Chemistry » Electrochemistry » Batteries and Fuel Cells

# Fuel Cells

## 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).

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.