(214e) Highly Dispersed Metal Catalyst for Fuel Cell Electrodes

Xiao, X., Savannah River National Lab
Rhodes, W., Savannah River National Laboratory

Methods are being developed for preparation and quality control of a supported-platinum catalyst with near 100% Pt-dispersion on an electrically-conductive support and characterization of achieved, maximum platinum loading.

One of the most significant barriers to fuel cell commercialization is the cost associated with expensive noble metals used in both anode and cathode electrodes. Further, sub-optimal dispersion with current technology limits electrical current density, affecting performance metrics. Accordingly, the thrust of this research project is to leverage advances in the industrial catalysis arena into the fuel cell arena, which is now verging on wide-spread commercial deployment.

Industrial precious metal catalysts (e.g., platinum, used in Platforming) are in a finely dispersed form; practically dispersed as single atoms or mono layer on porous catalyst supports. This is the optimum; for particle deposition, only atoms on the surface are available for catalytic action. The average ratio of surface atoms to total atoms is used to indicate how well the metal is dispersed, i.e., metal dispersion. A metal dispersion of 1.00 is defined as 100% availability of metal atoms for catalysis. Values less than 100% indicate crystallite growth or a surface interference. The metal dispersion of industrial catalysts is normally measured by interactions with selective probe molecules, indicating the number of reachable metal atoms, which correlates with catalyst activity.

Disassociate adsorption of oxygen or fuel is the rate-limiting step in fuel cell chemistry. Electrocatalytic activity could be enhanced remarkably simply by effectively dispersing noble metals within the catalyst support. Metal dispersion increases by 10 to 100 times if nano particles (10-100 nm) are dispersed as single atoms or as a mono layer. Consequently, the amount of noble metals could be reduced by the same factor while maintaining the same catalytic activity. To this end, highly-dispersed platinum catalysts on the electrical conductive porous supports are studied for fuel cell electrodes. The finely dispersed metal shall be in sub-nanometer scale and ultimately be single atom or mono layer, markedly reducing the precious metal requirement for fuel cell application.

In summary, to greatly reduce the quantity of requisite platinum group metal (PGM), a novel sub-nano scale manufacturing technique is proposed. Specifically, the electrode material is being prepared by loading a metal active component onto a high surface area support, resulting in novel sub-nano scale catalyst architecture. The metal loading and dispersion shall be subsequently characterized until a 90±10% dispersion is achieved.