AN OVERVIEW OF MOLTEN CARBONATE FUEL CELL (TECHNOLOGICAL PERSPECTIVE)
vijay tharad
Director Operations at Corporate Professional Academy for Technical Training & Career Development
Molten Carbonate Fuel Cell
In the molten carbonate fuel cell, the electrolyte consists of a molten mixture of potassium carbonate and lithium carbonate to transport carbonate-ions from the cathode to the anode. The CO32- transport needs supply of CO2 at the cathode side of the cell which is generally be obtained by recycling the anode off side gas. The operating temperature is about 850 °C which allows nickel to be used as catalyst material. The process occuring in a hydrogen-oxygen fuel cell operating at higher temperatures without an aqueous electrolyte might well be considered as oxide ions produces at the air electrode:
O2 + 4e- → 2O2-
which then move to the fuel electrode to oxidise the hydrogen:
H2 + O2- →?H2O + 2e-
and it might therefore be considered that a molten ionic oxide would provide the best electrolyte to encourage this process. However, simple ionic oxides have melting points greater than 1000 °C and therefore attention has been focused on salts melting at lower temperature. These salts are generally those with oxygen-containing anions, eg nitrates, sulfates, carbonates. At high temperature it is likely that the direct reaction of hydrocarbons at the fuel electrode is quite favorable and hence conversion of petroleum products to hydrogen or methanol is unnecessary. But consideration must be given to the effect of hydrocarbon oxidation at the fuel electrode on the choice of electrolyte. Carbon dioxide will be a major product that can be troublesome with some salts, for example:
CO2 + SO42- → CO32- + SO3
Hence it is most satisfactory to consider as electrolyte a molten carbonate or mixture of carbonates. A mixture of salts may have a considerable advantage since it will have a lower melting point than either of its components. A convenient way of maintaining the carbonate composition of the electrolyte invariant is to remove carbon dioxide as a gaseous product from the fuel electrode and transfer it to the oxidant electrode in the air or oxygen stream. Thus for a fuel such as carbon monoxide the overall electrode processes will be:
O2 + 2CO2 + 4e- → CO32-???? and???? CO + CO32- → 2CO2 + 2e-
Thus carbonate ion transfer within the electrolyte may be balanced by carbon dioxide transfer outside it. A similar mechanism could operate even for cells using hydrogen as a fuel.
?Anode reaction:?H2 +?CO32-?→ CO2 + H2O + 2e-??
Cathode reaction:??O2?+ CO2?+ 2e- → CO32-?
Overall reaction:?H2 + ?O2 → H2O?
Molten carbonate fuel cells (MCFCs) are currently being developed for natural gas and coal-based power plants for electrical utility, industrial, and military applications. MCFCs are high-temperature fuel cells that use an electrolyte composed of a molten carbonate salt mixture suspended in a porous, chemically inert ceramic lithium aluminum oxide matrix. Because they operate at high temperatures of 650°C (roughly 1,200°F), non-precious metals can be used as catalysts at the anode and cathode, reducing costs.
Improved efficiency is another reason MCFCs offer significant cost reductions over phosphoric acid fuel cells. Molten carbonate fuel cells, when coupled with a turbine, can reach efficiencies approaching 65%, considerably higher than the 37%–42% efficiencies of a phosphoric acid fuel cell plant. When the waste heat is captured and used, overall fuel efficiencies can be over 85%.
Unlike alkaline, phosphoric acid, and PEM fuel cells, MCFCs do not?require an external reformer to convert fuels such as natural gas and biogas to hydrogen. At the high temperatures at which MCFCs operate, methane and other light hydrocarbons in these fuels are converted to hydrogen within the fuel cell itself by a process called internal reforming, which also reduces cost.
The primary disadvantage of current MCFC technology is durability. The high temperatures at which these cells operate and the corrosive electrolyte used accelerate component breakdown and corrosion, decreasing cell life. Scientists are currently exploring corrosion-resistant materials for components as well as fuel cell designs that double cell life from the current 40,000 hours (~5 years) without decreasing performance.
Molten carbonate fuel cells (MCFCs) are currently being developed for natural gas and coal-based power plants for electrical utility, industrial, and military applications. MCFCs are high-temperature fuel cells that use an electrolyte composed of a molten carbonate salt mixture suspended in a porous, chemically inert ceramic lithium aluminum oxide (LiAlO2) matrix. Because they operate at extremely high temperatures of 650°C (roughly 1,200°F) and above, non-precious metals can be used as catalysts at the anode and cathode, reducing costs.
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Improved efficiency is another reason MCFCs offer significant cost reductions over phosphoric acid fuel cells (PAFCs). Molten carbonate fuel cells can reach efficiencies approaching 60%, considerably higher than the 37%–42% efficiencies of a phosphoric acid fuel cell plant. When the waste heat is captured and used, overall fuel efficiencies can be as high as 85%.
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Unlike alkaline fuel cells, PAFCs, and polymer electrode membrane fuel cells, MCFCs do not require an external reformer to convert more energy-dense fuels to hydrogen. Due to the high temperatures at which MCFCs operate, these fuels are converted to hydrogen within the fuel cell itself by a process called internal reforming, which also reduces cost.?
Molten carbonate fuel cells are not prone to carbon monoxide or carbon dioxide "poisoning" – they can even use carbon oxides as fuel – making them more attractive for fueling with gases made from coal. Because they are more resistant to impurities than other fuel cell types, scientists believe that they could even be capable of internal reforming of coal, assuming they can be made resistant to impurities such as sulfur and particulates that result from converting coal, a dirtier fossil fuel source than many others, into hydrogen.?
The primary disadvantage of current MCFC technology is durability. The high temperatures at which these cells operate and the corrosive electrolyte used accelerate component breakdown and corrosion, decreasing cell life. Scientists are currently exploring corrosion-resistant materials for components as well as fuel cell designs that increase cell life without decreasing performance.
A molten carbonate fuel cell consists of an electrolyte, typically a molten carbonate salt mixture suspended in a ceramic matrix, sandwiched between an anode (negatively charged electrode) and a cathode (positively charged electrode). The processes that take place in the fuel cell are as follows: 1. Hydrogen fuel is channeled through field flow plates to the anode on one side of the fuel cell, while oxygen from the air, carbon dioxide, and electricity (electrons from the fuel cell circuit) are channeled to the cathode on the other side of the cell. 2. At the cathode, the oxygen, carbon dioxide, and electrons react to form positively charged oxygen ions and negatively charged carbonate ions. 3. The carbonate ions move through the electrolyte to the anode. 4. At the anode, a catalyst causes the hydrogen combine with the carbonate ions, forming water and carbon dioxide and releasing electrons. 5. The electrolyte does not allow the electrons to pass through it to the cathode, forcing them to flow through an external circuit to the cathode. This flow of electrons forms an electrical current. 6. The carbon dioxide formed at the anode is often recycled back to the cathode.
