4
P. K. Shen
energy device and uses hydrogen and oxygen produced by solar cell to provide fuel
and oxidant. However, the electrode of fuel cell is in poor contact with membrane,
resulting in low initial current density. In order to improve this bad contact, the battery
is filled with strong acid solution, which also makes the water produced by the reaction not neutral. At high temperature, the first generation PEMFC is very unstable,
so Gemini spacecraft changed the membrane material to sulfonated polystyrene.
In 1970, DuPont invented Nafion (fully aerated sulfonic acid) membrane, which
can keep thermal stability even at temperature higher than 100 °C, and the ionic
conductor is difficult to dissociate, with high chemical stability, but it is expensive.
So far, only a few teams have been able to produce Nafion membrane with suitable
price. The power of proton exchange membrane fuel cell used in Gemini spacecraft is
about 50 W ft
−2 . In the mid-1970s, American General Electric Company transferred
fuel cell technology and patents to United Technologies Corporation of America
and Siemens Company of Germany. In 1983, Ballard Company of Canada further
explored proton exchange membrane fuel cell, including trying new membrane such
as Dow chemical membrane, which improved the thermal stability to 120 °C and
the pressure to 700 kPa. In 1993, Daimler-Benz Automotive Company of Germany
used this fuel cell which only needs to consume water and only generates water for
automobiles, which aroused widespread concern in the world and set off a global
upsurge of research and development of fuel cell electric vehicles. Up to now, the
proton exchange membrane fuel cell has gone deep into aerospace, transportation,
communication, military and other fields, which is a hot spot of capital investment
by government enterprises in various countries, and also makes great progress in the
research and development of fuel cells.
1.2.1 Working Principle of Proton Exchange Membrane
Fuel Cells (PEMFCs)
Membrane electrode of fuel cell is composed of three basic units, which are cathode,
anode and electrolyte. The cathode and anode are respectively connected with
conductive materials. In a common acid fuel cell (as shown in the figure), the cathode
and anode catalysts are all platinum, the anode is filled with fuel hydrogen, and the
cathode is filled with oxidant oxygen. Platinum particles are supported on carbon
carriers with high specific surface area to improve their utilization rate and catalytic
activity. At the anode, hydrogen oxidizes to generate hydrogen ions. Protons are
transmitted to cathode through proton exchange membrane, but electrons can only
be transmitted through external circuit because the membrane cannot transmit electrons. At the cathode, oxygen (usually air) is catalytically reduced under the action of
catalyst, and then reacts with protons to generate water. The general reaction equation
is as follows.
H 2 + 1/2 O 2 ↔ H 2 O
(1.1)
P. K. Shen
energy device and uses hydrogen and oxygen produced by solar cell to provide fuel
and oxidant. However, the electrode of fuel cell is in poor contact with membrane,
resulting in low initial current density. In order to improve this bad contact, the battery
is filled with strong acid solution, which also makes the water produced by the reaction not neutral. At high temperature, the first generation PEMFC is very unstable,
so Gemini spacecraft changed the membrane material to sulfonated polystyrene.
In 1970, DuPont invented Nafion (fully aerated sulfonic acid) membrane, which
can keep thermal stability even at temperature higher than 100 °C, and the ionic
conductor is difficult to dissociate, with high chemical stability, but it is expensive.
So far, only a few teams have been able to produce Nafion membrane with suitable
price. The power of proton exchange membrane fuel cell used in Gemini spacecraft is
about 50 W ft
−2 . In the mid-1970s, American General Electric Company transferred
fuel cell technology and patents to United Technologies Corporation of America
and Siemens Company of Germany. In 1983, Ballard Company of Canada further
explored proton exchange membrane fuel cell, including trying new membrane such
as Dow chemical membrane, which improved the thermal stability to 120 °C and
the pressure to 700 kPa. In 1993, Daimler-Benz Automotive Company of Germany
used this fuel cell which only needs to consume water and only generates water for
automobiles, which aroused widespread concern in the world and set off a global
upsurge of research and development of fuel cell electric vehicles. Up to now, the
proton exchange membrane fuel cell has gone deep into aerospace, transportation,
communication, military and other fields, which is a hot spot of capital investment
by government enterprises in various countries, and also makes great progress in the
research and development of fuel cells.
1.2.1 Working Principle of Proton Exchange Membrane
Fuel Cells (PEMFCs)
Membrane electrode of fuel cell is composed of three basic units, which are cathode,
anode and electrolyte. The cathode and anode are respectively connected with
conductive materials. In a common acid fuel cell (as shown in the figure), the cathode
and anode catalysts are all platinum, the anode is filled with fuel hydrogen, and the
cathode is filled with oxidant oxygen. Platinum particles are supported on carbon
carriers with high specific surface area to improve their utilization rate and catalytic
activity. At the anode, hydrogen oxidizes to generate hydrogen ions. Protons are
transmitted to cathode through proton exchange membrane, but electrons can only
be transmitted through external circuit because the membrane cannot transmit electrons. At the cathode, oxygen (usually air) is catalytically reduced under the action of
catalyst, and then reacts with protons to generate water. The general reaction equation
is as follows.
H 2 + 1/2 O 2 ↔ H 2 O
(1.1)