How a simple temperature difference can drive an electric current
What if you could generate power simply by heating one side of a metal wire? Through the Seebeck effect, the movement of electrons between different materials can turn thermal energy directly into electricity, creating a loop of power driven by nothing but heat.
The phenomenon relies on the behavior of electrons at the interface of two different metals. When these metals are placed in electric contact, electrons migrate from the material where they are less tightly bound to the one where they are more bound. This movement is governed by the Fermi level, which marks the boundary between occupied and unoccupied energy states within a metal's conduction band. The flow continues until the electrostatic potential—known as the contact potential—reaches an equilibrium where the Fermi levels of both metals align.
While a simple loop of two metals creates opposing potentials that cancel each other out, a net electromotive force emerges if a temperature gradient is introduced. This is the Seebeck effect, named after the German physicist Thomas Johann Seebeck. Because different metals respond to temperature changes in unique ways, maintaining a temperature difference between two junctions creates a measurable voltage. For instance, a thermocouple pairing iron with constantan—a copper and nickel alloy—can produce roughly five millivolts when one junction is at 0 °C and the other at 100 °C.
The relationship also works in reverse through the Peltier effect, named after Jean-Charles Peltier. Here, an applied voltage drives the absorption or release of heat at a junction. While metal-to-metal junctions are foundational, modern practical applications like refrigeration often use semiconductors. By connecting n-type and p-type bismuth telluride junctions in series, engineers can create efficient cooling systems where one side remains significantly colder than the heat-dissipating side.
Source: Make Electricity Go Round and Round - The Thermoelectric Effect
