A fuel cell produces electricity by converting the chemical energy of fuel directly to power in a controlled chemical reaction - without combustion and without moving parts. Fuel cells are therefore inherently ultra clean, highly efficient and reliable. The performance and structure of the fuel cell is explained below:
The performance and structure of the fuel cell is explained below:
1. Hydrogen molecules, which consist of single proton circled by a single electron, enter the fuel cell and come in contact with platinum. This catalyst helps to split the hydrogen into positively charged ions and negatively charged electrons.2. An "electrolyte", a special membrane or a substance screens out the electrons. These electrons, which create an electric current, are sent through the wire to power the vehicle's electric motor. Then they return to the fuel cell.3. The ions are able to pass through the electrolyte.4. In the third portion of the fuel cell, the hydrogen ions, the electrons and oxygen combine to make water. Water is continuously removed from the fuel cell as the ions and electrons keep flowing through the cell. It is the cell's only waste product.
The process works like this:Anode: 2 H2 = 4H + + 4e - Cathode: 4e - + 4H + + O2 = 2H2OOverall: 2H2 + O2 = 2H2Osee author's pages: http://www.pg.gda.pl/chem/Katedry/Maszyny/FC/FUEL_CELLS/fcns.htm There are several types of fuel cells that differ from each other mainly by the fuel or electrolyte used in the cell. At this time, the following types of fuel cells are used:
PAFC -Phosphoric Acid Fuel Cell
It uses liquid electrolyte in the form of ortho-phosphoric acid - H3PO4 and platinum as a catalyst. The electrolyte is placed between porous electrodes made of graphite, in Teflonated casing, filled with Silicone Carbide (SiC). The role of SiC is to keep the electrolyte in the proper place, avoiding its leakage. The oxidizer (O2 in this case - may be taken directly from air decreasing the efficiency only to the 36-42%) is reduced. The water vapor is evolved to the excess of air or O2 therefore it may be easily disposed from the fuel cell, avoiding the same the dilution of the electrolyte. Otherwise, it may lead to the decrease of the ionic conductivity of electrolyte and dropping the system efficiency. The power density of PAFC is equal to 1.7 kW/m2 - 1.9 kW/m2 of the FC active surface. PAFC has high sensitivity of the electrolyte toward overheating. At the temperature 210oC the phosphoric acid decomposes, what demands usage of advanced cooling systems. Electrolyte diffusion through the electrodes and escapes with the overflowing gases, what demands refilling it just after a few hours of operation. It causes a very troublesome maintenance.
MCFC -Molten Carbonate Fuel Cell
This kind of fuel cells uses molten lithium carbonates (Li2CO3) and molten potassium carbonates (K2CO3) as an electrolyte. The research on MCFC has started in 1960's when the idea of applying hard coal as a fuel in a fuel cell appeared. Molten electrolyte working at the temperature of 650oC is mixed with a chemically inactive porous ceramic material (for instance LiAlO2). The anode is made of porous nickel sinter enriched with chromium to avoid deformation during operation. The cathode is formed of nickel oxide and lithium sinter. The high working temperature enables to use Ni catalyst instead of more noble metals that decreases the costs. MCFC can run on carbon monoxide, formed for instance during incomplete combustion of coal, or hydrogen. In case of the usage of the latter fuel, the following reaction on the anode occurs: H2 + CO3 2- = H2O + CO2 + 2e- Due to this reaction, the electrons flow through the external circuit and to the fuel inlet water vapor and carbon dioxide evolves. The CO2 should be gathered because it must be used in the further process of carbonate ion recombination on the cathode. The CO2 may be gathered by combustion in the air of the fuel-hydrogen-residue. In the case if the CO2 will not be separated from H2 and together will be supplied to the oxidizer, an explosion will occur (autoignition temperature of H2 is equal to 565.56 degC). In the future there is planned to use some membrane separators. In the case of using carbon monoxide as a fuel, the following reaction occurs on the anode: CO + CO32- = 2CO2 + 2e- Due to this reaction carbon dioxide is evolved, then, like in the case of H2 as a fuel, must be gathered and used in the cathodic processes: 2CO2 + O2 + 4e- -> 2CO32- As the end process of MCFC operation, carbonate anions are formed. This type of fuel cells has the efficiency equal to 50-60% and may use some other fuels that make them a bit superior over PAFC. Thanks to the high working temperature, the evolving heat may be used to increase the total electrical efficiency of the whole system. It may be done by using the excess of heat in the traditional systems, where steam rotates turbines producing mechanical energy that is transformed into electricity later on. There is a need of using high-speed flowing gas as a cooler that produces considerable amount of noise. MCFC has high sensitivity towards changes of electrolyte temperature. For instance, cooling electrolyte from 650degC to 600degC results in such a high increase of ionic conductivity resistance that the output voltage falls down by 15%. Last disadvantage of MCFC is high corrosion of cathode.
