Hydrogen Technologies: A Critical Review and Feasibility Study

Abstract

Nowadays, one of the most important areas in refining the energy sector in the developed countries is the transition to environmentally friendly technologies, and hydrogen energy production is the most promising of them. In this rapidly advancing area, significant progress in creating new technologies for hydrogen fuel generation, transportation, storage, and consumption has been recently observed, while a fast-growing number of research papers and implemented commercial projects related to hydrogen makes it necessary to give their general review. In particular, the combination of the latest achievements in this area is of particular interest with a view to analyzing the possibility of creating hydrogen fuel supply chains. This paper presents an analytical review of existing methods of hydrogen production, storage, and transportation, including their key economic and energy-related characteristics, and proposes an approach to the creation, analysis, and optimization of hydrogen supply chains. A mathematical model has been developed to determine the cost of hydrogen, taking into account the supply chain, including production, transport and storage. Based on the results of modeling in the given scenario conditions for 2030, 2040 and 2050, promising hydrogen supply chains have been established. Under the various scenario conditions, hydrogen production by 2050 is most preferable by the method of steam conversion of methane with a cost of 8.85 USD/kg H₂. However, due to the environmental effect, electrolysis also remains a promising technology with a cost of hydrogen produced of 17.84 USD/kg.

1. Introduction

Today, governments of many countries have updated their energy strategies [1,2] to add new goals to reduce harmful emissions into the environment, primarily carbon dioxide emissions. This trend, first and foremost, is motivated by the problem of global climate change. According to [3], the energy sector makes the greatest contribution to greenhouse gas emissions, accounting for more than 42% of the total emissions.

Hydrogen is one of the most common elements occurring in nature, and its potential as a source of energy has long attracted the attention of scientists and engineers [4]. In recent years, interest in hydrogen technologies has only intensified, and this is not surprising as hydrogen can become a key factor in the transition to more environmentally friendly and more efficient production and transport options, as well as in light of the need to reduce greenhouse gas emissions and shift to more environmentally friendly energy sources [5], since hydrogen combustion does not produce carbon dioxide emissions, but only water.

In addition to environmental cleanliness, one of the main advantages of hydrogen is its high energy density; this means that small amounts of hydrogen can be used to produce a large energy bulk. In addition, hydrogen can be obtained from several sources, including water, biomass, and various gases, such as methane [6], which makes it more affordable and more cost-effective [7].

The use of hydrogen in different areas is already beginning to gain momentum. It can be used as fuel for cars, trains, and aircraft, which will significantly reduce emissions of harmful substances and decrease dependence on oil [8]. Hydrogen can also be of use in electricity generation, for instance, as a source of energy for households and industry [9,10,11,12,13].

Considering policies and measures that governments around the world have already put in place, it is estimated that the hydrogen demand could reach 115 Mt by 2030. In the power sector, the use of hydrogen and ammonia is attracting more attention; announced projects stack up to almost 3.5 GW of potential capacity by 2030 [14]. Benefiting from abundant water and renewable electricity sources, alkaline water electrolysis by using electricity generated from renewable energy sources through electrochemistry is believed to be one of the key techniques for the hydrogen production in future [15,16]. According to [17], although the world market scale of hydrogen economy is merely USD 80 USD in 2015, it will rapidly increase to USD 400 billion by 2030, USD 800 billion by 2040, and USD 1600 billion by 2050.

The great number of different methods of hydrogen production, storage, and transportation dictate the need to develop approaches to selecting the most promising “hydrogen supply chains” in order to identify the most economically advantageous ways to supply fuel to industrial consumers. This paper presents an analytical overview of existing and commercially feasible methods of hydrogen fuel production, storage, and transportation; it also outlines an approach to creating the most cost-effective fuel supply chains.

