Types Of Fuel Cells Engineering Essay

Types Of Fuel Cells Engineering Essay

A fuel cell is basically a battery that does non necessitate reloading. Equally long as H and O fuel are supplied, it can go on to provide heat and an electrical current indefinitely. A fuel cell consists of an electrolyte ( a music director of charged atoms ) between an anode ( negatively charged electrode ) and a cathode ( a positively charged electrode ) . Once activated by a accelerator, the H gas separates into protons and negatrons, and the negatrons are conducted through a wire, organizing an electrical current. The protons move through the electrolyte, where they combine with O and other negatrons to bring forth heat and a H2O by-product.

Sir William Grove developed the first fuel cell in England in 1839. His experiments during this clip on electrolysis, the usage of electricity to divide H2O into H and O, led to the first reference of a device that would subsequently be termed the “ fuel cell. ”

Grove believed that if it was possible to divide H2O into H and O with electricity, the contrary of the electrolysis procedure, to bring forth electricity from the reaction of O with H, should besides be possible. To prove this theory, he enclosed two Pt strips in separate certain bottles, one containing H and the other incorporating O. When these containers were immersed in dilute sulfuric acid, a current began to flux between the two electrodes and H2O was formed in the gas bottles. To increase the electromotive force produced, Grove linked several of these devices in series and produced what he referred to as a “ gas battery. ” The chemists Ludwig Mond and Charles Langer coined the term “ fuel cell ” in 1889 as they attempted to construct the first practical device utilizing air and industrial coal gas.

Scientists and applied scientists shortly learned that they would hold to get the better of many hurdlings if this new engineering was to be commercialized. By the terminal of the nineteenth century, the internal burning engine was emerging and the widespread development of fossil fuels sent the fuel cell the manner of scientific wonder.

An applied scientist, Dr. Francis Thomas Bacon, at Cambridge University in England, wrote the following major chapter in the fuel cell narrative. In 1932, Bacon resurrected the machine developed by Mond and Langer and implemented a figure of alterations to the original design. These included replacing the Pt electrodes with less expensive Ni gauze. He besides substituted the sulfuric acid electrolyte for alkali K hydrated oxide, a substance less caustic to the electrodes. This device, which he named the “ Bacon Cell, ” was in kernel the first alkaline fuel cell ( AFC ) . Another 27 old ages would go through until Bacon could bring forth a genuinely feasible fuel cell. In 1959, Bacon demonstrated a machine capable of bring forthing 5 kilowatt of power, plenty to power a welding machine.

Harry Karl Ihrig of Allis-Chalmers, a farm equipment maker in the U.S. , was besides intrigued with fuel cell engineering. His discovery, tardily in 1959, was showing the first fuel cell-powered vehicle. By uniting 1008 cells, he produced a fuel cell stack, which could bring forth 15 kilowatt and was capable of powering a 20 horsepower tractor.

Get downing in the late fiftiess and early 1960s, there was renewed involvement in the fuel cell. NASA was looking for a manner to power a series of upcoming manned infinite flights. Using batteries for power had already been ruled out due to weight considerations. Solar energy was excessively expensive at the clip and atomic power was determined to be excessively hazardous. In NASA ‘s hunt for an option, the fuel cell was thought to be a possible solution. NASA sponsored attempts to develop practical working fuel cells that could be used during these infinite flights. These attempts led to the development of the first Proton Exchange Membrane Fuel Cell ( PEMFC ) .

In 1955, while NASA was carry oning research, a scientist working at General Electric ( GE ) modified the original fuel cell design. Willard Thomas Grubb used a sulphonated polystyrene ion-exchange membrane as the electrolyte. Three old ages subsequently another GE chemist, Leonard Niedrach, devised a manner of lodging Pt onto this membrane, which finally became known as the “ Grubb-Niedrach fuel cell. ” GE and NASA developed this engineering together ensuing in its usage on the Gemini infinite undertaking. This was the first commercial usage of a fuel cell.

