Wet Hydrogen Research Articles

The effect of oxygen and water vapor partial pressures on the total conductivity of BaCe0.7Zr0.1Y0.2O3–δ

The effect of oxygen and water vapor partial pressure on the total conductivity of the proton-conducting BaCe0.7Zr0.1Y0.2O3–δ material is investigated in the present work. Single-phase and dense ceramic materials have been successfully obtained using the citrate–nitrate synthesis method. The contributions of partial conductivities (hole, oxygen-ionic, protonic) are evaluated based on electrical and emf measurements. At 900 °C in air atmosphere, ionic and hole conductivities almost equivalently contribute to the total conductivity, while in reducing temperatures, the transport of the studied material becomes ionic; the predominant protonic transport (t H ≈ 1) realizes under wet hydrogen atmospheres at temperatures below 700 °C. Based on the measurements of total conductivity as a function of water vapor partial pressure, it is found that the increase of conductivity in reducing atmospheres is associated with the growth of proton conductivity. A non-monotonic change of total conductivity in oxidizing atmospheres is caused by the competing effects, namely decreasing the hole conductivity and increasing the protonic one.

Tin doped PrBaFe2O5+δ anode material for solid oxide fuel cells

PrBaFe1.9Sn0.1O5+δ shows excellent redox stability, high electrical conductivity, and ASR of a symmetrical cell as low as of 0.095–0.285 Ω cm2 from 850–750 °C in wet hydrogen, better than or comparable to the best of ceramic anodes in the open literature.

Effects of process variables in decarburization annealing of Fe-3%Si-0.3%C steel sheet on textures and magnetic properties

In Fe-3%Si-0.3%C steel sheet, a relatively strong //ND texture can evolve in the surface layer through the α→γ→α phase transformation in relatively low vacuum (4 Pa) for an annealing time of 10 min and at a cooling rate of 20 K/s. Oxidation of the steel sheet surface prevents the evolution of the //ND texture. However, vacuum-annealing under a vacuum pressure of 1.3×10-3 Pa causes decarburization of the steel sheet, which suppresses oxidation of the steel sheet surface, and subsequent annealing in wet hydrogen of 363 K in dew points causes a columnar grain structure with the //ND texture. After the two-step-annealing (the vacuum annealing under a vacuum pressure of 1.3×10-3 Pa and subsequent decarburizing annealing in wet hydrogen of 363 K in dew points), the decarburized steel sheet exhibits good soft magnetic properties in NO with 3%Si, W15/50 (core loss at 1.5T and 50 Hz) = 2.47 W/kg and B50 (magnetic flux density at 5000 A/m) = 1.71 T.

Oxygen transport and chemical compatibility with electrode materials in scheelite-type LaWxNb1−xO4+x/2 ceramic electrolyte

LaWxNb1−xO4+x/2 ceramics (x = 0.16) were prepared via a solid state route and studied with respect to phase stability and mixed ionic and electronic conductivity under conditions of technological relevance for fuel cell applications. The chemical compatibility against standard cathode materials revealed that Sr-doped LaMnO3 could be used without detectable chemical interaction up to at least 1000 °C. Impedance spectroscopy measurements performed in the range 400–850 °C, using different atmospheres (air and N2+H2, both dry and water vapour saturated), suggest oxygen transport numbers equal to 1 under oxidising conditions, and decreasing when exposed to extreme reducing conditions. The total conductivity at 800 °C increases from 1.4·10−3 S cm−1 in air to 2.5·10−3 S cm−1 in wet hydrogen and 6.1·10−3 S cm−1 in dry hydrogen, but the observed onset of n-type conductivity has little practical impact under typical fuel cell operating conditions.

Failure analysis of a carbon steel pipeline exposed to wet hydrogen sulfide environment

Abstract Stress Corrosion Cracking (SCC) is one of the most common failure phenomena in the wet hydrogen sulfide environment. In this paper, the fracture failure of a fuel gas pipeline during operation has been analyzed. Through service environmental investigation, crack morphology detection, and stress analysis of fuel gas pipeline, the fracture has the morphology and characteristic of wet hydrogen sulfide SCC in the welding joint between pipeline and flange. The analysis shows that the abnormal martensitic microstructure in the pipeline has provided the advantage for SCC.

