How Fuel Cells Work
Prerequisites
A battery stores energy in its electrodes and eventually runs out. A fuel cell is fed fuel continuously and runs as long as hydrogen flows. Same electrochemical principle (anode, cathode, electrolyte), fundamentally different architecture.
A proton exchange membrane (PEM) fuel cell splits hydrogen gas at the anode. A platinum catalyst strips electrons from H2 molecules, leaving protons (H+). The polymer membrane allows protons to cross but blocks electrons, forcing them through an external circuit (producing electricity). At the cathode, protons, electrons, and oxygen from air recombine to form water. The only byproduct is H2O.
Trace the energy flow. Hydrogen enters at the anode. Chemical energy converts to electrical energy as electrons flow through the circuit. Water exits at the cathode. No combustion, no moving parts, no CO2.
If fuel cells are clean and efficient, why don't they power everything?
The efficiency and cost reality. PEM fuel cells convert hydrogen to electricity at 40-60% efficiency. But producing the hydrogen (by electrolysis) was only 60-70% efficient. Round-trip efficiency for renewable electricity to hydrogen to electricity: roughly 25-35%. Compare to batteries at 85-95% round-trip. Fuel cells also require expensive platinum catalysts, adding cost. Fuel cells make sense only where batteries cannot work: long range, heavy loads, or long-duration storage.
In a PEM fuel cell, the membrane allows protons to cross but blocks electrons. This separation is essential because:
The membrane creates an electrochemical potential difference. By blocking the direct path for electrons, it forces them through an external circuit where their flow can do electrical work. Without this separation, the hydrogen and oxygen would simply recombine without generating electricity.
The answer is CLesson complete
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