“Yes, my friends, I believe that water will one day be employed as fuel, that hydrogen and oxygen which constitute it, used singly or together, will furnish an inexhaustible source of heat and light, of an intensity of which coal is not capable... When the deposits of coal are exhausted we shall heat and warm ourselves with water.” 1874, Jules Verne, “The Mysterious Island”
Introduction has accelerated accordingly. Unfortunately, human
beings have only been able to realize that this
IT IS WELL KNOWN THAT, SINCE THE excessive consumption can have extremely serious
Industrial Revolution that started in the middle consequences such as global climate change, as well
of the 19th century, fossil fuel resources namely, as environmental pollution in recent years. Fossil
coal then oil and natural gas were used to meet the fuel companies have constantly underestimated
world energy demand. While the increase in energy other alternatives in this well-profitable sector for
use with industrialization has increased the living their own interests and have used their power to
standards of countries, fossil fuel consumption exclude them from the decision-makers (Türe,
2021: para.3). Alternative energies such as sun, the world reaches almost 8 trillion dollars per year
wind, and small streams, which are known as (Greenpeace, 2020Greenpeace (2020). The source article does not provide a separate full bibliographic entry for this citation.).
environmentally friendly are considered to be more Hydrogen has many advantages over the fossil
expensive than fossil fuels. Intermittent natures of fuels currently used. In a fuel cell where hydrogen
these resources were also another reason why they will be used as a fuel, energy is obtained with high
were not accepted by society. efficiency, while only pure water comes out as
waste. The use of water as a source of hydrogen constitutes one of the main advantages of hydrogen. Economical storage and transportation are still the Hydrogen has many advantages most important problems of hydrogen technologies
over the fossil fuels currently used. waiting to be solved. However, studies in recent
In a fuel cell where hydrogen will be years show that these problems will be overcome
used as a fuel, energy is obtained with in a short period of time. Hydrogen technology
high efficiency, while only pure water is gaining importance with the continuous
comes out as waste. development of its usage area and the addition of
methods to increase energy efficiency. According to the cost calculations, using hydrogen technology
As it is known, when fossil fuels such as coal, systems are more expensive than the existing fossil
oil, and natural gas are used, some dust particles fuel systems but along with that the increasing oil
are released into the environment along with and natural gas prices in the near future, equality
various gases. There are carbon oxides, sulfur in this regard will be achieved in the next ten years.
oxides, hydrocarbons, poly-nuclear aromatic Classified as the social cost of fossil fuels; global
hydrocarbons (PAH), olefins, aldehydes and some climate change, air pollution, oil spills, mining
other pollutants in these released gas mixtures accidents, etc. when this damage done by the
and particles. The effects of air pollution on the elements to the world is put on fossil fuel prices,
environment occur on a global, regional and local hydrogen becomes much more advantageous in
scale. On a global scale, it is possible to count terms of cost. As mentioned above, there is no
climate changes such as global warming caused by possibility that this situation will continue due to
greenhouse gases, especially carbon dioxide, and the limited fossil fuels and environmental disasters
consequently increasing the intensity of hurricanes, that await our world. Considering that it is not
extreme drought, or flooding. On a regional scale, possible for people to renounce their comfort and
deterioration of ecological balance as the result of living standards, it is necessary to find a new
acid rains, forest destruction, and increased acidity synthetic fuel instead of fossil fuels. This fuel should
of lakes are the most important indications. At the be clean, environmentally friendly, renewable,
local scale, air pollutants such as CO, SO2 NOX, endless, ubiquitous, easily transportable, affordable,
and O3 cause adverse effects on human health, high calorific value, and efficient. Many years of
plants, structure, and materials. Currently, the total studies have shown that the ideal fuel is definitely
damage did by fossil fuels to the environment in hydrogen. Hydrogen is shown as the only solution
Figure 1. The Energy Content of Hydrogen Relative to Various Fuels (Mj/kg)
Source: Transport Geography, 2022.
to environmental problems and is also called an value per unit volume is low. The heating value of
“independence fuel” that can save countries from hydrogen gas is given as approximately 12 Mega
fossil fuels. As a result of the eruption of the energy Joules per cubic meter (Türe, 2021: para.7).
crisis in 1973 and the scientific community’s search Hydrogen is the cleanest energy carrier. In
for a solution to this problem, hydrogen energy view of the high efficiency of hydrogen and the
came to the fore in the world. environmental damage of fossil fuels, hydrogen is
When hydrogen gas, which is odorless and the most cost-effective fuel. It does not produce
colorless under normal temperature and pressure, greenhouse gases that cause global climate change,
combines with oxygen, the most important does not cause acid rain, and does not produce
substance for life, namely water, is obtained. chemicals that damage the ozone layer (Türe, 2021:
Hydrogen is a very light gas; its density is 1/14 of para. 8).
air and 1/9 of natural gas. The density of hydrogen, Hydrogen is secondary energy just like
which becomes liquid when cooled to -253˚C at electricity, so it is a carrier and must be produced
atmospheric pressure, is 1/10 of that of gasoline. from primary energy sources. Obtaining hydrogen
Hydrogen is the most efficient fuel. On average, it from clean energy sources and water means
is 26% more efficient than fossil fuels. Hydrogen both endless energy and the world getting rid
has the highest energy content per unit mass of of all environmental problems, especially global
all known fuels. In Figure 1, the energy content of warming. For example, as a result of the separation
hydrogen compared to other fuels is given. 1 kg of of water into hydrogen and oxygen with solar
hydrogen has the same energy as 2.1 kg of natural energy, the transportation of the obtained hydrogen
gas or 2.8 kg of oil (Türe, 2021: para.6). to the desired location through pipelines or storing,
Considering that, the heat of combustion of and then combusting with oxygen again, waste
liquid hydrogen is 120.7 MJ/kg, while the heating material of the resulting energy is again a few drops
value of aviation gasoline is only 44 megajoules of pure water or water vapor (Türe, 2021: para. 9).
per kg, it is easy to understand the usage of liquid Hydrogen is considered to be the fuel not only
hydrogen as rocket fuel. However, its heating for this century but also for the next 5 billion years,
Figure 2. Various Methods Used for Obtaining method is an average of 2 US dollars per kg.
Hydrogen from Water However, carbon dioxide gases are also released as a result of obtaining hydrogen from fossil fuels such as coal. Obtaining hydrogen from fossil fuels becomes even more expensive when the cost of the technology to store CO2 by burying it in the ground is taken into account. When hydrogen is obtained from fossil fuel sources, it is called “blue hydrogen” to indicate that the source is not clean (United States Department of Energy, 2020United States Department of Energy (2020). The source article does not provide a separate full bibliographic entry for this citation.). Since almost 95% of the hydrogen produced today is produced by these well-known and fully commercialized technologies, new technologies are mostly included here. Hydrogen obtained by electrolysis of water using renewable energy sources is called “green hydrogen” (Figure 3). The cost is approximately 3-7 US dollars per kilogram
Source: Online Library, 2017. of hydrogen with this method.