Room-temperature DNA-catalyzed hydrogen fuel cell

Motivated by previous experiences in identifying active reaction zones on plant pheophytins of the so-called semi-derivative morphology, for the catalytic decomposition of hydrogen gas, this current research aimed for similarly suggestive sites within DNA base pairs which exist in all living matters. Verified by the 1st-principle quantum mechanical simulations and subsequent wet and dry hydrogen fuel cell experiments, the feasibility of room-temperature DNA-catalyzed hydrogen oxidation reaction was unambiguously established. This implies that very low-cost DNA-catalyzed fuel cells, which contain no expensive, CO-sensitive platinum on the negative electrode side, can be put to work under room condition and thus might be practically available in every household in the very near future.

Synthesis of Polystyrene Beads for Hard-Templating of Three-Dimensionally Ordered Macroporosity and Hierarchical Texture of Adsorbents and Catalysts

Methods of polystyrene beads producing with properties appropriate for catalyst and adsorbent synthesis have been investigated. Hierarchical silicalite-1 and Fe-silicalite-1 with zeolitic MFI structure, as well as three-dimensionally ordered titania, silica, alumina and zirconia have been prepared by hard-templating method using polystyrene beads. The materials were characterized by X-ray diffraction, scanning and transmission electron microscopies, low-temperature nitrogen adsorption technique and mercury porosimetry. Developed meso- and macroporous structure of the templated materials facilitated the supply of macromolecular reactants to the material surface and reduced the negative effect of byproduct deposition, resulting in favored advantages of the materials in a wide range of processes: hydroconversion of heavy oil, wet hydrogen peroxide oxidation of organic substrates in water, photocatalysis and gas chromatographic analysis. The obtained results of the material applications showed their potential attractiveness as catalysts and adsorbents.

Synthesis and Characterization of CexSr1-xCr0.5Mn0.5O3-δ Perovskites as Anode Materials for Solid Oxide Fuel Cells (SOFC)

CexSr1-xCr0.5Mn0.5O3 (CeSCM) compounds with x=0.25 and 0.5 have been prepared in argon. In comparison to the non-doped manganite Ce0.25Sr0.75MnO3, synthesized in air, chromium for manganese substitution improves the stability in wet hydrogen atmosphere, characteristic of an SOFC anode. In argon, the electrical conductivity at 900°C is 32.8 and 34.9Scm−1 for CeSCM 25 and CeSCM 50, respectively. In wet hydrogen, it is about 1Scm−1 at 900°C for CeSCM 25 and only 0.2Scm−1 for CeSCM 50. The rate of hydrogen oxidation reaction has been studied by using dense cone-shaped electrodes. Two main limiting steps are observed: the transfer of ionic species at the anode/YSZ interface at high frequency and hydrogen adsorption process at the surface of the electrode material at low frequency. In particular, the low electrical conductivity of CeSCM 50 seems detrimental for the performance.

Remarkable catalytic properties of rare-earth doped nickel ferrites synthesized by sol-gel auto-combustion with maleic acid as fuel for CWPO of dyes

NiFe1.98RE0.02O4 (where RE=La, Sm, Gd and Dy) spinel ferrites were synthesized by sol–gel autocombustion method using maleic acid as fuel. The effect of rare-earth cations (RE) doping on structural, magnetic and catalytic properties of nickel ferrite is reported. XRD and FT-IR analysis revealed the successful insertion of the rare-earth cations into the spinel matrix in all samples. We observed a decreasing of crystallite and particle sizes (estimated from XRD patterns and TEM micrographs, respectively) as well as the magnetization value in the presence of lanthanide ions into the spinel structure. Additionally, these ferrites were employed as heterogeneous catalysts for catalytic wet hydrogen peroxide oxidation (CWPO) of Orange II azo-dye. The color removal efficiency was boosted from 30.6% for undoped nickel ferrite to 90.6% for the lanthanum doped nickel ferrite, after only 15min of reaction. The decolorization of Orange II solution followed the pseudo-first-order kinetics and was achieved via decay reaction as demonstrated by Langmuir-Hinshelwood model. The remarkable increase in catalytic performance of doped nickel ferrites with a very small amount of rare-earth cations was correlated with the size factor, expressed as the ratio between particle and crystallite size. The desirability function approach enabled to identify the optimal material (NiFe1.98La0.02O4) with the best catalytic performance; the smallest size factor and appropriate magnetic properties.

