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whay are fuel cells?
Fuel cells are energy conversion devices that continuously transform the chemical energy of a fuel and an oxidant into electrical energy. This energy conversion process is accomplished by means of an electrochemical reaction whereby the reactants are consumed, by-products are expelled, and heat may be released or consumed. Fuel cells will continue to generate electricity as long as both fuel and oxidant are available. Pure hydrogen, hydrocarbons, alcohols, and hydrazine are common fuels while pure oxygen and air are conventional oxidants. For space applications, pure hydrogen and oxygen function exclusively as the fuel and oxidant, respectively, while water and heat are the sole reaction products.
These are voltaic cells in which the reactants are continuously supplied to the electrodes. These are designed to convert the energy from the combustion of fuels such as H2, CO, CH4, etc. directly into electrical energy. Common example is hydrogen-oxygen fuel cell.
[Ref:MODERN'S abc of CHEMISTRY]
The principle of the fuel cell was discovered by German scientist Christian Friedrich Schonbein in 1838.Based on this work, the first fuel cell was demonstrated by Welsh scientist and barrister Sir William Robert Grove in the February 1839.
Hydrogen-oxygen fuel cell
In this cell hydrogen and oxygen are bubbled through a porous carbon electrode into concentrated aqueous sodium hydroxide of potassium hydroxide.
Hydrogen (the fuel) is fed into the anode compartment where it is oxidized.
The oxygen is fed into the cathode compartment where it is reduced.
The diffusion rates of the gasses into the cell are carefully regulated to get maximum efficiency.
The net reaction is the same as burning of hydrogen and oxygen to form water.
The reactions are:
2[h2o(g)+2oh-(aq) 2h2o(l)+2e-] at anode
O2(g)+2h2o(l)+4e- 4oh-(aq) at cathode
2h2o(g)+o2(g) 2h2o(l ) over all reaction
Each electrode is made up of porous compressed carbon containing a small amount of catalyst (Pt, Ag or CaO). This cell runs continuously as long as the reactants are fed. These fuel cells are more efficient than conventionally used methods of generating electricity on a large scale by burning hydrogen, carbon, fuels because these fuel cells converts the energy of the fuel directly into electricity.
This cell has been used for electric power in the APOLLO space program. Fuel cells offer great promises for energy conservation in future.
[Ref:MODERN'S abc of CHEMISTRY]
The fuel cell converts the energy of a fuel directly into electricity and therefore, they are more efficient than the conventional methods of generating electricity on a large scale by generating hydrogen, carbon fuels. Though we expect 100% efficiency in fuel cells, so far 60-70% efficiency has been achieved. The conventional methods of production of electrical energy involve combustion of a fuel to liberate heat which is then used to generate electricity. The efficiency of these methods is only 40%. [Ref: moderns abc of chemistry]
continuous source of energy
There is no electrode material to be replaced as in ordinary battery. The fuel can be fed continuously to produce power. For this reason, H2-O2 fuel cells have been used in space crafts.
[Ref: moderns abc of chemistry]
pollution free working
There are no objectionable by-products and, therefore, they do not cause pollution problems. Since fuel cells are efficient and free from pollution, attempts are being made to get better commercially practical fuel cells. .
[Ref: moderns abc of chemistry]
high power density
A high power density allows fuel cells to be relatively compact source of electric power, beneficial in application with space constraints. In a fuel cell system, the fuel cell itself is nearly dwarfed by other components of the system such as the fuel reformer and power inverter.
Fuel cells, due to their nature of operation, are extremely quiet in operation. This allows fuel cells to be used in residential or built-up areas where the noise pollution is undesirable.
The only disadvantage of the fuel cells associated with the cost. The two basic reasons are
High costs compared to other energy systems technology.
Operation requires replenish able fuel supply.
Fuel cell efficiency
The efficiency of a fuel cell is dependent on the amount of power drawn from it. Drawing more power means drawing more current, this increases the losses in the fuel cell. As a general rule, the more power (current) drawn, the lower the efficiency. Most losses manifest themselves as a voltage drop in the cell, so the efficiency of a cell is almost proportional to its voltage. A typical cell running at 0.7 V has an efficiency of about 50%, meaning that 50% of the energy content of the hydrogen is converted into electrical energy; the remaining 50% will be converted into heat.
For a hydrogen cell operating at standard conditions with no reactant leaks, the efficiency is equal to the cell voltage divided by 1.48 V, based on heating value (enthalpy), of the reaction.
Fuel cells are very useful as power sources in remote locations, such as
Remote weather stations,
A fuel cell system running on hydrogen can be compact and lightweight, and have no major moving parts. Because fuel cells have no moving parts and do not involve combustion, in ideal conditions they can achieve up to 99.9999% reliability.
Telecommunications - With the use of computers, the Internet, and communication networks steadily increasing, there comes a need for more reliable power than is available on the current electrical grid, and fuel cells have proven to be up to 99.999% (five nines) reliable.ÿ Fuel cells can replace batteries to provide power for 1kW to 5kW telecom sites without noise or emissions, and are durable, providing power in sites that are either hard to access or are subject to inclement weather Buses - Fuel cells are highly efficient, so even if the hydrogen is produced from fossil fuels, fuel cell buses can reduce CO2emissions. And emissions are truly zero if the hydrogen is produced from renewable electricity, which greatly improves local air quality. Because the fuel cell system is so much quieter than a diesel engine, fuel cell buses significantly reduce noise pollution as well.
Planes - Fuel cells are an attractive option for aviation since they produce zero or low emissions and also make barely any noise.ÿ The military is especially interested in this application because of the low noise, low thermal signature and ability to attain high altitude. Companies like Boeing are heavily involved in developing a fuel cell planes.
Consumer Electronics- Fuel cells will change the telecommuting world, powering
cellular phones, laptops and palm pilots hours longer than batteries. Companies have already demonstrated fuel cells that can power cell phones for 30 days with out recharging and laptops for 20 hours. Other applications for micro fuel cells include pagers, video recorders, portable power tools, and low power remote devices such as hearing aids, smoke detectors, burglar alarms, hotel locks and meter readers. These miniature fuel cells generally run on methanol, an inexpensive wood alcohol also used in windshield wiper fluid.
The automotive and mobile device markets are expected to be most affected by fuel cells over the coming years.
Fuel cells can be used anywhere that energy is required. Things such as highway road signs, often used where power is hard to come by, are currently being powered by prototype cells in New Jersey.
There are a number of commercial fuel cell generators now working around the world, and companies such as Plug Power are testing residential generators that not only produce electricity, but can also be used for water and space heating.