1,720,988 research outputs found
Political Animals in Seventeenth-Century Philosophy : Some Rival Paradigms (Hobbes and Gassendi),
No full textDevelopment of Electrochemical Impedance Spectroscopy Instrument for Survey on Fuel Cell
No full textAfter a description of Electrochemical Impedance
Spectroscopy methods, a new instrument extremely cheaper than
market ones and suitable for fuel cells investigation will be
presented. The characteristics for the system will be calculated
and presented also together with some measurements realized
Bioenergy from fuel cells: effects of hydrogen sulfide impurities on performance of PEMFC fed with biogas.
No full textBiogas, generally rich in CH4 and CO2, is one of the key to increase the share of renewable energy
sources in total energy consumption. Different technologies are currently available for gas energy
conversion but fuel cells are one of the most interesting because of their environmental benefits and
their high potentiality.
The high operating temperature of MCFC makes them particularly suitable for biogas use because CO
is, not only harmfulness, but represents an additional fuel. Furthermore CH4 can be internally
reformed.
Biogas impurities such as sulfur compounds, cause adverse effects on cell performance. In particular
hydrogen sulfide is harmful to the MCFC anode because nickel anodes react with H2S to form nickel
sulfide which can block active electrochemical reaction sites. [1-3]
The aim of this work is to study hydrogen sulfide effects on MCFC, establishing performance
dependence on hydrogen sulfide concentration. Initial studies to reduce the degree of sulfur
poisoning were carried out and some parameters like temperature, gas concentrations, mode
of system operation were modified.
[1] H.Devianto, S.P. Yoon, S.W. Nam, J. Han, T.-H. Lim, J.Power Sources 159 (2006) 1147.
[2] M. Kawase, Y. Mugikura, T. Watanabe, J. Electochem. Soc. 147 (2000) 1240.
[3] R. Bove, P.Lunghi, J.Power Sources 145 (2005) 588
Nanostructured coating layer for anode materials in fuell cell fed with biogas
No full textEnergy and environment challenges to promote security and sustainability are focused on research in energy technology in order to enhance the energy efficiency and the use of cleaner fuels. The conversion of biomass chemical energy into electrical energy using fuel cells plays a key role to address the issues related to the global energy security, the local energy independence, the environmental protection and the economic growth.
Molten carbonate fuel cell is especially suitable for bioenergy production because it can be fed directly with biogas, whose primary constituents all improve the performance of the cell. However hydrogen sulfide, which is the main biogas impurity, poisons the nickel based anode, affecting the power and the endurance of the cell. In order to overcame this problem, it has been developing innovative anode materials that resist against the sulfide corrosions. In particular, conventional nickel based anode covered with ceria thin layer performs sulphur tolerance and recovering capability
Investigation on hydrogen sulphide poisoning in molten carbonate fuel cells used for waste-to-energy conversion.
No full textBioenergy addresses three important social concerns: security of energy supply, lower greenhouse gas emissions and support for agriculture. Bioenergy is energy produced from the direct or indirect combustion of biomass material, such as energy crops, wood, manures and slurries or organic waste converted to biogas. Different technologies are currently available for bioenergy conversion but fuel cells are one of the most interesting because of their environmental benefits and their high efficiency.
High operating temperature of molten carbonate fuel cells (650°C) makes them particularly suitable for energy production from biogas, which is biomass derived gas rich in methane and carbon dioxide. In fact, methane can be internally reformed to hydrogen, carbon dioxide is a safe chemical participating in electrodic reactions, and carbon monoxide acts both as a hydrogen supplier and as a fuel.
Unfortunately, biogas impurities, such as sulfur compounds, halogen compounds, nitrogen compounds, hydrocarbons and siloxanes, cause adverse effects on cell performances. The most dangerous impurities are sulfur compounds. Hydrogen sulphide is the predominant and the most harmful sulfur compound in biogas. It reacts with nickel-based anode to form nickel sulphides and blocks electrocatalytic sites.