Long-term tests of Ni–Zr0.9Sc0.1O1.95 anode impregnated with CeO2 in H2 + H2O gas mixtures

The present paper reports the data on the long-term monitoring (during 1500 h at 800 °С in the atmosphere of wet hydrogen and 40% H2 + 60% H2O) of Ni–Zr0.9Sc0.1O1.95 anode polarization resistance before and after its impregnation with cerium oxide. In wet hydrogen difference between the rates of polarization resistance degradation before and after impregnation is insignificant and reaches a level close to stationary one after 500 h of testing. In 40% H2 + 60% H2O gas mixture a behavior of the initial anode is similar to the above mentioned, whereas, the high rate of increase the polarization resistance of impregnated anode and sintering cerium oxide species was observed. After the long-term tests, the re-impregnation allows increasing the anode activity. The re-impregnation of anode increases its activity the higher, the greater of anode degraded during the long-term tests.

Evaluation of the Durability and Performance of FBG-Based Sensors for Monitoring Moisture in an Aggressive Gaseous Waste Sewer Environment

Measurements of the rate of corrosion in concrete sewers need to take into consideration the humidity in the environment, and, thus, its accurate measurement becomes critically important. Introducing a novel approach to do so, tailored fiber Bragg grating (FBG)-based humidity sensors have been evaluated in situ to examine their durability, time response, and stability when used in measurements over an extended period of time under the aggressive gaseous environment of a gravity sewer, experiencing high levels of both humidity and hydrogen sulfide gas. The critical humidity monitoring element in the probe is based on a moisture-sensitive polyimide coated FBG, using the calibrated and reproducible peak wavelength shift in response to moisture variation, in this case operationally in the sewer. To optimize the device for this environment, two different designs of the probe assembly were configured using different material, thus aiming to provide durability in the harsh environment in the long term. The aim of the probe design evaluated was to achieve good sensitivity to humidity as well as to protect the sensing elements from the aggressive environment and which had rendered ineffective the electrical sensors placed in the sewer and used for cross comparison. A full evaluation of the packaged sensors in situ was undertaken over a period of five months, during which the sensors were constantly subjected to high, but varying levels of humidity and wet hydrogen sulfide gas. The results are highly encouraging, showing superior performance of the configured fiber optic sensors used over a conventional electrical sensor when the results of the cross-comparison study of the performance were evaluated. These outcomes show a promising future for optical fiber sensors to be employed for measurement of humidity in the long term in harsh environmental applications such as this.

Modeling the integrated heterogeneous catalytic fixed-bed reactor and rotating biological contactor system for the treatment of poorly biodegradable industrial agrochemical wastewater

An integrated system based on a heterogeneous catalytic wet hydrogen peroxide oxidation (CWHPO) and subsequent rotating biological contactors (RBCs) has been modeled for the treatment of agrochemical wastewater. One dimensional pseudo-homogeneous model was proposed for the CWHPO step. The reaction rate for TOC removal (k1) was 0.087 1/min. In the case of the RBCs, two different approaches were considered: the pseudo-homogeneous model was based on Kornegy and Clark equations and it is restricted to only one substrate limitation, TOC, for the microbial growth. The microbial growth was modeled by a Monod type equation. The uptake rate and saturation coefficient values were P=0.94g/dm2d and Ks=0.53g/dm3. The integrated non-pseudo-homogeneous model considers a two-phase bioreactor in which all the biochemical processes occur in the solid biofilm phase. In this model, processes such as biofilm growth and diffusion of nutrients into biofilm were taken into account. The microbial growth was modeled using a double Monod equation with substrate limitation by TOC and total nitrogen (TN). Both approaches were able to describe the CWHPO-RBCs performance at different operating conditions with an estimated growth rate (μMAX) of 3.62 1/d. The calculated TOC removal was in good agreement with the experimental results. The two-phase model was also able to predict the TN removal of the system. The modeling of the coupling CWHPO/RBCs process could be a useful guide in order to achieve a cost-effective process leading to optimum C/N composition of the treated effluent and resulting in better overall removal efficiency.