Molten Carbonate Fuel Cell (MCFC) Molten carbonate fuel cells use lithium potassium carbonate salt as an electrolyte, composed of a molten carbonate salt mixture suspended in a porous, chemically inert matrix, and operate at high temperatures of approximately 600 °C and above. Molten carbonate fuel cells can reach efficiencies approaching 60 %. Molten carbonate fuel cells (MCFCs) have been developed for natural gas, biogas, and coal-fired power plants, as well as for electrical utility, industrial, and military uses. Molten carbonate fuel cell disadvantages include slow start-up times because of their high operating Kemal Ermi? | 137 temperature; this makes the molten carbonate fuel cell systems not suitable for mobile applications. The electrolytes in the molten carbonate fuel cells are heated to 600°C, at which point the salts melt and conduct carbonate ions (CO3 2-) from the cathode to the anode. The hydrogen oxidation reaction mixes with carbonate ions at the anode, creating water and carbon dioxide and releasing electrons to the external circuit . Because oxygen is reduced to carbonate ions at the cathode by mixing with carbon dioxide and electrons from the external circuit. The electrochemical reactions occurring in the molten carbonate fuel cell are:
At the anode: H2 + CO3 2-→ H2 O + CO2 + 2e- (1)
At the cathode: ?O2 + CO2 + 2e- → CO3 2- (2)
The overall cell reaction: H2 + ?O2 + CO2 → H2 O + CO2 (3)
Schematic representation of the general operation of a molten carbonate fuel cell as shown in Fig
Molten Carbonate Fuel Cell (MCFC)
3.1. Working principle The structure of the Molten Carbonate Fuel Cell (MCFC) mainly includes a cathode, anode, electrolyte, and separator, of which the anode generally uses Ni-Al, Ni-Cr as a catalyst, and the cathode adopts lithiated NiO (LixNi1-xO) as a catalyst and the electrolyte is molten carbonate Highlights in Science, Engineering and Technology ERET 2023 Volume 59 (2023) 141 (Li2CO3 . Na2CO3 . K2CO3), the diaphragm uses a porous LiAlO2 membrane to carry molten carbonate. High conductivity of electrolytes Molten carbonate is a liquid obtained by melting the carbonate of ionic crystals at high temperatures above the melting point. It is composed of cations such as alkali metal ions and anions of carbonate ions. Molten carbonates used as MCFC electrolytes are ionic liquids above 500℃, pure solute electrolytes without solvents, and have higher ionic conductivity than other electrolyte systems. It can be said that the high conductivity of molten carbonate is due to the high operating temperature, which can reduce the internal resistance and inhibit the resistance polarization. Reaction mechanism The oxygen reduction reaction of MCFCs is carried out in molten carbonate electrolyte at 650℃, so the catalytic effect related to electrode materials is not high.[20] When working, air and CO2 are introduced into the cathode, and an electrochemical reaction: O2+2CO2+4e-=2CO3 2- (At the same time, electrons from the anode pass through the external circuit to the cathode, and do electrical work externally. For a schematic of a typical MCFC see Figure 4. At present, MCFC single cells adopt a flat plate structure, the power density of the single cell is over 160 mW/cm (working voltage 0.8V, pressure 0.1MPa, fuel utilization rate 20%), and the maximum area is 1 m2.[19] Fig 4. Working principle of MCFC [19] 3.2. MCFC for CO2 separation MCFCs are an innovative and flexible way to reduce CO2 emissions and provide energy more efficiently, fueled by fossil and renewable energy sources. MCFCs can operate as CO2 separators and concentrators when generating electricity and are therefore a valuable candidate for
Molten carbonate fuel cells (MCFCs)
High temperature cells
Molten Carbonate Fuel Cells (MCFCs) are another type of high temperature fuel cell. A molten mixture of salts: lithium, sodium, potassium carbonate is used as the electrolyte. These salts melt and conduct carbonate ions (CO32–) from the anode to the cathode when heated to about 600°C. Hydrocarbons have to be used as part of the fuel since the charge carriers in the electrolyte are carbonate ions. Hydrogen is also needed at the anode. It is gained by internal reforming of hydrocarbon based fuels. The electrodes should be resistant to poisoning by carbon. The high exhaust temperature makes cogeneration of electricity with turbines possible; hence the efficiency (60% without and 80% with hybrid technology) is relatively high compared to other fuel cell systems. MCFCs are mainly used for stationary power generation in the 50?kW to 5?MW range. Since it uses a liquid and high temperature electrolyte, it is rather unsuitable for mobile applications. The main problem with MCFC is the slow dissolution of the cathode in the electrolyte. Most of the research is therefore in the area of more durable materials and cathodes.
Molten Carbonate Fuel Cell
Molten-Carbonate Fuel Cell Working
The molten-carbonate fuel cell (MCFC) is similar to the solid oxide fuel cell (SOFC), but it uses carbonate ions as the charge carrier in a high-temperature liquid solution of lithium, potassium, or sodium carbonate as an electrolyte.
The MCFC operates at a temperature of 600° C to 700° C (1,112° F to 1,292° F), so it can generate steam that can be used to generate more power. It is best suited for large stationary power generators.
Because the MCFC has an operating temperature that is a bit lower than solid oxide fuel cells, it can use less exotic materials, which makes it a little less expensive to manufacture and operate.
The MCFC was first designed in the early 1930s along with the SOFC. Research on both devices continued to provide improvements until the 1950s when researchers found that fused molten-carbonate salts could be used as an electrolyte in the fuel cell.
Because MCFCs operate at extremely high temperatures, nonprecious metals such as nickel can be used as catalysts in the anode and cathode, rather than the platinum that is used in some other fuel cells.
Figure 6 shows a diagram of an MCFC. Hydrogen is ionized at the anode by the catalyst. After the carbonate ions (CO?23 pass through the electrolyte, they combine with the hydrogen ions (H+) to form water (H2O) and carbon dioxide (CO2), which is returned to the input.
The carbon dioxide and electrons from the external circuit combine with oxygen to supply more carbonate ions, and the process continues.
The net reaction is hydrogen plus oxygen, which produces water as in other fuel cells. High-temperature MCFCs can extract hydrogen from a variety of fuels, such as natural gas, diesel, or coal, and they are not subject to the contamination issues of other types of fuel cells.
Because the MCFC operates at very high temperatures, these fuels can be converted to hydrogen within the fuel cell itself without a separate reformer, which also reduces cost.
Figure 6 Operation of a Molten-Carbonate Fuel Cell (MCFC)
An important advantage of an MCFC is that it can be used as a large stationary power plant that can supply power to the main load or at peak times as needed.
In addition to its ability to use various fuels, these plants are clean and quiet. The fuel cell can be placed close to the point where it is used, so it allows electric companies to provide electricity without a large investment in transmission lines.
One other advantage of MCFCs is that the waste heat can be captured and used, thus raising the overall efficiency.
One major disadvantage of molten-carbonate technology is that it is more difficult working with a very hot liquid electrolyte rather than a solid electrolyte.
