Page 25 - Introduction to Transfer Phenomena in PEM Fuel Cells

14 Introduction to Transfer Phenomena in PEM Fuel Cells
1.2.1.1. Operating principle of fuel cells
The operating principle of fuel cells varies. It depends on the reagents
(H 2, methanol, etc.), the nature of the electrolyte (solid or liquid), the
residues of the electrochemical reaction and the operating temperature. The
following sections provide an illustration of the operating mode for each
type of battery.
1.2.1.2. Polymer-electrolyte membrane fuel cell (PEMFC)
The polymer-electrolyte membrane fuel cell (also called proton-exchange
membrane (PEM)) provides high power density and low weight, reasonable
cost and low volume. A PEM fuel cell comprises a negatively charged
electrode (anode), a positively charged electrode (cathode and an electrolyte
(the membrane). Hydrogen is introduced at the anode and oxygen at the
cathode. The protons are transported from the anode to the cathode through
the electrolyte membrane, and the electrons flow through an external circuit
represented by the charge. A typical PEM fuel cell has the following
reactions [SPI 07]:

– anode:
+
H (g) ⎯⎯→ 2H (aq) 2e − [1.1]
+
2
– cathode:
1 O(g) 2H (aq) 2e ⎯⎯→ H O [1.2]
−
+
+
+
2 2 2
– overall reaction:
H (g) + 1 O (g) ⎯⎯→ H O(liq) + Electricity + Heat [1.3]
2
2 2 2
These batteries work at a temperature below 100°C for a yield of around
50%. The low operating temperature gives them the ability to start up
relatively quickly. These batteries are developed to power small- and
medium-sized vehicles and fixed installations.

The power range of PEMFCs ranges from a few tens of watts to around
10 megawatts [BLU 07].