Electrochemical Properties of Tubular SOFC Based on a Porous Ceramic Support Fabricated by Phase-Inversion Method

In this work, a tubular ceramic-supported solid oxide fuel cell (SOFC) was successfully fabricated by a low cost and simple process involving phase-inversion, brush coating and co-sintering. Properties including sintering behavior, microstructure of the tubular support as well as the electrochemical properties of single cell were investigated. The results show that a porous tubular support with finger-like pores and macrovoids was obtained after phase-inversion process. The tubular support is proved to be gas-permeable after sintering at 1400 °C with shrinkage of about 34%. The maximum power density of single tubular SOFC is 100 mW/cm2 and 122 mW/cm2 at 850 °C when fed with wet methane and hydrogen, respectively. The current collection, thickness of electrolyte and gas permeability of tubular support should account for the large total resistance. The present tubular design could be expected to deliver a higher voltage for longer support with several segmented-in-series cell stacks.

Reduction Dynamics of Doped Ceria, Nickel Oxide, and Cermet Composites Probed Using In Situ Raman Spectroscopy.

The redox properties of gadolinium doped ceria (CGO) and nickel oxide (NiO) composite cermets underpin the operation of solid oxide electrochemical cells. Although these systems have been widely studied, a full comprehension of the reaction dynamics at the interface of these materials is lacking. Here, in situ Raman spectroscopic monitoring of the redox cycle is used to investigate the interplay between the dynamic and competing processes of hydrogen spillover and water dissociation on the doped ceria surface. In order to elucidate these mechanisms, the redox process in pure CGO and NiO is studied when exposed to wet and dry hydrogen and is compared to the cermet behavior. In dry hydrogen, CGO reduces relatively rapidly via a series of intermediate phases, while NiO reduces via a single‐step process. In wet reducing atmospheres, however, the oxidation state of pure CGO is initially stabilized due to the dissociation of water by reduced Ce(III) and subsequent incorporation of oxygen into the structure. In the reduction process involving the composite cermet, the close proximity of the NiO improves the efficiency and speed of the composite reduction process. Although NiO is already incorporated into working cells, these observations suggest direct routes to further improve cell performance.

Novel efficient process for methanol synthesis by CO2 hydrogenation

Methanol is an alternative fuel that offers a convenient solution for efficient energy storage. Complementary to carbon capture activities, significant effort is devoted to the development of technologies for methanol synthesis by hydrogenation of carbon dioxide. While CO2 is available from plenty of sources, cheap sources of H2 are less frequently found. An additional source of hydrogen at industrial scale is the wet hydrogen by-product of chlorine production.This study is the first to propose an efficient process for methanol synthesis by CO2 hydrogenation using wet hydrogen by-product from chlor-alkali production. A key feature of this novel process is the use of a stripping unit where the wet hydrogen flows in counter-current mode with the condensed methanol–water mixture resulting from the high-pressure low-temperature separator after the reaction. This operation has a double positive effect, as it removes the CO/CO2 from the methanol–water mixture thus allowing a complete recycle of CO2 and avoiding its presence in the product, while also removing the water from the wet hydrogen thus avoiding the negative impact of adding water on the equilibrium conversion – with consumption figures of 550kWh electricity and 0.48–1.16ton steam per ton methanol.

Two different carbon-hydrogen complexes in silicon with closely spaced energy levels

An acceptor and a single donor state of carbon-hydrogen defects (CHA and CHB) are observed by Laplace deep level transient spectroscopy at 90 K. CHA appears directly after hydrogenation by wet chemical etching or hydrogen plasma treatment, whereas CHB can be observed only after a successive annealing under reverse bias at about 320 K. The activation enthalpies of these states are 0.16 eV for CHA and 0.14 eV for CHB. Our results reconcile previous controversial experimental results. We attribute CHA to the configuration where substitutional carbon binds a hydrogen atom on a bond centered position between carbon and the neighboring silicon and CHB to another carbon-hydrogen defect.

Catalytic wet hydrogen peroxide oxidation of p-hydroxybenzoic acid over Fe/TiO2 and 0.5Ru–3Fe/TiO2

p-Hydroxybenzoic acid (p-HBZ) degradation was achieved using catalytic wet hydrogen peroxide oxidation over Fe/TiO2 and Ru–Fe/TiO2 under mild conditions. The results showed that 71 % of p-HBZ conversion was obtained after 10 min of reaction over the 0.5Ru–3Fe/TiO2 catalyst calcined under oxygen. The influence of the H2O2/p-HBZ molar ratio (5:1, 10:1 and 15:1), reaction temperature (25, 40 and 60 °C), Fe loading (1, 2 and 3 wt%) and thermal treatment was studied. Characterization studies were performed by X-ray diffraction, N2 physisorption at 77 K, H2-TPR and elemental analysis, showing that close interaction between Ru and iron oxide species is necessary to obtain active and stable catalysts. 0.5Ru–3Fe/TiO2 C catalyst shows a high activity for the degradation of p-HBZ at 60 °C by CWHPO in the presence of H2O2. The system could be considered as a Fenton-like reaction due to the generation of radicals from H2O2 as well as the presence of iron sites on the catalyst.

