Scientists at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory have developed a new lower cost electro catalyst that addresses the cost problems by generating hydrogen gas from water cleanly and with much more affordable materials.

The novel form of catalytic nickel-molybdenum-nitride is described in a paper published online May 8, 2012 in the journal Angewandte Chemie, International Edition.

Hydrogen gas offers one of the most promising sustainable fuel alternatives. But traditional methods of producing pure hydrogen face significant challenges in unlocking its full potential, either by releasing carbon dioxide when its sourced from natural gas or requiring rare and expensive chemical elements such as platinum hwne sourced from water by electrolysis.

The new electro catalyst surprised the scientists with its high-performing nanosheet structure, introducing a new model for effective hydrogen catalysis.

Brookhaven's Nickel Molybdenum Nitride Catalyst for Splitting Water

Brookhaven Lab chemist Kotaro Sasaki, who first conceived the idea for this research explains, “We wanted to design an optimal catalyst with high activity and low costs that could generate hydrogen as a high-density, clean energy source. We discovered this exciting compound that actually outperformed our expectations.”

Background – Water provides an ideal source of pure hydrogen its abundant and free of harmful CO2 gas byproducts. The electrolysis of water, or splitting water (H2O) into oxygen (O2) and hydrogen (H2), requires electric current and an efficient catalyst to break chemical bonds while shifting around the protons and electrons. To justify the effort, the amount of energy put into the reaction must be as small as possible while still exceeding the minimum required by thermodynamics, a figure associated with what is called ‘overpotential’.

For a catalyst to facilitate an efficient reaction, it must combine high durability, high catalytic activity, and high surface area. The strength of an element’s bond to hydrogen determines its reaction level, if its too weak, and there’s no activity; too strong, and the initial activity poisons the catalyst.  Unfortunately, the strongest traditional candidate for electro catalytic activity, platinum, comes with a prohibitive price tag.

Platinum is the top material for electro catalysis, combining low overpotential with high activity for the chemical reactions during water-splitting. But with rapidly rising costs, already hovering around $50,000 per kilogram, platinum and other noble metals discourage widespread use
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James Muckerman, the senior chemist who led the project takes up the explanation with, “People love platinum, but the limited global supply not only drives up price, but casts doubts on its long-term viability. There may not be enough of it to support a global hydrogen economy.”
The principal metals in the new compound developed by the Brookhaven team are both abundant and cheap: $20 per kilogram for nickel and $32 per kilogram for molybdenum – that’s 1000 times less expensive than platinum. But with energy sources, performance is often a more important consideration than 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. The result becomes this well-balanced Goldilocks compound – just right.”  That simple explanation makes clear what the team managed to do.

In the new catalyst, nickel takes the reactive place of platinum, but it lacks a comparable electron density. The scientists needed to identify complementary elements to make nickel a viable substitute, and they introduced metallic molybdenum to enhance its reactivity. While effective, it still couldn’t match the performance levels of platinum.

Now research associate Wei-Fu Chen, the paper’s lead author takes up the explanation, “We needed to introduce another element to alter the electronic states of the nickel-molybdenum, and we knew that nitrogen had been used for bulk materials, or objects larger than one micrometer. But this was difficult for nanoscale materials, with dimensions measuring billionths of a meter.”

The scientists expected the applied nitrogen to modify the structure of the nickel-molybdenum, producing discrete, sphere-like nanoparticles. But they discovered something else.

Subjecting the compound to a high-temperature ammonia environment infused the nickel-molybdenum with nitrogen, but it also transformed the particles into unexpected two-dimensional nanosheets. The nanosheet structures offer highly accessible reactive sites and more reaction potential.

Using a high-resolution transmission microscope in Brookhaven Lab’s Condensed Matter Physics and Materials Science Department, as well as x-ray probes at the National Synchrotron Light Source, the scientists determined the material’s 2D structure and probed its local electronic configurations.

“Despite the fact that metal nitrides have been extensively used, this is the first example of one forming a nanosheet,” Chen said. “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 new Brookhaven catalyst performs nearly as well as platinum, achieving electro catalytic activity and stability unmatched by any other non-noble metal compounds. “The production process is both simple and scalable,” Muckerman said, “making nickel-molybdenum-nitride appropriate for wide industrial applications.”

While this catalyst does not represent a complete solution to the challenge of creating affordable hydrogen gas, it does offer a major reduction in the cost of essential equipment. The team emphasized that the breakthrough emerged through fundamental exploration, which allowed for the surprising discovery of the nanosheet structure.

This is really good news.  Currently most industrial hydrogen is sourced from natural gas so coming up with a competitive water based source is quite useful.  Even as natural gas is at a very low price, the hydrogen needed could grow if the price could be driven furthr down.

For many experimenters aluminum has been the electro catalyst of choice.  Getting the new Brookhaven material out into the hands of the thousands of experimenters making Browns Gas.  The new material could be a step into much more and more efficient hydrogen use.


Comments

1 Comment so far

  1. Roy on June 14, 2012 4:18 PM

    I now have a plan for a hydrogen/oxygen water cooled combustor that can make super heated steam to drive a standard steam turbine without melting the combustor parts or the turbine. (It could work for NG also) It’ll have a much higher efficiency than a conventional gas plant, not having to drive nitrogen, and with no moving parts but the gas. I’m working on a table top demo unit now.
    With a heating value for H2 of around 120,000 BTUs/Kg, H2 production costs are going to have to come WAY down to compete with $3/MMBTU natural gas. (Of course you’ll have to add the cost of CO2 sequestation which is high for now to compare apples to apples.)But just the same, H2 costs have a long way to go.

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