As it can be seen in Table 1, although the which is estimated as the life of the sun (Türe, 2021: production cost of hydrogen from renewable para. 10). Considering the fuels that humanity has energy sources and nuclear energy is still higher used from the first days of mankind to today it is than fossil fuels, it is clear that this cost will decrease clearly seen that the hydrogen ratio in these fuels is increasing (Türe, 2001Türe (2001). The source article does not provide a separate full bibliographic entry for this citation.). It is certain that this fuel Figure 3. Green Hydrogen Cycle will be completely hydrogen in the next period.
Hydrogen Production Methods and Costs
Hydrogen can be obtained by various methods, depending on the use of different main energy sources (Figure 2). These include electrolytic, thermal, thermo-chemical, electrothermochemical, photolytic, and mixed methods. Nowadays, the methods used for the production of hydrogen by decomposition of water are summarized in Figure 2. Today, the most commonly used method in hydrogen production is to obtain high purity hydrogen from natural gas by the reforming Source: Türe, 2001. method. The cost of hydrogen produced by this
Table 1. Costs for Hydrogen Produced from Various Sources in the World
Source: Statista, 2020.
depending on the development of technology. types of electrolytic cells for the electrolysis of
Also, hydrogen from renewable sources is still water, including alkaline electrolysis, polymer
cheaper when the aforementioned social costs are electrolyte membrane (PEM), and solid oxide
added to fossil fuels. Since the usage of electrical electrolysis cells (SOECs).
energy to be obtained from renewable energy Hydrogen consumption increases by about
sources such as wind and sun is taken as the basis 6% per year and, its annual production is
here, it is possible to obtain hydrogen from water estimated to be around 80 million tons today. As
using alkaline or PEM electrolyzers. For this it is known, hydrogen is produced by reforming
reason, according to these technologies, hydrogen natural gas with steam which is a process that
costs are given comparatively and as an estimate. leads to greenhouse gas emissions to a large
As it is known, natural gas and electricity prices extent (Greenpeace, 2020: The Geography of
vary from country to country, as well as over the Transport Systems, 2022). Nearly 50% of global
years. In addition, factors such as the costs of hydrogen demand is covering currently through
the devices used for production and the amount steam reforming of natural gas, approximately
of hydrogen produced play an important role in 30% from oil/naphtha reform from refinery/
the cost of the product obtained. For the cost of chemical industrial waste gases, 18% from coal
hydrogen, the estimated price range is given in gasification, 3.9% from water electrolysis, and
Table-1 instead of the exact price depending on 0.1% from other sources.
various sources. Direct Decomposition Methods Hydrogen Production from Solar, Wind,
Hydraulic, and Geothermal Energies Separation of Water at High Temperature
(Thermolysis) Electrolysis of water with the help of electricity
obtained from all renewable sources is the basic It is the process of chemical decomposition
method for obtaining hydrogen. For example, of water into hydrogen and oxygen when a
wind and solar energies are important renewable temperature of more than 2500 °C is applied.
energy sources used for the production of The hydrogen and oxygen must be effectively
hydrogen to be used as fuel. There are three main separated to prevent them from turning back
Figure 4. Thermochemical Hydrogen Production by Concentrated Solar Energy a) Central Receiver/Reactor Tower With Heliostats b) Modular Dish-Mounted Receiver/Reactor
Source: United States Department of Energy, 2022.
into the water due to the reaction is reversible. required for the thermolysis process, e.g. to
In this method, concentrated solar energy or 1200-1500 °C, intermediates (catalysts) are
waste heat of nuclear power reactions can be used.
used as a source. Depending on the heat source
used with this method, very few or hardly Electrolysis (Alkaline)
ever greenhouse gases are emitted into the
atmosphere. Electrolysis of water or the decomposition
During the electrolysis of water with the of water into oxygen and hydrogen is a known
thermochemical method, a temperature of and commercially used method since the
(500-2000) °C is required for a series of chemical 1890s. Electrolysis is basically a process that
reactions at a temperature of (500-2.000) °C to breaks the chemical bonds in the water mo-
decompose the water. The chemicals used in lecule by adding a substance such as KOH or
the process are reused in each cycle, creating NaOH that increases conductivity in the water
a closed cycle that consumes only water and and passes a direct current through this liquid.
produces hydrogen and oxygen. The high It is also defined as the separation of chemical
temperatures required for the processes are compounds dissolved in a liquid by applying an
provided by eco-friendly intensive solar energy external electric current through metal electro-
(Figure 4; United States Department of Energy). des immersed in the electrolytic liquid.
In order to reduce the high temperature Electrolysis is the most essential method used
to obtain pure hydrogen. Electrodes in the ele- from the exterior, 99.9% pure hydrogen comes
ctrolysis cell can be selected from different me- out from the cathode and oxygen gas from the
tals according to the electrolytic liquid used. anode. In the case of an electrolytic cell with
This cell consists of two electrodes that are dis- KOH or NaOH mixed, the reactions at the cat-
solved into a compound divided into positive hode and anode are given below respectively;
and negative charged ions and these electrodes
are adjusted by means they do not touch each At the Cathode 2 H2O +2e- → H2 + 2OH- (1)
other (usually 5-20 cm between two electro-
des). For instance, nickel-based electrodes such At the Anode 2OH- → 0.5 O2 + H2O + 2e- (2)
as nickel-aluminum alloys are preferred in al-
kaline electrolysis cells. When sulfuric acid, Overall reaction: H2O → H2 + 0.5 O2 (3)
which increases conductivity, is added to water,
platinum, which is not affected by acid, should A schematic of an alkaline electrolyzer is shown
be used as an electrode. Although platinum is a below.
highly productive electrode, it is not preferred
with regard to cost. When a voltage of at least Proton Exchange Membrane ( PEM)
1.23 volts is applied between the electrodes Proton Permeable Membrane Electrolyzer-
Figure 5. Alkaline Electrolysis Cell Proton Exchange Membrane (PEM): This type
of electrolyzer is designed to produce hydrogen electrochemically at pressures of 2000 psi and with an efficiency of 85% or more. Thus, it is not necessary to use a compressor to compress the hydrogen later. The PEM electrolyzer usually uses a solid polymer-based membrane instead of a liquid electrolyte. Another advantage of this type of electrolyzer is that it can produce high purity hydrogen alongside low parasitic losses. PEM electrolyzers are one of the most studied subjects in recent years due to their simple structure and hydrogen production, as well as their ability to store gas under pressure. Today, fuel cells, which are defined as “Regenerative Fuel Cell”, work conversely and act as electrolyzer, as well as can, produces electricity from hydrogen as a fuel cell, and pure water is again produced as waste. PEM elect-
Source: Nelly Hydrogen, 2022. rolyzer/fuel cell diagram is given in Figure 6.
Figure 6. PEM Electrolyzer ions (O2)- at high temperatures, usually (700-1000)
°C, and use a solid ceramic material as the electrolyte. In the system, firstly, electrons from the external circuit combine with water at the cathode in order to form hydrogen gas and negatively charged (O2)- ions. Then, the oxygen ions pass through the ceramic membrane and react at the anode to form oxygen gas and provide electrons to the external circuit. The process can also be expressible as a high-temperature steam electrolyzer. Solid-oxide electrolyzers have much higher efficiency than proton permeable membrane (PEM) electrolyzers (Tucker, 2020Tucker (2020). The source article does not provide a separate full bibliographic entry for this citation.; Zheng, et al., 2021Zheng, et al. (2021). The source article does not provide a separate full bibliographic entry for this citation.).
