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Abstract: This paper explains the various types of fuel cells and the main areas where these fuel cells plays great role. Fuel cell is like a rose, you can get the best result provided you are cautious about the disadvantages and harmful effects. New advances in various fields help to use fuel cells to the maximum extent protecting our Mother Earth.
INTRODUCTION
The discovery of Petroleum brought forth Industrial Revolution in the world. The whole population started exploiting petroleum just like water without even thinking about Earth. So we can try to extract fuel from water and its derivatives. This would not only protect Earth but also shift the whole economy towards renewable and sustainable development.
Fuel cells are devices which converts chemical energy of the fuel (such as hydrogen) and an oxidant directly into electrical energy. Principal behind working of every fuel cell is same. The reaction occurs in Physical Piece of equipment called the photon exchange membrane which contains a cation and an anion react with one another, a chemical reaction occurs and thus electricity is produced.
FUEL CELLS:-
A) Definition:-
A Fuel cell is a device which continuously changes the chemical energy of a fuel and an oxidant into electrical energy. A Fuel cell can be compared to battery which can be recharged when we consume power from it.
B) Construction:-
Every fuel cell consist of two electrodes an anode and a cathode. The anode is which is negative and the cathode which is positive is sandwiched around an electrolyte. The electrolyte known as Photon Exchange Membrane (PEM) is specially treated so as to conduct only positively charged ions. To speed up the process of the reaction without effecting the anode and cathode, we use a rough porous powder catalyst which thinly coats carbon paper or cloth so that a maximum surface area can be exposed to Hydrogen or Oxygen.
Working:-
Hydrogen gas is fed to the anode and oxygen gas is fed to the cathode. Reacting upon its own pressure the hydrogen atoms are forced through the catalyst. Once it comes in contact with the catalyst, the hydrogen forms two hydrogen ions and two electrons. The photon, positively charged ions, and the electrons, the negatively charged ions, travel to the cathode.
On cathode side, oxygen gas in presence of catalyst forms two oxygen ions. The two ions have strong negative charge and thus attract two positive hydrogen ions, which results in formation of water.
Involved Reactions:-
Anode side: 2H2 => 4H+ + 4e-
Cathode side: O2 + 4H+ + 4e- => 2H2O
Net reaction: 2H2 + O2 => 2H2O
This fuel cell can only generate a small amount of voltage (i.e. , 0.7 V). So to make the voltage to realistic level many individual fuel cells are combined.
DIFFERENT TYPES OF FUEL CELLS AND USES
A) Alkaline Fuel Cell (AFC)
This is oldest successful design of fuel cell used to power Apollo Spacecraft of NASA. Recent design has proved that it can be operated at lower temperatures from 230C to 700C .
Advantage:-
1) AFCs have very high performance as they undergo very fast chemical reaction.
2) This results into the efficiency level of upto 60%.
Disadvantage:-
1) They are very susceptible to CO2 as a small amount of it can contaminate the fuel cell and thus ruin the entire fuel cell.
2) Decontamination process is too costly.
ENERGY DEMANDS OF HYDROGEN-CONSUMING FUEL CELLS
The successful fuel cells used in Apollo space craft ran on pure liquefied hydrogen and oxygen. Combining a kilogram of hydrogen with oxygen to produce water releases 33000 watt-hours of energy. Whereas lead storage battery delivers only around 30 watt-hours per kg. Due to very low density of Hydrogen atom at atmosphere, it is very difficult to extract Hydrogen which is the main challenge behind using hydrogen as a fuel.
COST OF HYDROGEN
The price of liquid Hydrogen ranges from $0.93 to $2.80 for the energy equivalent of one gallon of gasoline. The New Energy Laboratory of Fuji Electric Corporation research and development has developed a 93.2% efficient cell that electrolyses water to produce an Hydrogen and Oxygen. One gallon of gasoline, when burns, produces 127500 BTU .
The most common source of hydrogen in the world is methane gas.
CH4 + H2O => CO + 3H2 (Temp. 700-11000C)
The byproduct of the reaction , CO, which is often burnt to produce for the reaction.
CO + H2O => CO2 + H2 (Temp. 3600C)
The second reaction is known as coal gasification reaction.
Hydrogen can also be obtained by electrolysis of water but due to its high requirements it is not feasible for commercial usage.
APPLICATIONS
Fuel cells can be used in a variety of applications, which can be categorized into three groups:
1) Portable power generation. Compact, portable fuel cell systems can be used to recharge batteries or directly power consumer electronics (such as laptops and smartphones). Portable fuel cells can also supply off-the-grid backup power (in remote locations, for instance) or on-the-go power.
2). Stationary fuel cells can be an important part of distributed generation, and are often used as primary or backup power for large energy infrastructures. They are highly efficient: 50 percent for electricity generation, and more than 90 percent with heat recovery (plus there is no need for long transmission lines, with their associated power loss). There are three main uses for stationary fuel cells: combined heat and power (CHP), uninterruptible power supplies (UPS), and primary power units.
a. CHP systems range from 0.5 kilowatt (kW) to several megawatts (MW), and use both the heat and electricity generated by the fuel cell to maximize fuel efficiency (the heat, which is lost in other systems, can be used to heat water and/or provide space heating for a building, for instance). A fuel cell CHP system runs with 80-95 percent efficiency. More than 120,000 fuel cell CHP units have been installed in Japanese homes. In the United States, CHP fuel cells have been installed in grocery stores, hospitals, corporate facilities, and other sites ranging from 200 kW to more than 1 MW.
b. UPS systems are sources of uninterrupted power, and are primarily used as backup power during grid outages. They can replace diesel-powered emergency generators in critical facilities like hospitals and server farms. Cellphone towers equipped with fuel cells were able to keep running during Hurricane Sandy, keeping vital communication links open.
c. Primary power units are large stationary units that can be used to generate power for facilities or for the grid. Companies such as Apple, eBay, Macy’s, and Verizon use fuel cells as primary power units. A 14.9-MW Dominion fuel cell facility—the largest in the United States—was put into service in December 2013. A 59-MW facility near Seoul in South Korea is the world's largest.