To make the catalyst, Adzic deposited tiny clusters of platinum and rhodium on tin oxide nanoparticles. In earlier studies, rhodium had been shown to break bonds between carbon atoms, but only if vaporized at high temperatures in an ultrahigh vacuum. The combination of rhodium with the tin oxide allowed it to break these bonds as a solid and at the relatively low temperatures needed for portable fuel cells. The platinum plays a key role in producing protons and electrons from hydrogen atoms in ethanol.
Significant challenges remain before the catalyst can be commercialized in ethanol fuel cells. In addition to facing the challenges of incorporating it into fuel cells and engineering these to produce electricity efficiently at high currents, the researchers will need to find ways to reduce costs. Rhodium is the most expensive precious metal–it’s even more expensive than platinum–so it will either need to be replaced with another element, or techniques must be developed to reduce the amount of rhodium required.
Still, the new catalyst is a significant improvement over previous attempts. “Breaking the carbon-carbon bond at low temperatures is an extremely hard problem,” Herring says. “The fact that [Adzic] is breaking that bond is pretty exciting.” But he adds that “it’s just one step on the pathway toward this dream of a direct ethanol fuel cell.”