Photonic Energy (Photolysis)
Photolysis involves the chemical decompositi-
Source: Kumar & Himabindu, 2021. on of water into hydrogen and oxygen by photonic
Solid Oxide Electrolysis Cell- (SOEC) energy. Since the potential for water separation is
1.23 eV, the wavelength of the photons equivalent
Solid-oxide electrolyzers are electrolysis cells to it is 1008 nm, corresponding to infrared light.
that selectively apply negatively charged oxygen That shows the separation of water is theoretically
Figure 7. Solid-Oxide Electrolysis Cell
Source: Tucker, 2020; Zheng, et al., 2021.
possible with infrared light, but industrial appli- nificantly reduces the electrical energy demand
cation is not available. Recently, more intensive and speeds up the electrolytic reaction kinetics
studies have been carried out on the separation of at high temperatures. Alkaline electrolysis opti-
water by the photocatalytic method under lower mally operates at a high temperature of close to
frequency radiation instead of high frequency 200 °C and is used for industrial-scale hydrogen
(Tee, et al., 2017Tee, et al. (2017). The source article does not provide a separate full bibliographic entry for this citation.; Waterhouse, et al., 2013Waterhouse, et al. (2013). The source article does not provide a separate full bibliographic entry for this citation.). production. PEM electrolyzers typically ope-
rate below 100 °C (more efficient than alkaline
Biochemical Method electrolysis) and are increasingly available for
Hydrogen is obtained by fermenting carbohyd- commercial practices. SOEC electrolyzers are
rates in an anaerobic (oxygen-free) environment the most electrically efficient but least enhanced.
by various bacteria. The fermentation process can SOEC technology faces challenges with rapid
produce hydrogen in the absence of oxygen by the material degradation and limited long-term sta-
following reaction (Tokio, 1979Tokio (1979). The source article does not provide a separate full bibliographic entry for this citation.). bility (Chao, 2019Chao (2019). The source article does not provide a separate full bibliographic entry for this citation.; Baniasadi, 2012Baniasadi (2012). The source article does not provide a separate full bibliographic entry for this citation.).
Biophotolysis C6H12O6 + 2H2O → 2CH3COOH + 2 CO2 + 4H2 Biophotolysis of water involves oxygenic pho-
Indirect (Multi-Step) Methods tosynthesis by microorganisms (i.e. green micro-
algae and cyanobacteria) with the combined use Thermo-electrolysis of biochemical and photonics energy for hyd-
Thermo-electrolysis of water involves the che- rogen production by direct and indirect metho-
mical decomposition of water with the combined ds. In direct biophotolysis, when microorganis-
use of electrical and thermal energy. It is more ms split water into hydrogen and oxygen ions by
efficient and economical at high temperatures capturing sunlight, the hydrogen ions produced
because a significant part of the required energy are further converted into hydrogen by the enzy-
is supplied by cheaper thermal energy, which sig- me hydrogenase (i.e. 2H2O + sun → 2H2 + O2). In
Figure 8. Photocatalytic Water Decomposing: A) Water Decomposing With Semiconductor Photocatalyst B) Semiconductor Band Structure and Water Decomposition Redox Potential
Source: Kudo & Miseki, 2009; Hisatomi, vd., 2014; Tee, et al., 2017.
indirect biophotolysis, solar energy is captured active only under ultraviolet light radiation. Howe-
by microorganisms through photosynthesis and ver, ultraviolet light (<400 nm) accounts for only
stored in a type of carbohydrate 6CO2 + 12H2O 4% of total solar energy, while visible light (400-
+ sun → C6H12O6 + 6O2, which is then used to 800 nm) and infrared light (>800 nm) account for
produce hydrogen, then C6H12O6 + 12H2O + sun 53% and 43% of total solar energy, respectively.
→12H2 + 6CO2 decomposes into hydrogen and Photo-Electrochemical Decomposition carbon dioxide as a result of the reaction (Kam-
ran & Fazal, 2021). Photo-electrochemical systems decompose water
molecules using solar energy and hydrogen is ob- Photocatalytic Water Decomposition (Photained as a result of a chemical reaction. The bigtocatalysis) gest advantage of photo-electrochemical methods
The photocatalytic method is simply the produ- is that they only need water beside the sun as an
ction of hydrogen with the help of photon energy energy source and they have serious potential for
and a catalyst. For instance, the use of TiO2 as a the future (Fujishima & Honda, 1972; Nozik,1978;
photocatalyst with solar energy is among the most Chen, 2010). Photoelectrochemical systems consist
studied subject in this field. A photocatalytic semi- of three basic parts: photo-anode, photo-cathode,
conductor that attracts light is needed for water to and electrolyte (see Figure 9). The photo-anode be-
break down with photon energy. Simply, the reac- comes electron-hole pairs with the sunlight falling
tion is given like that: on them, and the water molecule that comes into
Solar contact with the surface of the photo-anode is oxidi-
H 2O H2 + ½ O2 zed, resulting in an oxygen molecule and a positively
Photocatalysis charged hydrogen molecule. The features of semiconductors used as pho-
tocatalysts are that they provide conductivity by Figure 9. Photoelectrochemical Electrolysis Cell
passing the electrons from the valence band to Diagram
the conduction band with the incoming photon energy. The energy of the radiance falling on the semiconductor photocatalyst should be at least equal to the forbidden gap energy value given in eV between the valence band and the conduction band of this semiconductor. The most commonly used photocatalysts are TiO2, CdS, Fe2O3, and SnO. In the photo-catalytic method, the photo-catalysts in the UV and visible region of the light provide hydrogen production by performing the reaction of reduction of water to hydrogen in the conduction band with light absorption (Kudo & Miseki,
2009; Hisatomi, et al., 2014). Source: Fujishima & Honda, 1972; Nozik, 1978; Chen,
So far, most of the photocatalysts reported are 2010; Ruth et al., 2017.
Photovoltaic Integrated Electrolysis
cal Water Decomposing A) Photovoltaic System and External Electrolyzer
B) Photovoltaic İntegrated Solar-Driven Water
As it is known, photovoltaic cells are electro- Splitting Device
nic devices that convert solar energy directly into electricity and can provide the necessary electrical energy to the electrolyzer to obtain hydrogen by decomposing water. Such a system is given in Figure 10 below. A crystalline silicon-based photovoltaic cell has an efficiency of 18% and when integrated with an electrolyzer with an efficiency of 80%, the combined electrolyzer system which is solar-powered operates with an efficiency of
≈14.19%. With the separate structure of the solar Source: Kudo & Miseki, 2009; Hisatomi, vd., 2014;
cell and the electrolyzer, the solar cell does not Tee, et al., 2017.
require immersion in the electrolyte and therefore Hydrogen Production from Hydrogen does not cause corrosion. Photovoltaic integrated Sulfide (H2S) solar water decomposition uses a direct renewable
source of solar energy and does not emit green- Studies conducted for many years show that there is
house gases during hydrogen production. a huge amount of hydrogen sulfide in the Black Sea,
Current and future estimated costs for hyd- and this amount is increasing by 2.73 x 106 metric
rogen production from commercially used Alka- tons every year. This reason is that the five great ri-
line, PEM, and Solid-oxide electrolyzers are given vers Kuban, Don, Dnieper, Nistru, and Danube still
in the tables below (Türe, 2005Türe (2005). The source article does not provide a separate full bibliographic entry for this citation.). drain their organic compounds into the Black Sea.