1. Hydrogen molecules, which consist of single proton circled by a single electron, enter the fuel cell and come in contact with platinum. This catalyst helps to split the hydrogen into positively charged ions and negatively charged electrons.2. An "electrolyte", a special membrane or a substance screens out the electrons. These electrons, which create an electric current, are sent through the wire to power the vehicle's electric motor. Then they return to the fuel cell.3. The ions are able to pass through the electrolyte.4. In the third portion of the fuel cell, the hydrogen ions, the electrons and oxygen combine to make water. Water is continuously removed from the fuel cell as the ions and electrons keep flowing through the cell. It is the cell's only waste product.
The process works like this:Anode: 2 H2 = 4H + + 4e - Cathode: 4e - + 4H + + O2 = 2H2OOverall: 2H2 + O2 = 2H2Osee author's pages: http://www.pg.gda.pl/chem/Katedry/Maszyny/FC/FUEL_CELLS/fcns.htm There are several types of fuel cells that differ from each other mainly by the fuel or electrolyte used in the cell. At this time, the following types of fuel cells are used:
PAFC -Phosphoric Acid Fuel Cell
It uses liquid electrolyte in the form of ortho-phosphoric acid - H3PO4 and platinum as a catalyst. The electrolyte is placed between porous electrodes made of graphite, in Teflonated casing, filled with Silicone Carbide (SiC). The role of SiC is to keep the electrolyte in the proper place, avoiding its leakage. The oxidizer (O2 in this case - may be taken directly from air decreasing the efficiency only to the 36-42%) is reduced. The water vapor is evolved to the excess of air or O2 therefore it may be easily disposed from the fuel cell, avoiding the same the dilution of the electrolyte. Otherwise, it may lead to the decrease of the ionic conductivity of electrolyte and dropping the system efficiency. The power density of PAFC is equal to 1.7 kW/m2 - 1.9 kW/m2 of the FC active surface. PAFC has high sensitivity of the electrolyte toward overheating. At the temperature 210oC the phosphoric acid decomposes, what demands usage of advanced cooling systems. Electrolyte diffusion through the electrodes and escapes with the overflowing gases, what demands refilling it just after a few hours of operation. It causes a very troublesome maintenance.
MCFC -Molten Carbonate Fuel Cell
This kind of fuel cells uses molten lithium carbonates (Li2CO3) and molten potassium carbonates (K2CO3) as an electrolyte. The research on MCFC has started in 1960's when the idea of applying hard coal as a fuel in a fuel cell appeared. Molten electrolyte working at the temperature of 650oC is mixed with a chemically inactive porous ceramic material (for instance LiAlO2). The anode is made of porous nickel sinter enriched with chromium to avoid deformation during operation. The cathode is formed of nickel oxide and lithium sinter. The high working temperature enables to use Ni catalyst instead of more noble metals that decreases the costs. MCFC can run on carbon monoxide, formed for instance during incomplete combustion of coal, or hydrogen. In case of the usage of the latter fuel, the following reaction on the anode occurs: H2 + CO3 2- = H2O + CO2 + 2e- Due to this reaction, the electrons flow through the external circuit and to the fuel inlet water vapor and carbon dioxide evolves. The CO2 should be gathered because it must be used in the further process of carbonate ion recombination on the cathode. The CO2 may be gathered by combustion in the air of the fuel-hydrogen-residue. In the case if the CO2 will not be separated from H2 and together will be supplied to the oxidizer, an explosion will occur (autoignition temperature of H2 is equal to 565.56 degC). In the future there is planned to use some membrane separators. In the case of using carbon monoxide as a fuel, the following reaction occurs on the anode: CO + CO32- = 2CO2 + 2e- Due to this reaction carbon dioxide is evolved, then, like in the case of H2 as a fuel, must be gathered and used in the cathodic processes: 2CO2 + O2 + 4e- -> 2CO32- As the end process of MCFC operation, carbonate anions are formed. This type of fuel cells has the efficiency equal to 50-60% and may use some other fuels that make them a bit superior over PAFC. Thanks to the high working temperature, the evolving heat may be used to increase the total electrical efficiency of the whole system. It may be done by using the excess of heat in the traditional systems, where steam rotates turbines producing mechanical energy that is transformed into electricity later on. There is a need of using high-speed flowing gas as a cooler that produces considerable amount of noise. MCFC has high sensitivity towards changes of electrolyte temperature. For instance, cooling electrolyte from 650degC to 600degC results in such a high increase of ionic conductivity resistance that the output voltage falls down by 15%. Last disadvantage of MCFC is high corrosion of cathode.
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