Souping-Up Bio-Waste into Supercapacitors

Hauling bins of industrial leftovers into his lab, Dr. David Mitlin is the model of a very resourceful guy - not Boy Scout resourceful, Macgyver or Navy Seal resourceful. Through his research, he spends every day redefining the concept of "waste." Instead of quickly landfilling unwanted detritus, Mitlin works hard to find productive uses for industrial discards. He won't call it an obsession, but his colleagues do, and consider him one of the leading practitioners of high-utility waste-streaming.

Dumpster diving

Although he received a specialized doctorate in materials science from UC Berkeley in 2000, and then worked as an integration engineer at IBM for two years, followed by a fellowship at the Los Alamos National Laboratory, his proclivity seems to be high-tech dumpster diving, where he finds and reuses bio-waste to improve batteries and electrodes. After he moved to the University of Alberta in 2004, his research group explored a wide range of industrial misfits: foul-smelling, cringeable specimens of bio-waste ranging from peat moss to discarded eggshells. Speaking from experience, "You can do really interesting things with bio-waste. We've pretty much figured out the secret sauce of it," says Dr Mitlin confidently.

Pseudo-graphite

The essence of that "secret sauce" is a process that zeros in on the perfect plant - or carbon source - and tailors it by optimizing its organic structure to a selected device. "We turned banana peels into a dense block of carbon - called it pseudo-graphite - and that's great for sodium ion batteries," he explained. This philosophy gelled two years ago, when Mitlin replaced activated carbon electrodes in supercapacitors with carbonized eggshell membranes. The idea came after his team had started to use the membranes as a design template for their new supercapacitor. But after testing, the egg shell membranes turned out to be far more efficient than anything they'd cobbled together, even the activated carbon they wanted to replace.

Mitlin says the membranes excelled because they're so rich in nitrogen, which absorbs energy, and, along with a porous structure, boost the ability to store and release a charge quickly. So a moment of serendipity became a research philosophy, moving from bio-mimicry back to the original - mother nature. Again, he found a low-cost source by getting his eggshell membranes from an industrial farm that sold the yokes for medical and cosmetics experimentation.

A fraction of the cost

Two years later, he upped the ante and replaced the graphene in supercapicitor electrodes. Although graphene is considered the best nanomaterial for the job, it's expensive and costs as much as $2,000 per gram. Mitlin eventually developed a process to convert industrial hemp waste into a graphene-like nanomaterial, which could also be made for a fraction of the cost - less than $500 per ton - and actually outperform graphene.

"If you look at hemp waste, it makes sheets with high surface area - and that's very conducive," he told an audience last August when he presented his latest research at the National Meeting of the American Chemical Society (ACS) in San Francisco. (Watch his press conference.) "Our device's electrochemical performance is on par with or better than graphene-based devices," Mitlin said, who's now with Clarkson University in New York. "The key advantage is that our electrodes are made from biowaste using a simple process, and therefore, are much cheaper - a thousandth of the price."

A cheap and unlimited supply

It's shouldn't be a surprise that Mitlin found an industrial facility that processed hemp into rope, clothing, oil, and plastic just miles away from his Alberta home. That's where he found tons of leftover bast fiber just siting in a large storage area, "They don't know what to do with it," He told BBC News. "It was a waste product they were almost paying to take away."