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 CellThe fuel cell is the physical structure that makes these

electrochemical reactions happen and captures and utilizes the current generated by electrons as well.

Anode catalyst

Cathodecatalyst

H+H+

H+

H+

H+H+

Electric circuit e-e-e-e-

e-e-

H2

Fuel

O2

From air

O2

O2

O2

H2OExhaust

PolymerElectrode membrane

H2

Anode catalyst

Cathodecatalyst

H+H+

H+

H+

H+H+

Electric circuit e-e-e-e-

e-e-

H2

Fuel

O2

From air

O2

O2

O2

H2OExhaust

PolymerElectrode membrane

H2

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).

Anode catalyst

Cathodecatalyst

H+H+

H+

H+

H+H+

Electric circuit e-e-e-e-

e-e-

H2

Fuel

O2

From air

O2

O2

O2

H2OExhaust

PolymerElectrode membrane

H2

Anode catalyst

Cathodecatalyst

H+H+

H+

H+

H+H+

Electric circuit e-e-e-e-

e-e-

H2

Fuel

O2

From air

O2

O2

O2

H2OExhaust

PolymerElectrode membrane

H2

LikeSaltyWater

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-

Anode catalyst

Cathodecatalyst

H+H+

H+

H+

H+H+

Electric circuit e-e-e-e-

e-e-

H2

Fuel

O2

From air

O2

O2

O2

H2OExhaust

PolymerElectrode membrane

H2

Anode catalyst

Cathodecatalyst

H+H+

H+

H+

H+H+

Electric circuit e-e-e-e-

e-e-

H2

Fuel

O2

From air

O2

O2

O2

H2OExhaust

PolymerElectrode membrane

H2

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.

Anode catalyst

Cathodecatalyst

H+H+

H+

H+

H+H+

Electric circuit e-e-e-e-

e-e-

H2

Fuel

O2

From air

O2

O2

O2

H2OExhaust

PolymerElectrode membrane

H2

Anode catalyst

Cathodecatalyst

H+H+

H+

H+

H+H+

Electric circuit e-e-e-e-

e-e-

H2

Fuel

O2

From air

O2

O2

O2

H2OExhaust

PolymerElectrode membrane

H2

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

Anode catalyst

Cathodecatalyst

H+H+

H+

H+

H+H+

Electric circuit e-e-e-e-

e-e-

H2

Fuel

O2

From air

O2

O2

O2

H2OExhaust

PolymerElectrode membrane

H2

Anode catalyst

Cathodecatalyst

H+H+

H+

H+

H+H+

Electric circuit e-e-e-e-

e-e-

H2

Fuel

O2

From air

O2

O2

O2

H2OExhaust

PolymerElectrode membrane

H2

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

Anode catalyst

Cathodecatalyst

H+H+

H+

H+

H+H+

Electric circuit e-e-e-e-

e-e-

H2

Fuel

O2

From air

O2

O2

O2

H2OExhaust

PolymerElectrode membrane

H2

Anode catalyst

Cathodecatalyst

H+H+

H+

H+

H+H+

Electric circuit e-e-e-e-

e-e-

H2

Fuel

O2

From air

O2

O2

O2

H2OExhaust

PolymerElectrode membrane

H2

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