2. Hydrogen Production Technologies

Today, there are a lot of hydrogen production methods, which can be classified depending on the volume of harmful emissions they involve. For the sake of simplicity, produced hydrogen is divided using “colors”, which characterize the environmental friendliness of the production process. To date, there are many different color classifications of hydrogen production methods; one of the most common is a six-color classification into grey, blue, turquoise, green, purple, and others. The latter covers a number of methods that cannot be attributed to emissions produced with the previous five techniques, e.g., biomass-based methods.

Green hydrogen is the most environmentally friendly and is associated with the lowest emissions in the aggregate of all processes necessary for its production. An example of green hydrogen production methods is electrolysis for which electricity comes from environmental sources of electricity, such as renewable energy sources (e.g., solar power plants, wind farms, etc.) [18].

Purple hydrogen is like green hydrogen in terms of its characteristics and production method; however, electricity for electrolysis is supplied from nuclear power plants, with no CO₂ emissions in electricity generation, though it is less environmentally friendly because of radioactive waste.

Nowadays, most hydrogen is produced by steam methane reforming in which natural gas is converted into H₂ and CO₂ using superheated steam [19]. With this production method, the resulting hydrogen is “gray”, that is, the production process releases carbon dioxide into the atmosphere. A solution to this problem is the technology of CO₂ capture and storage (CCS), which, however, increases the cost of resulting “blue” hydrogen [20].

The “turquoise”, promising method to produce hydrogen from fossil fuel is pyrolysis, which is the decomposition of organic matter at high temperatures (500–800 °C) [21]. Methane pyrolysis can be used to produce hydrogen and fixed carbon, which makes this method more environmentally friendly.

Water splitting occurs mainly in electrolyzers, which are commissioned at an ever-increasing pace [22]. There are many different types of electrolyzers, though proton exchange membrane (PEM) electrolyzers, alkaline electrolyzers and solid oxide electrolyzer cells (SOEC) are the most widely used ones to date.

Water can also be decomposed by thermolysis in which water splitting occurs at a high temperature (>2500 °C) [23]. The reaction temperature can be reduced with the use of catalysts to achieve thermochemical decomposition at 600–1600 °C, depending on the catalyst type.

The production of gray hydrogen using coal gasification technology is one of the least environmentally friendly methods due to the high level of greenhouse gas emissions. However, the solution may be the use of CCS, but additional capital costs for disposal will increase the final cost of hydrogen for the consumer [24,25].

2.1. Steam Methane Reforming

The process of producing hydrogen by steam reforming of methane (SMR) is one of the most common methods of hydrogen production in industry [26,27]. In the USA, about 95% of hydrogen is produced on an industrial scale by steam reforming of methane in catalytic reactors [28,29]. It is based on the reaction of methane with steam in the presence of a catalyst, which produces hydrogen and carbon monoxide. In this case, the reaction of methane with steam occurs, which is accompanied by the release of heat and the formation of hydrogen and carbon monoxide.

Therefore, SMR-based hydrogen production is an endothermic process requiring high temperatures (usually 700 to 1100 °C) and high pressure (1 to 3 MPa) to achieve a high methane conversion factor.

Natural gas steam reformers typically use reactors with external heating and coated metal catalysts. Steam methane reformers typically use inexpensive nickel catalysts, and the two most important steam reforming parameters are the steam-to-carbon ratio and the process temperature. From the point of view of energy efficiency, their low values are preferable, but they increase the risk of carbon formation in the catalyst bed and its poisoning.

The steam reforming process is carried out in tube furnaces, with reactor furnace designs from different companies, such as Howe-Baker (USA), Haldor Topsoe (Denmark), Foster Wheeler Corp. (USA), Technip (France), and various schemes for heating reactor tubes with a catalyst are used. However, in all furnace designs, flue gas heat is used to produce steam, as well as to preheat raw materials and air supplied to the burners. The location of the burners can be vertical (the most common option), lateral and terraced. For installations of low productivity, a number of companies offer tube furnaces with a lower supply of raw materials and a lower location of the burners.

