A new electrocatalyst developed at Brookhaven’s National Laboratory can finally make hydrogen fuel cell vehicles a viable reality and can bring cheap electricity for all (hopefully). The researchers discovered how a new form of catalytic nickel-molybdenum-nitride can successfully replace platinum, which sells at $50,000 a kilo these days.
“We wanted to design an optimal catalyst with high activity and low costs that could generate hydrogen as a high-density, clean energy source,” said Brookhaven Lab chemist Kotaro Sasaki, who first conceived the idea for this research. “We discovered this exciting compound that actually outperformed our expectations.”
Burning hydrogen doesn’t emit any carbon, but storing it is indeed the greatest challenge ever. In this respect, water is a very good storage medium, but breaking it apart takes a lot of energy, which can be considered as being taken from the overall efficiency of the system. The most efficient catalyst in water splitting so far has been platinum, but, as I said earlier, the technology’s main drawback is not its performance, but its highly prohibitive price.
“We needed to create high, stable activity by combining one non-noble element that binds hydrogen too weakly with another that binds too strongly,” said James Muckerman, the senior chemist who led the project. “The result becomes this well-balanced Goldilocks compound – just right.
On the other hand, nickel costs $20 a kilo and molybdenum just $32, which translates into a composite material 1000 times cheaper than platinum. Previous attempts at using nickel and molybdenum pretty much failed, as the final material didn’t come up to the efficiency expectations of the scientists.
For the first time ever, they introduced nitrogen to alter the electronic states of the nickel-mylobdenum. This method had been used before in bulk materials, but never at the nanoscale level.
By subjecting the nickel-molybdenum compound to a high-temperature ammonia environment, the scientists infused it with nitrogen and also turned the compound particles into two-dimensional nanosheets, thus increasing the total surface area available for reaction. “Nitrogen made a huge difference – it expanded the lattice of nickel-molybdenum, increased its electron density, made an electronic structure approaching that of noble metals, and prevented corrosion.”
The resulting cheap catalytic material proved itself able to help splitting water almost as well as platinum, and was also stable compared to previous platinum alternatives.