To increase ZT, researchers typically try to increase a material's electrical conductivity as much as possible while holding down its thermal conductivity. In 2008, researchers led by Jeffrey Snyder, a materials scientist at the California Institute of Technology in
But thallium is toxic, so Snyder and his colleagues wanted to determine if they could match the improvement with other additives. Earlier this year, Snyder and his team at Caltech reported in Energy & Environmental Science that substituting sodium for thallium produced a ZT of 1.4. Now, Snyder's team, in combination with researchers from the Chinese Academy of Sciences' Shanghai Institute of Ceramics, report online today in Nature that adding selenium and sodium gives them a maximum ZT of 1.8. The selenium not only further improves the electrical conductivity, it also reduces the thermal conductivity, Snyder explains.
The Caltech Researchers discuss the new bulk thermoelectrics and their applications.
"These new materials are roughly twice as effective as anything seen before, and they work well in a temperature range of around 400 to 900 degrees Kelvin," says Snyder. "Waste heat recovery from a car's engine falls well within that range."
In other words, the heat escaping out your car's tailpipe could be used to help power the vehicle's electrical components—and not just the radio, wipers, and headlights. "You'll see applications wherever there's a solid-state advantage," Snyder predicts. "One example is the charging system. The electricity to keep your car's battery charged is generated by the alternator, a mechanical device driven by a rubber belt powered by the crankshaft. You've got friction, slippage, strain, internal resistance, wear and tear, and weight, in addition to the mechanical energy extracted to make the electricity. Just replacing that one subsystem with a thermoelectric solution could instantly improve a car's fuel efficiency by 10 percent."