Objectives
• Understand how a fuel cell makes
electricity
– A fuel cell must separate electrons from our
fuel to create electricity
• Examine and assess classroom fuel cells
– Hydrogen production
– Fuel cell testing
Fuel Cells
• Fuel cells are mainly classified
by their electrolyte
– Polymer electrolyte membrane
(PEM) fuel cells
• Also called proton exchange
membrane fuel cells
• deliver high power density
• the advantages of low weight and
volume
• use a solid polymer as an
electrolyte and porous carbon
electrodes containing a platinum
catalyst.
• They need only hydrogen, oxygen
from the air, and water to operate
and do not require corrosive fluids
like some fuel cells
Basic Chemistry
• The chemical reaction within a fuel cell is called an
electrochemical reaction. That just means it requires
the transfer of electrons.
• In a fuel cell, the electrochemical reaction causes the H2
to be oxidized into H+ ions and electrons at the anode:
2H2  4H+ + 4e-
• The electrons are separated and move to form an
electric current.
• They travel to the cathode where the oxygen is reduced:
O2 + 4H+ + 4e-  2 H2O
• The net reaction forms water from the two gases.
2H2 + O2  2 H2O
The Fuel Cell
The fuel cell is the physical structure that makes these
electrochemical reactions happen and captures and utilizes the
current generated by electrons as well.
Two Key Components
• Electrodes catalyze the electrochemical reactions.
• Electrolytes facilitate the transfer of hydrogen ions from the anode
to the cathode.
– In this case the electrolyte is a PEM (polymer electrode
membrane).
Like
Salty
Water
How Fuel Cells Operate:
A Three Stage Process
• The complete fuel cell process may be
divided into three stages:
• Two of these stages involve the chemical
reactions at the electrodes
• The third is the ion conduction through
the electrolyte membrane.
Step 1
At the anode:
• Hydrogen fuel is supplied to
react at the anode.
• Electrons are released to be
conducted through a circuit to
some load.
2H2  4H+ + 4e-
Step 2
Through the electrolyte medium:
• The special membrane allows only hydrogen
ions to diffuse through it. These ions are
transported to the cathode where they react
with oxygen.
Step 3
•
•
•
•
Meanwhile, at the cathode:
Oxygen molecules O2 diffuse through the oxygen
electrode (cathode).
Electrons are transported to this electrode through
the external electric circuit
H+ ions are transported through the PEM
Together, they react:
O2 + 4H+ + 4e-  2 H2O
Overall
• Electrons are created at the anode
• Electrons are used at the cathode
• The movement of electrons through the
external circuit are used in an electrical
load.
 the electric motor on a fuel cell vehicle
Review
• What do we need to generate to produce the electricity
required
• for the car motor?
– Electrons
• What type of chemical reaction produces electrons
– Electrochemical
• What are the overall reactants and products of a fuel
cell?
– Oxygen, Hydrogen, Water
• What are the main physical components of a fuel cell?
– Electrodes, Electrolyte (PEM)
The Fuel Cell
Flow Plate – Air Side
Flow Plate – Hydrogen Side
The Fuel Cell