Another disadvantage is that the chemical reactions at the anode use carbonate ions from the electrolyte, making it necessary to inject carbon dioxide at the cathode and thus requiring a supply of carbon dioxide.
The principle of Fuel Cell
Oxygen and hydrogen, when mixed together in the presence of enough activation energy have a natural tendency to react and form water, because the Gibbs free energy of H2O is smaller than that of the sum of H2 and ?O2 added together (Hence, we don’t smoke our pipes on Zeppelins!). If hydrogen and oxygen were combined directly, we would see combustion:
H2 + ?O2 → H2O
Combustion involves the direct reaction of H2 gas with O2. The hydrogen donates electrons to the oxygen . We say that the oxygen has been reduced and the fuel oxidised. This combustion reaction releases heat energy.
The fuel cell separates hydrogen and oxygen with a gas-impermeable electrolyte through which only ions (e.g. H+, O2-, CO32–) can migrate. Hence two half reactions occur at the two electrodes. The type of reactions at the electrodes is determined by the type of electrolyte.
Grove's fuel cell is one of the simplest examples.
The half-reaction at the anode: H2 → 2H+ + 2e–
The half-reaction at the cathode: O2 + 4e–+ 4H+ → 2H2O
The net reaction is the combustion reaction: H2 + ?O2 → H2O
Activation polarization is caused by the energy intensive activity of the making and breaking of chemical bonds: At the anode, the hydrogen molecules enter the reaction sites so that they are broken into ions and electrons. The resulting ions form bonds with the catalyst atoms and the electrons remain in the vicinity until new hydrogen molecules start bonding with the catalyst, breaking the bond between the earlier ion. The electrons migrate through the bipolar plate if the bonding energy of the ion is low enough and the ions diffuse through the electrolyte. A similar process occurs at the cathode: Oxygen molecules are broken up and react with the electrons from the anode and the protons that diffused through the electrolyte to form water. Water is then ejected as a waste product and the fuel cell runs (can supply a current), as long as fuel and oxygen is provided.
The exact reactions at the electrodes depend upon which species can be transported across the electrolyte. Fuel cells are classified according to the type of electrolyte . The most common electrolytes are permeable for protons and the reactions are as discussed above. The second most common electrolytes, found in solid oxide fuel cells (SOFCs), are permeable for oxide ions and the following half-reactions occur:
The half-reaction at the anode: H2 + O2– → H2O + 2e–
The half-reaction at the cathode: O2 + 4e– → 2O2– The net reaction is the same as before:
H2 + ?O2 → H2O?
A third type of electrolyte, used for molten carbonate fuel cells at high temperatures conducts carbide ions (CO32–):
The half-reaction at the anode: H2 + CO32– → H2O + CO2 + 2e–
The half-reaction at the cathode: ?O2 + CO2 + 2e– → CO32–
The net reaction is the combustion reaction: H2 + ?O2 → H2O?
We also commonly see alkaline electrolytes, across which OH– is the transported species. In this case the half-reactions would be:
The half-reaction at the anode: H2 + 2OH– → 2H2O + 2e–
The half-reaction at the cathode: O2 + 4e– + 2H2O → 4OH–
The net reaction is the combustion reaction: H2 + ?O2 → H2O
Historical summary
Both the solid oxide and the molten carbonate fuel cells are high temperature devices. ?Their development followed similar lines until the late 1950's. First, E. Baur and H. Preis experimented with solid oxide electrolytes in Switzerland. The technical problems they encountered were again tackled by the Russian scientist O.K. Davtyan without success though. In the late 1950's, Dutch scientists G.H.J. Broers and J.A.A. Ketelaar focused on molten carbonate salts as electrolyte. By 1960, they reported the first MCFC prototype. In the mid-1960's, the US Army’s Mobility Equipment Research and Development Center (MERDC) tested several MCFCs made by Texas Instruments ranging from 100 to 1000 Watts. Ishikawjima Heavy Industries showed in Japan in the early 1990s that a 1000 Watt MCFC power generator can operate for 10000 hours continuously. Other large power plants with outputs of up to 3 megawatts are already planned.
M-C Power's molten carbonate fuel cell power plant in San Diego, California, 1997. Smithsonian Institution, from the Science Service Historical Images Collection, courtesy of National Energy Technology Laboratory.
The MCFC has been under development for 15 years as a stationary electric power plant. Although when most problems with the Solid Oxide Fuel Cell are solved, work on the MCFC might be stopped.
MCFC Electrolyte
In most cases, the electrolyte of the MCFC is made of a lithium-potassium carbonate salt heated to 600-1000°C. At this temperature, the salt is in liquid phase and can conduct ions between the two electrodes. The typical mixture ratio of the electrolyte is 62?m/o Li2CO3 and 38?m/o K2CO3 (62/38 Li/K). This particular mixture of carbonate salts melts at 550°C and when it is mixed with lithium aluminate (LiAlO2 is a ceramic matrix retaining the molten salts, it can be used both as an ion-conducting electrolyte and gasketing for the fuel cell stack. Negative carbonate ions (CO32–) are responsible for conduction. As discussed above, the long term performance is an issue for MCFCs.
The following properties of the electrolyte have to be taken into account:
Loss of electrolyte mainly occurs at the cathode via hydrolysis:
MeCO3 + H2O?? 2MeOH + CO2
Especially the electrolyte that has been used unaltered for a long time , Li2CO3/K2CO3 (38/62) eutectic, has a relatively high volatility. This causes the fuel cell to dry out.
The partial pressure due to MeOH varies with the square root of water vapour to carbon dioxide vapour pressures:
p(MeiOH)=Ki(T)pH2OpCO2
Ki(T) is the equilibrium coefficient of the carbonate ion in the melt according to the equilibrium equation:
CO32– + H2O?? CO2 + 2OH–
The anode off-gas on the other hand can be mixed with air after combustion and reused in the cathode chamber with a sufficiently high air excess. Here oxygen and carbon dioxide are consumed in a ratio of 1:2 (molar) by the cathode process.
The change in composition of the electrolyte due to segregation and the volatility of certain species may result in a change in melting temperature. The electrolyte can solidify, causing the fuel cell to malfunction and sometimes allowing gases to break through. Carbonate ions from the electrolyte are used up in the reactions at the anode, so that we have to compensate for the loss by injecting carbon dioxide at the cathode.
Segregation occurs as the potassium concentration increases near the cathode. This leads to an increased cathode solubility and hence a decline of cell performance.
Recent studies show, that using Na instead of K can decrease the amount of segregation. In a molten binary salt with a common anion, segregation occurs due to the difference in mobilities of the cations. The heavier and bigger potassium and sodium cation is faster lithium in mixtures that have a higher potassium concentration that K2CO3=0.32 (Chemla effect), whereas below this isotachic concentration, lithium is faster.
