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Degradation and disintegration of the nickel base cermet anode is a serious problem in direct utilization of hydrocarbon fuels, especially for liquid fuels such as kerosene. Cell operation test was carried out for the SOFC with nickel – scandia stabilized zirconia (Ni-ScSZ) cermet anode by direct feeding of several liquid hydrocarbons at 1073 K at S/C = 2.0. For n-dodecane (C12H26) fuel, hydrogen produced by reforming reaction on the anode was mainly used for electrochemical oxidation reaction. In contrast, for desulfurized kerosene test, cell operation was only possible by lower current density. Furthermore, noticeable nickel particles growth occurred. This nickel sintering should be enhanced by remaining minor impurities, including sulfur, in the desulfurized kerosene. From the thermodynamic consideration, Ni-S eutectics can be stably formed under some SOFC operation conditions with 100 ppm of sulfur. Carbon deposition was observed on the nickel surface for both Ni-yttria stabilized zirconia (YSZ) and Ni-ScSZ systems, but was noticeably suppressed for Ni-gadolinia doped ceria (GDC) system.
Many physical and chemical problems in solid oxide fuel cells (SOFC) are induced by the operating temperature of approximately 800 ~ 1000°C. The focus of the research in SOFC’s is, thus, on running the systems at the intermediate operating temperature range below 800 °C. A way to achieve this includes changing the electrolyte material in order to get a good ionic conductivity in the intermediate temperature range below 800 °C. In this work, gadolinium doped ceria is selected as the electrolyte, which was mixed with NiO for the anode material, and tape cast and laminated to produce a novel graded IT-SOFC . The cross-section of the SOFC cell was observed using Scanning Electron Microscope (SEM) showing a dense electrolyte layer. The operating temperature to test the cell was 500 and 550 °C. The electrochemical properties of the cell were measured using impedance spectroscopy. The ASR of unit cells was found to be between 2.67 and 4.62 Ω·cm2. The electrochemical performance is discussed under the effect of porosity gradients at 500 and 550 °C.
Fe-Cr-Mn alloy is a common material used for the metallic interconnector of solid oxide electrolyte fuel cells (SOFC). However, its high temperature oxidation resistance needs to be strengthened to improve the performance of SOFC. In this study, the effect of trace additions of Ti, Mo, Co and La on the high-temperature behavior of Fe-Cr-Mn alloy was investigated. The omposition of Fe-22Cr-2Mn-X (X = Ti, Mo, Co, La) alloys was designed to maintain a bcc structure with the aid of the thermal-calc software. These alloys tended to form Cr-rich oxide in the inner layer and Mn-rich oxide in the outer layer of the specimens after oxidative tests at 850℃, thus reducing the likelihood of chromium oxide evaporation. The experimental results indicated that the addition of Co and La produced better oxidation resistance at high temperatures than Ti and Mo. In addition, the influence of trace elements on electrical resistance of the interconnector material was examined as well.
Doped ceria-based (DC) materials have recently been considered as the most promising solid electrolytes for intermediate temperature solid oxide fuel cell (IT-SOFC) applications. Doped ceria is usually prepared via thermal decomposition of its water soluble salts, especially, acetates and nitrates. The properties of the obtained final product directly influenced by the starting material and the decomposition products. Therefore, it is crucial to understand the decomposition steps and intermediate products. Number of experimental work have been reported using various in-situ and ex-situ techniques such as thermogravimetry with mass spectrometry (TG/DTA-MS), X-ray diffraction with differential scanning calorimeter (XRD-DSC). However, the available literature data is limited and not reasonably in agreement with each other. High Temperature FT-IR spectroscopy, TG/DTA-MS, XRD, techniques were used and results are compared with literature. A good agreement between the thermal analyses and HT-FTIR results were obtained. Possible decomposition mechanism is discussed.
A Ni-modified La0.6Sr0.4Fe0.8Co0.2O3 / Ce0.9Gd0.1O2 catalyst was prepared by incipient wetness. The product thus obtained was calcined at 1100°C for 2 h in static air. After thermal activation, Ni was mainly present as highly dispersed La2NiO4 on the surface of perovskite surface. The thermal reduction at 800 °C caused the occurrence of metallic Ni on the surface. Surface area was determined by BET measurement. The catalyst was used as anode in IT-SOFCs fed with methanol. Studies under steam reforming, partial oxidation and autothermal reforming of methanol were carried out at 800°C. A comparison was made between the performance of SOFCs fed with syngas or methanol. The results with methanol are promising both in terms of energy density as well as suitable performance for portable power sources.
Dendrimers are highly branched organic macromolecules with successive layers or “generations” of branch units surrounding a central core. We show that tinchlorides complexes to the imines groups of a spherical polyphenylazomethine dendrimer in a stepwise fashion according to an electron gradient, with complexation in a more peripheral generation proceeding only after complexation in generations closer to the core has been completed. By further extending this strategy, it should be possible to control the number and location of metalchlorides incorporated into dendrimers for advanced nano-materials, such as nano-catalysts.
