Page 42 - Introduction to Transfer Phenomena in PEM Fuel Cells

Introduction to Hydrogen Technology 31
an external reformer. This type of fuel cell has a zinc tank that regenerates
the fuel. Indeed, zinc is in the form of small granules that will react (they
will be consumed) with the electrode (the anode) by releasing electrons, and
thus forming an electric current; at the cathode, oxygen reacts with the
electrons from the anode, forming potassium zincates K 2ZNO 2 [SME 00].
The efficiency of the system using zinc regeneration is approximately 30 to
50%.
The advantage of this technology (zinc–air) is the remarkably high
specific energy rate. In addition, the cost is relatively low since zinc is an
abundant element.

The disadvantage of this type of battery is that the zinc anode is
consumed by an electrochemical reaction and it must be replaced regularly.
The applications of these batteries are generally dedicated to electric
vehicles, and consumables of electronic devices for military applications.

1.2.1.10. Proton ceramic fuel cell (PCFC)
These are the new types of fuel cells based on the use of a ceramic
electrolyte with high proton conductivity at high temperature and high
energy efficiency [COO 03]. This type of battery is fundamentally different
from other fuel cells, because the transport of protons through the electrolyte
becomes more efficient at high temperatures. PCFC batteries have the same
kinetic and thermal characteristics as an MCFC or SOFC because of their
high operating temperature (~ 700°C) [SPI 07].

1.2.1.11. Bio-fuel cell (BFC) or microbial fuel cell (MFC)
The bio-fuel cell is an electrochemical device that converts biochemical
energy into electrical energy. Indeed, it is a redox reaction of an organic
substrate (glucose, methanol, acetate, etc.) using micro-organisms or
enzymes as catalysts. This type of cell is promising, but long term [LAR 03].
It should be noted that PCFC and BFC batteries are the most recent types of
batteries and they are still in the research and development stage. The direct
methanol (DMFC) or direct ethanol (DEFC) fuel cells directly consume the
hydrogen contained in alcohol. Very compact, they are destined to power
microelectronics and portable tools.