The partial pressure of carbon dioxide has a much smaller effect on the current voltage curves than the partial pressure of oxygen. Mass transfer limitations are not observed for CO2 but for oxygen at low partial pressures. CO2 transport also hinders the cathode operation much less than oxygen transport since this gas has a much better solubility in carbonate melts than O.
Only the Li2CO3/Na2CO3 eutectic with much lower sodium vapour pressures could assure long term performance of fuel cells. We can conclude that the Li/Na electrolyte is more reliable and safer than Li/K. Since the ionic conductivity of Li/Na carbonate melts is higher than that of Li/K carbonate melts, Li/Na is preferred material as the electrolyte. But since the electrolyte is in the liquid phase, the fuel cell needs a more complex design, compared to other technologies using a solid electrolyte.
MCFC Electrochemistry
External fuel processors are not needed for MCFCs since the fuels can be reformed internally at the high operating temperatures. Internal reforming includes converting methane and steam into a hydrogen rich gas.
CH4 + H2O?? CO + 3H2
At the anode, hydrogen reacts with the carbonate ions to produce water, electrons and carbon dioxide.
H2 + CO32– ??H2O + CO2 + 2e–
The electrons are conducted away by an external circuit to do useful work to the cathode. Oxygen from the air and carbon dioxide from the anode react at the cathode with electrons to form water and carbonate ions.
O2 + CO2 +2e– ??CO32-
The carbonate ions migrate through the electrolyte to the anode, and complete the electrical circuit.CO32– is used up at the anode; CO2 is needed at the cathode.
MCFC Electrodes
A significant advantage of the MCFC is that non-noble metals can be used as electrodes. At the high operating temperature, a Nickel anode and the Nickel oxide cathode is able to promote the electrochemical reaction. This means lower production costs compared to low temperature fuel cell, where the catalyst electrode is usually made of platinum. The Ni electrodes are less prone to CO poisoning, hence coal based fuel can be used, especially since internal reforming can take place.
Solubility of electrode in electrolyte
The main problem with the electrodes is their solubility in the electrolyte by Ostwald ripening, which is a dissolution/reprecipitation process. It decreases the internal surface of the porous nickel oxide cathode, causing it to deteriorate. The solubility of nickel oxide (cathode material) is dependant on the cathode potential and temperature. The solubility of Ni and NiO in Li/Na was found to be lower than in Li/K melts.
Although Li/Na melts have been found to have superior performance compared to Li/K melts, the lower oxygen solubility reduces the cathode performance on lean gas with a low oxygen partial pressure (below 0.1?bars).
Molten Carbonate Fuel Cell Applications
? Mainly used for stationary power generation.
Molten carbonate fuel cells have a power output of 10 kW to 3 MW that achieves 47% electrical efficiency and can utilize combined heat and power (CHP) technology to obtain higher overall efficiencies .
? Consumer electronics
? Light traction vehicle
? Commercial and industrial distributed power generation
? Emergency backup power supply
SPECIFICS OF MCFC
FUEL CELL TYPE : MOLTEN CARBONATE FUEL CELL
RATED POWER : 1 KW TO 1 MW
APPLICATION : Large distributed generation -Electric utility
ADVANTAGE : -Suitable for combined heat and power -High efficiency -Fuel flexibility -Can use a variety of catalysts -High-speed reactions.
DISADVANTAGES: -High temperature enhances corrosion and breakdown of cell components -Slow start-up -High intolerance to sulphur.
What is a Molten Carbonate Fuel Cell (MCFC)?
What is a Molten Carbonate Fuel Cell (MCFC)?
Molten Carbonate Fuel Cell, referred to as MCFC, is a fuel cell composed of a porous ceramic cathode, a porous ceramic electrolyte separator, a porous metal anode, and a metal plate. Its electrolyte is molten carbonate. Molten carbonate fuel cells (MCFCs) were developed for natural gas, biogas (produced by anaerobic digestion or biomass gasification), and coal-based power plants for use in power, industrial and military applications.
How do Molten Carbonate Fuel Cells work?
MCFCs operate based on the principles of electrochemical reactions occurring at the anode and cathode, separated by a molten carbonate electrolyte.
1. Anode (Fuel Electrode):
At the anode, a gaseous fuel, such as hydrogen (H2) or a hydrocarbon like methane (CH4), is supplied. The fuel undergoes an oxidation reaction with carbonate ions (CO32-) from the electrolyte, producing water (H2O), carbon dioxide (CO2), and releasing electrons. The anode is usually made of a porous material, such as nickel, that allows reactant flow and electron transfer.
Anode reaction (fuel oxidation):
H2?+ CO32- → H2O + CO2?+ 2e–
2. Cathode (Air/Oxidant Electrode):
At the cathode, typically exposed to ambient air, oxygen (O2) is provided. Oxygen reacts with carbon dioxide (CO2) and accepts electrons from the external circuit to form carbonate ions (CO32-). The cathode is also made of a porous material, often containing a catalyst like silver, to facilitate the oxygen reduction reaction.
Cathode reaction (oxygen reduction):
?O2?+ CO2?+ 2e–?→ CO32-
3. Molten Carbonate Electrolyte:
The molten carbonate electrolyte, consisting of a mixture of lithium carbonate and potassium carbonate, allows the migration of carbonate ions (CO32-) from the cathode to the anode. It acts as a conductive medium for the ions and enables the electrochemical reactions to take place. The carbonate ions migrate through the electrolyte matrix driven by concentration and charge gradients, ensuring the continuous supply of reactants to the electrode surfaces.
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Overall Cell Reaction:
The net reaction occurring in an MCFC is the combination of the fuel oxidation reaction at the anode and the oxygen reduction reaction at the cathode. The overall cell reaction results in the production of water (H2O) and carbon dioxide (CO2) as reaction products.
H2 + ?O2?→ H2O + CO2
MOLTEN CARBONATE FUEL CELLS (MCFC)
Molten carbonate fuel cells (MCFC) represent an high temperature technology of fuel cells which are currently being developed as a solution for static electrical power generation or to work with other static generation applications which are already on the market like coal based power plants or some industrial facilities.
MCFC are a technology of fuel cells which operates at temperatures up to 650 °C using a liquid solution of alkali carbonate salts as the electrolyte. MCFC represent an high temperature fuel cell technology which can reach an efficiency of 45% that can be potentially raised up to 60% - 70% if the waste heat is correctly utilized. Due to the high temperature, MCFCs can be fueled with gases like methane, natural gas or coal reformed gases. However due to the same high temperature they suffers from many problems such as fast degradation of the cell structure, due to mechanical/corrosion problems, and constant loss of the electrolyte, due to evaporation, inside the cell (which implies the need to refuel it continuously).
Molten carbonate fuel cells use an electrolyte that conducts carbonate (CO3 2– ) ions from the cathode to the anode. This is the opposite of many other types of fuel cells, which conduct hydrogen ions from the anode to the cathode. The electrolyte is composed of a molten mixture of lithium and potassium carbonates. This mixture is retained by capillary forces within a ceramic support matrix of lithium aluminate. At the fuel cell operating temperature, the electrolyte structure is a thick paste, and the paste provides gas seals at the cell edges. Molten carbonate fuel cells operate at about 1200 0F (650 0C) and a pressure of 15 to 150 psig (1 to 10 barg). Each cell can produce up to between 0.7 and 1.0 VDC.