Table 2. Electrolyzer Costs
Source: Türe, 2005.
Table 3. H2S Concentrations in the Black Sea at Different Depths
Source: Türe, 2004; Brewer, et al., 1974; Lein & Ivanov, 1990; Weber, et al., 2001.
The extremely organic matter is too much for the as. It usually occurs when organic matter breaks
bacteria that would normally break it down aero- down in the absence of oxygen, such as bacteria,
bically, it renders the anaerobic bacteria dominate swamp, and sewer. It also occurs in volcanic ga-
via consuming the dissolved oxygen supply. These ses, natural gas, and some well water. The odor in
organisms form H2S as residual gas in the pro- the gas produced as a result of the activities of H2S
cess, by taking oxygen from sulfate ions which is a producing bacteria in the human large intestine
component of seawater. It has been found that the is substantially the result of trace amounts of H2S
H2S concentration in the Black Sea conforms to gas. This type of bacterial action can contribute
two different regimes, one from the surface to 700 to bad breath in the mouth. About 10% of total
m and the other from 700 m to the bottom (Türe, global H2S emissions are due to human activities
2005; Dimitrov, P., & Dimitrov, D., 2004). (Rubright, et al., 2017Rubright, et al. (2017). The source article does not provide a separate full bibliographic entry for this citation.). H2S production takes pla-
The currently existing H2S reservoir in the Bla- ce mostly in oil refineries by the hydro-desulphu-
ck Sea is estimated to be 5.27 x 109 metric tons. rization process, and it decomposes sulfur from
Decomposing hydrogen from this high amount petroleum by the action of hydrogen. The obtai-
of H2S in the Black Sea will both contribute to ning H2S is converted to elemental sulfur by the
the economy and prevent future environmental Claus process and partial combustion. The Claus
disasters. According to the results obtained, the method is also used for the production of hyd-
hydrogen acquired by the electrolysis of hydrogen rogen from hydrogen sulfide, but some steps of
sulfide is 3 times more economical than the elect- the method have been changed here. It is a two-
rolysis of water (COSIA, 2017COSIA (2017). The source article does not provide a separate full bibliographic entry for this citation.). Hydrogen sulfide, step process, generally thermal and catalytic rea-
H2S, is a colorless, poisonous, and responsible for ctions.
the rotten egg odor, flammable gas. Because hyd- (a): Thermal Step: H2S is partially oxidized
rogen sulfide is heavier than air, it tends to accu- with air. This is executed in a high temperature
mulate near the ground in poorly ventilated are- (1000-1400) °C reaction furnace. Sulfur is for-
med, but some H2S remains unreacted, and small Hydrogen Production from Biomass
amounts of SO2 are produced in these reactions. Biomass sources such as wood, manure, organic was-
H2S + 3/2 O2 SO2 + H2O (1) step tes, etc. can be converted into hydrogen with gasifi-
cation, steam reforming or biological conversion like
2 H2S + SO2 3/n Sn + 2 H2O (2) step
biocatalyzed electrolysis or fermentative technique.
General reaction for the process. Studies have shown that hydrogen can be produced
from biomass sources more economically. This re-
3 H2S +3/2 O2 3/n Sn + 3 H2O source, especially obtained by energy agriculture, by
(b): Catalytic Step: The remaining H2S reacts growing energy crops such as fast-growing sorghum
with SO2 to make more sulfur, the rate of that is on relatively barren lands that do not compete with
approximately 99.8%. The Claus method used for agriculture, is extremely useful for hydrogen produ-
hydrogen production is simply shown in Figure ction. In addition to methods such as pyrolysis, hete-
11. rotrophic, and photo fermentation, bacteria are also
Due to the presence of hydrogen sulfide dissol- used to obtain hydrogen from biomass. In case of hyd-
ved in seawater, it is necessary to pump sufficient rogen is produced from biomass, the CO2 balance in
density of H2S from the deep water to the surface the atmosphere will not change and there will be no
before it is separated from water. Details of this environmental damage since CO2 that was previously
highly complex system are given in the related absorbed through photosynthesis while the plant was
publication (Naman, et al., 2008Naman, et al. (2008). The source article does not provide a separate full bibliographic entry for this citation.). growing will be released.
Figure 11. Classic Claus Process (Method)
Source: Naman, et al., 2008.
Hydrogen Production from Seawater in the electrolysis of the sodium chloride solution
in the brine which is remaining from seawater tre- Considering the amount of water in the seas, and atment. Along with the ions formed by trace elethe potential of wind and solar energies, billions ments, except for Na+ and Cl-, are neglected at the of tons of hydrogen could be produced and that first stage, it should not be ignored that they are will be the ultimate solution to the world’s envialso matter of economic importance and may also ronmental, energy and water shortage problems affect the operating life of the electrodes. The stan- (Türe, 2021: para.14). At this point, since chlorine dard half-cell potentials of the reactions which are gas causes pollution of the electrodes in electrolysis compared with the standard hydrogen electrode due to the salt (NaCl) in seawater, either the water have indicated by E0. must be purified first by known techniques such as
reverse osmosis or making some new technologi- Cathode reduction reactions: :
cal development on the electrode is required. This
2 Na+(aq) + 2 e- → Na(s) E0 = -2,71 V
two-stage technique which can be realized using
renewable energy sources is schematically given 2 H2O(l) + 2 e- → H2(g) + 2 OH-(aq) E0= -0,83 V
below.
Apart from water (H2O) and salt (NaCl), sea Anode oxidation reactions:
water contains many minerals such as magnesium 2 Cl-(aq) → Cl2(g) + 2e- E0= 1,36 V
and calcium. The reactions that will take place at
the electrolysis of pure molten salt are half-cell re- 2 H2O(l) → O2(g) + 4 H+(aq) + 4 e- E0= 1,23 V
actions that neutralize the salt ions. Whereas, two The standard battery potential of the electrocreduction and two oxidation reactions of both wahemical battery is equal to the potential difference ter and salt will compete at the cathode and anode between the standard cathode potential (E0cathode) and the standard anode potential (E0 anode),
Figure 12. Hydrogen Production Alternatives from i.e, the half-cell potential difference between redu-
Seawater ction and oxidation.
