{"72179":{"#nid":"72179","#data":{"type":"news","title":"Platinum Nanocrystals Boost Catalytic Activity","body":[{"value":"\u003Cp\u003EA 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.  \u003C\/p\u003E\n\u003Cp\u003EThe new platinum nanocrystals, whose \u0022tetrahexahedral\u0022 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.  \n\u003C\/p\u003E\n\u003Cp\u003E\u0022If we are going to have a hydrogen economy, we will need better catalysts,\u0022 said Zhong Lin Wang, a Regents Professor in the School of Materials Science and Engineering at the Georgia Institute of Technology.  \u0022This 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.\u0022\n\u003C\/p\u003E\n\u003Cp\u003EThe 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 \u0022square wave\u0022 electrical potential applied to them.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022This electrochemical technique is vital to producing such tetrahexahedral platinum nanocrystals,\u0022 said Shi-Gang Sun, an Eminent Professor in the College of Chemistry and Chemical Engineering at the Xiamen University in China.  \u0022The technique used to produce the new platinum nanostructures may also have applications to other catalytic metals.\u0022\n\u003C\/p\u003E\n\u003Cp\u003EThe 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 were reported in the May 4 issue of the journal \u003Cem\u003EScience\u003C\/em\u003E.\n\u003C\/p\u003E\n\u003Cp\u003EPlatinum 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 \u0022low-index\u0022 facets, characterized by the numbers {100} or {111}.  Because of their higher catalytic activity, \u0022high-index\u0022 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.\n\u003C\/p\u003E\n\u003Cp\u003EThe nanocrystals produced by the U.S.-Chinese team have high energy surfaces that include numerous \u0022dangling bonds\u0022 and \u0022atomic steps\u0022 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.\n\u003C\/p\u003E\n\u003Cp\u003EThough the process must still be fine-tuned, the researchers have learned to control the size of the particles by varying the processing conditions.  They are able to control the size such that only 4.5 percent of the nanocrystals produced are larger or smaller than the target size.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022In nanoparticle research, two things are important: size control and shape control,\u0022 said Wang.  \u0022From a purity point of view, we have been able to obtain a high yield of nanocrystals whose shape was a real surprise.\u0022\n\u003C\/p\u003E\n\u003Cp\u003EDepending on conditions, the new nanocrystals can be as much as four times more catalytically active per unit area than existing commercial catalysts. But since the new structures tested are more than 20 times larger than existing platinum catalysts, they require more of the metal - and hence are less active per unit weight. \n\u003C\/p\u003E\n\u003Cp\u003E\u0022We need to find a way to make these nanocrystals smaller while preserving the shape,\u0022 Wang noted.  \u0022If we can reduce the size through better control of processing conditions, we will have a catalytic system that would allow production of hydrogen with greater efficiency.\u0022 \n\u003C\/p\u003E\n\u003Cp\u003EProduction of the new crystals begins with polycrystalline platinum spheres about 750 nanometers in diameter that are electrodeposited onto a substrate of amorphous - also known as \u0022glassy\u0022 - carbon.  Placed in an electrochemical cell with ascorbic acid and sulfuric acid, the spheres are then subjected to \u0022square wave\u0022 potential that alternates between positive and negative potentials at a rate of 10 to 20 Hertz.  \n\u003C\/p\u003E\n\u003Cp\u003EThe electrochemical oxidation-reduction reaction converts the spheres to smaller nanocrystals over a period of time ranging from 10 to 60 minutes.  The role of the carbon substrate isn\u0027t fully understood, but it somehow enhances the uniformity of the nanocrystals.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022The key to producing this shape is to tune the voltage and the time period under which it is applied,\u0022 Sun noted.  \u0022By changing the experimental conditions, we can control the size with a high level of uniformity.