The problem of catalyst poisoning with sulfur in the implementation of steam reforming of methane was successfully solved by Haldor Topsoe by reducing the overall activity of the catalyst or using a pre-reformer for preliminary conversion under mild conditions of heavier methane homologues [30]. Now, the main efforts of engineers are aimed at improving heat and mass transfer, optimizing the process and minimizing the size of the reactor.

An important element of the technological scheme for the conversion of natural gas into synthesis gas is the synthesis gas compressor. Compression of synthesis gas leads to its significant heating, and the presence of up to 70% hydrogen in synthesis gas leads to the need to use special alloys resistant to hydrogen embrittlement for the manufacture of reformers.

Therefore, in some cases, the synthesis gas compressor may be the most expensive unit in the entire process chain. The disadvantages of the steam reforming method include the fact that the composition of the resulting synthesis gas does not always correspond to the required indicators for its subsequent processing, as well as the fact that a large amount of natural gas is consumed for external heating of the reaction tubes.

SMR is a good process for hydrogen production due to its high efficiency and low carbon emissions. In addition, it can be integrated with other industrial processes, such as natural gas reforming or gasification, to further increase its effectiveness and reduce costs.

Despite the potential advantages, some problems are still associated with this process, including catalyst deactivation and the production of carbon monoxide, which is a toxic gas [31]. Another important problem in the development of technologies using methane and other hydrocarbons is the need to ensure reliable fire safety [32]. Nevertheless, current studies are focused on addressing the above problems and increasing the overall process performance.

2.2. Plasma Reforming for Hydrogen Production

One hydrogen production method is plasma reforming, which is based on the use of superheated plasma for converting hydrocarbon materials into hydrogen [33].

The process of plasma reforming starts with the supply of hydrocarbon material to the reactor, where it is subjected to a high-frequency electric discharge. This leads to the production of plasma with a temperature of about 10,000 °C; therefore, the process requires the use of special materials to withstand such temperatures. Under the influence of high temperatures, hydrocarbon molecules split into hydrogen and carbon molecules.

The produced hydrogen is purified and cooled down to room temperature. Plasma reforming results in high-quality hydrogen, which can be used in several areas, such as power generation, the chemical industry, and transport.

One of the main advantages of plasma reforming is its high efficiency and environmental cleanliness. Unlike conventional hydrogen production methods, plasma reforming does not require the use of catalysts and does not release harmful emissions into the atmosphere. Moreover, this process can involve different types of hydrocarbon materials, which makes it a versatile and flexible hydrogen production technique.

Among the shortcomings, of note is the high level of electrode erosion when operating at elevated pressure, as well as high energy consumption. To date, one of the promising areas for the development of this method of hydrogen production is the use of microwave technologies [34].

Therefore, plasma reforming is a promising method of hydrogen production, which can significantly increase the efficiency and environmental cleanliness of the production of this gas.

2.3. Coal Gasification for Hydrogen Production

Coal gasification is a process in which coal is turned into fuel gas. One of the main components of the resulting gas is hydrogen [35].

The process of coal gasification begins with the preparation of coal, which is placed in a special reaction chamber. By a high-temperature reaction, coal is then decomposed into gases, such as hydrogen, methane, carbon monoxide, etc.

The resulting gas is passed through a cleaning system to remove impurities and other contaminants. After that, the gas is supplied as fuel for various production processes, including electricity generation.

There are several techniques used to produce synthesis gas (syngas) from coal, including direct and indirect coal gasification.

Direct gasification is carried out by heating coal in a gas mixture consisting of steam and oxygen. The output of this process is syngas, which can be used in the production of different chemicals and fuel.

Indirect gasification is carried out by superheating coal in the reactor without oxygen. The output of this process is syngas, which can be used in the production of different chemicals and fuel.