Advantages of Molten Carbonate Fuel Cells:
? It has support spontaneous internal reforming of light hydro-carbon fuels.
? It has generate high-grade waste heat.
? It has fast reaction kinetics.
? It has high efficiency.
Disadvantages of Molten Carbonate Fuel Cells:
? It has a liquid electrolyte, which introduces liquid handling problems.
? It has require a considerable warmup period.
? It has a high intolerance to sulphur. The anode in particular cannot tolerate more than 1-5 ppm of sulphur compounds in the fuel gas without suffering a significant performance loss.
Molten Carbonate Fuel Cell Structure
The base structure of a MCFC is made with a ceramic matrix containing the electrolyte Fig. (8) which is surrounded by the anode, fueled by hydrogen rich fuel, and the cathode, fueled by oxygen (usually air).
There are actually two mixtures of molten carbonate salts (the high temperature is required in order to melt this mixture) that could be used as the electrolyte. The two mixtures can be a combination of lithium carbonate and potassium carbonate or lithium carbonate and sodium carbonate.
Those electrolytes are dispersed inside a porous and chemically inert ceramic matrix made with lithium aluminate (LiAlO2). Inside this structure ceramic powder and fibers are used in order to reinforce the whole mechanical strength. Furthermore a special polymer is used to create many sheets with constant thickness which are then impregnated with the electrolyte to confine it.
Regarding the electrodes thanks to the high operating temperature, a relatively cheap catalyst like nickel can be used instead of the much expensive ones like platinum. The metal material used for the construction of the anode and the cathode result exposed to both highly oxidizing and reducing environments. This implies that in order to be used those metal have to respect a certain array of strict requirements. The anode is a porous electrode made with a nickel alloy (Ni-5Cr, Ni-xAl) as the catalyst. This alloys contains a small percent of aluminum or chromium in order to suppress the hot creep inside the electrode structure. The cathode is realized with a porous nickel catalyst. During the cell start-up, the nickel in contact with the electrolyte (eutectic mixture of Li2CO3 and K2CO3) is converted to high conductive lithium doped nickel oxide (LixNi1-xO2).
The cell requires time in order to start since it needs to reach a temperature of 650 °C. Upon reaching this temperatures the carbonate salts begin to melt and becomes conductive by carbonate ions (CO3
2-). These ions are transported from the cathode to the anode where they combine with hydrogen to produce water, carbon dioxide and electrons. These electrons are then collected by the anode and routed, through an external circuit, to the cathode thus generating electricity and heat .
A particular configuration of MCFCs do not need external reformers in order to convert fuels into hydrogen. In fact due to the high temperatures the fuels can be directly converted to hydrogen through a process called catalytic internal reforming which takes places in a pre-chamber inside the anode compartment. The main problem of this configuration is the coarseness of the reforming catalyst, which reduce the life-time of the system.
6.2. Molten Carbonate Fuel Cell Characteristics and
Applications
MCFCs are currently being developed and demonstrated in several countries around the world like USA, Japan, Korea and Germany. The applications that are being demonstrated ranges, regarding the generated power, between 125 kW and 1 MW .
The main advantages that the technology detain are summarized as follows:
? MCFCs efficiency goes up to 45% and, since high temperature and steam is generated, if they are used with combined cycles heath systems the efficiency of the MCFCs applications exceeds 50% – 60%;
? MCFCs can use a wide array of hydrogen rich fuel like natural gas or coal gasified gasses and, if the fuel reforming takes place inside the cell, the construction of an external reformer is not needed. These characteristics greatly reduce power generation costs;
? the possibility to use standard and low cost materials such as stainless steel and nickel based alloys greatly participate in the reduction of the cell construction costs. However the high temperatures involved and the electrolytes chemistry are the cause of the following disadvantages:
? a low operative life cycle due to the corrosion caused by the electrolyte used, the loss of the electrolyte due to the ? high temperatures and the dissolution of the cathode inside the electrolyte matrix, with the possibility to short-circuit the cell;
? slow starting times determined by the need to reach an operative temperature of 650 °C;
? impossibility to re-start the cell stack after a shut-down. Therefore although there are demonstration programs all around the world, there is still a large effort in terms of research and development which is being carried on by many organizations, industrial companies and universities. Those efforts are focused upon the improvement of the cell operative life cycle and the increase of the power density of the cell..
The main actors involved in this environment of research are FuelCell Energy (FCE, USA), CFC Solutions (Germany), Ishikawajima Harima Heavy Industries (IHI, Japan), POSCO/KEPCO consortium and Doosan Heavy Industries (Korea), GenCell Corportation (USA).
What are the advantages of Molten Carbonate Fuel Cells (MCFCs)?
1. Efficiency: MCFCs offer high electrical efficiency, reaching up to 60%. The high operating temperature enables better utilization of fuel and waste heat recovery, making them suitable for combined heat and power (CHP) applications.
2. Fuel Flexibility: MCFCs can utilize a variety of hydrocarbon fuels, making them adaptable to existing infrastructure. This characteristic allows for the utilization of biogas from landfills, wastewater treatment plants, and other renewable sources.
3. Carbon Capture Potential: The high-temperature operation of MCFCs enables the integration of carbon capture and storage (CCS) technologies. By capturing and sequestering carbon dioxide (CO2) from the fuel stream, MCFCs can help mitigate greenhouse gas emissions.
a schematic representation of an MCFC that works using hydrogen as fuel.
MCFCs could work with an efficiency of up to 60% reaching an operating power of 100 MW . Using waste heat from the system, fuel efficiency can be as high as 85%, a value above performance in PAFCs, another clear comparative advantage. In this vein,
MCFCs compete very well with PAFCs, PEMFCs and other types of fuel cells, because do not require an external reformer to convert other types of fuels into hydrogen and due to the range of working temperatures, any hydrocarbon that is injected into the cell will be transformed into hydrogen through “anodic reforming reactions” of traditional fuels or flue gas but also biofuels , natural gas (from coal) , which translates into a significant decrease in operational costs.
MCFCs are not affected by carbon monoxide or carbon dioxide poisoning, on the contrary, these cells produce CO2 (+ CO) through an anodic oxidation reaction, which will be used in anodic reformation transforming the injected hydrocarbons into the cell in combustible hydrogen . In this sense, it is interesting to note that the MCFC could use carbon oxides themselves as fuel, which place them at the forefront of fuel cells in terms of the role they can play in capturing CO2 In this way, MCFCs can act as CO2 separators or concentrators when they act integrated into a thermoelectric power plant , forming a hybrid MCFC-GT system and and others “hybrid systems” with thermophotovoltaic technology, MCFC-TPVC , or various solar thermal systems (PTC, LFR and PDC) in addition with an Organic Rankine Cycle (ORC) .
