RAS question
Hydrogen fuel cells produce electricity with which byproduct?
Correct answer: (A) Water.
Hydrogen fuel cells produce electricity with water as the byproduct, along with heat.
Explanation
A hydrogen fuel cell converts the chemical energy of hydrogen into electricity through an electrochemical reaction with oxygen. The reaction is commonly represented as 2H2 + O2 -> 2H2O + electricity + heat, so the material product formed is water. The Department of Energy notes that when hydrogen is the fuel, the products are electricity, water and heat, and hydrogen fuel cells emit only water with no air pollutants at the point of operation. That is why water is the correct byproduct, not a carbon- or sulphur-based gas. Applications such as buses, trucks, forklifts, backup power and space missions use this basic advantage: usable electricity is produced without tailpipe-style emissions at the point of use.
Why the other options are wrong
- (B) Carbon dioxide is not formed in a hydrogen-oxygen fuel-cell reaction, which produces water, electricity and heat instead of a carbon-based gas.
- (C) Sulphur dioxide would require sulphur in the fuel or reaction path, but a hydrogen fuel-cell reaction combines hydrogen and oxygen to form water.
- (D) Methane is a hydrocarbon fuel, not the byproduct of a hydrogen fuel cell; the reaction product is water.
Concept
This tests clean-energy basics under Science and Technology: how fuel cells convert chemical energy into electrical energy. It recurs in RAS because hydrogen fuel cells connect electrochemistry with zero-emission-at-use transport and power applications.