-H2 at 850 °C, which was significantly higher than that of 52.8 mWcm−2 in pure H2. The sulfur tolerance of the anode was attributed to the mitigation of the sulfur occupation and promotion of the H2 adsorption and dissociation by the (Co, Ni)9S8 -MoS2 materials. The cell performance was maintained relatively stable during a preliminary test of 110 min in H2S-containing atmosphere, indicating (Co, Ni)9S8-MoS2 as promising sulfur-tolerant anode materials for SOFC applications.

H2S-tolerant oxygen-permeable ceramic membranes for hydrogen separation with a performance comparable to those of palladium-based membranes

We propose a new method for hydrogen separation using an oxygen-permeable ceramic membrane, and achieve a high hydrogen separation rate comparable to those of Pd-based membranes and excellent stability under a H2S-containing atmosphere.

Vanadium-Containing Oil Ash Corrosion of Boilers Under Oxidizing and Syngas Atmospheres

Corrosion in oil-fired boilers is accelerated in the presence of vanadium, sodium, and sulfur from low grade fuels. Several iron-based alloys and a nickel-based alloy were studied in order to verify the effect of different Cr and Al contents under conditions typical for the partial oxidation process. Materials performance was analyzed by means of substrate recession rate and metallographic characterization. Samples were exposed to H2S-containing syngas atmosphere in order to simulate boiler operating conditions without ash deposition. The prevailing corrosion mechanism under this reducing atmosphere was sulfidation. In order to simulate boiler conditions with oil ash deposits, samples were immersed in 60 mol% V2O5–40 Na2SO4 salt in the same syngas atmosphere. The prevailing corrosion mechanism in this case was sulfidation under a reducing atmosphere and dissolution of iron or chromium from the substrate. The nickel-based substrate showed the best performance under these experimental conditions. In order to simulate air inlet due to shutdowns, samples were immersed in the same salt during exposure in air. The prevailing corrosion mechanism was still sulfidation in the oxidizing atmosphere accelerated by the presence of vanadate salt. This corrosion mechanism is characterized by the formation of a sulfide/oxide layer adjacent to the metal, the dissolution of oxides in the molten deposit, and their precipitation near the outer surface of the deposit.

Cu2ZnSnS4 thin film deposited by sputtering with Cu2ZnSnS4 compound target

Cu2ZnSnS4 (CZTS) thin films were prepared by a single sputtering process with a CZTS compound target or a co-sputtering process with Cu, ZnS, and SnS targets followed by annealing in a H2S-containing atmosphere at several temperatures. Between the CZTS thin films prepared by both single and co-sputtering processes annealed at 500 °C, there are no major differences in the X-ray diffraction patterns, optical properties, and chemical composition. However, there is a difference in the scanning electron microscopy images. Although the CZTS thin films prepared by the co-sputtering process have some voids, the CZTS thin films prepared by the single sputtering process have no voids. The solar cells prepared with the CZTS thin films deposited by the single sputtering process followed by annealing at 500 °C show a higher efficiency of 4.40% than those prepared with the CZTS thin films prepared by the co-sputtering process (2.06%).

Performance of Y0.9Sr0.1Cr0.9Fe0.1O3−δ as a sulfur-tolerant anode material for intermediate temperate solid oxide fuel cells

Perovskite-type Y0.9Sr0.1Cr0.9Fe0.1O3−δ maintained good chemical stability under a H2S-containing atmosphere based on results from X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FT-IR) in our previous study. In this research, the YSCF-based anode was studied using H2 and H2S-containing fuels. The activity of an electrode is closely related to its material composition, lattice structure, physic-chemical properties, and morphologic structure. Therefore, the characteristics of the YSCF powders and the cell were analyzed by XRD, Brunauer–Emmett–Teller (BET) surface area analysis, and scanning electron microscopy (SEM). The conductivities of YSCF were evaluated by four-probe method in 10% H2–N2, 1% H2S–N2 and air, respectively. Thermodynamic calculations and X-ray photoelectron spectroscopy (XPS) analysis have been used to investigate the stability of the elements in YSCF upon exposure to hydrogen sulfide (H2S) in hydrogen (H2) over a range of partial pressures of sulfur (pS2) and oxygen (pO2) that are representative of fuel cell operating conditions. In addition, the performance of the complete cell (YSCF–SDC|SDC|Ag) under H2S and H2 fuel mixtures was also evaluated by electrochemical impedance spectra (EIS) and I–V and I–P curves. The emergence of FeSO4 in the sulfur treatment should play an important role in preventing further sulfur-poisoning.

Dense cermet membranes for hydrogen separation

Dense cermet (i.e., ceramic–metal composite) membranes have been developed for separating hydrogen from mixed gases, particularly product streams generated during coal gasification and/or steam methane reforming. Hydrogen separation with these membranes yields high-purity hydrogen, thereby eliminating the need for post-separation purification steps. Extensive tests have been conducted with cermet membranes made by mixing ≈50–60vol.% Pd with Y2O3-stabilized ZrO2. Using several feed gas mixtures, the hydrogen permeation rate, or flux, for the membranes was measured in the temperature range 400–900°C. With pure hydrogen at ambient pressure as feed gas, an ≈18-μm-thick membrane on a porous substrate gave a measured flux of ≈26cm3[STP]/min-cm2 at 400°C and ≈52cm3[STP]/min-cm2 at 900°C. We also measured the hydrogen flux through a thicker (≈150μm) membrane at 400°C using a mixture of H2, CO, CO2, H2O, and He at ≈200 psig as feed gas. Hydrogen flux measurements in H2S-containing atmospheres showed that the cermet membranes are stable at 900°C in gases that contain ≈80% H2/400ppm H2S. Because formation of palladium sulfide (Pd4S) can seriously degrade hydrogen permeation through Pd-containing cermet membranes, the Pd/Pd4S stability phase boundary of the cermet membrane was determined in the temperature range 450–650°C using various feed gases that contained 10–73% H2 and 8–400ppm H2S. Given these promising results, longer studies using real-world coal gasification conditions should be pursued.

Enhanced H2 Separation through Mixed Proton–Electron Conducting Membranes Based on La5.5W0.8M0.2O11.25−δ

La(5.5) WO11.25-δ is a proton-conducting oxide that shows high protonic conductivity, sufficient electronic conductivity, and stability in moist CO2 environments. However, the H2 flows achieved to date when using La(5.5) WO11.25-δ membranes are still below the threshold for practical application in industrial processes. With the aim of improving the H2 flow obtained with this material, La(5.5) WO11.25-δ was doped in the W position by using Re and Mo; the chosen stoichiometry was La(5.5) W0.8 M0.2 O11.25-δ . This work presents the electrochemical characterization of these two compounds under reducing conditions, the H2 separation properties, as well as the influence of the H2 concentration in the feed stream, degree of humidification, and operating temperature. Doping with both Re and Mo enabled the magnitude of H2 permeation to be enhanced, reaching unrivaled values of up to 0.095 mL min(-1) cm(-2) at 700 °C for a La(5.5) W0.8 Re0.2 O11.25-δ membrane (760 μm thick). The spent membranes were investigated by using XRD, SEM, and TEM on focused-ion beam lamellas. Furthermore, the stability in CO2 -rich and H2 S-containing atmospheres was evaluated, and the compounds were shown to be stable in the atmospheres studied.