Question 1

How is a fuel cell different from a battery?

Accepted Answer

A battery stores chemical energy in its electrodes and gradually depletes those materials as it discharges, requiring recharging to restore them. A fuel cell is an open system that continuously consumes externally supplied hydrogen and oxygen, producing electricity as long as fuel is supplied—it does not deplete or need recharging in the same sense. Fuel cells can be refueled in minutes (like filling a gas tank), while battery recharging may take hours. However, batteries have simpler infrastructure and higher round-trip efficiency for short-duration storage.

Question 2

What is the role of the platinum catalyst in a PEM fuel cell?

Accepted Answer

Platinum catalyzes the hydrogen oxidation reaction (HOR) at the anode and the oxygen reduction reaction (ORR) at the cathode. Both reactions have high activation energies without a catalyst—the ORR in particular is kinetically sluggish and accounts for most of the efficiency loss in PEM fuel cells. Platinum provides active surface sites that adsorb and dissociate H2 and O2 molecules, lowering the activation energy. Platinum's high cost (~,000/kg) and scarcity are major barriers to fuel cell commercialization, driving research into platinum-group-metal-free catalysts.

Question 3

What are the three regions of a fuel cell polarization curve?

Accepted Answer

The voltage-current (polarization) curve shows how cell voltage decreases as current increases. At low current, the steep drop is dominated by activation losses—the energy needed to start electrode reactions. At intermediate current, voltage decreases linearly due to ohmic losses (resistance of membrane and electrodes). At high current, voltage drops sharply again due to mass-transport limitations—insufficient delivery of hydrogen or oxygen to the catalyst layer. Understanding these regions guides engineers to improve catalysts (activation), membrane conductivity (ohmic), and gas diffusion layers (mass transport).

⚡ Hydrogen Fuel Cell Polarization Curve

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