Commercial stainless steels, Ni-based alloys and physical vapor deposition (PVD) chromium nitride (CrN)-coated stainless steels were evaluated as possible metallic bipolar plate materials in ...conditions that resemble a typical PEMFC cathode environment with respect to their interfacial contact resistance (ICR) and corrosion resistance. Results show that stainless steels have a high ICR and undergo corrosion. Although Ni-based alloys showed an ICR value comparable as to that of graphite, their behaviour was not satisfactory in a corrosive acidic medium. Only CrN-coated stainless steels demonstrated to have low ICR values and a very good corrosion resistance.
Sustainability, safety and optimization of gasification systems for hydrogen production are strictly correlated to efficient monitoring devices and chemical gas sensors based on perovskite materials ...represent a very attractive technology for this purpose. The aim of this work is to evaluate sensing performances of LaFeO3 based materials for the application in integrated gasification-FC systems and their possible enhancements thanks to titanium partial substitution. Two perovskites, LaTi0.4Fe0.6O3 and LaFeO3, were therefore prepared via auto-combustion synthesis and tested in a bench scale reactor for CO, H2 and H2S exposures. Synthesis parameters were properly defined and set to Φ = 0.45, CA/M = 2.5 and pH = 7. Transition of conductive behaviour (from p- to n-type) was observed. Titanium partial substitution provided higher sensitivity to CO at higher temperatures. Sensitivity to H2 was greater for unsubstituted material, but titanium presence assured chemical and thermal stability. During H2S tests, instead, irreversible reaction with materials occurred compromising sensing performances.
•Chemoresistive gas sensors for biomass gasification to fuel cell system control.•An innovative perovskite material for high temperature CO, H2 and H2S measurements.•Titanium partial substitution on LaFeO3 based material was investigated.•Improved chemical and thermal stability under reducing atmosphere.•CO sensitivity enhanced up to 1.9 at higher temperatures.
The study is aimed at improving a methodology to purify nickel or cobalt ion containing effluents by an electrochemical filter. Consequently, a cell with reticulated vitreous carbon (RVC) cathode for ...Ni and Co depletion was designed to analyze, at room temperature and pH equal to 6, flowrates and cathodic potentials able to affect the electrochemical process. Starting with Ni and Co initial concentration of 150ppm, it is possible to reach a concentration lower than 0.1ppm for both metals in less than 1h, with a flowrate of about 1300ml/min and for a catholyte volume of 1000ml, under mass transport control conditions (for Ni −1.1V and for Co −1.2V cathodic potential versus Standard Calomel Electrode (SCE)). Moreover, the proposed work studied the process kinetics and fluid dynamics through the use of dimensionless relations such as Reynolds and Sherwood numbers. In addition considerations on current efficiency for reduction of both metal ions were done.
•Purification of effluents by electrowinning of nickel or cobalt ion•Characterization of the metal deposition on reticulated vitreous carbon•Dimensionless analysis for each ionic species electrodeposited•Efficiency analysis and cost estimation of a scale-up of the electrochemical system
► Perovskite conversion coating for corrosion protection of a 13-Cr stainless steel. ► Coating formation mechanism studied in two different molten salt bath compositions. ► Oxide basicity of the salt ...bath must be controlled to avoid substrate corrosion. ► Coating formation mechanism affected both perovskite grain size and MCFC performance. ► Precursor-template coating synthesis promoted excellent MCFC corrosion protection.
A feasibility study has been conducted to determine if a recently developed molten salt perovskite conversion coating process can be applied to protect an intrinsically low corrosion-resistant 13-Cr ferritic stainless steel in Molten Carbonate Fuel Cell (MCFC) demanding environments. The molten salt bath composition has been adapted to evaluate the influence of two different reaction mechanisms, namely dissolution-precipitation and precursor-template synthesis, on microstructure and MCFC corrosion resistance of the LaFeO3-based perovskite coatings. It has been found that the necessary strong basic/oxidizing chemistry conditions for the dissolution-precipitation mechanism to occur cause extensive substrate corrosion that contribute to coating porosity and poor MCFC corrosion protection. On the other hand, excellent corrosion protection of the 13-Cr steel is afforded by a perovskite conversion coating that had been produced via an iron oxide precursor-template route under milder basic conditions. The results show that a decreased salt bath basicity fully suppresses substrate corrosion, while promoting at the same a fine coating microstructure and virtual absence of coating through-porosity, thus markedly improving the barrier properties of coated 13-Cr steel against MCFC corrosion attack.
► Perovskite coatings were obtained by thermochemical conversion reactions in a molten carbonate bath. ► Potential method for corrosion protection of stainless steels against oxidation and hot ...corrosion. ► The conductive nature of the perovskite coatings is also promising for high temperature electrical applications. ► High quality dual-layer coating structure was obtained consisting of LaFeO
3 layer grown over a LiFeO
2 innermost layer. ► Molten carbonate corrosion of a 316L stainless steel was drastically decreased after the perovskite conversion treatment.
A novel conversion coating process has been developed to meet the stability requirements of stainless steel hardware in the demanding MCFC fuel cell environments. The process applies a perovskite-based coating by exploiting spontaneous oxidizing reactions of the metallic surface with La
2O
3 in eutectic alkali carbonate mixtures. By using well controlled synthesis procedures, conversion coating layers covering the entire metallic surface with a uniform and compact structure could be obtained. The as-formed coatings with a surface morphology of agglomerated crystallite particles consisted of a thin (<5
μm) LaFeO
3 perovskite layer grown over a thicker (>5
μm) LiFeO
2-rich layer. Test coupons of 316L stainless steel with the perovskite conversion coating were analyzed for corrosion protection and interfacial resistivity properties. It was found that the conversion coating is highly conductive while showing excellent long-term corrosion stability in simulated MCFC environments. These results suggested that perovskite coatings formed by molten salt conversion reactions could be particularly attractive to confer optimal protection and electrical continuity to MCFC current collectors.
