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As time progress, the population raise to the occasion and the demands in different sectors increases tremendously. The advancement in different technological areas thus calls for the advancement in the small but important industries like the fuel cell industry. Fuel cells are a important component of vehicles, cars, buses etc. that makes it possible for us to drive around. They are electrochemical systems which transfers the chemical energy of the convectional fuel into direct electrical energy (http://www.fuelcellknowledge.org/fuelcell_basics/types_of_fuelcell.html). In other words it is a demonstrations or application of the "first law of thermodynamics". Fuel cells are important since the conversion from fuel to energy takes place via an electrochemical process. It is more efficient than fuel burning since it's a clean, quite process. It operates somewhat similar to a battery but it does not requires charging and does not run down, once fuel is provided electricity and heat will be supplied from the fuel cell (Stephen Cohen and Nathan Bonnett May 18, 2007). Fuel cells work according to the principle of indirect and direct energy conversion, for indirect the energy is first converted to heat from which it is converted in mechanical energy and then to electrical energy (INSTITUTE OF ENERGY RESEARCH (IEF). In general all fuel cells have the same basic arrangement but they are classified according to the type of electrolyte being utilized. The electrolyte determines the type of chemical reaction that will occur and the temperature at which the reaction will proceed at. They are several different types of fuel cells that are available, they just vary in certain component but the operation for all of them is general. Two main type of electrochemical process occurs in all fuel cells (Stephen Cohen and Nathan Bonnett May 18, 2007). The first one occurs at the anode and is called anodic reaction while the other at the cathode and is called cathodic reaction. Hydrogen ions and electrons are released at the anode which is critical to the production of energy.
At the cathode the hydrogen ions, the electrons and the oxygen reacts to form water.
2 + ½ + 2
(University of Strathclyde in Glasgow). The water that is produced in then extracted by excess air flow. The basic process occurs for all the other fuel cell but with a change in the electrolyte taken from
General Principle of the Operation of Fuel Cells
The fuel cell is an electrochemical device which converts chemical energy of the fuel into electrical energy by combining gaseous hydrogen with air in the absence of combustion. The basic principle of operation of fuel cells is similar to that of the electrolyser in that the fuel cell is constructed with two electrodes with a conducted electrolyte between them (University of Strathclyde in Glasgow). The electrodes are two catalyst coated porous electrodes. One electrode is the anode and the other is the cathode. One is positive and the other is negative. The reaction that produces the electricity occurs at the electrodes. The electrolyte carries electrically charged particles from one electrode to the other while the catalyst speeds up the reaction at the electrodes. The basic fuel that is used in fuel cells is highly purified hydrogen but fuel cells also require oxygen (http://www.fuelcells.org/basics/how.html). The great thing about using hydrogen is that it generates electricity with very little pollution occurring. This is so since most of the hydrogen and oxygen used is converted in to a harmless byproduct namely water. It is important to used hydrogen since it can be produced from a wide range of energy resources some of which includes fossil fuel, natural gas, coals, nuclear energy and renewable energy such as solar, wind water and biomass also the high electrochemical activity of hydrogen (Stephen Cohen and Nathan Bonnett May 18, 2007). The purpose of a fuel cell is to produce an electric current that can be directed outside the cell to do work such as powering an electric motor or illuminating a light bulb. Due to the way electricity behaves, the current returns to the fuel cell completing the electric circuit. The chemical reactions that produce this current are the key to how fuel cells work. The process begins when the hydrogen molecules enters the fuel cell at the anode, where a chemical reaction strips the hydrogen of its electrons. The hydrogen ion is now ionized and carries a positive electrical charge. The negatively charged electrons provide the current through wires to do work. If alternating current (AC) is needed, the DC output of the fuel cell must be routed through a conversion device called an inverter. Oxygen enters the fuel cell at the cathode;
there it combines with electrons returning from the electrical circuit and hydrogen ions that have travel through the electrolyte from the anode (Stephen Cohen and Nathan Bonnett May 18, 2007). In some cell types the oxygen usually picks up the electrons and travel through the electrolyte to the anode where it combines with the hydrogen ions. The electrolyte has a key role to play in ensuring that only the appropriate ions to pass through the anode and the cathode. The chemical reaction would be disrupted if free electrons could have pass through the electrolyte. Whether they combine at the cathode or anode, together the hydrogen and oxygen forms water which is drains from the cell. The fuel cell will generate electricity as long as it is supplied with hydrogen and oxygen. INSTITUTE OF ENERGY RESEARCH (IEF
Diagram above shows the basic principle of operation of fuel cells
In the operating of a fuel cell; the required protons come from the anode transported through the electrolyte. A fuel cell reaction normally requires all three phases to be present, i.e. the solid phase (electron conductor), the liquid phase (ion conductor) and the gas phase (electrode pores). In fuel cells containing a liquid electrolyte, operating below the boiling point of water, an electrolyte circulation system with external water removal, e.g. evaporation, should be present. For fuel cells which operate with a solid electrolyte the water formed is directly passed from the electrolyte into the cathodic gas compartment and subsequently removed.
