Hierarchical Nanostructures for Fuel Cells and Fuel Reforming - Hierarchical Nanostructures for Energy Devices - page 86

d n 3 r 4 n g | 4

Figure 5.1 Polymer electrolyte membrane fuel cell (PEMFC) working principle.

side, thus creating an electric current and closing the circuit. The complete
global reaction reads

.

H 2 þ 0.5O 2 - H 2 O (5.3)

The fuel (hydrogen in this case) and oxidant (typically pure oxygen or
oxygen from air) is provided to the catalyst layer through the GDLs, ensuring
distributed and uniform supply of both reactants. The bipolar plates typi-
cally have four functions: 11 distribution of the fuel and oxidant within the
cell, facilitating water management within the cell, separation of the indi-
vidual cells in the stack, and transporting current away from the cell. They
facilitate the heat management as well, often assisted by additional cooling
plates. By combining individual cells to stacks, the electric power generation
increases, and each bipolar plate confines the anode flow channel and the
cathode flow channel of two adjacent cells, respectively.
The cost of the platinum catalyst in conventional low-temperature,
hydrogen-fed PEMFCs is a major obstacle for the widespread use of mass-
produced fuel cells. A tremendous amount of research has been conducted
to reduce the platinum loading, resulting in platinum loadings in the
membrane-electrode assembly in the order of 0.6-0.8 mg Pt cm 2 , while in-
creasing the power density up to 0.7 W cm 2 at cell voltages as high as 0.7 V at
80 1C and near-ambient pressure, 12 indicating a hydrogen-to-electricity e-
ciency of 58%. 13 The Pt loading-specific power densities of 0.85-1.1 g Pt kW 1