Corrosion behaviour of nitrided ferritic stainless steels for use in solid oxide fuel cell devices

Plasma nitriding was applied to ferritic stainless steel substrates to improve their performances as interconnects for solid oxide fuel cell devices. The samples underwent electrical conductivity test and SEM/EDS, TEM/EDS, environmental-SEM analyses. The first stages of corrosion were recorded in-situ with the e-SEM. Nitriding is effective in limiting the undesired chromium evaporation from the steel substrates and accelerates the corrosion kinetics, but its influence of the electrical conductivity is ambiguous. No intergranular corrosion is found in the steel substrate after long time operation. Nitriding helps commercially competitive porous coating to improve chromium retention properties of metal interconnects

Spotting Solid Oxide Fuel Cell Degradation Effects by Electron Microscopy

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 - August 2, 201

Properties of B-site substituted La0.5Sr0.5FeO3−δ{\mathbf{La}}_{{0.5}} {\mathbf{Sr}}_{{0.5}} {\mathbf{FeO}}_{{3 - {\mathbf{\delta }}}} perovskites for application in oxygen separation membranes

Mixed ionic-electronic conducting $$La_{0.5} Sr_{0.5} Fe_{1 - x} B_x O_{3 - \delta }$$ (B: Al, Cr, Zr, Ga, Ti, Sn, Ta, V, Mg, and In with x = 0, 0.1, 0.2) perovskite materials were produced via solid-state synthesis. In order to study the effect of B-site substitution on the expansion behavior of these materials, their thermal expansion in air up to 900°C and isothermal expansion at the same temperature from air to Ar were measured by dilatometry. Ti and Ta were found to be the most effective substitutions in suppressing the isothermal expansion. The isothermal expansion at 900°C from air to Ar was reduced by 50% by substitution of 20% Ti or 10% Ta. Therefore, these compositions were further characterized by 4-probe total DC conductivity and permeation measurements under air/Ar gradient. The total conductivity of $$La_{0.5} Sr_{0.5} FeO_{3 - \delta }$$ was decreased by more than one order of magnitude at low temperatures and from 430S/cm, which is the maximum, to around 100S/cm at 500°C with the addition of Ti and Ta. The normalized oxygen permeation of LSF at 900°C decreased from 0.18 to 0.05μmol/cm2s and 0.07μmol/cm2s with the substitution of 20% Ti and 10% Ta, respectivel

Oxygen transport in La0.5Sr0.5Fe1−yTiyO3− δ ( y =0.0, 0.2) membranes

The influence of partial substitution of Fe with Ti on the oxygen transport properties of La1−x Sr x FeO3 membranes was investigated in view of their application for oxygen separation. Samples of composition $$La_{{0.5}} Sr_{{0.5}} {\text{Fe}}_{{1 - y}} {\text{Ti}}_{y} {\text{O}}_{{3 - \delta }}$$ (y=0, 0.2) were prepared and their oxygen transport properties characterised by potential step relaxation and by oxygen permeation measurement in an air/argon gradient. With the first technique, chemical diffusion $${( {\widetilde{D}} )}$$ and surface exchange (k S) coefficients were obtained by fitting of the current relaxation data to a single expression valid over the complete time range. The Ti-substituted composition gave slightly larger values of $${\widetilde{D}}$$ and k S. The trend was opposite for the measured oxygen permeation flux. In the latter experience, ordering of oxygen vacancies was observed at lower temperature, reducing significantly the performance of the materia

Techno-economic evaluation of biomass-to-fuels with solid-oxide electrolyzer

Thermochemical biomass-to-fuel conversion requires an increased hydrogen concentration in the syngas derived from gasification, which is currently achieved by water–gas-shift reaction and CO2 removal. State-of-the-art biomass-to-fuels convert less than half of the biomass carbon with the remaining emitted as CO2. Full conversion of biomass carbon can be achieved by integrating solid-oxide electrolyzer with different concepts: (1) steam electrolysis with the hydrogen produced injected into syngas, and (2) co-electrolysis of CO2 and H2O to convert the CO2 captured from the syngas. This paper investigates techno-economically steam- or co-electrolysis-based biomass-to-fuel processes for producing synthetic natural gas, methanol, dimethyl ether and jet fuel, considering system-level heat integration and optimal placement of steam cycles for heat recovery. The results show that state-of-the-art biomass-to-fuels achieve similar energy efficiencies of 48–51% (based on a lower heating value) for the four different fuels. The integrated concept with steam electrolysis achieves the highest energy efficiency: 68% for synthetic natural gas, 64% for methanol, 63% for dimethyl ether, and 56% for jet fuel. The integrated concept with co-electrolysis can enhance the state-of-the-art energy efficiency to 66% for synthetic natural gas, 61% for methanol, and 54% for jet fuel. The biomass-to-dimethyl ether with co-electrolysis only reaches an efficiency of 49%, due to additional heat demand. The levelized cost of the product of the integrated concepts highly depends on the price and availability of renewable electricity. The concept with co-electrolysis allows for additional operation flexibility without renewable electricity, resulting in high annual production. Thus, with limited annual available hours of renewable electricity, biomass-to-fuel with co-electrolysis is more economically convenient than that with steam electrolysis. For a plant scale of 60 MWth biomass input with the renewable electricity available for 1800 h annually, the levelized cost of product of biomass-to-synthesis-natural-gas with co-electrolysis is 35 $/GJ, 20% lower than that with steam-electrolysis

