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Fuel cell electric vehicles PDF

Added on - 25 Jan 2022

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Executive Summary
The fuel cell electric vehicles which are often called FCEVs are a bit similar to battery electric
vehicles (BEVs) in terms of components like electric motors and power controllers or inverters.
But, the major difference is the main energy source. BEVs use the stored energy in the battery
whereas FCEVs use fuel cells as their energy source and it's very much more efficient than
batteries in various ways. The notable advantages in fuel cells are that they are very light weight
and compact which can produce the electricity if there is continuous supply of fuel. FCEV is
suitable for medium–large and long-range vehicles unlike BEVs. The principle involved in
FCEVs is that they use the low temperature fuel cells which generate electricity from hydrogen.
This energy can be used to drive vehicles or can also be stored in energy storage devices like
batteries and ultracapacitors. Low-temperature proton exchange membrane fuel cells (PEMFC)
is the best way to afford the high-energy densities and fast start-up times required for automotive
applications for low-carbon technologies. PEMFCs , which are fuelled by hydrogen, are capable
of generating electricity with the only local by-products which are water and heat. Since fuel
cells are completely reliant on chemical reactions to generate electricity which therefore results
in zero pollution due to absence of fuel combustion and produces much less heat than an ICE.
The by- product of a hydrogen fuel cell is hot water vapour. Fuel cells have the potential for high
reliability and low manufacturing cost because of absence of complex moving parts and irregular
shapes. Although FCEVs possess many limitations along with their significant advantages.
Transportation is nowadays categorized as a necessity, and has over the last few years, seen a
conversion from focus on the type of fuel used to the various modes and milieus of mobility.
Today, the automotive industry is going through rapid technological changes of several parts,
especially the motor technologies. This sector remains one of the critical contributors to total
global emissions worldwide due to its high dependency on fossil fuels as its primary source of
energy. Pressure is rising on the automotive industry and it is felt through consumer demand for
higher fuel efficiencies in addition to regulations which either require low emissions or in some
cases, no emissions at all. This pressure that comes from environmental concerns along with the
rising fuel prices surrounding the traditional internal combustion engines have led to a push for
encouraged to reduce pollution and implement healthier environmental management (Walker, Di
Sisto & McBain, 2008). Hence, over the last few years, the implementation of green innovation
in this industry has been capturing the attention of researchers, manufacturers and decision-
makers. In this context, automobile companies and manufacturers have had to review their
production techniques and come up with new technologies and concepts to overcome the
challenges. Such activities involve taking into account environmental protection purposes within
several companies and departments in order to comply with regulations and enhance the
environmental performance while relying on inventive environmental management or green
technologies (Greeno & Robinson, 1992). Extensive research has been performed on ICE cars in
order to improve efficiency and reduce emissions; however, as long-term solution to eliminating
the dependency on oil and fuel consumption for transportation, advanced vehicles are being
developed that are based on other sources of energy, such as fuel cell electric vehicles (FCEVs)
and battery electric vehicles (BECs). Electric vehicles can broadly be defined as vehicles with
electric propulsion capability; such vehicles include HEV, BEV and FCV. The main focus in this
paper will be on FCEVs that use hydrogen as primary source of energy, Hydrogen is one of the
main sources of clean energy that is the most abundant element in the universe and has a very
high energy potential (Mehmet et al, 2017).
Hydrogen can be used for several production procedures as well as it can be used as an
alternative fuel of hydrogen which could represent a solution for green energy production. It can
be obtained from numerous sources and this diversity delivers a significant advantage, it is a
clean fuel. It is a source of energy that can be burned or converted to electrical energy by means
of a fuel cell; hence it can be adapted in internal combustion engines (ICEs) in which water
vapor along with other emissions are released from the exhaust or incorporated in electrical
vehicles as FCEVs with zero CO2emissions. Recently, there has been a rapid progress in
generating green hydrogen which comes from different renewable energy sources. Although the
direct injection of hydrogen in the internal combustion engine has notable advantages, such as
high volumetric efficiency; there are some challenges that need to be overcome. Such challenges
include possible backfire and the increased formation of the NOxfrom the pre-ignition of the
hydrogen air mixture at high loading (A.G. Olabi, 2021).
The primary focus is on FCEVs as it is more convenient in terms of environmental aspects.