2 From a processing engineering point of view, the greatest disadvantage of MCFC technology is its low durability , which is a consequence of the range of operating temperatures and research objective of new technology .
Additionally, the corrosive nature of electrolytes accelerates the breakdown of cell components, reducing their useful life . Consequently, one of the largest research niches in this field is precisely in the study of new materials that can be used in the construction of MCFCs. Due to their electrochemical cycle, the cell concentrates the CO2 up to around 75–90% along with H2O and small amounts of H2. This CO2 can be concentrated even further since it is much easier to separate CO2 from water than from N2 in flue gas. Several studies have investigated the use of MCFCs as electrochemically active membranes to produce power and simultaneously concentrating CO2 removed from the effluent streams of coal plants , natural gas combined cycles (NGCC) . This concept has shown the largest reduction in energy required for CO2 capture when integrated into a modified natural gas power plant, where the fuel cell is located between the gas turbine and heat recovery steam generator. In this way, the MCFC consumes ~20% of the total plant’s fuel input and contributes to the electric power output by a similar fraction. Compared to a benchmark amine scrubbing process, the use of MCFC for concentrate CO2 shows considerably better performance (Primary Energy Consumption for CO2 0.31 MJ kg?1 CO2; Cost of CO2 avoided 50 $ tCO2) or even lower according to the US department of Energy (Cost of CO2 avoided 40 $ tCO2)
Figure 1. Schematic representation of a molten carbonate fuel cell (MCFC). Cathode chemical reactions are observed, anodic ones,
Molten-carbonate fuel cells (MCFCs) are high-temperature fuel cells that operate at temperatures of 600?°C and above.
Molten carbonate fuel cells (MCFCs) were developed for natural gaas, biogas (produced as a result of anaerobic digestion or biomass gasification), and coal-based power plants for electrical utility, industrial, and military applications. MCFCs are high-temperature fuel cells that use an electrolyte composed of a molten carbonate salt mixture suspended in a porous, chemically inert ceramic matrix of beta-alumina solid electrolyte (BASE). Since they operate at extremely high temperatures of 650?°C (roughly 1,200?°F) and above, non-precious metals can be used as catalysts at the anode and cathode reducing costs.
Improved efficiency is another reason MCFCs offer significant cost reductions over phosphoric acid fuel cells (PAFCs). Molten carbonate fuel cells can reach efficiencies approaching 60%, considerably higher than the 37–42% efficiencies of a phosphoric acid fuel cell plant. When the waste heat is captured and used, overall fuel efficiencies can be as high as 85%.
Unlike alkaline, phosphoric acid, and polymer electrolyte membrane fuel cells, MCFCs don't require an external reformer to convert more energy-dense fuels to hydrogen. Due to the high temperatures at which MCFCs operate, these fuels are converted to hydrogen within the fuel cell itself by a process called internal reforming, which also reduces cost.
Molten carbonate fuel cells are not prone to poisoning by carbon monoxide or carbon dioxide — they can even use carbon oxides as fuel — making them more attractive for fueling with gases made from coal. Because they are more resistant to impurities than other fuel cell types, scientists believe that they could even be capable of internal reforming of coal, assuming they can be made resistant to impurities such as sulfur and particulates that result from converting coal, a dirtier fossil fuel source than many others, into hydrogen. Alternatively, because MCFCs require CO2 be delivered to the cathode along with the oxidizer, they can be used to electrochemically separate carbon dioxide from the flue gas of other fossil fuel power plants for sequestration.
The primary disadvantage of current MCFC technology is durability. The high temperatures at which these cells operate and the corrosive electrolyte used accelerate component breakdown and corrosion, decreasing cell life. Scientists are currently exploring corrosion-resistant materials for components as well as fuel cell designs that increase cell life without decreasing performance.[1]
Molten carbonate FCs are a recently developed type of fuel cell that targets small and large energy distribution/generation systems since their power production is in the 0.3-3 MW range.[2] The operating pressure is between 1-8 atm while the temperatures are between 600 and 700?°C.[3] Due to the production of CO2 during reforming of the fossil fuel (methane, natural gas), MCFCs are not a completely green technology, but are promising due to their reliability and efficiency (sufficient heat for co-generation with electricity). Current MCFC efficiencies range from 60 to 70%.[4]
Reactions[5]
Internal Reformer (methane example):
CH4+H2O=3H2+CO
Anode (hydrogen example):
H2+CO32?=H2O+CO2+2e?
Cathode:
12O2+CO2+2e?=CO32?
Cell:
H2+12O2=H2O
Nernst Equation:
E=Eo+RT2FlogPH2PO212PH2O+RT2FlogPCO2,cathodePCO2,anode
Materials
Due to the high operating temperatures of MCFC's, the materials need to be very carefully selected to survive the conditions present within the cell. The following sections cover the various materials present in the fuel cell and recent developments in research.
Anode
Development Components MCFC components are limited by several technical considerations: Anode: Anodes are made of a Ni-Cr/Ni-Al alloy. The Cr was added to eliminate the problem of anode sintering. However, Ni-Cr anodes are susceptible to creep when placed under the torque load required in the stack to minimize contact resistance between components. The Cr in the anode is also lithiated by the electrolyte; then it consumes carbonate. Developers are trying lesser amounts of Cr (8 percent) to reduce the loss of electrolyte, but some have found that reducing the Cr by 2 percentage points increased creep. Several developers have tested Ni-Al alloy anodes that provide creep resistance with minimum electrolyte loss. The low creep rate with this alloy is attributed to the formation of LiAlO2 dispersed in Ni. Even though alloys of chromium or aluminum strengthened nickel provides a stable, non-sintering, creep-resistant anode, electrodes made with Ni are relatively high in cost. Alloys, such as Cu-Al and LiFeO2, have not demonstrated sufficient creep strength or performance. Because of this, present research is focused on reducing the manufacturing cost of the nickel alloy anodes. There is a need for better sulfur tolerance in MCFCs, especially when considering coal operation. The potential benefit for sulfur tolerant cells is to eliminate cleanup equipment that impacts system efficiency. This is especially true if low temperature cleanup is required, because the system efficiency and capital cost suffer when the fuel gas temperature is first reduced, then increased to the cell temperature level. Tests are being conducted on ceramic anodes to alleviate the problems, including sulfur poisoning, being experienced with anodes. Anodes are being tested with undoped LiFeO2 and LiFeO2 doped with Mn and Nb. Preliminary testing, where several parameters were not strictly controlled, showed that the alternative electrodes exhibited poor performance and would not operate over 80 mA/cm2 .