Since fuel cells produce electricity chemically, they are not subjected to the thermodynamics law that limits a convectional power plant. Therefore fuel cells are more efficient in extracting energy from fuel. The heat (waste) is also converted to electricity thus boosting the efficient further. Therefore it can be said that the reaction for extracting energy from fuel can have two pathways as shown below.
The indirect conversion of the fuels energy to electrical energy is based on the application of heat engines and thus the theoretical energetic efficiency () of the cell can be determined by an overall process characterized by the Carnot factor.
The inlet temperature T1 of the medium, doing work is higher than the outlet temperature T2, their difference corresponding to the deviation in the value Î·c Max. of the maximum quantity, i.e. 100%. The Carnot efficiency is characteristic of all energy converters, such as the steam turbine, the internal combustion engine, thermo ionic converter etc., which all work between a source and a sink temperature. The energy yield for a real system is always lower than that indicated by its corresponding Carnot factor and ranges between 30 and 40%, currently highly developed combined cycle plants between 55 and 60% INSTITUTE OF ENERGY RESEARCH (IEF). The
latter is available only in a very high power range and cannot be used, e.g. for automobile systems. The cause for the reduction in energetic efficiency is caused by energy losses at the different stages of the conversion process. The fuel cell competes with conventional thermomechanical energy conversion
Similarly to batteries, fuel cells produce low-voltage direct current. A battery or an accumulator consumes a chemical substance contained in the cell stack itself for electricity production. But in fuel cells, the fuels are continuously fed to the cell stack similarly to an internal combustion engine. The energetic conversion rate in a fuel cell (FC) is given by the relation.
INSTITUTE OF ENERGY RESEARCH (IEF)
The value H represents the corresponding enthalpy change of the combustion reaction. In a fuel cell only the energetic fraction G is converted directly into electricity, i.e. the maximum theoretical efficiency is given by the formula
INSTITUTE OF ENERGY RESEARCH (IEF)
where GT is the value of the free reaction enthalpy at the cell operating temperature TZ and H0 H0 is the standard value of the reaction enthalpy. The relation between G and H is known to be: G = H - T S
Hence follows the efficiency of the fuel cell as
INSTITUTE OF ENERGY RESEARCH (IEF)
INSTITUTE OF ENERGY RESEARCH (IEF)
Depending on the sign of the reaction entropy S, the efficiency may be smaller, equal to or even higher than 100 %. In the latter case, heat is extracted from the environment. The fuel cell directly supplies electric current of the theoretical d.c. voltage (Erev)
INSTITUTE OF ENERGY RESEARCH (IEF)
The most important fuel cell reaction is the reaction of hydrogen
INSTITUTE OF ENERGY RESEARCH (IEF)
At a pressure of 1 bar and a temperature of 25°C the corresponding d.c. voltage for this reaction is 1,229 volt INSTITUTE OF ENERGY RESEARCH (IEF). This voltage is a function of temperature, i.e. the same also applies to the efficiency.
The data presented above is the thermodynamics relations for the maximum energy efficiency of a fuel cell. Energetic losses occur during the operation of fuel cells and these losses usually stem from different factors. Some of these factors include: kinetic electrode reactions, cell structure, and the type of process carried out. Any fluid capable of undergoing oxidation can be utilized by a fuel cell but as explained earlier hydrogen is widely used. Catalyst formation at electrodes occurs sometimes when carbon based fuels at temperatures below 300°C reacts slow and only forms by-products INSTITUTE OF ENERGY RESEARCH (IEF). Conventional heat engines operate more efficiently at full load and show a greater performance drop in partial load operation. Conversely, the efficiency of fuel cell is more constant operating under different loads.
