Fuel cells and fuel cell catalysts

#The invention generally relates to fuel cells and catalysts for fuel cells.

#Fuel cells are electrochemical cells in which a free energy change resulting from a fuel oxidation reaction is converted into electrical energy. Applications for fuel cells include battery replacement, mini and microelectronics, car engines, power plants, and many others. One advantage of fuel cells is that they are substantially pollution-free.

#In hydrogen fuel cells, hydrogen gas is oxidized to form water, with a useful electrical current produced as a byproduct of the oxidation reaction. A solid polymer membrane electrolyte layer may be used to separate the hydrogen fuel from the oxygen. The anode and cathode are arranged on opposite faces of the membrane. Electron flow between the anode and cathode layers of the membrane electrode assembly may be exploited to provide electrical power. Hydrogen fuel cells are impractical for many applications, however, because of difficulties related to storing and handling hydrogen gas.

#FIG. 1 is a schematic of an exemplary fuel cell of the invention;

#FIG. 2 is a flowchart illustrating an exemplary method of making a catalyst of the invention;

#FIGS. 3(a) and (b) are data plots illustrating cell activity and power, respectively, vs. formic acid concentration for a first exemplary formic acid fuel cell of the invention;

#The schematic of FIG. 1 shows an exemplary direct organic fuel cell of the invention generally at 10. The fuel cell 10 includes an anode 12, a solid polymer proton-conducting electrolyte 14, and a gas diffusion cathode 16. The anode 12 is enclosed in an anode enclosure 18, while the cathode 16 is enclosed in a cathode enclosure 20. When an electrical load (not shown) is connected between the anode 12 and cathode 16 via an electrical linkage 22, electro-oxidation of an organic fuel occurs at the anode 12 and electro-reduction of an oxidizer occurs at the cathode 16.

#The occurrence of different reactions at the anode 12 and cathode 16 gives rise to a voltage difference between the two electrodes. Electrons generated by electro-oxidation at the anode 12 are conducted through the linkage 22 and are ultimately captured at the cathode 16. Hydrogen ions or protons generated at the anode 12 are transported across the membrane electrolyte 14 to the cathode 16. Thus, a flow of current is sustained by a flow of ions through the cell and electrons through the linkage 22. This current may be exploited to power an electrical device, for instance.

#The anode 12, solid polymer electrolyte 14, and cathode 16 are preferably a single multi-layer composite structure that may be referred to as a membrane electrode assembly (“MEA”). Preferably the solid polymer electrolyte 14 is a proton-conducting cation exchange membrane that contains an anionic sulfate, such as the perfluorinated sulfonic acid polymer membrane commercially available under the registered trademark NAFION from DuPont Chemical Co., Delaware. NAFION is a copolymer of tetrafluoroethylene and perfluorovinylether sulfonic acid. Other membrane materials can also be used, with examples including membranes of modified perfluorinated sulfonic acid polymer, polyhydrocarbon sulfonic acid, membranes containing other acidic ligands and composites of two or more kinds of proton exchange membranes.