GM Reveals Durable Mesoporous Electrically Conductive Titanium Metal Oxide Nano-Catalyst Supports for Fuel Cell

Mesoporous Electrically Conductive Metal Oxide Catalyst Supports

 FIG. 3 is a transmission electron microscopy image showing the mesoporous morphology of the catalyst support material after the first heat treatment but before the second heat treatment of the synthesis procedure. General Motors scientists have developed a titanium dioxide (TiO₂) catalyst support material for proton exchange membrane fuel cells that is superior to carbon based catalysts supports. The TiO₂ catalyst support material may be optionally being doped with a transition metal element.

According to  GM Global Technology Operations, Inc. (Detroit, MI) researchers in U.S. Patent Application 20090312181, the catalyst support material exhibits an electrical conductivity comparable to widely-used carbon materials. This is because the TiO₂ present is primarily arranged in its rutile crystalline phase. Furthermore, a mesoporous morphology provides the catalyst support material with appropriate porosity and surface area properties such that it may be utilized as part of a fuel electrode (anode and/or cathode).  

 According to researchers Thanh Ba Do,  Mei Cai, and Martin S. Ruthkosky, the TiO₂-based catalyst support material may be formed using a template method in which precursor titanium and transition metal alkoxides are hydrolyzed onto the surface of a latex template, dried, and heat treated.  The mesoporous catalyst material has pore diameters in the range of about two nanometers to about fifty nanometers. The catalyst support material may be made with titanium tetraisopropoxide and niobium pentaethoxide. Nano-polystyrene (PS) particles are used in manufacturing the catalyst support material. 

The support is suitable for application as a catalyst support where the enhanced electrical conductivity imparted by subsequent processing is not a requirement. Examples of catalyst particles that can be supported on such a support material include platinum, palladium, and platinum alloys such as those containing molybdenum, cobalt, ruthenium, nickel, tin, or other suitable transition metals.   

 Fuel cells--such as proton exchange membrane fuel cells--have generally been outfitted with electrocatalyst-containing electrode layers that include finely divided carbon powders as a catalyst support material. But the highly acidic and otherwise corrosive nature of fuel cells often degrades these carbon materials; incidents that can disturb optimal fuel cell operating conditions and lead to, among others, efficiency losses.

Catalyst support materials having TiO₂ as their main constituent, on the other hand, are more corrosion resistant than typical carbon powders. But these materials are not quite as electrically conductive as carbon and have proven difficult to synthesize with a morphology (surface characteristics) that meets the minimal desired criteria associated with fuel cell electrode applications. To address these and other related issues, General Motors scientists developed a synthesis technique that can fabricate a TiO₂-based catalyst support material that exhibits a mesoporous morphology and an electrical conductivity comparable to that of its carbon counterpart. This material can thus help improve the service life of fuel cell electrodes as well as the efficiency of the fuel cell.

While these mesoporous rutile TiO₂ materials were devised for proton exchange membranes fuel cell applications they may be used in other catalyst applications where their porosity, specific surface area, and low electrical resistivity may be utilized.

FIG. 2 is flowchart diagramming some of the steps for synthesizing the catalyst support material of GM's invention. 

FIG. 4 is a transmission electron microscopy image showing the presence of three pore types in the catalyst support material shown in FIG. 3.  The resulting catalyst support material can now be said to have the general formula Ti_0.92 Nb_0.08 O_2.04 due to the presence of TiO₂ and Nb₂O₅, and its mesoporous morphology can be seen in the TEM image of FIG. 3. FIG. 4 likewise shows a TEM image identifying the three types of pores exhibited by the material that help it achieve this morphology. As can be seen, (i.) widely open pores, (ii.) ink-pot open pores, and (iii.) closed pores are all present