After all the various reaction have occurred, individual fuel cells are placed in a series to form a fuel sacks (Stephen Cohen and Nathan Bonnett May 18, 2007) which are used in systems to provide the power needed to power up a vehicle or to supply a building with electricity.
Types of fuel cells
The classification of fuel cells are based mainly on the kind of electrolyte they utilized. This classification determines the kind of chemical reactions that take place in the cell, the kind of catalysts required, the temperature range in which the cell operates, the fuel required, and other factors (Stephen Cohen and Nathan Bonnett May 18, 2007). The applications for which these cells are most suitable is affected by the characteristics of these cells. There are several types of fuel cells currently under development, each with its own advantages, limitations, and potential applications. The following are a list of fuel cells that are commonly known: (Fuel Cells 2000 in Earthtoys)
Polymer Electrolyte Membrane (PEM) Fuel Cells
Solid Oxide Fuel Cells
Zinc Air Fuel Cells
Molten Carbonate Fuel Cells
Direct Methanol Fuel Cells
Alkaline Fuel Cells
Phosphoric Acid Fuel Cells
Regenerative Fuel Cells
Protonic Ceramic Fuel Cells
Microbial Fuel Cells
Brief description of each type of fuel cell mentioned above:
Polymer Electrolyte Membrane (PEM) Fuel Cells: Polymer electrolyte membrane (PEM) fuel cells, also called proton exchange membrane fuel cells is the leading fuel cell for passenger car application. It uses a polymer membrane as the electrolyte with porous carbon electrodes containing a platinum catalyst and operates at a relatively low temperature at about 175 Degree Celsius which leads to quick start up since less warm up is needed (http://www1.eere.energy.gov/hydrogenandfuelcells/fuelcells/fc_types.html#pem).
All this leads to the great durability of the fuel cell. These fuel cells need only hydrogen, oxygen (air) and water to operate and no corrosive fluids is required, as some other fuel cells do. These cells are basically fueled with pure hydrogen supplied from on-board storage tanks or reformers. It has a high power density and can vary its output quickly and is suited for applications where quick startup is necessary thus making it the leading fuel cell in the automobile industry (Fuel Cells 2000 in Earthtoys). This particular type of fuel cell is sensitive to fuel impurities. Some of its advantages includes light weight, small size etc (Fuel Cells 2000 in Earthtoys)
Solid Oxide Fuel Cells:
Solid oxide fuel cells (SOFC) utilize a hard, non permeable ceramic based compound as its electrolyte. With the electrolyte being a solid, SOFCs do not have to be fabricated in the plate like structure which is typical of other fuel cells. SOFCs efficiency is about 50% to 60% in electricity generation. In applications designed to capture and utilize the system heat wastage, i.e. co-generation, the overall efficiency could exceed 80% to nearly 85%. SOFCs operate at extremely high temperatures of around 1800°C Fuel Cells 2000 in Earthtoys. High temperatures eliminate the need for precious metals to be used of as a catalyst. Also, this allows SOFCs to internally reform fuels, enabling the use of a wide variety of fuels and reducing the cost as a result of adding a reformer to the cell. Also, SOFCs are the most resistant fuel cell type to sulfur; they can tolerate several magnitudes more of sulfur concentrations than other cells. Fuel Cells 2000 in Earthtoys
Additionally, they are not poisoned by carbon monoxide, which can even be utilized as a fuel. This allows for SOFCs usage of gases liberated from coal. A slow startup and significant thermal shielding to retain heat and protect personnel are required. These high operating temperatures also requires stringent durability requirements on materials Fuel Cells 2000 in Earthtoys. Development of low cost materials with high durability at cell operating temperatures is the key technical challenge currently facing SOFCs. Scientists are currently trying to developing lower temperature SOFCs which operates at or below 800°C, which have fewer durability problems and less expensive (Fuel Cells 2000 in Earthtoys). It is used mainly for large high power applications such as industrial generating stations since they require large temperatures.
