What Are Fuel Cells?


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A diagram is shown of a hydrogen fuel cell. At the center is a vertical rectangle which is shaded dark gray and labeled “Electrolyte.” This region has two labels for H superscript plus in it. To the right and left are narrow vertical rectangles shaded light gray. The one to the right is labeled “Cathode” and the one to the left is labeled “Anode.” To the left of the left-most light gray region is a white region shaped like a closed left bracket. A yellow arrow points in to the white region with the label to show “Fuel In.” In the middle of the white area are two yellow arrows pointing toward the gray shading labeled “H subscript 2.” At the bottom of the white region is a yellow arrow pointing out that is labeled “Excess Fuel.” On the right side is another white region that makes a right closed bracket shape. There are two arrows with the label “Air In” and “H subscript 2 O” in the upper left side of this area pointing in. One arrow is light blue and one is dark blue. In the middle to the white area is a light blue arrow pointing toward the gray shading. The arrow is labeled “O subscript 2.” Below that are two dark blue arrows pointing out from the gray shading to the white area labeled “H subscript 2 O.” At the bottom of the white region are the light blue arrow for O subscript 2 and the dark blue arrow for H subscript 2 O pointing out. This is labeled “Unused Gases Out.” Black line segments extend upward from the light gray shaded regions. These line segments are connected by a horizontal segment that has a curly shape in a circle at the center. This shape is labeled “Electric Current.” In the left light gray shaded region above the yellow arrows is a red arrow pointing up, the label e superscript minus above it, and then another red arrow. The black line segment above this area also has the label e superscript minus. Where the line turns right to connect to the Electric Current shape is a right-facing red arrow. On the other side of the shape where the line turns downward to connect to the other light gray shaded region is a red downward-facing arrow. Below that arrow in the light gray region is the label e superscript minus, followed by a red down arrow, followed by another e superscript minus label that stops before the light blue arrow pointing in to the shaded area.
Figure 1. In this hydrogen fuel cell, oxygen from the air reacts with hydrogen, producing water and electricity. Source: OpenStax Chemistry 2e

What are fuel cells? (OpenStax Chemistry 2e)

A fuel cell is a galvanic cell that uses traditional combustive fuels, most often hydrogen or methane, that are continuously fed into the cell along with an oxidant. (An alternative, but not very popular, name for a fuel cell is a flow battery.) Within the cell, fuel and oxidant undergo the same redox chemistry as when they are combusted, but via a catalyzed electrochemical that is significantly more efficient. For example, a typical hydrogen fuel cell uses graphite electrodes embedded with platinum-based catalysts to accelerate the two half-cell reactions:

These types of fuel cells generally produce voltages of approximately 1.2 V. Compared to an internal combustion engine, the energy efficiency of a fuel cell using the same redox reaction is typically more than double (~20%–25% for an engine versus ~50%–75% for a fuel cell). Hydrogen fuel cells are commonly used on extended space missions, and prototypes for personal vehicles have been developed, though the technology remains relatively immature.


Flowers, P., Theopold, K., Langley, R., & Robinson, W. R. (2019, February 14). Chemistry 2e. Houston, Texas: OpenStax. Access for free at: https://openstax.org/books/chemistry-2e

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