In the early 1960s, aircraft engine maker Pratt & A ; Whitney licensed the Bacon patents for the Alkaline Fuel Cell ( AFC ) . With the end of cut downing the weight and planing a longer-lasting fuel cell than the GE PEM design, Pratt & A ; Whitney improved the original Bacon design. As a consequence, Pratt & A ; Whitney won a contract from NASA to provide these fuel cells to the Apollo ballistic capsule. Alkali cells have since been used on most subsequent manned U.S. infinite missions, including those of the Space Shuttle.

During the 1970s, fuel cell engineering was developed for systems on Earth. The oil trade stoppage of 1973 and 1979 helped to force along the research attempt of the fuel cell as the U.S. Government was looking for a manner to go less dependent on crude oil imports.

A figure of companies and authorities organisations began serious research into get the better ofing the obstructions to widespread commercialisation of the fuel cell. Throughout the 1970s and 1980s, a big research attempt was dedicated to developing the stuffs needed, placing the optimal fuel beginning and drastically cut downing the cost of this engineering.

During the 1980s, fuel cell engineering began to be tested by public-service corporations and car makers. Technical discovery during the decennary included the development of the first marketable fuel cell-powered vehicle in 1993 by the Canadian company, Ballard.

They are five ( 5 ) types of fuel cell engineerings and they are classified by the sort of electrolyte employed. Knowing the electrolyte used, it can state us the sort of chemical reactions that occurs within the cell, the type of accelerator required, the scope of temperature the cell needs to run at and other factors. Each fuel cell has at that place ain advantages and disadvantages, and besides at that place ain potency applications. The five ( 5 ) types of fuel cells are:

Polymer Electrolyte Membrane Fuel Cells

Alkaline Fuel Cells

Phosphoric Acid Fuel Cells

Molten Carbonate Fuel Cells

Solid Oxide Fuel Cells

Polymer Electrolyte Membrane Fuel Cells ( PEMFC )

The Polymer Electrolyte Membrane Fuel Cell is used fundamentally for two applications, transit and stationary. This type of fuel cell is suited for the usage of autos and coachs because of its fast get down up clip and low sensitiveness to orientation. The electrolyte used in the PEMFC is a solid polymer and it uses a porous C electrode incorporating a Pt accelerator. Hydrogen, the O from air, and H2O are needed for this fuel cell to run. The pure H that is used to power fuel cells in vehicles and is on-board the vehicle, are required to be stored in pressurized armored combat vehicles as a tight gas.

The PEMFC operates at around 176A°F, which is considered to be a low temperature. At this low temperature, less warm up clip is needed so it starts quickly.Diagram: How a Polymer Electrolyte Membrane ( PEM ) fuel cell works. A PEM fuel cell consists of a polymer electrolyte membrane sandwiched between an anode ( negatively charged electrode ) and a cathode ( positively charged electrode ) . The procedures that take topographic point 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 O from the air is channeled to the cathode on the other side of the cell. 2. At the anode, a Pt accelerator causes the H to divide into positive H ions ( protons ) and negatively charged negatrons. 3. The Polymer Electrolyte Membrane ( PEM ) allows merely the positively charged ions to go through through it to the cathode. The negatively charged negatrons must go along an external circuit to the cathode, making an electrical current. 4. At the cathode, the negatrons and positively charged H ions combine with O to organize H2O, which flows out of the cell.

Alkaline Fuel Cells ( AFCs )

The Alkaline Fuel Cell was developed in the earlier yearss of fuel cell engineering. It was widely used on- board the U.S ballistic capsules to bring forth electrical energy and H2O. The type of electrolyte used in this type of fuel cell is a solution of K hydrated oxide in H2O and the accelerator at the anode and cathode used can be assortment of non-precious metals. The AFCs can run at both high and low temperatures. The high temperatures operates between a scope of 212A°F and 482A°F where as the low temperature AFC is a newer design that operates between a scope of 74A°F and 158A°F. The public presentation is dependent upon the rate at which chemical reactions take topographic point in the cell. The AFC has a disadvantage of being easy poisoned by C dioxide. The cell ‘s operation can be affected by a little sum of C dioxide in the air. Therefore, for the AFC to work efficaciously, both the H and O used in the cell, needs to be purified.Diagram: How a Phosphoric Acid Fuel Cell ( PAFC ) works. A PAFC consists of liquid phosphorous acid electrolyte sandwiched between an anode ( negatively charged electrode ) and a cathode ( positively charged electrode ) . The procedures that take topographic point 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 O from the air is channeled to the cathode on the other side of the cell. 2. At the anode, a Pt accelerator causes the H to divide into positive H ions ( protons ) and negatively charged negatrons. 3. The phosphorous acid electrolyte allows merely the positively charged ions to go through through it to the cathode. The negatively charged negatrons must go along an external circuit to the cathode, making an electrical current. 4. At the cathode, the negatrons and positively charged H ions combine with O to organize H2O, which flows out of the cell.

