INEFFICIENT: In a coal-fired power plant, as much as 60 percent of the coal’s energy goes not to power homes as electricity but instead dissipates into the air, a problem called waste heat that several Berkeley researchers and entrepreneurs are working to solve.

Waste heat:  It’s when heat
produced in a combustive process goes unused, dissipating into the air
or water. Automobiles, industrial facilities and power
plants all produce waste heat, and a lot of it. In a coal-fired power
plant, for example, as much as 60 percent of the coal’s energy doesn’t
go to power homes as electricity but instead disappears into thin air,
waste heat wasted.

For decades, that gross inefficiency has given the
industry ulcers and lured others to try to capture waste heat before all
that energy is lost. One solution has been an expensive
boiler-turbine system, but for many companies and utilities, it doesn’t
recover enough waste heat to make economic sense. Bismuth telluride, a
semiconductor material, has shown promise by employing a thermoelectric
principle called the Seebeck effect to convert
heat into an electric current, but it’s also problematic: toxic, scarce
and expensive, with limited efficiency.

While the search for clean, green energy has gotten
gobs of attention recently, a holy grail awaits anyone who can improve
the current fossil fuel system. One estimate places
the worldwide waste heat recovery market at one trillion dollars, with
the potential to offset as much as 500 million metric tons of carbon per
year.

What’s the magic solution? Some Berkeley engineers
believe the answer lies not in a sophisticated device, but in the basic
elements of the periodic table—materials: specifically,
finding a new material with spectacular thermoelectric properties that
can efficiently and economically convert heat into electricity.
(Thermoelectrics is the conversion of temperature differences, that is,
differences in the amplitude of atom vibration in
a solid, into an electric current.)

Over in Hearst Memorial Mining Building, materials
science and engineering assistant professor
Junqiao
Wu
may be onto something. Wu knew from earlier research that a good
thermoelectric material needed to have a certain type of density of
states, which is a mathematical description of distribution of energy
levels within a semiconductor. “If the density of states
is flat or gradual, the material won’t have very good thermoelectric
properties,” Wu says. “You need it to be spiky or peaky.”

BETTER MATERIALS, BETTER ENGINEERING: Assistant professor Junqiao Wu of materials science and engineering is working on a new, highly efficient and low-cost thermoelectric material that may one day improve the performance of power plants, factories, cars and computers.
COURTESY JUNQIAO WU

Wu knew that a specialized type of semiconductor
called highly mismatched alloys (HMAs) could be very peaky because of
their hybridization, the result of forcing together two
materials that don’t want to mix atomically, akin to mixing water and
oil. He hypothesized that mixing two semiconductors, zinc selenide and
zinc oxide, into an HMA, would produce a peaky density of states.

Beginning in late 2008, Wu collaborated with other
researchers to run computations on “Franklin,” a massive Cray XT4
supercomputer at Lawrence Berkeley National Laboratory. After
months of number crunching, Wu’s idea held up. Theoretically, at least,
mixing the two materials enhanced their thermoelectric performance
considerably, producing a new, highly efficient, potentially low-cost
thermoelectric material. The physics journal

Physical Review Letters published

the team’s paper in January.

“We’re now working on experimentally synthesizing
this material in the lab, doping it electrically [adding an impurity to
make it conductive] and measuring the thermoelectric
properties to prove what we predicted in our theory,” Wu explains.
Forcing the two materials together in a uniform atomic pattern and
keeping them together will be a challenging and potentially expensive
process that could take three to five years. It might
be another five years before Wu’s material is adapted into a
thermoelectric device and sent out to recover waste heat.

“We see a very promising future for this material,
but first we have to show that it works better than existing materials,”
Wu says.

Wu isn’t the only Berkeley engineer in
thermoelectrics. Materials science and engineering professors
Ramamoorthy
Ramesh,
who holds a joint appointment with the physics department, and Peidong
Yang, who holds a joint appointment with chemistry, are
both pursuing various lines of query.

In fact, last year Yang cofounded a startup called
Alphabet
Energy
with Berkeley Engineering alum Matt Scullin (M.S.’07, Ph.D.’09 MSE).
Recently, Alphabet Energy received $1 million in seed money from
Claremont Creek Ventures, a Berkeley venture capital firm, and CalCEF
Clean Energy Angel Fund.

“We’re commercializing the first highly scalable,
highly inexpensive thermoelectric platform that doesn’t require
additional infrastructure,” Scullin says. “Factories, car makers,
utilities, power plants, the military—they’re all interested in our
technology.”

Another prominent Berkeley researcher in
thermoelectrics is mechanical engineering and materials science and
engineering professor Arun Majumdar, who now directs the U.S. Department
of Energy’s Advanced
Research Projects Agency–Energy
(ARPA–E).

In February, ARPA–E awarded a $3 million grant to
thermoelectric startup
Phononic
Devices,
cofounded by Berkeley Engineering alum Patrick McCann (B.S.’81
Engineering Physics), who later earned his doctorate in electronic
materials from MIT. McCann, an electrical and computer engineering
professor at the University of Oklahoma, says work at Phononic
Devices is based on semiconductor fabrication technology that he helped
develop at Oklahoma.

“Thermoelectrics is a small world, and most good
things seem to connect through UC Berkeley or MIT,” McCann says. Like
Scullin and Yang, he is circumspect about revealing technical
details but says, “We’re implementing known physical principles within a
thermally insulating material to improve efficiency on a product that
will be cost friendly to manufacturing.”

If these Berkeley engineers are successful, their
thermoelectric materials may one day capture the energy that powers your
home or boosts your car’s fuel efficiency. The breakthroughs
may also cool the circuitry of electronics as large as server farms or
as small as tiny portable devices. For Junqiao Wu and others working in
the basic building blocks of Earth’s matter, all that magic is in the
material.