Why is hydrolysis the opposite of the reaction that occurs in a hydrogen fuel cell?

Hydrolysis is the process of breaking down water molecules into hydrogen and oxygen through the input of energy, typically via an electric current. In a hydrogen fuel cell, the opposite reaction occurs: hydrogen and oxygen combine to produce water, releasing energy in the form of electricity. Thus, while hydrolysis requires energy to split water, a hydrogen fuel cell generates energy by recombining those elements. This fundamental difference highlights the contrasting nature of these two processes.