Phosphoric Acid Fuel Cells ( PAFC )

Phosphoric acid fuel cells use liquid phosphorous acid as an electrolyte and porous C electrodes incorporating a Pt accelerator. The phosphorous acid fuel cell ( PAFC ) is considered the first coevals of modern fuel cells. It is one of the most mature cell types and the first to be used commercially. This type of fuel cell is typically used for stationary power coevals, but some PAFCs have been used to power big vehicles such as metropolis coachs.

PAFCs are more tolerant of drosss in fossil fuels that have been reformed into H than PEM cells, which are easy “ poisoned ” by C monoxide because C monoxide binds to the Pt accelerator at the anode, diminishing the fuel cell ‘s efficiency. They are 85 % efficient when used for the co-generation of electricity and heat but less efficient at bring forthing electricity entirely 37 % -42 % . This is merely somewhat more efficient than combustion-based power workss, which typically operate at 33 % -35 % efficiency. PAFCs are besides less powerful than other fuel cells, given the same weight and volume. As a consequence, these fuel cells are typically big and heavy. PAFCs are besides expensive. Like PEM fuel cells, PAFCs require an expensive Pt accelerator, which raises the cost of the fuel cell.Diagram: How a Phosphoric Acid Fuel Cell ( PAFC ) works. A PAFC consists of liquid phosphorous acid electrolyte sandwiched between an anode ( negatively charged electrode ) and a cathode ( positively charged electrode ) . The procedures that take topographic point 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 O from the air is channeled to the cathode on the other side of the cell. 2. At the anode, a Pt accelerator causes the H to divide into positive H ions ( protons ) and negatively charged negatrons. 3. The phosphorous acid electrolyte allows merely the positively charged ions to go through through it to the cathode. The negatively charged negatrons must go along an external circuit to the cathode, making an electrical current. 4. At the cathode, the negatrons and positively charged H ions combine with O to organize H2O, which flows out of the cell.

Molten Carbonate Fuel Cells ( MCFCs )

Molten carbonate fuel cells ( MCFCs ) are presently being developed for natural gas and coal-based power workss for electrical public-service corporation, industrial, and military applications. MCFCs are high-temperature fuel cells that use an electrolyte composed of a liquefied carbonate salt mixture suspended in a porous, chemically inert ceramic Li aluminium oxide ( LiAlO2 ) matrix.A They operate at highly high temperatures of approximately 1,200A°F and above, non-precious metals can be used as accelerators at the anode and cathode, cut downing costs.

Improved efficiency is another ground MCFCs offer important cost decreases over phosphorous acid fuel cells ( PAFCs ) . Molten carbonate fuel cells can make efficiencies nearing 60 % , well higher than the 37 % -42 % efficiencies of a phosphorous acid fuel cell works. When the waste heat is captured and used, overall fuel efficiencies can be every bit high as 85 % .

Phosphoric acid and polymer electrolyte membrane fuel cells, MCFCs do notA necessitate an external reformist to change over 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 procedure called internal reforming, which besides reduces cost.

Molten carbonate fuel cells are non prone to carbon monoxide or C dioxide toxic condition, they can even utilize C oxides as fuel, doing them more attractive for fueling with gases made from coal. They are more immune to drosss than other fuel cell types.

