Monday, May 14, 2012

Another New Water-Splitting Hydrogen Catalyst


 Another New
Hydrogen Catalyst

The above team of scientists at the U.S. Department of Energy’s (DOE) Brookhaven National Laboratory have developed a new catalyst to cheaply and effectively split water into Hydrogen and Oxygen. This one is based on nickel-molybdenum-nitride but the real secret is microscopic with a surface structure in the form of nano sheets.

The Magic is in the Surface Structure

The structure of the nano sheets of the metal alloy surprised scientists with its high-performance as a catalyst. The nanosheet structures offer highly accessible reactive sites – consider the surface area difference between bed sheets laid out flat and those crumpled up into balls – and therefore more reaction potential.

High efficiency catalyst have been hard to find. An electro catalyst to to split water needs:

(1)    To be highly durable and not dissolve away too quickly,
(2)    Have high catalytic activity i.e. uses little electricity to do the job,
(3)    Have a high surface area, and
(4)    Be of reasonably priced.

The strength of an element’s bond to hydrogen determines its reaction level – too weak, and there’s no activity; too strong, and the massive initial activity poisons the catalyst.

Platinum is the standard for electro catalysis. It combines low over-potential with high activity. With a price tag of around $50,000 per Kg platinum and other exotic metals are un-economic.

The metals in the new compound are both abundant and cheap at around $20 per Kg for nickel and $32 per Kg for molybdenum. It checks out at around a thousand times less expensive than platinum.

Efficiency Even More Important than Price

Nickel takes the reactive place of platinum in this catalyst, but lacks electron density. Molybdenum is able to enhance its reactivity. While effective, it still couldn’t match the performance levels of platinum. The team used Nitrogen, and expected the applied nitrogen to modify the structure of the nickel-molybdenum, producing discrete, sphere-like nano-particles. But they discovered something quite different.

Exposing the compound to high-temperature ammonia infused the nickel-molybdenum with nitrogen. It also changed the particles into unexpected two-dimensional nanosheets.

The new catalyst performs nearly as well as platinum but at one thousandth the price. The team emphasise that their new catalyst does not represent a complete solution to the challenge of creating affordable hydrogen gas, it does however offer a major reduction in the cost of essential equipment.


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