The objective of this work was to verify the feasibility of using low Cr ferritic stainless steels to improve IT-SOFC interconnect properties in terms of electrical conductivity and Cr evaporation ...resistance by taking advantage that low Cr ferritic stainless steels may form conductive and moisture-stable oxide layers of chromite spinels. In this context, surface degradation of a commercial 13Cr ferritic stainless steel (SS405) was studied at 700 °C in ambient air (containing ca. 3% H2O by volume) for up to nearly 5000 h. The results showed a slow, nearly linear oxidation rate indicating that the oxide scale could not act as a fully protective barrier during a prolonged exposure at 700 °C. Oxidation-induced degradation was mainly due to the effects of Cr depletion in the subscale matrix region and internal oxidation attack. However, analysis of the oxide scale after long-term exposure revealed the presence of an interesting example of all-spinel structure consisting of outer layer of iron-substituted Mn–Cr spinel particles on the top of an inner and continuous Fe–Cr spinel layer. Since SS405 steel contains also Al and Si as minor additions, the distribution of these elements in the spinel oxide scale was studied and found to be rather different. Whereas Si was present exclusively in the inner oxide regions, Al migrated also to the outermost part of the oxide scale. Possible explanations for this unexpected Al surface enrichment are discussed.
•Long-term oxidation of a commercial 13Cr ferritic stainless steel was studied.•A slight, but continuous linear weight gain was observed for oxidation at 700 °C.•Degradation was mainly caused by Cr depletion and internal oxidation attack.•Thermally grown oxide was composed of a dual-layer chromite spinel structure.•Aluminum cation migration to the outer oxide scale was observed.
The use of biomass and waste to produce alternative fuels, due to environmental and energy security reasons, is a high-quality solution especially when integrated with high efficiency fuel cell ...applications. In this article we look into the coupling of an anaerobic digestion process of organic residues to electrochemical conversion to electricity and heat through a molten carbonate fuel cell (MCFC). In particular the pathway of the exceedingly harmful compound hydrogen sulphide (H2S) in these phases is analysed. Hydrogen sulphide production in the biogas is strongly interrelated with methane and/or hydrogen yield, as well as with operating conditions like temperature and pH. When present in the produced biogas, this compound has multiple negative effects on the performance and durability of an MCFC. Therefore, there are important issues of integration to be solved. Three general approaches to solve the sulphur problem in the MCFC are possible. The first is to prevent the formation of hydrogen sulphide at the source: favouring conditions that inhibit its production during fermentation. Secondly, to identify the sulphur tolerance levels of the fuel cell components currently in use and develop sulphur-tolerant components that show long-term electrochemical performance and corrosion stability. The third approach is to remove the generated sulphur species to very low levels before the gas enters the fuel cell.
The effect was investigated of low H2S concentrations, simulating biogas impurity, on the poisoning behaviour of a Ni-based, molten carbonate fuel cell anode. A conventional Ni–Cr anode was coated ...with ceria using dip coating to form a rare earth metal oxide thin layer on the surface of the anode. Electrochemical studies of the Ni-based samples were performed in symmetric cells under anode atmosphere (H2, CO2, H2O and N2 as balance) with 2, 6, 12, and 24 ppm of H2S by means of electrochemical impedance spectroscopy.
The recorded data showed that the poisoning resistance was enhanced at low coating percentages of ceria; effects depend on H2S concentration and the applied load. These results were confirmed by electrochemical impedance tests where the cerium oxide addition appears through stable polarization behaviour up to 6 ppm of H2S, particularly in the mass transfer region. The protection is explained by the depression of poisoned Ni active sites and formation of a protective layer to the metal surface. The ceria coating layer is a potential solution to reduce H2S poisoning of MCFCs fuelled with biogas.
► Low H2S concentrations was used to simulate biogas impurity. ► Dip coating method was carried out to form a cerium oxide thin layer on the surface of the anode. ► Electrochemical studies was performed in symmetric and button cells under anode atmosphere. ► The cerium oxide addition forms a protective layer to the metal surface. ► The ceria coating layer is a potential solution to reduce H2S poisoning of MCFCs fuelled with biogas.
Synroc (
Syn
thetic
Roc
ks) materials have been regarded as the second generation of high level waste forms in the world. It allows incorporating into their crystal structures almost all of the ...elements present in high-level radioactive waste. One of the components of Synroc-C is perovskite (CaTiO
3
) which immobilize mainly fission products, but also allow immobilizing in his structure long-lived actinides such as plutonium (Pu). Perovskite phase has been fabricated by a sol–gel route. In the present work complex sol–gel process (CSGP Polish Patent PL 172618, 1997) and method of synthesis Me-titanates (Polish Patent PL 198039, 2001) were adapted to prepare of perovskite. Additions of 10 % molar Sr, Co, Cs and Nd into Ti–Ca–nitrate sols were carried out by CSGP. Gels obtained by evaporation of sols under reduced pressure were thermal treated according thermogravimetric (TG, DTA) analysis. Transformation of ascorbat–nitrate gels into doped orthorhombic perovskite phases was definitely lower (about 650 °C) than those pure nitrate gels (approx. 700 °C). All structures were confirmed by X-ray diffraction analyses. Surrogates were homogeneously distributed into crystalline structure of perovskite. It means that elaborated process can be applied for synthesis Synroc materials and it might be competitive to vitrification process.
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