Although climate-controlled car seats don’t spring to mind when you
think of energy efficiency, the latest technology underpinning this luxury automobile
feature is based on thermoelectrics—materials that convert electricity
directly into heating or cooling.
Conversely, thermoelectrics can also funnel excess heat from energy inefficient
systems, such as car engines or power plants, by recovering this ‘waste
heat’ and turning it into electricity. As a result, these materials offer
a potentially clean source of energy to reduce fuel consumption and CO2 emissions.
Using simple water-based chemistry to wrap a polymer that conducts electricity around a nanorod of tellurium, this composite nanoscale thermoelectric is easily spin cast or printed into a film.
Currently, this thermal energy is converted with high-efficiency, expensive
thermoelectric materials. In automotive exhaust systems, for example, solid-state
thermoelectrics recover waste heat that can result in fuel savings of up to
five percent, but their high cost bars them from being used in smaller-scale
settings. Boosting these savings through lower-cost materials could make a significant
impact in power generation for batteries or electronic components in computers.
Now, Lawrence Berkeley National
Laboratory (Berkeley Lab) scientists are tackling this challenge by “changing
the budget for thermal energy management,” said Jeff Urban, Deputy Director
of the Inorganic Nanostructures Facility at the Molecular Foundry, a nanoscience
user facility.
“Historically, high-efficiency thermoelectrics have required high-cost,
materials-intensive processing,” said Urban. “By engineering a hybrid
of soft and hard materials using straightforward flask chemistry in water, we’ve
developed a route that provides respectable efficiency with a low cost to production.”
In their approach, Urban and colleagues constructed a nanoscale composite material
by wrapping a polymer that conducts electricity around a nanorod of tellurium—a
metal coupled with cadmium in today’s most cost-effective solar cells.
This composite material is easily spin cast or printed into a film from a water-based
solution. Along with its ease of manufacture, this hybrid material also has
a thermoelectric figure of merit thousands of times greater than either the
polymer or nanorod alone—a crucial factor in boosting device performance.
“In recent years, we’ve seen tremendous gains in thermoelectric
efficiency, but there is a need for low-cost, moderate efficiency materials
that are easy to process and pattern over large areas,” said Rachel Segalman,
a faculty scientist at Berkeley Lab and professor of Chemical and Biomolecular
Engineering at University of California, Berkeley. “We had a lot of intuition
about what would work using polymers and nanocrystals, and will now explore
materials space to optimize these systems and switch to more earth-abundant
materials.”
A paper reporting this research titled, “Water-processable polymer-nanocrystal
hybrids for thermoelectrics,” appears in Nano Letters and is available
to subscribers online. Co-authoring the paper with Urban and Segalman were Kevin
See, Joseph Feser, Cynthia Chen and Arun Majumdar.
Portions of this work at the Molecular Foundry were supported by DOE’s
Office of Science.