Working principle and types of fuel cells

A fuel cell is an electrochemical device that converts the chemical energy of a fuel (hydrogen) and an oxidant (oxygen from air) directly into electricity, with water and heat as by-products. It works continuously while fuel is supplied, unlike a battery, which stores its reactants.

PEM fuel cell

          e- --> [ external load ] --> e-
          |                            |
   H2 --> | anode |    PEM    | cathode | <-- O2 / air
          |  Pt   |  H+ -->   |   Pt    |
          |       |           |         |
   unused H2 out                  H2O + heat out

Reactions

• Anode: $H_2 \rightarrow 2H^+ + 2e^-$
• Cathode: $\tfrac{1}{2}O_2 + 2H^+ + 2e^- \rightarrow H_2O$
• Overall: $H_2 + \tfrac{1}{2}O_2 \rightarrow H_2O$

Hydrogen is split on the platinum catalyst at the anode. The proton exchange membrane (Nafion) passes only H⁺ ions to the cathode, so the electrons travel through the external circuit from anode to cathode and do useful work. At the cathode, protons, electrons and oxygen combine to form water. The typical cell voltage is 0.6–0.8 V under load, so cells are stacked in series. The operating temperature is 60–80 °C.

Advantages

High efficiency (40–60 %), silent, no moving parts, near-zero emissions at the point of use, quick start and modular size.

Types of fuel cells