Zinc Air Fuel Cells:
In classical zinc air fuel cells (ZAFC) there's a gas diffusion electrode (GDE), a zinc anode separated by an electrolyte, and some form of mechanical separation. The GDE is a porous membrane which allows atmospheric oxygen to pass through Stephen Cohen and Nathan Bonnett May 18, 2007. The oxygen, after it has been converted into hydroxyl ions and water; the hydroxyl ions will be transported through the electrolyte where it reaches the zinc anode. Here it is reacted with the zinc, and forms zinc oxide. An electrical potential is created from this process. When a set of ZAFC cells are connected, the combined electrical potential generated which is used as a source of electricity. The electrochemical process occurring has some similarities to the PEM fuel cell; however the refueling is quite different and shares characteristics with batteries. ZAFCs contain a zinc "fuel tank" and a zinc refrigerator which automatically and silently regenerates the fuel needed http://www.fuelcellknowledge.org/fuelcell_basics/types_of_fuelcell.html). This closed loop system creates an electric current as the zinc and oxygen are mixed in the presence of an electrolyte, such as PEMFC, forming zinc oxide. When the fuel is utilized, the system is connected to the grid and the reverse process occurs, again depositing pure zinc fuel pellets. The key in generating electricity using these cells is that, the reversed process only about 5 minutes to be completed http://www.fuelcellknowledge.org/fuelcell_basics/types_of_fuelcell.html). Thus, the battery recharging time is not a dilemma. The main advantage the ZAFCs technology has over other battery technologies is its high energy specificity. This is a fundamental factor which determines the running time of a battery in relation to its weight and volume.
Molten Carbonate Fuel Cell
Molten carbonate fuel cell utilizes an electrolyte which contains a molten carbonate salt mixture suspended in a permeable chemically inert medium. This type of fuel cell operates at high temperatures usually at 650°C (Stephen Cohen and Nathan Bonnett May 18, 2007), due to this non-precious metals can be used as the catalyst at the anode and the cathode. It also requires carbon dioxide and oxygen to be delivered at the cathode. This helps in reducing the cost for the fuel cell also it can convert fuels into hydrogen within the fuel cell through the process called internal reforming (http://www.fuelcellknowledge.org/fuelcell_basics/types_of_fuelcell.html). The MCFC has been operated on various fuels some of which includes natural gas, landfill gas, carbon monoxide, propane etc (Stephen Cohen and Nathan Bonnett May 18, 2007). As such they are more resistant to poisoning from carbon monoxide and carbon dioxide. The MCFC has great efficiency which is 85% (http://www.fuelcellknowledge.org/fuelcell_basics/types_of_fuelcell.html) when the heat is converted to electricity also. Essentially the current disadvantage of MCFC technology is its durability.
Due to the high temperatures at which these cells operate and the corrosive nature of the electrolyte employed there is acceleration in the wearing and corrosion in the fuel cell, considerably decreasing the cell lifetime (Stephen Cohen and Nathan Bonnett May 18, 2007). Scientists are today exploring corrosion resistant materials for use as cell components as well as designs that increase cell life without decreasing performance. MCFC is used chiefly for utility, industrial, and military applications.
Direct Methanol Fuel Cells:
Direct methanol fuel cells (DMFC) use of a polymer membrane as their electrolyte thus being similar to the PEM. However, in the DMFC, the anode catalyst draws the hydrogen from the liquid methanol, eliminating the need for a fuel reformer (Fuel Cells 2000 in Earthtoys. DMFC efficiencies are expected to be about 40%, which would typically operate at a temperature between 120°F and 190°F (Fuel Cells 2000 in Earthtoys. This is a significantly low temperature range, making this fuel cell technology attractive for small to mid-sized applications; to power cellular phone, laptops and other gadgets (Fuel Cells 2000 in Earthtoys. DMFC efficiencies are achieved at higher temperatures. DMFCs' are powered by pure methanol, which is mixed with steam and fed directly to the fuel cell anode. These cells do not have many of the fuel storage problems typical of some fuel cells because methanol has a higher energy density than hydrogen but, less than gasoline or dieseline. Also, methanol is easier to transport and supply to consumers using current infrastructure because it is a liquid. Direct methanol fuel cell technology is relatively new when compared to hydrogen powered fuel cells, and its research and development is approximately 3 to 4 years behind that of the other fuel cell types (Fuel Cells 2000 in Earthtoys). Higher Designers are currently working on DMFC prototypes to be used by the military in the field for powering electronic equipment.
