Cobalt-graphene catalyst could challenge platinum in fuel cells
18 October 2012
There's a new contender in the race to find an inexpensive alternative to platinum catalysts for hydrogen fuel cells - a graphene sheet covered by cobalt and cobalt-oxide nanoparticles.
Brown University chemist Shouheng Sun and his students have developed a new material — a graphene sheet covered by cobalt and cobalt-oxide nanoparticles — that can catalyse the oxygen reduction reaction nearly as well as platinum does and is substantially more durable.
The oxygen reduction reaction occurs on the cathode side of a hydrogen fuel cell. Oxygen functions as an electron sink, stripping electrons from hydrogen fuel at the anode and creating the electrical pull that keeps the current running through electrical devices powered by the cell. "The reaction requires a catalyst, and platinum is currently the best one," said Sun. "But it's very expensive and has a very limited supply, and that's why you don't see a lot of fuel cell use aside from a few special purposes."
Thus far scientists have been unable to develop a viable alternative. A few researchers have developed new catalysts that reduce the amount of platinum required, but an effective catalyst that uses no platinum at all remains elusive.
This new graphene-cobalt material is the most promising candidate yet, the researchers say. It is the first catalyst not made from a precious metal that comes close to matching platinum's properties.
Lab tests performed by Sun and his team showed that the new graphene-cobalt material was a bit slower than platinum in getting the oxygen reduction reaction started, but once the reaction was going, the new material actually reduced oxygen at a faster pace than platinum. The new catalyst also proved to be more stable, degrading much more slowly than platinum over time. After about 17 hours of testing, the graphene-cobalt catalyst was performing at around 70 percent of its initial capacity. The platinum catalyst the team tested performed at less than 60 percent after the same amount of time.
Cobalt is an abundant metal, readily available at a fraction of what platinum costs. Graphene is a one-atom-thick sheet of carbon atoms arranged in a honeycomb structure. Developed in the last few years, graphene is renowned for its strength, electrical properties, and catalytic potential.
Sun and his team are optimistic that with more study their material could one day be a suitable replacement for platinum catalysts. "Right now, it's comparable to platinum in an alkaline medium," Sun said, "but it's not ready for use yet. We still need to do more tests."