Sewage-sludge-derived carbonaceous materials for catalytic wet hydrogen peroxide oxidation of m-cresol in batch and continuous reactors

In this study, four sewage-sludge-derived carbonaceous materials (SWs) were evaluated for their catalytic wet hydrogen peroxide oxidation (CWPO) performance of m-cresol in batch reactor and continuous reactor, respectively. The SWs were produced by carbonization (SW); carbonization with the addition of CaO (CaO-SW); HNO3 pretreatment (HNO3-SW) and steam activation (Activated-SW). The properties of SW catalysts were assessed by thermogravimetric analysis, Brunauer–Emmett–Teller, Fourier Transform Infrared Spectroscopy, X-ray Fluorescence, Scanning electron microscopy, energy dispersive X-ray analysis and zeta potential. The results showed that SW treated by HNO3 (HNO3-SW) had a high conversion of m-cresol in batch reactor and continuous reactor, respectively. Under the conditions of batch reaction (Cm-cresol = 100 mg L−1, CH2O2 = 15.7 mmol L−1, initial pH=7.0, 0.5 g L−1 catalyst, 80°C, 180 min adsorption and 210 min oxidation), the conversion of m-cresol reached 100% and total organic carbon removal was 67.1%. It had a high catalytic activity and stability on the treatment of m-cresol in CWPO for more than 1100 h. Furthermore, a possible reaction mechanism for the oxidation of m-cresol to 2-methyl-p-benzoquinone by CWPO was proposed.

Improved protonic conductivity and Vickers hardness for lanthanum tungstate with potassium doping (La,K)28−yW4+yO54+δ

The mechanical and electrical studies of a new series of materials, (La1−xKx)27.08W4.92O55.38−θ (y=0.92), are reported. The (La1−xKx)27.08W4.92O55.38−θ (x=0.00, 0.02, 0.04, 0.06, 0.08, 0.10) precursor powders were synthesized via a solid state reaction method. The results of X-ray diffraction studies show that single phase could be obtained after calcination at 1150°C, with a solid solubility limit of K+ doping x≤0.08. The sintering behavior measured by a dilatometer reveals the decrease in shrinkage of (La1−xKx)27.08W4.92O55.38−θ from room temperature to 1500°C with increasing K+ content. Scanning electron microscope observations demonstrated very dense morphology of the ceramics sintered at 1550°C. The Vickers hardness was evaluated and found to be enhanced by the slight K+ doping. Electrochemical impedance spectroscopy in air, wet air, hydrogen and wet hydrogen at various temperatures demonstrated the slight increase of the oxide-ionic and protonic conductivities of these materials with slight K+ doping.

High-performance anode-supported solid oxide fuel cell with impregnated electrodes

The 61%NiO + 39%Zr0.84Y0.16O1.92 (NiO-YSZ) and 56%NiO + 44%Zr0.83Sc0.16Ce0.01O1.92 (NiO-CeSSZ) composite powders have been prepared using two-steps and one-step combustion synthesis, respectively. The Ni-YSZ anode substrate with a low level of electrical resistance (less than 1 mOhm cm) and porosity of about 53% in the reduced state was fabricated. The functional layer of the anode with the high level of electrochemical activity was made of NiO-CeSSZ. The single anode-supported solid oxide fuel cell with the bi-layer Ni-cermet anode, Zr0.84Sc0.16O1.92 film electrolyte and the Pt + 3% Zr0.84Y0.16O1.92 cathode was fabricated. The power density and the U–I curves of the fuel cell at initial state and after impregnation of the cathode and anode by praseodymium and cerium oxides, respectively, have been measured at different temperatures. The maximum of power density of the initial fuel cell was 0.35 W cm−2 at conditions of wet hydrogen (air) supply to the anode (cathode) at 900 °C. After the electrodes were impregnated, the value of power density increased by seven times and was approximately 2.4 W cm−2 at 0.6 V. It was suggested that after the electrodes impregnation the polarization resistance of the fuel cell was determined by the gas diffusion in the supported anode.