The smallest battery

Scientists at the University of California, Irvine, have made the world's smallest battery -- about the size of the common-cold virus (Science, Vol 257 No 5074). Chemist Reginald Penner and his co-workers stumbled on to it while trying to prove that silver and copper could be deposited as closely-spaced nanodots on a graphite surface to cause certain chemical reactions. They found the potential energy difference between electrons of the two metals behaved like a small battery. Atoms from the copper moved on to the silver dot about 70 nanometres (one nanometre is one-thousand millionth of a metre) away.

Penner's nanobattery delivers only 20,000th of a volt for 45 minutes and has no practical use. But he thinks one day improved versions of this tiny battery could power molecule-sized motors.