E0battery = E0 cathode – E0 anode
When the cathode half-reactions are examined, since the reduction of sodium is much more negative comparatively the reduction of water, H2 will form at the cathode, and the Na+ ion will remain in solution. Except for some special catalysts, since the over potential of O2 is higher than the over potential of Cl2, undesirable toxic Cl2 gas, not O2, will be formed at the anode, although the battery potential is lower. Due to chlorine Cl2 and alkali NaOH(aq) Source: Türe, 2021. are the two main products in the processes, apart
Figure 13. Diaphragm Chlorine-Alkaline Process gas, are consisting in the gas mixture known as
air gas and widely used in many metropolitan of the world (Türe, 2021: para.25). Here are the reasons why hydrogen is safe: • Since it is 14 times lighter than air, it spreads quickly and becomes harmless; • In case the hydrogen tank is punctured, it does not ignite before it comes close to 35-40 cm; • When it burns, it creates only pure water; • Concentration in the air must be at least 4% for it to burn; • Does not emit heat such as wood, coal, or gasoline;
Source: Protank, 2018. • Extraction of pure water instead of toxic gas
and carcinogenic particles from the exhaust of from H2, the process is called chlor-alkali process. the vehicles. Cl2 is produced in the anode chamber, and H2 and Considering parameters such as flammability NaOH are produced in the cathode chamber in the limit in air, explosion energy, flame temperature diaphragm cell shown in Figure 13. The task of the and waste product, a higher safety factor (around diaphragm (Membrane) is to increase the yield of 1) has found for hydrogen, although the safety chlor-alkali product by preventing the formation factors of fossil fuels are between 0.5-0.80. These of undesirable intermediate products such as ClO-, findings clearly show that hydrogen is safer than ClO3-- and Cl- ions by preventing the contact of other fuels. An experiment on the safety of hyd- Cl2 with NaOH. The dissolution containing about rogen is shown in Figure 14 (Türe, 2021: para. 10-12% NaOH(aq) and 14-16% NaCl (aq) in the 26). cathode chamber is concentrated and purified by
evaporating some of the water and crystalli- Figure 14. Comparison of Hydrogen and Gasoline
zing NaCl(s). The final product is 50% NaOH Vehicles in Case of Fire
with up to 1% NaCl(aq).
Reliability of Hydrogen Fuel
The developing hydrogen technology remains much safer compared to the accidents that occur due to the wide use of nuclear fuels such as natural gas, oil, coal and uranium. In case of certain rules are followed in the use of hydrogen, the danger is reduced to a point where it is almost scarcely any. In fact, 50% hydrogen, 30% metha-
ne, and 7% carbon monoxide which is poisonous Source: Parsons, 2020.
Storage of Hydrogen International Energy Agency (IEA) and US
Department of Energy determined the target values The biggest problem in using hydrogen as a fuel is the for automotive implementation; for capacity: > 5-6%, lack of efficiency in its storage. Hydrogen generally for desorption temperature: <150 °C and for lifetime can be stored in three different ways: a) compressed, : >1000 fillings (Schulz, et al., 1999Schulz, et al. (1999). The source article does not provide a separate full bibliographic entry for this citation.). b) liquid and c) chemically bonded. Compressed and The importance of reliability and lightness in liquid hydrogen can be stored in pure form in tanks as the storage of hydrogen highlights the storage of well as physically stored in nanotubes. Chemically, it hydrogen in the hydride structure (Bilici, 2004Bilici (2004). The source article does not provide a separate full bibliographic entry for this citation.). is usually in the form of hydride. Storage in the form As seen in Figure 15, hydrides have a significant of hydride can be in solid form in metals as well as advantage in gas or liquid storage, especially in terms in liquid form in sodium boron compound. Research of hydrogen that can be stored in unit volume (Bilici, has shown that some alloys can store hydrogen at a 2004Bilici (2004). The source article does not provide a separate full bibliographic entry for this citation.). much higher density than pure hydrogen (Türe, 2021:
para. 27). Volumetric and gravimetric hydrogen Storage of Hydrogen with Metal Hydrides
density values that can be obtained with different Positive results have been obtained about the storage methods are given in Figure 15. storage of hydrogen as metal hydride in magnesium Based on the implementations that require the (Güvendiren, et al., 2004Güvendiren, et al. (2004). The source article does not provide a separate full bibliographic entry for this citation.). In these studies, 6% above-mentioned storage, the features intended for storage capacity has reached, but the desorption hydrogen storage in summarize; temperature remained above the target values. The • Recyclable storage capacity as high as possible; system needs improvements in terms of resistance • As low a desorption temperature as possible; to poisoning (Güvendiren, et al., 2003Güvendiren, et al. (2003). The source article does not provide a separate full bibliographic entry for this citation.). Currently, • Resistance to poisoning and therefore as high as studies are carried out on the basis of the Mgpossible reproducible filling numbers. Al-B system in line with the above-mentioned target values. The storage of hydrogen as metal Figure 15. Storage Types in Hydrogen and
Obtainable Volumetric and Gravimetric Density hydride in Mg2Ni and similar systems is carried
Values out at Osmangazi University and the studies on the
numerical modeling of hydrogen storage in LaNi5 in terms of heat are carried out at Nigde University (Mat & Kaplan, 2001Mat & Kaplan (2001). The source article does not provide a separate full bibliographic entry for this citation.).
Storage of Hydrogen with Boron Hydrides
Sodium boron hydride (NaBH4) is a strong reducing agent, can react with many organic and inorganic compounds, and contains more hydrogen atoms per unit volume than other boron hydrides. Although it has been used for different purposes in various parts of the industry for years, its hydrogen Source: Ewald, 1998. carrying capacity and being a boron-containing
compound have made sodium boron hydride a Figure 16. Operating Scheme of a Commercial
NaBH 4 - PEMFC System much more well-known compound recently (Bilici, 2004Bilici (2004). The source article does not provide a separate full bibliographic entry for this citation.). Sodium boron hydride has firstly obtained by the method known as the Schlesinger process, as seen in the equation below, as a result of the conversion of boric acid to trimethyl borate (B(OCH3)3) with methanol and then its reduction with sodium hydride.
B(OH)3 + CH3OH → B(OCH3)3 + 4NaH →NaBH4 + 3NaOCH3 Source: Güvendiren & Öztürk, 2003. When the stoichiometric ratios in the equation
are examined, it is seen that 75% of the required the amount of moisture.
sodium is converted to sodium methoxide which Some advantages of using sodium borohydride
is a by-product. This low efficiency hinders the are:
applicability of the method on a larger scale and • The controllability of the reaction is ultrahigh
is the biggest factor affecting the production cost (reaction stops when the catalyst is removed from
of sodium borohydride (Ortega, 2003Ortega (2003). The source article does not provide a separate full bibliographic entry for this citation.). 66% of the the environment, e.g. Ruthenium, platinum, etc.);
world’s sodium metal is produced in the USA, 14% • The reaction takes place at room temperature
in the UK, and the rest in Germany, France, Japan and pressure (no additional energy is required to
and Russia. Annual sodium metal production is 250 liberate the hydrogen).
thousand tons. When sodium boron hydride and • It is a simpler and cheaper method compared to
water react, 10.8% by weight of hydrogen is released other methods for the production of small amounts
in accordance with the following exothermic of hydrogen.
reaction and sodium metaborate (NaBO2) is • The reaction rate is quite stable and the H2
produced as a by-product (Li, et al., 2003Li, et al. (2003). The source article does not provide a separate full bibliographic entry for this citation.). production is slow and stable. Catalysts can be used
many times.
