Practically any kind of crap can boost graphene's properties as a catalyst—even chicken droppings, say the authors of a new tongue-in-cheek study.
Graphene is often hailed as a wonder material—flexible, transparent, light, strong, and electrically and thermally conductive. Such qualities have led researchers worldwide to consider weaving these one-atom-thick sheets of carbon into advanced devices. Scientists have also explored graphene's properties as a catalyst for the kinds of oxygen reduction reactions often used in fuel cells and the hydrogen evolution reactions used to split apart water molecules to generate hydrogen fuel.
To further enhance graphene's catalytic properties, researchers have tried doping it with a variety of elements. Seemingly all such studies have claimed graphene’s catalytic abilities improved, regardless of whether the doping materials had contrasting properties with each other. This is "contrary to what any material scientist might expect," says Martin Pumera, a materials scientist at the University of Chemistry and Technology in Prague.
Before long, scientists began doping graphene with pairs of elements, claiming even better results "due to a 'synergistic effect’” Pumera says. Then, three elements were used for what was called “super-doping." In the new work, Pumera and his colleagues decided to take this argument a step forward "with chicken droppings, a soup of elements," he says. "Why not?"
The researchers started with a combination of graphite oxide and chicken droppings. They heated the mixture and exfoliated it—just as you would exfoliate your skin—to slough off layers of the guano-doped graphene from the mixture.
A colleague of Pumera's had a farm with chickens that supplied the researchers with the droppings. "We chose guano because there is very interesting history surrounding it—countries fighting wars over shit rights, because you can make gunpowder from it," Pumera says.
The researchers found that graphene treated with bird droppings did indeed perform much better at catalyzing oxygen reduction reactions and hydrogen evolution reactions than regular graphene.
Jokingly, the researchers suggested future research could experiment with chicken feed to further improve the quality of guano-doped graphene. “...We believe that bird droppings can become a high-value-added product such as guano was in the past," they satirically write in their study, which appeared online 14 January in the journal ACS Nano.
In summary, "All these papers on doping seem like just a waste of time and resources to me—there just seems to be so much hype around the never-ending story of doping," Pumera says.
Instead, he suggests researchers not only report when doping does not improve graphene's properties, but also when it makes them worse. And he suggests that although some researchers find that graphene's electrocatalytic properties appear to improve even when not doped with metal, they should make sure they did not accidentally contaminate the graphene with trace levels of metal that produced those enhancements.
"The main point of science is to not just report the best materials ever, but to report the truth about how nature works," Pumera says.
The scientists also found very similar improvements with rabbit droppings procured from Pumera's colleague's farm. "But I'm not looking to publish those results," Pumera says. "Don't want to tell the same joke twice."