Charged Up About Findings : UCI Scientists Have Created the World’s Smallest Battery

UC Irvine scientists have created the world’s smallest battery--so tiny that it is 1/100 the diameter of a red blood cell.

The battery has not yet powered anything. But UCI chemists say once they find a way to harness its electrical charge, the battery could be an energy source for microscopic motors and transistors of the future.

“This is a small step forward that may allow the miniaturization of electronics to an even greater extent than we see today,” said electrochemist Reginald Penner, an assistant professor of chemistry at UCI.

On a more basic level, Penner said, this breakthrough will allow them to study how metal corrodes at the microscopic level. Corrosion is a little-studied electrochemical process, and a rusting iron pipe acts like a low-power oxygen-iron battery.

“We have never been able to see corrosion happening on such a scale before,” Penner, 32, said. “If you can see corrosion happening at its atomic source, then presumably you could develop a method to inhibit it.”

Dubbed a “nanometer-scale galvanic cell,” the battery is made of pillars of copper and silver on a sheet of graphite. It can produce about 1/50 of a volt of electricity for 45 minutes.

Penner and his colleagues created the battery with a special microscope known as a “scanning tunneling microscope,” they report in today’s issue of the Journal of Physical Chemistry. The microscope makes it possible to work at the level of nanometers, or billionths of a meter.

The research began as a test of whether chemical reactions that occur on a large scale also work at microscopic levels. UCI graduate student Wenjie X. Li created the copper and silver pillars on depressions in the graphite, then immersed them in a copper-plating solution.

What happened next surprised and initially stumped the researchers.

Electrically charged copper ions deposited themselves on the silver battery terminal until it was completely coated in a copper jacket two atoms thick. In conventional chemistry, however, copper and silver should have remained stable.

“It was working like a battery when it shouldn’t have,” Penner said. “We sat around for a month with this beautiful data, but we couldn’t explain it.”

Finally, Penner and postdoctoral researcher Jorma Virtanen, a visiting chemist from Finland, came up with a possible solution--an electrochemical phenomenon known as “underpotential deposition.”

Essentially, the two metals have slightly different energy potentials, which caused the copper to be attracted to the silver. But once the silver surface was completely covered with copper atoms, the electrochemical process stopped.

Penner said they have been able to duplicate the process in a larger-scale version with a beaker of copper-plating solution and wires of silver and copper, an experiment they said they will detail in a forthcoming research paper.

The UCI team’s findings have generated enthusiasm among chemists who heard Penner describe his findings at a recent conference in Denver. But some scientists remain skeptical about the force that drives the world’s smallest battery.

“It’s very interesting, but I think some of the mechanisms of how this works are still not nailed down yet,” said Bruce Parkinson, a chemistry professor at Colorado State University.

“But that’s the most interesting thing about science: If you totally understood everything, it wouldn’t be any fun.”

The next step will be to try to make these minute batteries using other metals, such as silver and cadmium, and even gold.

“With gold, we should see closer to half a volt of electricity,” Penner said.