Scientists have built a new electrocatalyst for fuel-cell vehicles that uses palladium instead of carbon to protect the expensive layer of platinum needed to drive a cell’s reactions, according to the U.S. Department of Energy’s Brookhaven National Laboratory.
In current fuel-cell technology, normal stop-and-go driving wears down the platinum catalyst, causing its reactivity to plummet over time. Researchers see this as one of the major hurdles to large-scale production and use of fuel-cell technology.
But according to Brookhaven chemist Radosalve Adzic, a palladium or palladium-gold alloy nanoparticle core has proved to be a worthy protector of the precious metal in lab tests.
“Our studies of the structure and activity of this catalyst — and comparisons with platinum-carbon catalysts currently in use — illustrate that the palladium core ‘protects’ the fine layer of platinum surrounding the particles, enabling it to maintain reactivity for a much longer period of time,” he said in a statement.
The research appeared recently in the journal Angewandte Chemie.
Researchers hope that the new catalyst will “greatly enhance the practicality of fuel-cell vehicles and may also be applicable for improving the performance of other metallic catalysts,” according to a statement released by Brookhaven’s Center for Functional Nanomaterials.
“In conventional fuel-cell catalysts, the oxidation and reduction cycling — triggered by changes in voltage that occur during stop-and-go driving — damages the platinum. Over time, the platinum dissolves, causing irreversible damage to the fuel cell,” researchers said.
“In the new catalyst, palladium from the core is more reactive than platinum in these oxidation and reduction reactions. Stability tests simulating fuel cell voltage cycling revealed that, after 100,000 potential cycles, a significant amount of palladium had been oxidized, dissolved, and migrated away from the cathode. In the membrane between the cathode and anode, the dissolved palladium ions were reduced by hydrogen diffusing from the anode to form a ‘band,’ or dots.”
The platinum, the most expensive and rare metal needed to make fuel cells, remained “almost unaffected, except for a small contraction of the platinum monolayer.”
“This indicates the excellent durability of this electrocatalyst, especially when compared with simpler platinum-carbon catalysts, which lose nearly 70 percent of their reactivity after much shorter cycling times,” Adzic said. “This level of activity and stability indicates that this is a practical catalyst. It exceeds the goal set by DOE for 2010-2015 and it can be used for automotive applications.”