(702a) Fuel Cell Electrocatalysts Obtained From Bimodal Nano-Porous Templates

The development of hierarchically-structured electrocatalysts and their supports can effectively address some of the current limitations of fuel cells. It is highly desirable to decrease Pt loading, while increase the obtainable power densities and improve durability of fuel cells. One way to increase the current density is through designing of the electrocatalyst not only with high surface area but also with high amount of accessible three-phase sites. Porous structures can effectively minimize transport limitations, thus increasing the accessibility of the active sites by gas and electrolyte phases. The durability requirements of the fuel cells can be met through improvement of the corrosion stability of the current supports and design of novel corrosion resistant supports. The procedure discussed here allows to create materials that will address both, mass-transport and durability limitations of the fuel cells.

Hierarchical bimodal porous silica templates were obtained through oil/water/surfactant microemulsion templating. The first type of pores is in the range of 10-40 nm and is determined by dimensions of microemulsion droplets. The second type of pores is around 5 nm and is determined by micellar dimensions.

Silica was used as a template to make a range of materials. First, carbon supported platinum electrocatalysts will be discussed. The role of the small nanopores here is to lock Pt particle size in the range of 3-5 nm. Next, non-noble electrocatalysts based on pyridinic and cobalt precursors will be discussed. Here, small nanopores of the silica template play role of sites for creation of Me-Nx centers. Large nanopores are channels necessary for complete infiltration of the template with precursor materials and formation of the catalyst and/or catalyst support backbone. Synthesis conditions, such as amount of precursors, temperature of pyrolysis and conditions of removal of the silica template play an important role in formation of porous structure of electrocatalyst. Ability to control these conditions enables to create electrocatalytic materials with better transport properties.