In an effort to maintain a pollution-free environment, the scientists around the world have intensified their search for efficient and clean power generating systems; researchers have designed two different types of fuel cell with improved efficiency, namely, lithium cell and alkaline fuel cell. The revival of interest in fuel cells is due to increasingly greater concern for the global environment. Fuel cell is a device that directly converts chemical energy of fuel into electricity. It does not cause sound or air pollution and therefore is clean. Following are the differences between the two types of fuel cells.
The Alkaline fuel cell (AFC) works on compressed oxygen and hydrogen. It uses aqueous solution of potassium hydroxide as electrolyte. They work at relatively lower temperatures and are one of the most efficient fuel cell technologies.
Lithium being of the lightest metal, it has the greatest electrochemical potential making it one of the most reactive metals. The lithium cells produce voltages over twice the voltage of an alkaline cell. It works on thionyl chloride and lithium tetrachloroaluminate, which act as the cathode and electrolyte, respectively.
Alkaline fuel cells have been used since 1960s by NASA for its various space exploration missions like the Apollo and space shuttles. During the chemical reactions in the cell, there is very little pollution along with power generation. These cells operate at efficiencies up to 70%. Another advantage is that its manufacturing cost is comparatively less since any kind of material can be used as catalyst on the electrodes.
Lithium cells are highly useful since their energy density is twice that of the alkaline cells. They are light weight, making it a perfect choice for automobiles. They can also store more energy despite having a compact size. Lithium cells do not produce any harmful residues and are long-lasting. Some of their variants are rechargeable, making it an attractive technology.
One of the major drawbacks of AFCs is that the cells need pure hydrogen and oxygen since it is very sensitive to CO2, which may be present in the fuel. The electrolyte reacts with CO2, thus poisoning it and interfering with the chemical reactions of the cell. This degrades the fuel cell performance; hence it is restricted to closed environment such as that in spacecrafts and military equipment. Therefore its commercial application has been so far limited.
Due to its high reactivity with water as well air, the lithium cells should be cautiously handled. These cells gets short circuited if temperature or pressure builds up; therefore they should be carefully designed to prevent accidents. They are comparatively expensive than the alkaline version.
As mentioned above, AFCs are extensively used in aerospace engineering, but the commercial potential for AFC lies with the new version that uses a bi-polar plate, which is comparatively superior to the mono-plate version. HYRA, the world’s largest fuel cell ship, utilizes AFC technology.
Lithium cells find application in many long-lasting and crucial medical devices like artificial pacemaker. Replacing the conventional alkaline cells, nowadays they are extensively used in devices like cameras, clocks, calculators and toys. They are also used in computers, mobile phones and remote car locks, hence minimizing battery replacement.