Alkaline fuel cells (AFC):
This fuel cell was one of the first fuel cell technologies to be developed, and were the first type widely used in the US space program by NASA to produce electricity and water on board space shuttles e.g. On the Apollo space craft. AFCs make use of a solution of aqueous potassium hydroxide in water as the electrolyte and can utilize a variety of metals as a catalyst contained at the anode and cathode. High temperature AFCs operate at temperatures between 100°C and 250°C (Stephen Cohen and Nathan Bonnett May 18, 2007). Newer AFC designs operate at relatively lower temperatures of roughly 23°C to 70°C. AFCs' high performance is due to the rate at which chemical reactions take place in the cell and
they have demonstrated efficiencies of approximately 60% in space applications (Stephen Cohen and Nathan Bonnett May 18, 2007). These fuel cells are very susceptible to carbon dioxide poisoning, so they require pure hydrogen and oxygen (Stephen Cohen and Nathan Bonnett May 18, 2007). Actually, even the small amount of carbon dioxide in the air can affect these cells' operation, making it a necessity to purify both the hydrogen and oxygen used by the cell. This is one of the major disadvantages of this cell and contributes greatly to its cost since the purification process is very expensive (Stephen Cohen and Nathan Bonnett May 18, 2007). Also it tampers with the lifetime of the cell, causing it to be replaced frequently. Scientist is now looking ways to make the cell more cost efficient and less susceptible to carbon poisoning.
Phosphoric Acid Fuel Cell:
The phosphoric acid fuel cell is one of the most commercially developed fuel cells. It generates electricity at more than 40% efficiency and when co-generation is done approximately 85% efficiency is yielded (Stephen Cohen and Nathan Bonnett May 18, 2007). The PAFC used liquid phosphoric acid as the electrolyte contained in Teflon- bonded silicon carbide matrix and a porous carbon electrode with a platinum catalyst (Stephen Cohen and Nathan Bonnett May 18, 2007). It operates at a temperature of approximately 450 degrees F. PAFCs are more tolerant of impurities in fossil fuels that have been reformed into hydrogen than PEM cells, which are easily `"poisoned" by carbon monoxide because carbon monoxide binds to the platinum catalyst at the anode(http://www1.eere.energy.gov/hydrogenandfuelcells/fuelcells/fc_types.html). Thus it can use impure hydrogen which is one of its advantages. (Stephen Cohen and Nathan Bonnett May 18, 2007)
PAFC has been used for powering of hospitals, nursing homes, hotels, office building, schools, utility power plants, landfill and waste water treatment plant. PAFCs can tolerate carbon monoxide concentrations of about 1.5 percent; due to this its fuel choice is broaden. If gasoline is used as a fuel the sulphur should be removed from it (Fuel Cells 2000 in Earthtoys). PAFCs are less powerful than other fuel cells, given the same weight and volume. The result of this is that,
these fuel cells are typically bulky and heavy. PAFCs are notably very expensive. In comparison to PEM fuel cells, PAFC fuel cells require an expensive platinum catalyst http://www1.eere.energy.gov/hydrogenandfuelcells/fuelcells/fc_types.html, which further raises the cost of the fuel cell.
Regenerative Fuel Cell:
Regenerative fuel cells are young fuel cells that are currently under research by NASA and other research companies' worldwide (Stephen Cohen and Nathan Bonnett May 18, 2007). It involves a closed loop type of power generation; where water is separated into hydrogen and oxygen by a solar powered electrolyser (Fuel Cells 2000 in Earthtoys). The hydrogen and oxygen is then fed into the fuel cell which generates electricity, heat and water. The water produced is then recirculated back into the solar powered electrolyser and the process is repeated.