The primary disadvantage of current MCFC engineering is lastingness. The high temperatures at which these cells operate and the caustic electrolyte used accelerate constituent dislocation and corrosion, diminishing cell life. Scientists are presently researching corrosion-resistant stuffs for constituents every bit good as fuel cell designs that addition cell life without diminishing performance.Diagram: How a Molten Carbonate Fuel Cell ( MCFC ) works. A MCFC consists of an electrolyte, typically a liquefied carbonate salt mixture suspended in a ceramic matrix, sandwiched between an anode ( negatively charged electrode ) and a cathode ( positively charged electrode ) . The procedures that take topographic point 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 O from the air, C dioxide, and electricity ( negatrons from the fuel cell circuit ) are channeled to the cathode on the other side of the cell. 2. At the cathode, the O, C dioxide, and negatrons react to organize positively charged O ions and negatively charged carbonate ions. 3. The carbonate ions move through the electrolyte to the anode. 4. At the anode, a accelerator causes the H combine with the carbonate ions, organizing H2O and C dioxide and let go ofing negatrons. 5. The electrolyte does non let the negatrons to go through through it to the cathode, coercing them to flux through an external circuit to the cathode. This flow of negatrons signifiers an electrical current. 6. The C dioxide formed at the anode is frequently recycled back to the cathode.

Solid Oxide Fuel Cells ( SOFCs )

Solid oxide fuel cells ( SOFCs ) use a difficult, non-porous ceramic compound as the electrolyte. Because the electrolyte is a solid, the cells do non hold to be constructed in the plate-like constellation typical of other fuel cell types. SOFCs are expected to be about 50 % -60 % efficient at change overing fuel to electricity. In applications designed to capture and use the system ‘s waste heat ( co-generation ) , overall fuel usage efficiencies could exceed 80 % -85 % .

Solid oxide fuel cells operate at really high temperatures around 1,830A°F. High-temperature operation removes the demand for precious-metal accelerator, thereby cut downing cost. It besides allows SOFCs to reform fuels internally, which enables the usage of a assortment of fuels and reduces the cost associated with adding a reformist to the system.

SOFCs are besides the most sulfur-resistant fuel cell type ; they can digest several orders of magnitude more of S than other cell types. In add-on, they are non poisoned by C monoxide ( CO ) , which can even be used as fuel. This propertyA allows SOFCs to utilize gases made from coal.

High-temperature operation has disadvantages. It consequences in a slow startup and requires important thermic screening to retain heat and protect forces, which may be acceptable for public-service corporation applications but non for transit and little portable applications. The high operating temperatures besides place rigorous lastingness demands on stuffs. The development of low-priced stuffs with high lastingness at cell runing temperatures is the cardinal proficient challenge confronting this engineering.

Scientists are presently researching the potency for developing lower-temperature SOFCs operating at or below 800A°C that have fewer lastingness jobs and cost less. Lower-temperature SOFCs green goods less electrical power, nevertheless, and stack stuffs that will work in this lower temperature scope have non been identified.Diagram: How a Solid Oxide Fuel Cell ( SOFC ) works. An AFC consists of a non-porous metal oxide electrolyte ( typically zirconium oxide ) sandwiched between an anode ( negatively charged electrode ) and a cathode ( positively charged electrode ) . The procedures that take topographic point 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 O from the air is channeled to the cathode on the other side of the cell. 2. At the cathode, a accelerator causes negatrons from the electrical circuit to unite with O to make negatively charged O ions. 3. The negatively charged O ions flow through the electrolyte to the anode. 4. At the anode, the accelerator causes the H to respond with the O ions organizing H2O and free negatrons. 5. The negatively charged negatrons can non flux through the electrolyte to make the positively charged cathode, so they must flux through an external circuit, organizing an electrical current. 6. At the cathode, the negatrons combine with O to make negatively charged O ions, and the procedure repetitions.

Fuel Cell Type

Park

Electrolyte

Operating Temperature

System Output

Electrical Efficiency

Combined Heat and Power ( CHP ) Efficiency

Applications

Polymer Electrolyte Membrane ( PEM ) *

Solid organic polymer poly-perfluorosulfonic acid

50 – 100A°C

122 – 212A°F

& lt ; 1kW – 250kW

53-58 % ( transit )

25-35 % ( stationary )

70-90 % ( low-grade waste heat )

Alkaline ( AFC )

Aqueous solution of K hydrated oxide soaked in a matrix

90 – 100A°C

194 – 212A°F

10kW – 100kW

60 %

& gt ; 80 % ( low-grade waste heat )

i⤠Military

Phosphorous Acid ( PAFC )