One of the main advantages of coal gasification is the high efficiency of the process and the possibility of obtaining a large amount of hydrogen from a relatively small amount of coal. To date, the efficiency of modern coal gasification plants can reach 80–90% [36,37]. To improve the environmental efficiency in the production of hydrogen by gasification technology, the most promising solution may be the use of technologies for capturing and storing carbon dioxide. However, the use of CCS significantly increases the capital cost in the hydrogen production chain.

Thus, coal gasification is an effective and promising method for producing hydrogen, which can be used in various industries.

2.4. Methane Pyrolysis

Methane pyrolysis is a promising hydrogen production method. This process is based on methane thermal decomposition at high temperatures to produce hydrogen and carbon [38].

The process starts with the supply of methane to the reactor, where it is treated with high temperatures. The temperature in the reactor can reach 800 to 1000 °C. Under such conditions, methane begins to split into hydrogen and carbon molecules.

The produced hydrogen will be purified and cooled down to room temperature. Methane pyrolysis results in high-quality hydrogen, which can be used in different areas, such as power generation, the chemical industry, and transport.

Several techniques are used to produce hydrogen by hydrogen pyrolysis, including direct and indirect pyrolysis.

The direct method involves heating methane in the presence of a catalyst. It ensures a high concentration of hydrogen but can also cause carbon formation on the catalyst surface.

The indirect method involves decomposing hydrocarbons into hydrogen and carbon. It is more stable and more efficient, although it requires additional stages of processing.

One of the main advantages of methane pyrolysis is that this process can involve different types of hydrocarbon materials, which makes it a versatile and flexible hydrogen production technique [39].

Catalyst regeneration is one of the key problems on the way to the widespread use of pyrolysis technology for hydrogen generation. The use of activated carbon is accompanied by rapid deactivation of the catalyst due to carbon deposition. Today, the search for cheap and efficient catalysts is one of the key directions [40].

2.5. Hydrogen Production from Biomass using Dark Fermentation

Dark fermentation is a process wherein bacteria generate hydrogen from organic matters in the absence of light. In the context of hydrogen production, dark fermentation can be used to decompose biomass into hydrogen and carbon dioxide [41,42].

During dark fermentation, bacteria such as Clostridium produce hydrogen by enzymatic decomposition of organic matter [43]. To produce hydrogen by dark fermentation, biomass, such as plant waste or manure, is placed in a reactor where it is exposed to bacteria. As a result of this process, the decomposition of organic substances into molecules of hydrogen and carbon dioxide occurs.

One of the main advantages of dark fermentation is its ability to use different types of biomass to produce hydrogen. Food waste, plant residues, and animal husbandry waste have the greatest potential for use as a substrate for hydrogen production. To date, for the commercial application of the technology, there are not enough studies on the effect of fermentation conditions on the efficiency of biohydrogen production, namely the temperature, pressure, and pH level in the reactor.

2.6. Electrolysis

Electrolysis is one of the most common methods for the production of hydrogen [44]. During electrolysis, an aqueous electrolyte solution is subjected to an electric current, which leads to the decomposition of water into oxygen and hydrogen.

During electrolysis, an electric current is passed through the electrolyte, which leads to the dissociation of water molecules into oxygen and hydrogen ions. Oxygen ions move to the anode, where they are oxidized to form oxygen molecules and electrons. Hydrogen ions travel to the cathode, where they accept electrons to form hydrogen molecules.

Different electrolyte systems developed for water electrolysis include alkaline water electrolysis, proton exchange membranes (PEM), alkaline anion exchange membranes (AEM), and solid oxide water electrolysis (SOE) [45]. Different materials and operating conditions are used in these systems. On the basis of different operating temperatures, low- and high-temperature water electrolysis are also possible.

The main types of electrolyzers are: with proton membranes, alkaline and solid oxide. The main differences are the materials that determine the temperature and pressure of the reaction, current density and voltage. Alkaline electrolyzers currently have the lowest capital intensity, but they are also the least efficient. This type of electrolytic cell is the most common, and its production is already well established.

