ZPEnergy.com - Platinum nanocrystals boost catalytic activity for fuel oxidation, hydrogen prod

A research team composed of electrochemists and materials scientists from two continents has produced a new form of the industrially-important metal platinum: 24-facet nanocrystals whose catalytic activity per unit area can be as much as four times higher than existing commercial platinum catalysts.

The new platinum nanocrystals, whose "tetrahexahedral" structure had not previously been reported in the metal, could improve the efficiency of chemical processes such as those used to catalyze fuel oxidation and produce hydrogen for fuel cells.

"If we are going to have a hydrogen economy, we will need better catalysts," said Zhong Lin Wang, a Regents Professor in the School of Materials Science and Engineering at the Georgia Institute of Technology. "This new shape for platinum catalyst nanoparticles greatly improves their activity. This work also demonstrates a new method for producing metallic nanocrystals with high-energy surfaces."

The new nanocrystals, produced electrochemically from platinum nanospheres on a carbon substrate, remain stable at high temperatures. Their sizes can be controlled by varying the number of cycles of "square wave" electrical potential applied to them.

"This electrochemical technique is vital to producing such tetrahexahedral platinum nanocrystals," said Shi-Gang Sun, an Eminent Professor in the College of Chemistry and Chemical Engineering at the Xiamen University in China. "The technique used to produce the new platinum nanostructures may also have applications to other catalytic metals."

The research was supported by the Natural Science Foundation of China, Special Funds for Major State Basic Research Project of China and the U.S. National Science Foundation. Details will be reported in the May 4 issue of the journal Science.

Platinum plays a vital role as a catalyst for many important reactions, used in industrial chemical processing, in motor vehicle catalytic converters that reduce exhaust pollution, in fuel cells and in sensors. Commercially available platinum nanocrystals – which exist as cubes, tetrahedra and octahedra – have what are termed "low-index" facets, characterized by the numbers {100} or {111}. Because of their higher catalytic activity, "high-index" surfaces would be preferable – but until now, platinum nanocrystals with such surfaces have never been synthesized – and therefore have not been available for industrial use.

The nanocrystals produced by the U.S.-Chinese team have high energy surfaces that include numerous "dangling bonds" and "atomic steps" that facilitate chemical reactions. These structures, characterized by {210}, {730} or {520} facets, remain stable at high temperatures – up to 800 degrees Celsius in testing done so far. That stability will allow them to be recycled and re-used in catalytic reactions, Wang said. ...

More: http://www.physorg.com/news97422618.html
Source: Georgia Institute of Technology
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