Liquid phosphorous acid soaked in a matrix

150 – 200A°C

302 – 392A°F

50kW – 1MW

( 250kW module typical )

& gt ; 40 %

& gt ; 85 %

Molten Carbonate ( MCFC )

Liquid solution of Li, Na, and/or K carbonates, soaked in a matrix

600 – 700A°C

1112 – 1292A°F

& lt ; 1kW – 1MW

( 250kW module typical )

45-47 %

& gt ; 80 %

Solid Oxide ( SOFC )

Yttria stabilized zirconium oxide

600 – 1000A°C

1202 – 1832A°F

& lt ; 1kW – 3MW

35-43 %

& lt ; 90 %

i⤠Auxiliary power

Comparison of Fuel Cell Technologies

Proton Exchange Membrane Fuel Cells ( PEMFC )

This engineering was invented by General Electric in the 1950s and was used by NASA to supply power for the Gemini infinite undertaking. It is now the fuel cell type most favoured by car companies as a replacing for the internal burning engine. PEM fuel cells are besides known as polymer electrolyte membrane, solid polymer electrolyte and polymer electrolyte fuel cells.

This diagram below shows the basic design of the PEM fuel cell.

hypertext transfer protocol: //www.che.sc.edu/centers/PEMFC/fuelcell_overview_files/fuel_cell.gif

In the PEM fuel cell the electrolyte is a thin polymer membrane ( such as poly [ perfluorosulphonic ] acid, NafionTM which is permeable to protons, but does non carry on negatrons, and the electrodes are typically made from C. Hydrogen flows into the fuel cell on to the anode and is split into H ions ( protons ) and negatrons. The H ions permeate across the electrolyte to the cathode, while the negatrons flow through an external circuit and supply power. Oxygen, in the signifier of air, is supplied to the cathode and this combines with the negatrons and the H ions to bring forth H2O. These reactions at the electrodes are as follows:

Anode: 2H2http: //www.che.sc.edu/centers/PEMFC/fuelcell_overview_files/rightarrow.gif4H+ + 4e-

Cathode: O2 + 4H+ + 4e- hypertext transfer protocol: //www.che.sc.edu/centers/PEMFC/fuelcell_overview_files/rightarrow.gif2H2O

Overall: 2H2 + O2http: //www.che.sc.edu/centers/PEMFC/fuelcell_overview_files/rightarrow.gif2H2O + energy

PEM cells operate at a temperature of around 80A°C. At this low temperature the electrochemical reactions would usually happen really easy so they are catalysed by a thin bed of Pt on each electrode.

This electrode/electrolyte unit is called a membrane electrode assembly ( MEA ) and it is sandwiched between two field flow home bases to make a fuel cell. These home bases contain channels to impart the fuel to the electrodes and besides carry on negatrons out of the assembly. Each cell produces about 0.7 V, approximately adequate power to run a light bulb, in contrast to around 300 Vs needed to run a auto. In order to bring forth a higher electromotive force a figure of single cells are combined in series to organize a construction known as a fuel cell stack.

PEM fuel cells have a figure of properties that make them ideal campaigners for usage in automotive applications and little domestic applications, such as replacings for rechargeable batteries. They operate at comparatively low temperatures which allows them to get down up quickly from cold and have a high power denseness which makes them comparatively compact. In add-on, PEM cells work at high efficiencies, bring forthing around 40-50 per cent of the maximal theoretical electromotive force, and can change their end product rapidly to run into displacements in power demand.

At present, demonstration units capable of bring forthing 50 kilowatts are in operation and units bring forthing up to 250 kilowatts are under development. There are, nevertheless, still a figure of barriers that need to be overcome before this engineering becomes more widespread. The chief issue is cost as the membrane stuffs and accelerators are expensive but on-going research and development is invariably cut downing cost, and economic systems of graduated table will kick in one time these cells are mass produced.

The other drawback of PEM cells is that they need pure H to run as they are really susceptible to poisoning by C monoxide and other drosss. This is mostly due to the low operating temperature of the cell which necessitates the usage of a extremely sensitive accelerator. Again, work is being carried out to bring forth more tolerant accelerator systems along with membranes capable of operating at higher temperatures.