The anode material typically consists of a porous (3-6 μm, 45-70% material porosity) Ni based alloy. Ni is alloyed with either Chromium or Aluminum in the 2-10% range. These alloying elements allow for formation of LiCrO2/LiAlO2 at the grain boundaries, which increases the materials' creep resistance and prevents sintering of the anode at the high operating temperatures of the fuel cell. Recent research has looked at using nano Ni and other Ni alloys to increase the performance and decrease the operating temperature of the fuel cell. A reduction in operating temperature would extend the lifetime of the fuel cell (i.e. decrease corrosion rate) and allow for use of cheaper component materials. At the same time, a decrease in temperature would decrease ionic conductivity of the electrolyte and thus, the anode materials need to compensate for this performance decline (e.g. by increasing power density). Other researchers have looked into enhancing creep resistance by using a Ni3Al alloy anode to reduce mass transport of Ni in the anode when in operation.
Cathode
Cathode: An acceptable material for cathodes must have adequate electrical conductivity, structural strength, and low dissolution rate in molten alkali carbonates to avoid precipitation of metal in the electrolyte structure. Cathodes are made of lithiated NiO that have acceptable conductivity and structural strength. However, in early testing, a predecessor of UTC Fuel Cells found that the nickel dissolved, then precipitated and reformed as dendrites across the electrolyte matrix. This decreased performance and eventual short-circuiting of the cell. Dissolution of the cathode has turned out to be the primary life-limiting constraint of MCFCs, particularly in pressurized operation. Developers are investigating approaches to resolve the NiO dissolution issue. For atmospheric cells, developers are looking at increasing the basicity of the electrolyte (using a more basic melt such as Li/NaCO3). Another approach is to lower CO2 (acidic) partial pressure. To operate at higher pressures (higher CO2 partial pressure), developers are investigating alternative materials for the cathodes and using additives in the electrolyte to increase its basicity. Initial work on LiFeO2 cathodes showed that electrodes made with this material were very stable chemically under the cathode environment; there was essentially no dissolution. However, these electrodes perform poorly compared to the state-of-the-art NiO cathode at atmospheric pressure because of slow kinetics. The electrode shows promise at pressurized operation, so it is still being investigated. Higher performance improvements are expected with Co-doped LiFeO2. It also has been shown that 5 mol lithium-doped NiO with a thickness of 0.02 cm provided a 43 mV overpotential (higher performance) at 160 mA/cm2 compared to the state-of-the-art NiO cathode. It is assumed that reconfiguring the structure, such as decreasing the agglomerate size, could improve performance. Another idea for resolving the cathode dissolution problem is to formulate a milder cell environment. This leads to the approach of using additives in the electrolyte to increase its basicity. Small amounts of additives provide similar voltages to those without additives, but larger amounts adversely affect performance. Another approach to a milder cell environment is to increase the fraction of Li in the baseline electrolyte or change the electrolyte to Li/Na rather than the baseline 62/38 Li/K melt. Within the past 10 years, a lower cost stabilized cathode was developed with a base material cost comparable to the unstabilized cathode. A 100 cm2 cell test of the lower-cost stabilized cathode with a Li/Na electrolyte system completed 10,000 hours of operation.
On the other side of the cell, the cathode material is composed of either Lithium metatanate or of a porous Ni that is converted to a lithiated nickel oxide (lithium is intercalated within the NiO crystal structure). The pore size within the cathode is in the range of 7-15 μm with 60-70% of the material being porous. The primary issue with the cathode material is dissolution of NiO since it reacts with CO2 when the cathode is in contact with the carbonate electrolyte. This dissolution leads to precipitation of Ni metal in the electrolyte and since it is electrically conductive, the fuel cell can get short circuited. Therefore, current studies have looked into the addition of MgO to the NiO cathode to limit this dissolution. Magnesium oxide serves to reduce the solubility of Ni2+ in the cathode and decreases precipitation in the electrolyte. Alternatively, replacement of the conventional cathode material with a LiFeO2-LiCoO2-NiO alloy has shown promising performance results and almost completely avoids the problem of Ni dissolution of the cathode.
Electrolyte
Electrolyte: Present electrolytes have the following chemistry: lithium potassium carbonate, Li2CO3/K2CO3 (62:38 mol percent) for atmospheric pressure operation and lithium sodium carbonate, LiCO3/NaCO3 (52:48 o 60:40 mol percent) that is better for improved cathode stability under pressurized operation and life extension. The electrolyte composition affects electrochemical activity, corrosion, and electrolyte loss rate. Evaporation of the electrolyte is a life-limiting issue for the molten carbonate fuel cell. Li/Na electrolyte is better for higher pressure operation than Li/K because it gives higher performance. This allows the electrolyte matrix to be made thicker for the same performance relative to the Li/K electrolyte. Thicker electrolytes result in a longer time to shorting by internal precipitation. Li/Na also provides better corrosion resistance to mitigate acidic cathode dissolution. However, it has lower wettability and greater temperature sensitivity. Additives are being investigated to minimize the temperature sensitivity of Li/Na. The electrolyte has a low vapor pressure at operating temperature, and may slowly evaporate. Stack testing has shown that the electrolyte vapor loss is significantly slower than expected. The evaporation loss is projected to have minimal impact on stack life.
MCFC's use a liquid electrolyte (molten carbonate) which consists of a sodium(Na) and potassium(K) carbonate. This electrolyte is supported by a ceramic (LiAlO2) matrix to contain the liquid between the electrodes. The high temperatures of the fuel cell is required to produce sufficient ionic conductivity of carbonate through this electrolyte. Common MCFC electrolytes contain 62% Li2CO3 and 38% K2CO3. A greater fraction of Li carbonate is used due to its higher ionic conductivity but is limited to 62% due to its lower gas solubility and ionic diffusivity of oxygen. In addition, Li2CO3 is a very corrosive electrolyte and this ratio of carbonates provides the lowest corrosion rate. Due to these issues, recent studies have delved into replacing the potassium carbonate with a sodium carbonate. A Li/Na electrolyte has shown to have better performance (higher conductivity) and improves the stability of the cathode when compared to a Li/K electrolyte (Li/K is more basic). In addition, scientists have also looked into modifying the matrix of the electrolyte to prevent issues such as phase changes (γ-LiAlO2 to α-LiAlO2) in the material during cell operation. The phase change accompanies a volume decrease in the electrolyte which leads to lower ionic conductivity. Through various studies, it has been found that an alumina doped α-LiAlO2 matrix would improve the phase stability while maintaining the fuel cell's performance.
MTU fuel cell
The German company MTU Friedrichshafen presented an MCFC at the Hannover Fair in 2006. The unit weighs 2 tonnes and can produce 240?kW of electric power from various gaseous fuels, including biogas. If fueled by fuels that contain carbon such as natural gas, the exhaust will contain CO2 but will be reduced by up to 50% compared to diesel engines running on marine bunker fuel. The exhaust temperature is 400?°C, hot enough to be used for many industrial processes. Another possibility is to make more electric power via a steam turbine. Depending on feed gas type, the electric efficiency is between 12% and 19%. A steam turbine can increase the efficiency by up to 24%. The unit can be used for cogeneration.
