Hierarchical Nanostructures for Fuel Cells and Fuel Reforming - Hierarchical Nanostructures for Energy Devices - page 85

materials in these fuel cells and in fuel reforming systems. Fuel reforming
is the process of converting primary fuels, typically alcoholic or higher
hydrocarbons, to a hydrogen-rich gas mixture, which can be effectively
converted by fuel cells. 6-9

d n 3 r 4 n g | 4

5.2 Types of Fuel Cells

5.2.1 Low-temperature Polymer Electrolyte Membrane Fuel
Cells
For the last couple of decades, low-temperature polymer electrolyte mem-
brane or proton exchange membrane fuel cells (PEMFCs) have been iden-
tified as the most promising type of fuel cell, particularly for automotive
applications. Some of the several examples of research initiatives for auto-
motive fuel cell systems are the New Generation of Vehicles program and the
FreedomCAR by the U. S. Department of Energy and the U. S. Council for
Automotive Research (USCAR) in the United States, the Fuel Cells and
Hydrogen Joint Technology Initiative (FCH) launched in 2008 by the
European Union, and the Next-Generation Automobile Fuel Initiative in
Japan. The major goal of these initiatives was, and still is, to enable the
mass production of ecient and affordable hydrogen-powered vehicles
and to establish a hydrogen-supply infrastructure. 10 PEMFCs are typically
favored for automotive applications due to their quick start-up thanks to
their low operating temperature, high power density, simple thermal man-
agement at low operating temperature, and fast response to transient load
dynamics.

.

5.2.1.1 Set-up of Low-temperature Polymer Electrolyte
Membrane Fuel Cells
In PEMFCs, so-called bipolar plates impermeable to the reactants separate
the oxidative and the reductive half reaction. As pictured in Figure 5.1, the
set-up of a basic PEMFC comprises three main components: two flow
channels (often referred to as bipolar or separator plates) and a membrane-
electrode assembly (MEA). The MEA is an assembly of a polymer membrane,
two catalyst layers or electrodes, and two gas diffusion layers (GDLs). On the
anode side of the electrolyte membrane, the half reaction

2H 1 þ 2e

H 2 - (5.1)

takes place and on the cathode side, the half reaction

0.5 O 2 þ 2H 1 þ 2e - H 2 O (5.2)

occurs. The membrane is impermeable to gas species, however, conductive
for protons. Since it is not conductive for electrons, the electrons created on
the anode side are forced to flow through an external circuit to the cathode