Catalyst Sodium metaborate can be reused in the
production of sodium borohydride.
NaBH4 + 2 H2O → NaBO2 + 4H2 ∆H = -218 kJ.mol-1
Hydrogen gas produced in this way can be used
As can be seen, the amount of hydrogen released as fuel in vehicles with a small change to be made
as a result of the reaction is twice that of the hydrogen in internal combustion engines. The flow diagram
bonded in the form of hydride, and 4 moles of H of the liquid-based sodium boron hydride system
come from NaBH4 and 4 moles of H from H2O. Since required for the fuel systems of vehicles using
the reaction is exothermic, the hydrogen obtained sodium boron hydride is shown schematically in
from the system is moist and depending on the Figure 16.
environment in which it will be used, the hydrogen Sodium boron hydride, NaBH4, is a white-looking,
gas must be passed through a system that regulates non-toxic, stable compound up to 300°C in dry
Figure 17. Comparison of Chemical Hydrides H-capacity of substances has been used as a measure
of storage capacity. NaBH4 has more hydrogen storage qualifications than many hydrogen alloys (Figure 17). Also, studies have shown that sodium borohydride has the ability to hold more hydrogen than the densest compressed air tank (Andersson & Grönkvist, 2019Andersson & Grönkvist (2019). The source article does not provide a separate full bibliographic entry for this citation.).
Sodium Boron Hydride Synthesis and Hydrolysis Costs
Source: International Journal of Hydrogen Energy, 2019. The Bayer process is the most widely used
commercial process for the synthesis of sodium
form. It can be found in powder form, granule form, borohydride. In this process, certain amounts of
or as a 12% solution in NaOH. Sodium hydroxide anhydrous borax, sodium metal, and quartz are
(NaOH) is added to these solutions in order to heated under 3 atm hydrogen pressure at 500°C
extend the shelf life of the sodium borohydride in a stirrer type autoclave for 2-4 hours. After
solution. Under normal storage conditions, the extraction of the reaction product with ammonia
annual loss of NaBH4 solution in 12% NaOH is less and evaporation of the ammonia, NaBH4 is obtained
than 0.1%. in a high yield. Sodium metasilicate is formed as a
Sodium borohydride slowly decomposes into secondary product. The reaction is given below:
sodium metaborate and hydrogen when gets
into contact with moisture in the air due to its 1/4 Na2 B4O7 + 4Na + 2H2 + 7/4 SiO2 → NaBH4 + 7/4
hydroscopic nature. Rapid and controlled hydrogen Na2SiO3
production from NaBH4 can be achieved by the ∆Gº (298) = -411.3 kJ/mol-NaBH4 ; ∆Hº (298)=addition of acidic compounds or metals that act 541.348 kJ/mol NaBH4 as catalysts such as ruthenium, nickel, cobalt, and
platinum. As a result of the exothermic hydrolysis By calculating the enthalpies of the reacting raw
reaction of sodium borohydride solution using materials and reaction products at the reaction
a catalyst, 2.37 liters of H2 /g NaBH4 is released. temperature, the energy cost required for the
Half of the hydrogen released comes from sodium reaction was calculated as approximately $2/kg
boron hydride and the other half comes from water. for the production of 1kg of sodium borohydride.
Therefore, the hydrogen content released from the However, ideal conditions were assumed and the
concentrated sodium borohydride solution is quite energy cost required to remove by-products from
high and can easily compete with other known the system was not taken into account in this
mobile hydrogen storage technologies in terms of calculation. The cost of the raw materials required
energy content per weight. The theoretical hydrogen for the Bayer process is a minimum of $10 for the
capacity produced by hydrolysis from sodium production of 1 kg of NaBH4.
boron hydride is 10.8% by weight. The mass-based If the sodium borohydride required for the
hydrolysis reaction of sodium boron hydride will vehicles. Considering the commonly used fuels
be produced by the Bayer process as above, and today, we see that most of them can only be used for
then used in hydrolysis, the cost of NaBH4 for the certain applications. It is inappropriate to use coal in
synthesis of 1 kg H2 is approximately $50 under ideal automobiles or airplanes in terms of practicality. It is
conditions. However, a catalyst such as ruthenium possible to use hydrogen easily almost everywhere.
must also be used in this reaction. According to It can be easily used instead of natural gas in
the type of catalyst, the cost of obtaining 1 kg of heaters, ovens, and geysers for heating purposes
hydrogen from sodium borohydride reaches $80/ in homes. Hydrogen can give energy not only with
kg, and this cost can be higher depending on the flaming combustion but also with very different
type and amount of catalyst. On the other hand, it cycles such as catalytic combustion, chemical, and
should be noted that if NaBH4 is not produced in electrochemical conversion, unlike fossil fuels.
the system by the Bayer process and is purchased at It is possible to use hydrogen fuel in all vehicles
$47, the cost reaches $222, and if the catalyst cost is such as buses, trucks, automobiles, tractors, and
added to this, the hydrolysis reaction cost will reach agricultural machinery since it provides high-
approximately to $260 (Türe, et al., 2006Türe, et al. (2006). The source article does not provide a separate full bibliographic entry for this citation.). efficiency use in vehicles by generating electricity
It is important for the continuation of the system with fuel cells as well as internal combustion engines.
cycle that the sodium metaborate, which is released Since fuel cells used for electricity generation
next to the hydrogen as a result of hydrolysis, is from hydrogen have a very important place today
converted back to sodium borohydride and given and in the future, this matter is given below in
to the system. Studies have shown that NaBH4 more detail. Hydrogen can be used in fuel cells or
recycling can occur by using the MgH2 (Amendola vehicles instead of gasoline and in radiators, ovens,
et al., 2000) dynamic hydration/dehydration process and water heaters instead of natural gas in homes.
or using Mg2Si. In this study, the cost of conversion Today, hydrogen is used almost everywhere from
reaction from NaBO2 to NaBH4 using Mg2Si was Figure 18. Usage Areas of Hydrogen calculated as approximately $15/kg H2. As a result, by combining all these costs, in ideal conditions, the total cost of sodium borohydride synthesis, hydrogen synthesis, and recycling of sodium metaborate to sodium boron hydride is determined as approximately US$ 110/kg H2 without taking into account system losses. However, as mentioned above, if sodium borohydride is not produced in the system and purchased, this cost will be approximately $290/ kg H2 (Türe, et al, 2006Türe, et al. (2006). The source article does not provide a separate full bibliographic entry for this citation.).