Protonic Ceramics Fuel Cell:
Protonic ceramic fuel cells (PCFC) are a new type of fuel cell based on an electrolytic ceramic material which exhibits high protonic conduction at high temperatures (Fuel Cells 2000 in Earthtoys). At high temperature (700 degree C) operations the PCFC shares similar advantages with the molten carbonate and solid oxide fuel cells that is same thermal and kinetic advantages (Fuel Cells 2000 in Earthtoys). It exhibits all the intrinsic benefits of proton conduction as in PEM and PAFC. High electrical fuel efficiency with hydrocarbons fuels are accomplished at these elevated temperatures. Fossil fuels are electrochemically oxidized at the anode since the PCFCs operates at high temperatures (Fuel Cells 2000 in Earthtoys). By doing this the costly reforming process is eliminated. In the presence of water vapour, the gaseous hydrocarbon molecules are absorbed at the surface of the anode and the hydrogen atoms are easily removed by absorption in the electrolyte with the main product being carbon dioxide. (Fuel Cells 2000 in Earthtoys) So as, to ensure that the membrane does not dry out, as with PEM or the liquid does not leak out, as with PAFCs the PCFCs have a solid electrolyte. (Fuel Cells 2000 in Earthtoys)
Microbial Fuel Cell:
The catalytic reaction of microorganism, example bacteria, is used in the microbial fuel cells to convert practically any organic matter into fuel (Fuel Cells 2000 in Earthtoys). Some of these organic materials consist of glucose, acetate, and waste water (Fuel Cells 2000 in Earthtoys). The organic compounds are now oxidized or consume by bacteria and other microbes when they are enclosed in the oxygen free anode (Fuel Cells 2000 in Earthtoys). Part of the digestion process entails the pulling of electrons from these compounds and they are transported into the circuit with the help of an inorganic material. MFCs operate best under mild conditions relative to other types of fuel cells, such as between 20°C and 40°C and are capable of being 50% efficient (Fuel Cells 2000 in Earthtoys). MCFs are most suitable for small scale applications, such as developing medical devices fueled by glucose in the blood stream or larger applications (Fuel Cells 2000 in Earthtoys), such as in water treatment plants or breweries producing organic waste that could be used to fuel MFCs.
Detailed Explanation of the process involved in the operation of the Alkaline Fuels Cells looking at present applications and projected trends in its technology
All fuel cells systems are based on a central design where the two electrodes, a negative anode and a positive cathode, are separated by a liquid or solid electrolyte that carries electrically charged particles between them (Gemma Crawley). The Alkaline fuel cell (AFC) uses an electrolyte that is an aqueous (water based) solution of potassium hydroxide (KOH) retained in a permeable stabilized medium in order to operate (Gemma Crawley). The concentration of potassium hydroxide can vary depending on the temperature range at which the operation is carried out. (Gemma Crawley) AFC systems are classified as low temperature systems; as such they would normally operate between the temperature ranges of sixty to two hundred and twenty degrees Celsius; newer designs of AFC have been reported to operate at temperatures as low as twenty three to seventy degrees Celsius (Gemma Crawley). As a result of the low operating temperatures it is not necessary to employ a platinum catalyst into the system and thus; a variety of non precious metals can be utilized. In this case a nickel catalyst is used to speed up the chemical reactions occurring both at the anode and the cathode (Gemma Crawley). It is the most common catalyst used by AFC units. As a result of the rate of the chemical reaction of the AFC; energy efficiencies between 45 to 70 percent (Gemma Crawley) have been exhibit by their systems. Therefore they can generate up to 20kW (Gemma Crawley) of electric power. The AFCs have been placed among the most energy efficient fuel cells. The hydroxyl ion (OH-) is the charge carrier for the AFC; it migrates from the cathode to the anode where it reacts with the hydrogen ion to yield water and electrons http://www.fctec.com/fctec_types_afc.asp. Hydroxyl ions are then regenerated from the water which forms at the anode that is redirected to the cathode http://www.fctec.com/fctec_types_afc.asp. The chemical reactions occurring at the anode and cathode for the AFC are shown below. These reactions in the fuel cell produce electricity with heat as the by-product. http://www.fctec.com/fctec_types_afc.asp
2 H2+ 4 OH-=>4 H2O + 4 e-
O2+ 2 H2O + 4 e-=>4 OH-
Overall Net Reaction:
2 H2 + O2 =>2 H2O
The AFCs disadvantages are that they are very sensitive to carbon dioxide that may be present in impure fuel and in the air (Gemma Crawley). The carbon dioxide reacts with the electrolyte poisoning it rapidly and severely degrading the fuel cells performance. It also reduces the conductivity of the electrolyte. Consequently AFCs are limited to closed environments such as space and undersea vehicles and must be run on pure hydrogen and oxygen. Moreover molecules such as CO, CH4, and H2O etc which have no effect on other fuel cells would be very poisonous to the AFCs. http://www.fctec.com/fctec_types_afc.asp. Purification of both hydrogen and oxygen are very costly. In addition susceptibility to poisoning by the AFC can reduce the cells life this means that AFCs needs to be replaced faster than other fuel cells (Gemma Crawley). The electrolyte material of the AFC is also corrosive and since it is in a liquid form it makes the sealing of the anode and cathode gases more problematic when compared to a solid electrolyte http://www.fctec.com/fctec_types_afc.asp. On the other hand, AFCs are one of the cheapest fuel cells to manufacture since the catalyst that is required at the electrode can be anyone of the relatively inexpensive metals when compared to the catalyst that are used by other fuel cells.
