What a fantastic question! I shall describe a
particular topic that, if we find the right
materials for, could revolutionize how energy is
There are many applications that thermal
energy is used for, e.g., as a source of heat.
Often times though, it is an unwanted form of
waste energy due to friction or other inefficient
processes. The fact that the car hood gets very
hot after you drive is because the combustion
reaction that drives the engine is an extremely
inefficient chemical process.
see picture here
But what if we could harvest that waste
energy into useful energy?
It turns out we can! With a set of materials
known as thermoelectrics.
The basic idea is this: Thermoelectrics
convert a temperature difference into
electricity. How can this be?
You may have learned in your science classes
that matter is made up of many extremely tiny
particles known as
(side note: not the most accurate depiction
of the atom, but it will do here).
A solid is made up of many of these atoms
(1026, that's 1 with 26 zeros behind
read this link If you take a bar of
material, heat up one side and cool down the
other, you will get a voltage, which can drive
electric current. Why is this so?
The particles that are responsible for
carrying electric current are the electrons.
When you heat one end of the bar, you are giving
the electrons on this particular side more thermal
energy to move about. This means the electrons are
more mobile than the ones on the cold side. The
temperature difference across the bar causes the
electrons to flow from hot to cold. This results
How thermoelectronics work
But here it gets a little complicated. You need
the temperature difference to drive the flow of
electrons, but the electrons also carry heat with
them, which diminishes the temperature difference.
So you need a material that is both
electrically conductive (i.e., electrons
flow easily from one side to another) but is
thermally insulating (i.e., heat doesn't
travel as easily, so you maintain a temperature
difference). That's saying you want the electronic
properties of a metal but the thermal properties
of a glass. These are two very different,
seemingly contradictory criteria!
This is where material scientists and
clever engineering come in. It turns out thermal
conductivity is also determined by what kind of
atoms are in the system, and by tuning which atoms
in the periodic table are in the material, we can
tune the thermal conductivity, while still
maintaining electrical conductivity. The biggest
materials challenge in this area is to find a
material that is efficient enough at turning waste
heat into electricity.
While this currently limits the wide-scale
commercialization of thermoelectrics, there are a
few technologies with thermoelectrics already in
One really cool application that I just learned
about from one of my classmates is the use of
thermoelectrics in the
radioisotope thermoelectric generator RTG An
RTG uses nuclear fission to provide the heat
source and the coldness of space as the heat sink.
If you have read (or watched) The Martian, this
might sound familiar to you. An RTG is currently
providing the power for
Voyager I , which is the first spacecraft
ever to enter interstellar space (beyond our own
solar system!). It has been running for almost 40
years using the power generated from the RTG, for
which one of the key parts is the