These systems, that depend on hydrogen as a fuel for generating electric energy in FC; and drive
the vehicle with electrical structure, show similarities to EVs in the technical maneuver. The
merits of FCEVs are many; some of the main advantages represent zero emission (only water),
Notwithstanding, FCEVs come with disadvantages too, such as limited range, storage and safety
Furthermore, rather than overflowing into the hands of consumers, FCEVs are trickling due to
the hydrogen infrastructure which is almost a decade behind BEV- recharging stakes; hence in
technology can present a serious solution to the fossil fuel emission's problem, and with extended
exploration, can prove to be more efficient or convenient than BEVs. After all, BEVs mainly rely
on lithium-ion batteries which are complex products with a convoluted production chain that is
associated with environmental and economic risks. Hence, regulations concerning these batteries
are being forced with the need of recycling rechargeable batteries as it is induced by cleaner
production principles and better handling of the available resources. Therefore, working on
improving the field FCEVs is an attractive scheme. In this paper we aim to discuss..
Operation principles of fuel cells
A fuel cell is an electrochemical energy conversion device that uses hydrogen to generate
electricity. The principle feature of a fuel cell is that it can convert the chemical energy contained
in the fuel into electricity with higher efficiencies than traditional mechanical systems. The
electromechanical process doesn't include any thermal or mechanical processes and only requires
oxygen to trigger the reaction (A.G. Olabi, 2021). Since hydrogen gas contains a substantial
amount of chemical energy, when ignited, it will react with oxygen in the surroundings and
release its energy by means of explosion. The crucial characteristic of this reaction is that the
only waste product is water; hence there are no emissions of CO2or other toxic gases. The
process delivers electricity in the form of low-voltage DC that provides direct work. Digging
deeper into the components and the workings on a fuel cell, the working principles resemble
those of a battery, both the fuel and the oxidant that are in gaseous phase form the anode and the
cathode and are channeled towards the electrolyte to feed the reaction. However, it should be
noted that unlike a battery, a fuel cell does not store electrical or chemical energy; the electrical
energy is directly extracted from a chemical reaction (Brown et al, 2021). In this case, the fuel
which is hydrogen is fed to the anode and the air is fed to the cathode. The electrolytes come in
several forms (liquid, gas, solid), operate at low or high temperatures and conduct electricity. For
automotive applications, the most common and relative fuel cells use a low temperature solid
electrolyte conducting hydrogen ions.
Oxygen is the most commonly used cathode material due to its abundance in air and high
reactivity while hydrogen is considered as a very effective fuel owing to high electrochemical
reactivity compared to other possible fuels, such as hydrocarbons or alcohols. In simple terms,
the process goes as follows: Hydrogen H2that is located inside the anode has the tendency to
pass to the other side and react with oxygen; nonetheless, the electrolyte present in between does
not allow for the hydrogen to pass. The electrolyte only lets positively charged particles to pass
through it, hydrogen atoms consist of one proton and one electron hence they are neutral
particles and cannot pass through the electrolyte. This is why another material is located in
between which is the catalyst, the catalyst separates the electrons of the hydrogen atoms from
their protons which allows the presence of positively charged protons also known as H+ that can
actually move through the electrolyte to meet up with the oxygen. However, in order for the
reaction to take place, electrons are also needed and since only protons are present on the other
side, the electrons also have to be transported to the anode to formulate hydrogen. The
transferring of hydrogen electrons is actually simple, it happens using a wire that connects both
sides (the cathode and anode); the electrons and protons are now both present in the anode and
can formulate hydrogen that can react with oxygen. The reaction between oxygen and hydrogen
produces water and releases energy that can be converted to electricity for many usages. Note
that the use of catalyst is not always mandatory such as for high-temperature operating fuel cells.
The types of electrolytes used in these fuel cells can conduct negatively charged ions. However
for automotive applications, a fuel cell with a catalyst is usually required.
Fuel Cell Types:
Fuel cells usually differ in the type of electrolyte utilized, which actually affects the operational
temperature of the fuel cell; for instance, the so-called high-temperature fuel cells operate at
temperatures above 1100 F (600 C). Under such conditions, hydrocarbon fuels such as methane
directly reform into hydrogen and efficiently promote the electrochemical reactions without
requiring a catalyst. On the other hand, efficiency is inversely proportional to the reaction
temperature, meaning that an increase in temperature above certain thresholds greatly affects the
energy released (A.G. Olabi, 2021). Common high-temperature fuel cells are molten carbonate
(MCFC) and solid oxide (SOFC).
Molten carbonate fuel cell (MCFC):
The design of MCFC is complex due to the use of liquid electrolyte instead of solid; usually the
electrolyte consists of sodium (Na) and potassium (K) carbonate. Continuous CO2 should be
provided to meet the consumption of CO2 at the cathode. Hence, due to the production of CO2
during fossil fuel reforming, MCFCs are not a completely green technology. However, they are
promising due to their reliability and efficiency, especially when a cogeneration system is
implemented where an efficiency of 80% can be obtained. Current research is focused on
fabrication techniques and material development to reduce cost and improve efficiency. MCFC
cogeneration technology is widely used today. In this fuel cell type, carbonate salts are the
electrolyte. At high temperatures, the salt melts and conducts ions (CO2-3) from the cathode to the
anode. At the anode, the ions react with hydrogen to produce water, carbon dioxide and
electrons. The electrons return to the cathode through an external circuit providing electrical
power; at the cathode, the carbon dioxide from the anode reacts with oxygen from air to form
CO2-3ions that replenish the electrolyte and conduct current through the fuel cell.
