A chemical cell stops producing a voltage after a period of time, whereas a hydrogen-oxygen fuel cell can continue to produce a voltage for as long as it is supplied with fuel. Explain the difference between how a chemical cell and a hydrogen-oxygen fuel cell produce a voltage, and why only one of them will eventually stop working.

A chemical cell uses two metal electrodes and an electrolyte to convert stored chemical energy into electrical energy. When the reactants at the electrodes (or the electrolyte) are consumed, the cell can no longer sustain the redox reaction and the voltage falls to zero.

A hydrogen‑oxygen fuel cell is also an electrochemical cell, but it is fed continuously with hydrogen and oxygen. The reaction H₂ + ½O₂ → H₂O takes place at the electrodes, producing a voltage as long as the gases are supplied.

Because the fuel cell’s only product is water, the reactants are not stored inside the cell; they are supplied from outside, so the cell does not run out of reactants and can keep working indefinitely.