Electrochemical performance of Nd1.95NiO4+δ cathode supported microtubular solid oxide fuel cells

Nd1.95NiO4+δ (NNO) cathode supported microtubular cells were fabricated and characterized. This material presents superior oxygen transport properties in comparison with other commonly used cathode materials. The supporting tubes were fabricated by cold isostatic pressing (CIP) using NNO powders and corn starch as pore former. The electrolyte (GDC, gadolinia doped ceria based) was deposited by wet powder spraying (WPS) on top of pre-sintered tubes and then co-sintered. Finally, a NiO/GDC suspension was dip-coated and sintered as the anode. Optimization of the cell fabrication process is shown. Power densities at 750°C of ~40 mWcm-2 at 0.5V were achieved. These results are the first electrochemical measurements reported using NNO cathode-supported microtubular cells. Further developments of the fabrication process are needed for this type of cells in order to compete with the standard microtubular solid oxide fuel cells (SOFC).The authors thank grant MAT2009-14324-C02-01 and MAT2012-30763, financed by the Spanish Government (Ministerio de Ciencia e Innovación) and Feder program of the European Community, for funding the project.Peer Reviewe

Techno-economic comparison of 100% renewable urea production processes

Urea is widely used in agriculture, industry, and food, while it is also a potential fuel. Large-scale urea production relies on fossil fuels, thus there is a strong need for green urea given the increasing penetration of renewable energy sources. A potential alternative is biomass-to-urea; however, it cannot fully convert the biomass carbon into urea. To achieve full carbon conversion, innovative integrated biomass- and power-to-urea processes are designed conceptually. The two green urea production processes are evaluated techno-economically and compared with state-of-the-art methane-to-urea. The results show that the methane-to-urea achieves a system efficiency of 58% (LHV), while biomass-to-urea only has 39% (LHV) with unconverted biomass carbon of up to 60%. The integrated power- and biomass-to-urea has outstanding heat integration performance which fixes all biomass carbon into urea, with an efficiency enhanced up to 53%. Due to the electricity demand, the levelized cost of the urea of integrated biomass- and power-to-urea is 15 – 38 and 58 – 87% points higher than those of the biomass-to-urea and methane-to-urea for the scale of 10 – 60 MWth urea production. The available annual hours and electricity price of renewable electricity have a significant impact on the levelized cost of the urea. When the available annual hours decrease from 7200 to 3600 with an electricity price of 73 $/MWh, the levelized cost of urea increases on average by 13$/GJ with the plant capacity being 10 – 60 MWth urea. However, when electricity price is reduced from 73 $/MWh to 35$/MWh with available annual hours of 3600, the levelized cost decreases on average by 15% from 59 $/GJ with the same plant capacity

TEM investigation on zirconate formation and chromium poisoning in LSM/YSZ cathode

Cell durability is a crucial technological issue for SOFC commercialization, and considerable progress has been made in recent years. A number of degradation pathways have been established, amongst which microstructural changes, poisoning effects and formation of less conductive phases. In this study, transmission electron microscopy was used to observe submicron-scale effects on selected cathode zones of an anode supported cell tested in SOFC stack repeat element configuration. The test has been performed with a dedicated segmented test bench, at 800°C for 1900h, which allowed to spatially resolve degradation processes, and therefore to improve their correlation with localized post-test analysis. Evidence is presented of reaction products (mainly SrZrO3) at the LSM/YSZ interfaces as well as of contaminants, in particular Cr, but also Si. A polarized cell segment is compared to an unpolarized one, to assess any influence of cathode polarizatio

Activation of Stainless Steel 316L Anode for Anion Exchange Membrane Water Electrolysis

publishedVersio

Ethanol internal steam reforming in intermediate temperature solid oxide fuel cell

This study investigates the performance of a standard Ni-YSZ anode supported cell under ethanol steam reforming operating conditions. Therefore, the fuel cell was directly operated with a steam/ethanol mixture (3 to 1 molar). Other gas mixtures were also used for comparison to check the conversion of ethanol and of reformate gases (H2, CO) in the fuel cell. The electrochemical properties of the fuel cell fed with 4 different fuel compositions were characterized between 710 and 860°C by I-V and EIS measurements at OCV and under polarization. In order to elucidate the limiting processes, impedance spectra obtained with different gas compositions were compared using the derivative of the real part of the impedance with respect of the natural logarithm of the frequency. Results show that internal steam reforming of ethanol takes place significantly on Ni-YSZ anode only above 760°C. Comparisons of results obtained with reformate gas showed that the electrochemical cell performance is dominated by the conversion of hydrogen. The conversion of CO also occurs either directly or indirectly through the water-gas shift reaction but has a significant impact on the electrochemical performance only above 760°C