Hydrogen Energy Applications
It is of great importance that fuel can be used everywhere, for example in industry, homes, and
Table 4. General Commercial Uses of Fuel Cells
Source: Xiao, 2021.
cell phones to airplanes. Since high-efficiency it produces pure water as waste, does not cause
electricity can be produced with fuel cells, the usage environmental pollution, and noise and does not
areas of these batteries are very wide. In Figure 18, contain moving parts. Fuel batteries are generally
some of the vehicles and products that run with fuel classified as polymer electrolyte (PEM), alkali,
cells are shown. It is possible to count among that, the phosphoric acid, molten carbonate, and solid oxide
vehicles such as cars, buses, motorcycles, bicycles, golf fuel cells, depending on the type of electrolyte
carts, forklifts, utility vehicles, electrical backup units, used in the cell. PEM fuel cell is especially used in
aircraft, locomotives, submarines, etc. Hydrogen is vehicles. Fuel cells are more energy-efficient than
widely used in various fields from margarine making conventional internal combustion systems used in
to metal processing in the industry. automobiles and certainly create less pollution. In
addition to this, system size, weight, commissioning Fuel Cells time, operating life, and price are key areas required
Fuel cells are described as high-efficiency for improving automotive applications.
electrochemical energy conversion devices and The fuel cell has an important place in the use
basically composed of an electrolyte placed between of hydrogen. Fuel cell systems can be used in a
the anode and the cathode. These devices which portable way, as well as in transportation, mobile
produce electricity as a result of the chemical systems, and stationary applications. As well as
reaction of hydrogen used as fuel with oxygen, fuel cells can generally be used wherever electrical
are seen as the energy production source of the energy is needed, their commercial use, in general,
future. The main advantages of the fuel cell are that is as in Table 4. While mobile phones, laptops,
digital cameras, and camera batteries can be given contact with the electrolyte, while the gaseous fuel is
as examples for portable applications, hospitals, continuously fed from the anode, while the oxidizing
workplaces, homes, and computer networks where gas is continuously fed from the cathode. H2 from the
generators and uninterruptible power supplies are fuel is converted to H+ at the anode in PEM electrode
used can be examples for stationary applications. reactions. H+ passes through the polymer electrolyte
The world’s leading automobile manufacturers in the membrane and combines with O2 at the cathode to
transportation sector have completed the production produce water. The operating temperature is around
of fuel cell-powered automobiles and bus prototypes. 80ºC.
A five-year project was started in 2003 for the 1MW As an electrolyte membrane has two functions to
locomotive. In addition, fuel cells have been started provide ionic communication between the anode and
to be used in mining due to their safety. cathode, and to separate the two reacting gases. Today,
the standard electrolyte material used is Nafion which PEM (Proton Exchange Membrane-Polymer) is a Teflon-based material produced by DuPont in the Fuel Cell mid-1960s for space applications. The electrodes used
PEM Fuel cells, also known as Proton Exchange in the PEM cell are typical gas diffusion electrodes and
Membrane or Polymer Electrolyte Membrane, are isolate the hydrogen gas into protons and electrons.
a type of fuel cell developed for use in vehicles, The layer thickness of the catalyst is 5-50 µm and
especially in the USA, Japan, and Germany. Its first contains Pt microcrystals with a diameter of 2-4 nm.
major application is the use of a PEM fuel cell with Pt has been determined as a suitable catalyst for
1 kW output by GE in the Gemini spacecraft. Pure Figure 19. PEM Fuel Cell Diagram water produced as a by-product has also been used as drinking water by astronauts. There has been a great increase in studies that will improve both the cost and performance of PEM fuel cells in the last 5 years (Wilkinson & Steck, 1997Wilkinson & Steck (1997). The source article does not provide a separate full bibliographic entry for this citation.). It has been demonstrated that complete fuel cell systems can be used for many transport applications (including city transit buses and coaches). Recent studies have focused on cost reduction and the production of catalysts, membranes, and bipolar plates in large quantities. These studies also coincide with studies on increasing power density, improving water management, operating in ambient conditions, increasing tolerance to converted fuel and increasing module life. A schematic of an example PEMYP cell is shown in Figure 19. In PEM, as in other fuel cells, the fuel cell module
has two electrodes with high gas permeability and in Source: NIST, 2004.
both anode and cathode reactions today. However, Phosphoric Acid Fuel Cell
it is tried to be used in a minimum amount by using
many methods since it is expensive. Carbon/graphite If the alkaline fuel cell used in space
plates for current collection and distribution, gas applications is not counted, the closest fuel cell
distribution, and thermal management have using to commercialization is the Phosphoric Acid Fuel
in most PEM cells. The thickness of this layer is ~350 Cell today. This fuel cell, in which 100% phosphoric
µm and has a catalyst layer attached to one side. acid is used as the electrolyte, operates at 150-
220°C. The phosphoric acid which is acting as the
Direct Methanol Fuel Cell electrolyte has fixed in a porous layer between
The first studies on these batteries, which are also the electrodes. Both anode and cathode are gas
admitted as a type of PEM fuel cell, were made by diffusion electrodes. This fuel cell is operated
Shell and ESCO-Exon in the 1960s-70s. They obtained at high temperatures due to phosphoric acid is a
low current density due to the negative effect of direct poor conductor at low temperatures. In addition to
methanol usage on the Pt-Ru catalyst and overvoltage this disadvantage, phosphoric acid provides many
at the anode. Research has been carrying on these advantages as an electrolyte. Among them, it is
batteries, which were ignored because the efficiency possible to count its excellent thermal, chemical
obtained in the early 1990s was below 25%. As such and electrochemical stability and relatively lower
in PEM, acidic solid polymer Nafion is used as the volatility than other inorganic acids above 150°C.
electrolyte, and Pt-Pd superimposed carbon is used Molten Carbonate Fuel Cell as the electrode. The most important feature that
distinguishes these batteries from PEM is that the fuel The molten carbonate fuel cell operates at
methanol/ethanol can be used directly without the very high temperatures such as 600-650 °C and
need for a fuel converter, and since it does not contain is one of the second-generation fuel cells which
a fuel processing unit, it is less complex, lighter, and has developed recently, i.e., it needs a lot of
cheaper than other types. development in order to be commercialized. A
mixture of alkaline carbonates, for example (Na Alkaline Fuel Cell and K), or a mixture of Li2CO3-K2CO3 is used
In an alkaline fuel cell, 35-50% KOH is used as an as the electrolyte. This electrolyte has attached
electrolyte in low temperature (at 120°C) applications. to a ceramic matrix structure. Those are can
In the high temperature (at 250°C) alkaline fuel cell be counted as the advantages, that the cell can
used in the spacecraft Apollo, 85% KOH was used as be produced by printing technique from easily
the electrolyte. Low-temperature alkaline systems can available metal sheets, that Ni catalyst is sufficient
operate at room temperature and have the highest instead of expensive precious metal catalysts in
voltage efficiency among all fuel cell systems. Cells cell reactions, that CO is a type of fuel that can
and electrodes can be produced from carbon and be used directly, that the steam released in the
plastics at a low cost. It has a long life of 15,000 hours cell is at a high enough temperature to be used in
due to adapt well to many materials. In addition, there turbines or cogeneration applications. However,
are many catalyst options available for these fuel cells the Molten Carbonate fuel cell has disadvantages
such as Ni, Ag, and metal oxides. such as operating at high temperatures, causing
corrosion, and thus reducing the life of the cell to reach very high temperatures (1000°C),
components. the fuel can be used directly in the fuel cell
without the need for expensive catalysts as in Solid Oxide Fuel Cell low-temperature applications. Since the gas
The solid oxide electrolyte is tempting for passage is low and the electronic conductivity
industrial applications due to some specific of the electrolyte is high, these batteries can
benefits. Non-porous metal oxides as a catalyst give at least 96% of the theoretical voltage in
are used ZrO2 which is containing 8-10% (mol) an open circuit. Among the advantages can be
Y2O3. Although pure zircon is an insulator, it counted of solid oxide fuel cells are that it does
shows conductivity with the addition of Y2O3. not cause problems like other electrolytes in the
Using CeO2 instead of ZrO2 can lower the operating conditions of the cell due to the solid
operating temperature. In this fuel cell, porous electrolyte is very stable, there are no problems
gas diffusion electrodes are used as in other fuel such as interface problems, water overflow from
cells. While porous Pt has been used as anode the pores, the necessity of wetting the catalyst
and cathode, Ni-ZrO2 (containing Y2O3) or CO- since there is no liquid phase. For a general
ZrO2 as anode and LaMnO3 with Sr loaded as comparison, the types and properties of fuel cells
a cathode are used recently. Since it is possible are given in Table 5.