Solid oxide electrolyzers (SOE) are just beginning to enter the commercial market; however, they have the potential to have the highest efficiency of the three options and moderate capital intensity due to the use of cheap metals and high electrolysis parameters. At the moment, these are the most expensive electrolyzers with the highest efficiency.

Table 1. Main characteristics of electrolyzers.

Electrolyzer Type	Capital Cost, USD/kWel [46,47]	Efficiency, % [45,48]	Temperature, °C	Maturity
Alkaline	Up to 1400	Up to 70%	20–80 °C	Commercial
PEM	Up to 1800	Up to 85%	20–200 °C	Early commercial
AEM	-	>75%	20–85 °C	R&D
SOE	>2800	Up to 100%	500–1000 °C	R&D

shows the main characteristics of electrolyzers.

One of the priority areas for the development of technologies for the production of batteries using electrolyzers is the development and application of new efficient materials and catalysts [49], which will correspond to the reduction in the final cost of materials for consumers.

Another promising method for the production of hydrogen using water splitting is photovoltaic electrolysis [50]. The integration of solar power plants with hydrogen production systems can contribute to the development of the “green” hydrogen economy, including through the accumulation of energy from renewable sources in the form of hydrogen.

Thus, electrolysis can be used to produce hydrogen from water using an electric current and an electrolyte. This method has a few advantages, such as the possibility of hydrogen production at the place of its use, zero carbon dioxide emissions and other contaminants into the environment. However, the electrolysis process requires significant energy costs, which may be an obstacle to its widespread use in the industry.

2.7. Thermochemical Decomposition of Water and Thermolysis

Thermochemical water splitting is a process in which water decomposes into hydrogen and oxygen at a high temperatures in the presence of a catalyst [51]. There are several cycles based on this process, such as the sulfur–iodine cycle [52]. In the sulfur–iodine cycle, water is first treated with sulfuric acid to produce sulfate and hydroxide ion. Then, the mixture is heated to isolate hydroxide ion, to be further used to oxidize sulfuric acid. This results in the production of gases, i.e., hydrogen and oxygen, which will then be separated. In the Czerny–Turner cycle, water is treated with ammonia to produce nitrate ions and hydrogen. These processes also require high temperatures and catalysts to improve the efficiency.

Thermolysis is the process of decomposition of chemical compounds at high temperatures. One example is the decomposition of water at temperatures above 2500 K into hydrogen and oxygen. High temperatures are required to achieve an acceptable degree of dissociation. So, at a temperature of 3000 K and a pressure of 1 bar, the degree of dissociation is 64% [22]. One of the problems associated with this method of generating hydrogen is the separation of hydrogen and oxygen. Existing semi-permeable membranes can be used at temperatures below 2500 K. Rapid cooling of the mixture to 1500–2000 K and the use of palladium membranes avoids this problem [53].

Both methods can be effective to produce hydrogen. However, they require high temperatures and catalysts and, therefore, they cannot be used for low-scale applications. It is also important to consider the environmental implications of these processes, because some of them can produce acid gases, which can negatively affect the environment.

2.8. Hydrogen Production by Photocatalysis

Photocatalysis is a process involving the use of photo-energy to activate a catalyst, which in turn contributes to a chemical reaction. In the context of hydrogen production, photocatalysis can be used to decompose water into hydrogen and oxygen [54].

During photocatalysis, a photocatalyst usually consisting of semiconductor materials, absorbs photo-energy and generates electron–hole pairs. Electrons and holes move in different directions, which creates the potential for chemical reactions.

To produce hydrogen by photocatalysis, water is exposed to light in the presence of a photocatalyst. As a result, water molecules split into hydrogen and oxygen molecules. The resulting hydrogen can be used either as fuel or a raw material to produce other chemical compounds.