\u0022\n\u003C\/p\u003E\n\u003Cp\u003EScanning electron microscopy shows that the sizes average 81 nanometers in diameter, with the smallest just 20 nanometers.  The microscopy also found that the structures were composed of single crystals with no dislocations.\n\u003C\/p\u003E\n\u003Cp\u003E\u0022Not only do we have a beautiful shape - which was observed for the first time in this research - but we also have a very valuable catalyst,\u0022 Sun added.  \u0022And because these nanocrystals are stable, the shape is preserved after the catalytic reaction, which will allow us to use the same nanocrystals over and over again.\u0022\n\u003C\/p\u003E\n\u003Cp\u003EIn addition to Sun and Wang, the research team included Na Tian and Zhi-You Zhou from the College of Chemistry and Engineering at Xiamen University in China and Yong Ding from the School of Materials Science and Engineering at Georgia Tech in the United States. \n\u003C\/p\u003E\n\u003Cp\u003E\u003Cstrong\u003EResearch News \u0026amp; Publications Office\u003Cbr \/\u003E\nGeorgia Institute of Technology\u003Cbr \/\u003E\n75 Fifth Street, N.W., Suite 100\u003Cbr \/\u003E\nAtlanta, Georgia  30308  USA\u003C\/strong\u003E\n\u003C\/p\u003E\n\u003Cp\u003E\u003Cstrong\u003EMedia Relations Contact\u003C\/strong\u003E: John Toon (404-894-6986); E-mail: (\u003Ca href=\u0022mailto:jtoon@gatech.edu\u0022\u003Ejtoon@gatech.edu\u003C\/a\u003E).\n\u003C\/p\u003E\n\u003Cp\u003E\u003Cstrong\u003ETechnical Contacts\u003C\/strong\u003E: Zhong Lin Wang (404-894-8008); E-mail: (\u003Ca href=\u0022mailto:zhong.wang@mse.gatech.edu\u0022\u003Ezhong.wang@mse.gatech.edu\u003C\/a\u003E) or Shi-Gang Sun; E-mail: (\u003Ca href=\u0022mailto:sgsun@xmu.edu.cn\u0022\u003Esgsun@xmu.edu.cn\u003C\/a\u003E).\n\u003C\/p\u003E\n\u003Cp\u003E\u003Cstrong\u003EWriter\u003C\/strong\u003E: John Toon\n\u003C\/p\u003E","summary":null,"format":"limited_html"}],"field_subtitle":[{"value":"New form of catalytic metal could improve hydrogen production"}],"field_summary":[{"value":"A research team composed of electrochemists and materials scientists 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.","format":"limited_html"}],"field_summary_sentence":[{"value":"A new platinum structure could improve catalysis"}],"uid":"27303","created_gmt":"2007-05-04 00:00:00","changed_gmt":"2016-10-08 03:03:29","author":"John Toon","boilerplate_text":"","field_publication":"","field_article_url":"","dateline":{"date":"2007-05-04T00:00:00-04:00","iso_date":"2007-05-04T00:00:00-04:00","tz":"America\/New_York"},"extras":[],"hg_media":{"72180":{"id":"72180","type":"image","title":"Platinum nanocrystal close-up","body":null,"created":"1449177434","gmt_created":"2015-12-03 21:17:14","changed":"1475894651","gmt_changed":"2016-10-08 02:44:11"},"72181":{"id":"72181","type":"image","title":"Platinum nanocrystal","body":null,"created":"1449177434","gmt_created":"2015-12-03 21:17:14","changed":"1475894651","gmt_changed":"2016-10-08 02:44:11"}},"media_ids":["72180","72181"],"related_links":[{"url":"http:\/\/www.mse.gatech.edu\/","title":"Georgia Tech School of Materials Science and Engineering"},{"url":"http:\/\/www.mse.gatech.edu\/FacultyStaff\/MSE_Faculty_researchbios\/Wang\/wang.html","title":"Zhong Lin Wang"}],"groups":[{"id":"1188","name":"Research Horizons"}],"categories":[{"id":"141","name":"Chemistry and Chemical Engineering"},{"id":"144","name":"Energy"},{"id":"149","name":"Nanotechnology and Nanoscience"},{"id":"135","name":"Research"}],"keywords":[{"id":"2506","name":"catalyst"},{"id":"7287","name":"electrochemical"},{"id":"7562","name":"nanocrystal"},{"id":"7531","name":"platinum"}],"core_research_areas":[],"news_room_topics":[],"event_categories":[],"invited_audience":[],"affiliations":[],"classification":[],"areas_of_expertise":[],"news_and_recent_appearances":[],"phone":[],"contact":[{"value":"\u003Cstrong\u003EJohn Toon\u003C\/strong\u003E\u003Cbr \/\u003EResearch News \u0026amp; Publications Office\u003Cbr \/\u003E\u003Ca href=\u0022http:\/\/www.gatech.edu\/contact\/index.html?id=jt7\u0022\u003EContact John Toon\u003C\/a\u003E\u003Cbr \/\u003E\u003Cstrong\u003E404-894-6986\u003C\/strong\u003E","format":"limited_html"}],"email":["jtoon@gatech.edu"],"slides":[],"orientation":[],"userdata":""}}}