Table 5. Types and Features of Fuel Cells
Source: Fuel Cell Today Industry Review, 2008.
Current Uses of Hydrogen Energy
The applications of hydrogen as an energy carrier in almost every field are now well known. It is inevitable that these will increase even more in
the near future. Some of the vehicles which utilize Applications of Hydrogen in Marine Vehicles
hydrogen fuel are shown in Figure 20. Due to the increasing awareness of climate The H2 City Gold model developed by Toyota change and marine pollution in recent years, can travel 400 km with 5 hydrogen tanks with a restrictions have been imposed on ships total capacity of 37.5 kg placed on the roof of the operating with petroleum-derived fuels, bus. The bus, whose fuel tanks can be filled in especially in the ports of northern countries less than 8 minutes, reveals its environmentalist such as Sweden and Norway, and the use of clean identity by only releasing water vapor. fuels such as hydrogen on ships has begun to be Today, almost all automobile companies have encouraged. Examples of hydrogen watercraft vehicles working with hydrogen fuel, and it has are shown in Figure 22. been announced that they will increase their Commercial ship operators and shipyard owners production rapidly in the coming years. Large oil in Turkey have also started work on the use of companies such as Shell and BP are also opening hydrogen fuel in this context. There are still many hydrogen filling stations rapidly (Figure 21). ships operating with hydrogen fuel in the world,
Figure 21. Hydrogen Filling Stations and their number is increasing. Shown below are
hydrogen-fueled ships still in circulation. Hydrogen/ oxygen fuel cells (especially low-temperature fuel cells such as PEMFC) have ideal features for powering submarines. They do not need air, can operate under the sea if fuel (hydrogen) and oxide (oxygen) are stored. They produce no absorption or waste material other than water, thus maintaining zero buoyancy. Since they have no moving parts, they operate silently, reducing the sonar (sea radar) signal. They release heat at low temperatures and
thus produce very little thermal traces. They are of hydrogen/hydrogen combination cooling systems
enormously productive. They provide long cruises in space heating and cooling and, in freezers.
and little waste of time. Either flame combustion or catalytic burners can
be used for cooking. It is very important to design Hydrogen-Powered Airplanes combustor vessels so that the hydrogen/air velocity
Liquid hydrogen has many advantages as a fuel is always greater than the flame propagation velocity
in commercial subsonic and supersonic aircraft. The in hydrogen/air mixtures to prevent backfire
key advantage of liquid hydrogen is its high energy propagation.
content (142 MJ/kg), which is 2.8 times the energy Conclusion and Recommendations content of conventional jet fuels. For this reason,
an aircraft powered by liquid hydrogen must carry Hydrogen is a safe, clean and endless fuel in all
less fuel, up to one-third the mass of a conventional respects, and it has no harmful side. The only
aircraft. A hydrogen-powered subsonic airliner disadvantage that can be considered as a disadvantage
needs on average 16% less fuel (energy-wise) to today is that the price is expensive since it is not in
complete the same flight compared to a regular widespread commercial use yet, so that is valid for
airplane. This advantage would be even higher each new technological product. For example, it is
(28%) in supersonic aircraft. Airbus and Boeing are well known that the prices of technological products
working intensively on hydrogen-fueled aircraft. such as mobile phones or calculators when they
Despite popular opinion, hydrogen is a safer fuel first hit the market are tens of times their current
for air transport and is currently used as jet fuel. The prices. In addition, it has been calculated that the
damage and loss in a liquid H2 fuel aircraft collision investment made in this sector since the discovery
will be less than in a standard fuel aircraft collision. of oil is estimated to be 160 trillion (160,000 billion)
In April 1988, one of three liquid hydrogen-powered Dollars. Hydrogen pumps must be set up at petrol
turbofan engines of a commercial airliner’s aircraft filling stations and, of course, large amounts of
(Tupolev 155) was demonstrated in the USSR. On hydrogen must be produced due to widespread usage
June 19, 1988, American pilot, William H. Conrad, of hydrogen. Studies in this area have started in many
became the first person who operate an airplane countries. For instance, in April 2004, California
(Grumman-American “Cheetah”) powered entirely Governor Arnold Schwarzenegger started work to
by liquid hydrogen (Maniaci, 2008Maniaci (2008). The source article does not provide a separate full bibliographic entry for this citation.). increase the number of hydrogen filling stations from
12 to 200 in the next 6 years within the framework of Hydrogen Applications in Buildings the “Hydrogen Highways” project and gave the good
Hydrogen can be used to heat or cool an area. news that there will be filling stations for hydrogen
Likewise, with minor modifications, it is suitable cars every 30 km from now on (Türe, 2020Türe (2020). The source article does not provide a separate full bibliographic entry for this citation.).
for water heating as natural gas is used today. In Similar to natural gas or air gas, hydrogen gas can
addition, hydrogen can be used in catalytic burners be transported anywhere easily and safely through
by directly heating and humidifying the air instead pipelines. It is possible to give that as an example of
of flame combustion. Since no further emissions the transportation of hydrogen by pipe, the 80 km
are produced, these burners can also be used safely long pipe network used by the petroleum industry
indoors. The usage of hydrogen will be in the form in Texas, and the 204 km pipeline that was put into
operation in Germany in 1938 in the Ruhr basin there should be a producing country instead of
and still continue to transport hydrogen under 15 technology transfer, which is an expensive method.
atmospheres pressure. In order for Turkey to get rid of foreign
Sodium boron hydride, which has gained great dependency in the field of energy and to become
importance as a hydrogen storage and transport a developed country, it is necessary to make good
medium today, also has an important potential use of the hydrogen energy opportunity. Informing
in special boron chemicals. When the features of the Turkish society about hydrogen starting from
sodium borohydride such as being able to store primary school, directing the studies of scientists in
more hydrogen than other compounds with similar Turkey to hydrogen, especially hydrogen production
purposes, being non-flammable and non-explosive, using renewable energy sources are crucial issues.
and releasing hydrogen with an easily controllable In order for Turkey to get rid of foreign dependency
reaction, are evaluated together with new and clean in the field of energy and to become a developed
energy policies, it will create a widespread and country, it is necessary to make good use of the
permanent consumption area for the rich boron hydrogen energy opportunity.
resources of our country. Turkey, which has to References
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