One of the main advantages of photocatalysis is its environmental safety and efficiency. This method does not require the use of high temperatures or high pressure, as is the case with SMR, which makes it possible to reduce energy costs and mitigate the negative impact on the environment.

Therefore, photocatalysis is a promising hydrogen production method, which can be used in several industries. Its environmental safety and efficiency make it a good choice for hydrogen production.

2.9. Biomass Gasification

Biomass gasification is a promising hydrogen production method. In the process of gasification, biomass is subjected to thermochemical conversion to decompose into gaseous components, such as hydrogen, methane, carbon dioxide, etc. [55,56].

Biomass gasification can be carried out at various temperatures and with different pressures, depending on the reactor type and goals of the process. One of the most widely used types of reactors is a fixed-bed reactor, with biomass placed in the upper part of the reactor to be exposed to hot gas coming from below.

In the process of gasification, biomass is treated in several stages, i.e., drying, pyrolysis and gasification. At the first stage, the moisture content of biomass evaporates to be further removed from the reactor. At the second stage, at an increased temperature, organic substances decompose into solid, liquid, and gaseous fractions. Finally, at the third stage, gaseous fractions pass through the catalyst, where they are converted into hydrogen and other gases.

One of the advantages of biomass gasification is the use of different types of biomass to produce hydrogen, these including wood, straw, agricultural waste, etc. [57]. In addition, biomass gasification can be carried out at relatively low temperatures and at a relatively low pressure, thus reducing energy costs and mitigating the negative impact on the environment.

Biomass gasification is therefore a promising hydrogen production method, which can be used in several industries. The use of different types of biomass and environmental safety make it a good option for hydrogen production.

2.10. Biophotolysis

One of the promising approaches to producing hydrogen is biophotolysis by photosynthesis carried out by photosynthetic bacteria and algae [58,59].

Biophotolysis occurs with the capture of energy from sunlight to generate chemical energy of hydrogen. In this process, photosynthetic organisms absorb light energy and transport it using the photochemical apparatus. Then, energy is used to split water into hydrogen and oxygen as a result of the photo-oxidation reaction carried out by the enzymatic systems. The produced hydrogen can be used as fuel, thus replacing conventional energy sources, such as oil and gas.

However, the efficiency of biophotolysis varies depending on different factors, including light intensity, temperature, pH, and hydrogen/oxygen concentrations. Optimization of these factors is vitally important for making the biophotolysis process more efficient and improving hydrogen generation performance.

Consequently, the study of biophotolysis has great potential for the study of new approaches to enabling environmental remediation and improving energy efficiency. Continuing biophotolysis studies will optimize the conditions for hydrogen production and provide a robust source of environmentally friendly fuel to satisfy present-day needs.

2.11. Cost Characteristics of Hydrogen Production

Table 2. Comparative characteristics of various hydrogen production methods.

Production Method	Advantages	Disadvantages	Efficiency, %	Hydrogen Cost, USD/kg
Steam reforming	Established technology.	The by-product is CO, CO2.	74–85	2.27
Dark fermentation, photolysis	Near-zero CO2 emissions; Used in waste management.	Destruction of fatty acids; low specific generation of H2; the need for a huge reactor.	60–80	2.57
Coal gasification	Established technology; Cheap raw materials.	Fluctuating output due to raw material quality; High emissions without CCS.	30–40	1.77–2.05
Pyrolysis	Established technology; Cheap raw materials; Near-zero CO2 emissions.	Fluctuating output due to quality and seasonal availability.	35–50	1.59–1.70
Thermolysis	Near-zero CO2 emissions; By-product—O2.	High capital investment; toxicity of structural elements; High temperature.	20–45	7.98–8.40
Electrolysis	Established technology; Near-zero CO2 emissions; By-product—O2.	High capital investment.	70	10.30

shows the main comparative characteristics of various hydrogen production methods.

The obtained data and conducted research were used to provide the following recommendations.

