Fuel Cells

A fuel cell is a device that converts chemical energy into electrical energy. Fuel cells are similar to batteries but require a continuous source of fuel, often hydrogen. They will continue to produce electricity as long as fuel is available. Hydrogen fuel cells have been used to supply power for satellites, space capsules, automobiles, boats, and submarines (see the figure below).

A diagram is shown of a hydrogen fuel cell. At the center is a narrow vertical rectangle which is shaded tan and labeled “Electrolyte.” To the right is a slightly wider and shorter purple rectangle which is labeled “Cathode.” To the left is a rectangle of the same size which is labeled “Anode.” Grey rectangles that are slightly wider and longer are at the right and left sides, attached to the purple and blue rectangles. On the right side, a white region overlays the grey rectangle. This white region provides a pathway for O subscript 2 to enter at the upper left, move inward and along the interface with the purple region, and exit to the lower right. A similar pathway overlays the grey region on the left, allowing a pathway for the entry of H subscript 2 from the upper right along the interface with the blue rectangle, allowing for the exit of H subscript 2 O out to the lower left of the diagram. Black line segments extend upward from the blue and purple regions. These line segments are connected by a horizontal segment that has a yellow zig zag shape at the center. This shape is labeled “Electric power.” At the left of the diagram, in the upper left white region, 2 H subscript 2 is followed by an arrow that points right and down to H subscript 2. An arrow points right into the blue region to H subscript 2 O. A curved arrow point up to e superscript negative. Another e superscript negative is placed nearby and has an upward pointing arrow extending up to the left of the line segment extending from the purple region. A second arrow points upward along this segment with the label “e superscript negative” to its left. A curved arrow extends down and to the left from the H subscript 2 O into the white region. A second H subscript 2 O is shown below the first in the blue region repeating the arrow patterns established above. At the lower left, an arrow points left, to the exit of the white region. At the tip of this arrow is the label “2 H subscript 2 O.” In the central brown region, O superscript 2 negative is listed twice with arrows pointing left, to the H subscript 2 O formulas in the blue region. At the upper right, O subscript 2 is shown with an arrow pointing left and down to O subscript 2 in the white region. An arrow points left from this point into the purple region. From the tip of the arrow, two arrows point to the two O subscript 2 negative structures in the brown central region. An arrow, labeled “e superscript negative” points downward to the right of the line segment above the purple region. A second arrow extends down into the purple region, pointing to e superscript negative. Three additional e superscript negative symbols appear nearby. An arrow extends from them to the point where the arrows meet in the purple region.

In this hydrogen fuel-cell schematic, oxygen from the air reacts with hydrogen, producing water and electricity.

In a hydrogen fuel cell, the reactions are

\(\begin{array}{}\underset{¯}{\begin{array}{l}\text{anode:}\phantom{\rule{0.2em}{0ex}}2{\text{H}}_{2}+{\text{2O}}^{2-}\phantom{\rule{0.2em}{0ex}}⟶\phantom{\rule{0.2em}{0ex}}2{\text{H}}_{2}\text{O}+{\text{4e}}^{\text{−}}\\ \text{cathode:}\phantom{\rule{0.65em}{0ex}}{\text{O}}_{2}+{\text{4e}}^{\text{−}}\phantom{\rule{0.2em}{0ex}}⟶\phantom{\rule{0.2em}{0ex}}{\text{2O}}^{2-}\end{array}}\\ \hline \text{overall:}\phantom{\rule{0.92em}{0ex}}2{\text{H}}_{2}+{\text{O}}_{2}\phantom{\rule{0.2em}{0ex}}⟶\phantom{\rule{0.2em}{0ex}}2{\text{H}}_{2}\text{O}\end{array}\)

The voltage is about 0.9 V. The efficiency of fuel cells is typically about 40% to 60%, which is higher than the typical internal combustion engine (25% to 35%) and, in the case of the hydrogen fuel cell, produces only water as exhaust. Currently, fuel cells are rather expensive and contain features that cause them to fail after a relatively short time.

Optional Video:

Watch this video below to learn more about fuel cells.

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Electrochemistry

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