POWER April 2021 - 34

FUEL CELLS
Understanding Fuel Cells
and Their Role in the
Green Energy Revolution
Future propulsion and energy systems must be designed to meet the social challenges
of climate change, increased energy requirements, and the mobility and energy
demands of a growing world population. Fuel cells could be a vital piece of that
puzzle.
Michele Bozzolo, Georg Fink,
Benjamin Oszfolk, and
Philippe Gorse, PhD
T
he potential of fuel cell technology
is convincing, as is hydrogen as a
storage medium within an overall
energy system. Strong arguments for
using and promoting this technology are
high reliability, scalability, and the ability
to use renewable energy sources.
With their modular design, fuel cell
systems are easily adaptable to match
output with demand, and their low maintenance
requirements and low running
costs also make them attractive. Furthermore,
fuel cell technology is ready to be
brought to market and suitable for commercial
use. The rapidly developing market
offers good growth opportunities for
zero-emissions fuel cell technology.
How Fuel Cells Work
Fuel cells work differently compared to
combustion engines. They convert a
fuel's chemical energy directly into electricity,
which can then be used to drive
a growing number of electrified systems.
This conversion is more efficient
than with combustion engines, as the
intermediate thermo-mechanical steps
required with conventional energy converters
(heat engines) are eliminated.
The greatest plus point arises when
the fuel used is regeneratively produced
hydrogen because it allows both pollutant
and climate-damaging gas emissions
to be reduced to zero. In this way,
fuel cells have an enormous potential to
become an essential technology component
for decarbonizing propulsion and
energy systems.
The low-temperature proton exchange
membrane fuel cell, or PEM (sometimes
called polymer electrolyte membrane
fuel cell), currently represents the most
suitable technology for developing and
34
1. Proton exchange membrane fuel cells include an anode, cathode, and electrolytic membrane.
Courtesy: Rolls-Royce Power Systems
growing the Rolls-Royce Power Systems
portfolio. This low-temperature fuel cell
has a high power density enabling even
small units to achieve sizeable outputs.
Low-temperature fuel cells have operating
temperatures of up to about 100C,
posing minimal hazards to both materials
and people, while high-temperature fuel
cells reach 250C to 1,000C. The PEM has
good load-following characteristics as opposed
to other types, allowing it to respond
to changes of power requirement
within seconds.
One advantage of the compact PEM
fuel cell is its very high electrical efficiency,
especially at part load. They typically
run on a hydrogen fuel source; however,
they can operate on a wide variety of
hydrocarbon fuels (such as methanol,
diesel, or natural gas). This is achieved by
using well-known reforming techniques
to convert the fuels into hydrogen. This
gives PEM fuel cells a very wide-ranging
field of applications.
The PEM fuel cell is a galvanic cell
that electrochemically reacts fuel and an
oxidant (usually air) to produce electricity
and exhaust products. It works quietly
and without much in the way of vibration.
Similar to batteries, fuel cells also
generate
direct-current voltage. Howwww.powermag.com
ever,
unlike batteries, fuel cells require a
constant inflow of fuel and oxidant.
With a PEM fuel cell, a chemical process
takes place between the electrodes
(anode and cathode) in which the positive
ions (protons) migrate from the anode to
the cathode, and the electrons are conducted
externally from the anode to the
cathode via an electrical conductor. The
product of this process is electrical power
that can be withdrawn and used. The
electrodes are coated with a platinum or
palladium catalyst and separated from
each other by an electrolyte. Without the
catalyst, hydrogen and oxygen would not
react to produce heat and electricity. The
electrolyte consists of an ion-conducting
membrane, and it is important for this
membrane to be permeable for protons
and impermeable to electrons.
Improving Upon Well-Established
Technology
The name " polymer electrolyte membrane
fuel cell " indicates that the membrane
is a key feature of this fuel cell. This
is usually made of plastic and is similar
to Teflon. The water-saturated polymer
membrane, which serves as an electrolyte,
allows only protons-the positively
charged atomic nucleus of hydrogen-to
POWER | April 2021

http://www.powermag.com

POWER April 2021

Table of Contents for the Digital Edition of POWER April 2021