Benefits of Fuel Cell Usage
Some of the major benefits offered by fuel cell technology are:
Challenges for Fuel Cells to be Adopted in India
While fuel cells hold tremendous potential, certain challenges need addressing for their extensive adoption in India:
Key Applications of Fuel Cells
Some key applications where fuel cell technology can make a significant impact include:
Some Real-World Examples of Fuel Cells
Government Initiatives and Policies for Fuel Cell
The Government of India has recognized the importance of fuel cell technology and taken initiatives like:
Molten Carbonate Fuel Cells: an alternative and cleaner power supply for ships
A new application of Molten Carbonate Fuel Cell (MCFC) has been developed by the European-funded MC WAP research project to be eventually used as an alternative power supply for ships. This will be cleaner and avoid the pollution of the marine diesel engines which currently provide the power in the vast majority of the world’s ships
The research into molten carbonate fuel cells has it origins as early as the 1930s, Emil Baur and H.Preis in Switzerland experimented with high-temperature, solid oxide electrolytes. At the initial stages the research was applicable to both molten carbonate and solid oxide fuel cells which are both high-temperature devices. The technical history of both cells seems to follow a similar line of research. A divergence in the development appeared in the late 1950s. From then on, the Molten Carbonate Fuel Cell (MCFC) was developed from a purely experimental prototype to today’s practical demonstrator. Molten carbonate fuel cells demand very high operating temperatures (600°C and above) and most applications for this kind of cell are limited to large, stationary power plants. The envisaged initial application is associated with waste heat, industrial processing, and in steam turbines to generate more electricity. The MC WAP project has developed a molten carbon fuel cell which uses hydrogen obtained from a system that converts diesel oil into a hydrogen-rich gas, and air coming from the compressor of a microturbine. The reaction produces electricity and heat, without combustion. To operate the MCFC on board a ship, researchers of the MC-WAP project have developed two major elements: The Fuel Processor Module and the Fuel Cells Module. The Fuel Cells Module is a chemical plant. It is fed from one side by compressed air and from the other side by a gas called syngas (produced from diesel) by the Fuel Processor Module. This gas is currently being tested in Germany, at the University of Freiberg. The chemical reaction between air and syngas then generates electricity. The energy produced by the current system, corresponds to about 250 kilowatts, and represents one production unit of reserve energy that can power the essential systems on board, such as the control systems, communication, lighting and main auxiliary systems. Although at this time it will not power the propulsion, it will be able to contribute to it in some cases. No combustion means fewer greenhouse gas emissions from the many tourist and cargo ships that carry the millions of people and goods around the coasts of Europe and the world. The cleaner ship exhausts are better for the environment and will help the operators to meet the new green legislation. Cleaning the exhausts involves removing the traces of sulphur and carbon di-oxide that remain after normal combustion, resulting in clean exhaust gases. The system releases virtually no harmful substances: the fuel is transformed into synthetic gas which is then used in the fuel cell, without creating pollution. Furthermore the lack of moving parts in the MCFC will reduce the overall ship vibrations which will result in a more comfortable journey for the passengers.
Countries
Austria, Belgium, Bulgaria, Cyprus, Czechia, Germany, Denmark, Estonia, Spain, Finland, France, Hungary, Ireland, Italy, Lithuania, Luxembourg, Latvia, Malta, Netherlands, Poland, Portugal, Romania, Sweden, Slovenia, Slovakia, United Kingdom
FREQUENTLY ASKED QUESTIONS:
What are molten carbonate fuel cells?
A schematic drawing show the working principle of the MCFC can be seen in Figure 1-2. Oxygen is reduced with CO2 at the cathode, while hydrogen is oxidized at the anode to produce water and CO2. In the electrolyte, carbonate ions provide the means of ionic transport between the cathode and the anode.6 Feb 2024
What is the temperature of molten carbonate fuel cell?
around 650 °C
The molten carbonate fuel cell (MCFC) operates at around 650 °C and has been developed principally for large-scale stationary power generation applications.
What is the cathode material in molten carbonate fuel cell?
On the other side of the cell, the cathode material is composed of either Lithium metatitanate or of a porous Ni that is converted to a lithiated nickel oxide (lithium is intercalated within the NiO crystal structure). The pore size within the cathode is in the range of 7-15 μm with 60-70% of the material being porous.
What are the reactions of molten carbonate fuel cell?
The electrode reactions for MCFCs are as follows. oxide ion from cathode to anode. Electrons produced at the anode pass through an external circuit before flowing to the cathode, and thus electric power can be extracted.
What is the use of molten carbonate?
Molten carbonate fuel cells (MCFCs) are currently being developed for natural gas and coal-based power plants for electrical utility, industrial, and military applications.
What are fuel cells?
Fuel cells are devices that generate electricity through an electrochemical reaction between a fuel (hydrogen, methanol etc.) and an oxidant (oxygen/air) instead of combustion. They convert the chemical energy in the fuel directly to electrical energy without burning the fuel.
How are fuel cells different from batteries?
Batteries store electrical energy chemically within them. Once discharged, they need to be recharged by supplying electricity. Fuel cells can generate electricity as long as fuel is supplied, similar to engines or turbines. They do not need recharging.
Which ministry is responsible for fuel cell development in India?
The Ministry of New and Renewable Energy (MNRE) is the nodal ministry coordinating fuel cell-related policies, schemes and development in India.
What are the advantages of fuel cells?
Fuel cells offer benefits like low/zero emissions, high efficiency of around 60%, reliability, modularity, fuel flexibility, low noise and vibration, and capability to combine with renewable energy sources.
How can fuel cell adoption be promoted in India?
Policy measures like subsidies, funding R&D, building hydrogen infrastructure, promoting domestic manufacturing, and public awareness campaigns can help increase fuel cell adoption in India.
What are the advantages and disadvantages of fuel cell?
Advantages of flexible fuel cells include high energy density, easy integration, potential cost effectiveness, and portability. Disadvantages include unsatisfactory power density, bulky fabrication process, and incomplete flexibility.
What are the limitations of molten carbonate fuel cell?
The primary disadvantage of current MCFC technology is durability. The high temperatures at which these cells operate and the corrosive electrolyte used accelerate component breakdown and corrosion, decreasing cell life.
What are the applications of molten carbonate fuel cells?
Molten Carbonates from Fuel Cells to New Energy DevicesThis greenhouse effect gas can be extracted from the flue gas of a combined cycle power plant while generating electricity, avoiding loss in plant efficiency and consequent increase in primary energy consumption.
What is the efficiency of molten carbonate fuel cells?
Thus, MCFCs can use gases derived from coal or carbon oxides as fuel. Second, the MCFC has a cost advantage, because nonprecious metals can be used as catalysts at its anode and cathode (again because they operate at high temperatures). Third, MCFCs can attain high energy efficiencies, almost 60% in some cases.
What are the reactions of molten carbonate fuel cell?
The electrode reactions for MCFCs are as follows. oxide ion from cathode to anode. Electrons produced at the anode pass through an external circuit before flowing to the cathode, and thus electric power can be extracted.
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