Fuel cell technology has merged in recent years as a keystone for future energy supply. The proton exchange membrane fuel cell (PEMFC) is one of the most promising projects of this energy technology program; the PEMFC is made of a conducting polymer that usually operates at temperatures in the range 20-80°C. In order to reach high energy consumption application like transportation, the using temperatures need to be increased above 100°C. Sol-gel organic/inorganic hybrids have been evaluated as materials for membranes to full file the high temperature using requirement. These new materials for membrane need to retain water content and therefore proton conductivity property with using temperature and time. The membranes also need to be chemical-resistant to strong acidic conditions and to keep their mechanical properties regarding stacking requirements. In order to! answer all these specifications, the proposed hybrid membranes are based on nanoporous inorganic phase embedded in an organic polymer in which chemical grafting and conductivity network microstructure are optimized to preserve both wateruptake and proton conductivity at higher temperatures. Such very promising results on these new hybrids are presented and discussed regarding electrochemical properties/microstructure.
Direct Methanol Fuel Cells (DMFCs) are promising candidates for portable electric power sources because of their high energy density, lightweight, compactness, simplicity as well as easy and fast recharging. Recently, the attention has been focused on portable applications with passive-feed DMFCs. Under this configuration, DMFCs operate without any external device for feeding methanol and blowing air into the cells. An investigation of properties and operating parameters of a passive DMFC monopolar mini-stack, such as catalyst loading and methanol concentration, was carried out. From this analysis, it was derived that a proper Pt loading is necessary to achieve the best compromise between electrode thickness and number of catalytic sites for the anode and cathode reactions to occurs at suitable rates. Methanol concentrations ranging from 1 M up to 10 M (40 vol%) and an air-breathing operation mode were investigated. A maximum power of 225 mW was obtained at ambient conditions for a three-cell stack, with an active single cell area of 4 cm2 corresponding to a power density of about 20 mW cm-2.
pages 277-282
Leonardo Giorgi, Rossella Giorgi, Serena Gagliardi, Elena Salernitano, Theodoros Dikonimos, Nicola Lisi, M. Federica De Riccardis, Marco Alvisi
Extensive efforts are focused on the development of Direct Methanol Fuel Cells, due to the intrinsic advantages of this type of devices for mobile power supply system. One of the major drawback of the DMFC resides in the easy poisoning of the anode electrocatalyst (platinum) by COlike reaction intermediates, which implies the need of high platinum load in order to obtain reasonable performances. The development of platinum alloys is considered one of the promising routes for overcoming this problem: the second metal in fact acts as inhibitor of the Pt poisoning. In this work we have combined the use of unconventional methods to deposit the electrocatalyst nanoparticles with unconventional carbon supports. PtAu alloys have been deposited by sputter deposition process on carbon nanofibers with platelet morphology grown by plasma enhanced chemical vapour deposition on carbon paper. Cyclic voltammetry in H2SO4 was used to determine the electrochemical active surface and the electrocatalytic performance for methanol oxidation reaction. Even at lower Pt load, respect to the ones prepared with commercial catalysts supported on carbon black, the innovative electrodes showed higher performance and stability.
By analogy with the development of nuclear power and photovoltaics, the position of MCFC technology is evaluated in the context of today’s energy supply. A brief review is presented of the technical status of MCFC materials and challenges left open. At system level, a number of more or less niche applications prove to be promising for approaching early markets and an update is given of some important figures on construction and deployment of MCFC systems worldwide.
It is widely recognized that metallic corrosion of the cathode current collector is a key technological problem that must be fully resolved before Molten Carbonate Fuel Cells can be commercialized on a more competitive basis. This paper presents a short overview on the corrosion mitigation strategies that appear more appropriate for MCFC current collectors. As alternative to the current use of the 300-series austenitic stainless steels, specialty high-Mn stainless steels, corrosionresistant Ni-based alloys and sol-gel coatings of thin conductive spinel or perovskite ceramic layers are seen as the most promising corrosion solutions for the cathode-side environment. The use of basic additives into electrolyte for inhibiting molten carbonate corrosion is a further mitigation option yet with less practical perspectives due to the high constraints on the electrolyte properties. Recent and current studies conducted at ENEA on MCFC corrosion solutions are also mentioned.
The potential use of multi-walled carbon nanotubes (MWCNTs) produced by chemical vapour deposition (CVD) as a conductive agent for electrodes in Li-ion batteries has been investigated. LiNi0.33Co0.33Mn0.33O2 (NCM) has been chosen as active material for positive electrodes, and a nano-sized TiO2-rutile for the negative electrodes. The electrochemical performances of the electrodes were studied by galvanostatic techniques and especially the influence of the nanotubes on the rate capability and cycling stability has been evaluated. The addition of MWCNTs significantly enhanced the rate performances of both positive and negative electrodes and improved the capacity retention upon cycling. The obtained results demonstrated that the addition of MWCNTs in low amounts to the electrode composition enables an increase in both energy and power density of a Li-ion battery.
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