AFCs are one of the most developed technologies which were used since in the mid 1960s by NASA in the Apollo and space shuttle programs (Gemma Crawley). These fuel cells provide electrical power and provide drinking water. Today AFCs are used mostly in niches of transportation application, powering forklifts trucks, boats and submarine. It is still used in space application and NASA continues to operate several AFC systems. If AFCs become more cost effective and reach operating time over 40,000 hours they would become one of the best fuel cells Gemma Crawley.
In the early 1930s the AFCs were developed by a man F.T.Bacon and are one of the oldest fuel cell technologies. A six cell battery that produced 50W (Gemma Crawley) of electricity was produced in 1954 and in 1956 a 40 cell fuel cell was constructed based on the same design of the six cells (Gemma Crawley). These large units produced 6kW (Gemma Crawley) and were used to power fork-lifts trucks, welding material and circular disk. An Energy Conservation Ltd and company were formed by Beacon in 1961. This company, seeked to produce fuel cells on a commercial basis. Two licenses were granted to technology patent in 1959 one of these licenses went to Patt and Whitney and then in 1962 the company began to produce AFC power plant for the Apollo Space programme (Gemma Crawley). The AFC units were used to provide drinking water and electricity for life support; guidance and communication function during a two week expedition on the moon (Gemma Crawley). After that the AFCs became widely used in the U.S Space Programme.
Allis Chalmer manufacturing company in 1959 developed the first vehicle to be powered by fuel cell. The AFC powered tractor was used to plough fields in Wisconsin, USA before being donated to the Smithsonian Institute. In 1962 an AFC powered golf chart was developed which
used hydrazine and provided 4-10 kW of continuous electricity (Gemma Crawley). Several other AFC powered vehicles was then produced between 1962-1963, which included a submarine. Following this achievement was the development of the first AFC motorbike in 1967 by Karl Kordesch (Gemma Crawley). It used hydrazine and could have travel over 200 miles per gallon hydrazine. The motor bike traveled over 300 miles at a speed of 25 miles per hour (Gemma Crawley). He also develops a Austin A4 car which was able to seat four persons and operated at a 180 miles (Gemma Crawley). Even though the AFC was one of the first fuel cell to be develop it is not have widespread applications. The space programme still has application for AFC units on the space craft. The market for AFC is currently limited when compared to other fuel cells. Astris Energi a manufacturer of AFC system developed AFC powered generators both portable and stationary. AFCs are also commonly used in a variety of niche transportation applications.
Eneco another company founded in February of 2002 (Gemma Crawley) developed fuel cells for stationary and transportation application including hybrid vehicles which include the AFC powered bus. The company also provided AFC units for use in educational purposes. Despite that they are numbers of companies working on the development of fuel cells; the future prospects still look narrow. A small market is left for the development of AFC with the introduction of all the other fuel cell technology. Attempts are being made to improve upon the already well developed and established AFC technology and in doing so create further commercial applications for these systems (Gemma Crawley). However, many believe that AFCs have already reached the limits of their technological capability and in doing so will remain the least commercially successful of all the fuel cell technologies.