What are fuel cells ? Discuss `H_(2)-O_(2)` fuel cell. List some advantages of fuel cells over other cells.

Explanation

Fuel cell. A fuel cell is a device used to convert chemical energy present in a fuel, directly into electrical energy.
Construction and working. The figure shows the working of a `H_(2)-O_(2)` fuel cell. It consists of porous carbon electrodes. suitable catalysts are added to these porous carbon electrodes to accelerate the electrode reaction, as reaction between hydrogen and oxygen at the operation temperature (400 K) of the is not very fast. these catalysts are mixed in and pressed with the carbon. at anode, suitable catalysts are finely divided platinum or palladium, at cathode cobaltous oxide (CoO), platinum or silver. concentrated KOH or NaOH solution placed between electrodes acts as an electrolyte. hydrogen and oxygen are bubbled through the porous electrodes, at high pressure into the electrolyte. the following electrode reactions take place.
At anode: `2H_(2)(g)+4OH^(-)(aq) to 4H_(2)O(l)+4e^(-)`
At cathode: `O_(2)(g)+2H_(2)O(l)+4e^(-)to4OH^(-)(aq)`
Overall reaction: `2H_(2)(g)+O_(2)(g) to 2H_(2)O(l)`

The gases being consumed are continuously supplied.
The construction of fuel cell is, however, faced with certain difficulties. a few of these are as follows.
(i) Providing contact between gaseous fuel, liquid electrolyte and solid electrode.
(ii) High cost of the catalyst used in the electrodes (e.g., Pt, Pd, Ag, etc.)
(iii) Problem of handling gaseous fuels at low temperature and high pressures.
Advantages over other cells. (i) Pollution free working (ii) high efficiency (iiii) compactness (iv) light in weight (v) higher reliability (no moving parts as in generators). thus they are extremely suitable for certain applications like long manned space flights.