The promise of thermoelectric materials has, it seems, run hot and cold over the decades. These materials, which can directly convert heat into electricity (and vice versa), could be a boon for everything from power generation to microprocessor cooling. But except in a few niche applications, these solid-state heat pumps have proven too inefficient to be practical. As much as engineers would like to grab waste heat from, say, a cars engine and turn it into electricity, thermoelectric materials just havent been up to the job.

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