Institute Of Nuclear Energy Research (Long Tang, Taoyuan, TW) scientists Chun Ching Chien, King Tsai Jeng, Shean Du Chiou and Su Hsine Lin reveal preparations of noble metal catalysts, i.e., platinum and platinum alloys, on suitable supports with nanonetwork structures and high catalytic efficiencies in U.S. Patent Application 20090312180. The prepared catalysts have characteristics of a three-dimensional (3-D) nano network with rigid structure, uniform hole-size and high surface area. In addition, the platinum and platinum alloys catalysts prepared by the Chien et al’s methods will significantly improve the performances of direct methanol fuel cells (DMFCs) and proton exchange membrane fuel cells (PEMFCs) due to robust structure, resistance to recombination, and high catalytic surfaces.
A compact structure of a monolayer or a few layers is formed by self-assembly of organic polymer, e.g., polystyrene (PS), nanospheres or inorganic, i.e., silicon dioxide (SiO2), nanospheres on a support surface. In the void spaces of such a compact arrangement, catalyst is formed by filling with catalyst metal ion-containing aqueous solution and reduced by chemical reduction, or formed by vacuum sputtering.
When using organic polymer nanospheres as the starting or structure-directing material, the polymer particles are removed by burning at a high temperature and the catalyst having a nanonetwork structure is obtained. In the case of using silicon dioxide nanospheres as the starting material, silicon dioxide particles are dissolved with hydrofluoric acid solution and evaporated away leading to formation of a similar nanonetwork structure made of catalyst.
The catalysts prepared by these methods possess characteristics of robust in structure, uniform in hole size and high in catalytic surface area. Their main applications include uses as catalysts in direct methanol and proton exchange membrane fuel cells, as well as in chemical reactors, fuel reformers, catalytic converters, etc.
Polystyrene nanospheres or silicon dioxide nanospheres are used as the starting or structure-directing material to form a perfectly arranged, layered structure through a self-assembly process on a support. The catalyst is then formed and filled in the void spaces of the layered structure by chemical reduction or vacuum sputtering. Removing the starting material by means of burning or chemical dissolution, a catalyst with nanonetwork structure is obtained.
Due to the advancement of nanotechnologies, nanostructures can be readily fabricated. Briefly, inorganic nanoparticles are used as a precursor and mixed with organic polymer to form a homogeneous thermoplastics compound. The organic polymer is then removed by sintering at a high temperature and a nanostructure is formed. However, in general these nanostructures are suitable for used as catalyst supports only rather than as catalysts. It would be very beneficial if a catalyst itself can be fabricated into a nanostructure with excellent resistances to recombination, recrystallization and sintering while providing high surface area and high catalytic efficiency.
In conventional preparation of platinum catalysts for DMFC and PEMFC applications, high surface area carbon supports, such as Cabot Vulcan XC-72 and Chevron Shawinigan, are commonly used. In general, catalyst metal in ions or colloidal sols are adsorbed to carbon support surfaces and reduced by chemical reactions. High temperature reduction using hydrogen gas is also commonly used. However, such prepared nanocatalysts suffer from drawbacks of re-construction, re-crystallization and sintering when in use to form larger particles and substantially lose their catalytic surfaces. These give rise to significantly lower catalytic efficiencies and shorter service lives. Novel approaches are needed to prepare and stabilize catalysts under all application conditions, which researchers from the Institute Of Nuclear Energy Research believe they have succeeded in developing.
In fact, using some Institute Of Nuclear Energy Research nanomaterials, e.g., polystyrene nanospheres and silicon dioxide nanospheres, as structure-directing agents, do provide a new approach to achieve this goal. These nanospheres readily form closely packed, layered structures of one to several layers on a smooth support surface when applied at diluted conditions. With these unique characteristics of such nanomaterials, the researchers are able to prepare novel catalysts with nanonetwork structures on suitable supports that are totally different from those of the conventional nano catalysts. The advantages are to overcome the drawbacks encountered by conventional nanocatalysts and provide more durable and efficient fuel cell catalysts.
Catalysts play key roles in most of the important chemical reactions, including syntheses of organic compounds, reforming production of hydrogen from methanol, natural gas and gasoline, catalytic conversion of carbon monoxide, nitrogen oxides and unburned fuels, etc. In particular, platinum and platinum alloys are indispensable catalysts for direct methanol and proton exchange membrane fuel cells with respect to electro-reduction of oxygen and electro-oxidation of fuel.
The world fuel cell market is estimated at $8.8 billion for 2009 and is expected to achieve a value of more than $14 billion by 2014 showing a compound average growth rate of about 9.6% according to iRAP report Fuel Cells, Hydrogen Energy and Related Nanotechnology—A Global Industry and Market Analysis. The still infant fuel cell and hydrogen energy industry is highly fragmented. Worldwide about 3870 organizations are involved in research or the supply chain for fuel cells, hydrogen energy and related nanotechnology. Those organizations spent an estimated $8.4 billion in 2008. More than 2180 organizations are involved in nanotechnology research and development related to fuel cells and hydrogen energy and are estimated to have spent a total of $4.7 billion for fuel cells and hydrogen energy incorporating nanotechnology in 2008. Of that $4.7 billion, about $2 billion represents the value of nanotechnology for fuel cells and hydrogen energy separate from all other expenditures. The $2 billion includes both nanomaterials incorporated into fuel cells and the cost of nanotechnology research directed at the fuel cell industry.