Anode Reaction: CO2-3+ H2→ 2H2O + CO2+ 2e-
Cathode Reaction: 1/2O2+ CO2+ 2e-→ CO2-3
Overall Reaction: H2+ 1/2O2→ H2O
Solid oxide fuel cell (SOFC):
The solid oxide fuel cell uses solid oxide or ceramic electrolyte. These types of fuel cells operate
at high temperatures hence they do not require expensive platinum catalysts. Similar to MCFCS,
the high operation temperature allows for hydrocarbon fuels to be internally reformed with the
anode. This technology can deliver high combined heat and power efficiency, low emissions,
long-term stability and relatively low cost. However, there are some disadvantages associated
with SOFCs related to longer start-up times in addition to chemical and mechanical compatibility
issues due to the high operating temperature. Vulnerability to sulfur poisoning has been detected
in this technology; hence it is essential for sulfur to be removed before entering the cell using
adsorbent beds or other means. This fuel cell is usually made up from four layers, three of which
are ceramics which become ionically and electrically active at high temperatures. In the cathode,
oxygen is reduced into oxygen ions, these ions then diffuse through the solid electrolyteto the
anode where they can electrochemically oxidize the fuel. This reaction produces a water
byproduct in addition to two electrons; These electrons then flow through an external circuit
generating electricity and the cycle repeats.
Anode Reaction: O2-+ H2→ H2O + 2e-
Cathode Reaction: 1/2O2+ 2e-→ O2-
Overall Reaction: H2+ 1/2O2→ H2O
Fuel cells that operate below 480 ºF (250 ºC) are classified as low-temperature fuel cells. They
require catalysts which are usually made of expensive materials and an external source of
hydrogen. The lower temperature ranges allow for shorter start up times and do not cause much
material degradation while in use. These characteristics make the low-temperature fuel cells
attractive for automotive applications.Common low-temperature fuel cells are alkaline (AFC),
and proton exchange membrane (PEMPC).
Alkaline fuel cell (AFC):
Alkaline fuel cells are among the most efficient fuel cells, having a potential efficiency of around
70%. These cellsconsume hydrogen and pure oxygen, to produce water, heat, and electricity.
The anode and cathode are separated by a porous matrix saturated with an aqueous alkaline
solution, such as potassium hydroxide KOH (T.B. Ferriday, 2021). These cells usually operate
on pure oxygen or purified air since the use of carbon dioxide can cause the fuel cell to become
“poisoned” through the conversion ofpotassium hydroxide to potassium carbonate (K2CO3) by
the following reaction:CO2(g) + 2KOH(aq) → K2CO3(aq) + H2O(l).The chemicals reactions
occurring in the fuel cell are:
Anode Reaction: 2OH-+ H2→ 2H2O + 2e-
Cathode Reaction: 1/2O2+ H2O + 2e-→ 2OH-
Overall Reaction: H2+ 1/2O2→ H2O
Proton exchange membrane (PEMPC):
PEM fuel cells operate with an electrolyte conducting hydrogen ions (H+ ) from the anode to the
cathode. The electrolyte is made of a solid polymer in a form of acidified Teflon. These types of
fuel cells are the most commonly used for vehicle applications; since they afford high-energy
densities and fast start-up times required for automotive applications for low-carbon technologies
with the only local by-products being water and heat. A single fuel cell consists of an anode, a
cathode andmembrane joined together to form a membrane electrode assembly (MEA) where
hydrogen and oxygen are combined (Billy. Wu, 2012). In the anode section, hydrogen molecules
are split into protons and electrons. The membrane separating the cathode and the anode is a
Nafion polymer that only allows for the conduction of hydrogen protons. Electrons are not able
to move through the membrane and thus must flow around an external circuit where electrical
work can be extracted. The chemicals reactions occurring in the fuel cell are:
Anode Reaction: H2→ 2H++ 2e-
Cathode Reaction: 1/2O2+2H++ 2e-→ H2O
Overall Reaction: H2+ 1/2O2→ H2O
For automotive applications, to achievepractical voltages, multiple MEAs and bipolar plates are
joined together to form an FC stack. The operating voltage is then the summation of the
individual cell voltages (Billy. Wu, 2012).
Classification of most prominent fuel cells
Fuel cell
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