Poisoning mechanism of hydrogen sulphide depends on operational conditions such as current density, anodic gas composition, temperature and pressure. The aim of this work is to study hydrogen sulphide effects on MCFCs with multivariate mathematical approaches. In this way it is possible to define the main sulfur poisoning mechanism under MCFC operating conditions, quantify the effect of current density, hydrogen and hydrogen sulphide on sulfur poisoning and identify the interaction between these parameters. Also it is possible to formulate a multivariate model to predict sulfur poisoning
Molten carboate fuel cell fed with biogas
No full textRenewable and sustainable energy sources have to be considered to overcome problems such as energy security and climate change associated with fossil fuel. Drivers for bioenergy technologies development are environmental and socio-economic politics. First biomass has a carbon neutral life cycle and promotes climate change benefits that can be realized through reduction of GHG emissions. A sustainable energy crops production, which does not compete with the use of land and water for food production, can have a positive impact toward food security because promote rural development providing energy access to remote communities and creating employment. Finally bioenergy guarantee energy security because it promotes the energy supplies diversification and the reduction of dependency on a few exporters of oil and natural gas. Fuel cells play a key role to overcome the low energy content of the biomass, because they are highly efficient and environmentally friendly. High temperature fuel cells, such as molten carbonate fuel cell (MCFC) and solid oxide fuel cell (SOFC), are particularly suitable for bioenergy production because they can be fed with biogas directly: methane can be transformed to hydrogen by internal reforming , carbon dioxide is a safe diluent and carbon monoxide acts as both a direct fuel, because is an electroactive specie, and a hydrogen supplier by water gas shift reaction. However biogas contains other chemicals, biomass processing byproducts, affecting cell performances. Among these, hydrogen sulfide is the most important because is able to poison the cell at low ppm levels. This work includes studies of biogas composition on MCFC performance, studies of sulfur poisoning mechanisms, identification of selection criterions for sulfur-tolerant materials, and preliminary characterization of alternative anode materials with high corrosion resistance and with high recovering capability.
Hydrogen sulfide affects cell performance because it reacts with both the anode and the electrolyte. Electrolyte poisoning occurs is due to the replacement of carbonate ions with sulfide and sulfate ions. Anode degradation is due to bulk chemical reactions, chemisorption, physical adsorption and electrochemical reactions. Multivariate analysis was performed to study poisoning mechanisms and develop a model with predictive capability. Results show that sulphur poisoning occurs via electrochemical mechanisms mainly. At low hydrogen sulfide levels just two poisoning reaction types occur: physical and chemical absorptions on nickel surface; replacement of carbonate ions with sulfide and sulfate ions. In fact, formations of bulk nickel sulfides are thermodynamically forbidden. However when it is applied a current at the cell, the anodic potential increases up to right values for nickel sulfide formations via electrochemical mechanisms. It means that under current load MCFC is more sensible to hydrogen sulfide attack.
Poisoning levels depend on applied current, hydrogen sulfide concentrations and hydrogen concentrations.Irreversible poisoning effects are due to stable nickel sulfide formations, Ni3S2. Selection criteria for alternative anode materials with a high resistance to hydrogen sulfide corrosion have to include evaluations of both thermochemical parameters such as Gibbs free energy of sulfuration reactions and electrochemical parameters such as electrode potential for sulfide depositions. Proposed anode materials include to two different categories: anodes made of an electrocatalyst and a hydrogen sulfide trap such as NiCr covered with either CeO2 or CeO2-ZrO2; anode made of a hydrogen sulfide resistance electrocatalyst such as NiAl
SULFUR POISONING IN MOLTEN CARBONATE FUEL CELL FED WITH BIOGAS
No full textAlternative energy sources have to be considered to overcome problems such as energy security and climate change associated with fossil fuel. Biomass is one of the most interesting alternative sources because is renewable, sustainable and widely available. Also biomass which is carbon-based differs from the other renewable energy sources because of their utilization for the energy carrier supply obtained by biological or thermochemical process. Biofuels need high efficient energy conversion technologies such as fuel cells because of their low energy content. Fuel cells are clean, efficient and silent, but need pure hydrogen as fuel. High temperature fuel cells (HTFCs) are more suitable for application of biofuel because they can include an internal reforming which give them fuel flexibility and because their electrodes are more tolerance against fuel contaminants. The research is focussed on molten carbonate fuel cell (MCFC) because of its technology that is more advanced than Solid Oxide Fuel Cell (SOFC) and because of its soon appearing at the marketplace as a commercial product. The most suitable biofuel for MCFC is biogas because reformed methane and carbon monoxide are fuels and carbon dioxide is a diluent. Biogas impurities such as sulphur compounds, mercaptanes, siloxanes and halogenated hydrocarbons affect cell performances. Hydrogen sulphide, which is the most important biogas impurities, reacts either chemically or electrochemically with the electrolyte and the anode affecting the power density and lifetime of the cell [1-4]. The aim of this work is to study the mechanism and the kinetic of hydrogen sulphide poisoning to be able to select alternative anode materials with high sulphur tolerance and high regenerative capability
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
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