A study was carried out to apply electricity cost variance. The study reflects the variability of the price for per kilogram of hydrogen per kWh of electricity, depending on the region, and shows how hydrogen production processes change, depending on changes in the cost of electricity.

As can be seen in Figure 1 below, electricity is necessary to produce hydrogen regardless of the method, while the price of hydrogen produced by each of them increases with an increase in the price of electricity. However, whereas in case of electrolysis and photocatalysis, electricity costs are one of the main expenditure items, and they have grown from 8.2 USD/kg up to 31 USD/kg and from 17 USD/kg up to 169.7 USD/kg, respectively; the main steam reforming and coal gasification costs are associated with other items, and they have grown insignificantly from 1.9 USD/kg up to 2.2 USD/kg and from 1.1 USD/kg up to 1.5 USD/kg, respectively. Accordingly, we can conclude that in regions with a high price of electricity, it is better to apply SMR or coal gasification, while in the case of electrolysis used as a method of hydrogen production, one needs to be sure that electricity prices will be stable. Thus, the cost of hydrogen production is directly determined by the cost of electricity and the chosen production technology. A significant influence is exerted on electrolysis, in which the maximum consumption of electrical energy with a price increase of 20 USD/MWh unit cost increases by 2.2 USD/kg H₂. In turn, the influence on coal gasification and steam reforming of methane is less significant, but the cost of greenhouse gas emission quotas will be a more determining factor for these methods.

There was a study carried out to apply CO₂ emission charge variance. The study reflects the variability of the price per kilogram of hydrogen per kilogram of CO₂, depending on whether this charge is provided for by law and what its value is.

As can be seen on the diagram below, not all methods of hydrogen production make hydrogen more expensive with the imposition or growth of CO₂ emission charges; this is because not all the methods cause CO₂ emissions (Figure 2). Electrolysis, NPP-based electrolysis, thermolysis, photocatalysis and biophotolysis produce green hydrogen and, therefore, the price of raw materials produced by these methods does not change depending on CO₂ emission charges. By contrast, the cost of hydrogen produced by all other methods will increase greatly with the imposition of this type of tax, starting with hundreds of millions of rubles. Accordingly, we can conclude that, if the tax is not imposed, usual coal gasification, SMR and biomass gasification will be more cost-efficient. However, if the federal authorities introduce such a tax, the best options will be those methods that produce green hydrogen.

3. Hydrogen Storage Methods

Hydrogen storage is an important link in hydrogen supply chain, since under normal conditions H₂ has a low volumetric energy density and rather high gravimetric energy density.

This dictates the need to reduce the volume of stored hydrogen and increase its weight content in the tank, since a large volume of stored hydrogen requires a big area and weight of the shell. Therefore, there are many storage methods that can be divided into physical and chemical ones (

Table 3. Main characteristics of hydrogen storage methods.

Storage Method	Mass Ratio of H2 and Shell, %	Storage/Conversion Temperature, °C	Storage Pressure, MPa	Storage Density, kg H2 /m3	Storage Cost, USD/kg H2
Steel pressure vessel (all-metal construction) [62]	up to 1	20–40	15	10.9	0.19–0.24
Pressure vessel (mostly metal, composite overwrap) [63]	5–7	20–40	35	23	0.22–0.27
Pressure vessel (all-composite construction) [63]	10.5–13.8	20–40	70	40	-
Cryogenic tanks for liquefied hydrogen [64,65]	up to 7.1	-252	0.1	70.8	1.67–2.04
Liquid organic hydrides [66]	up to 7.2	20–40/180–280	0.1–1	70	-
Metal hydrides [67]	1.5–8	20–40/100–300	0.1–5	110	-
Liquid ammonia [68]	17	25/400–600	1	107	0.91–1.09

). Physical methods apply to compressed and liquid hydrogen, while chemical methods are used to hydrogen in the form of ammonia and combined hydrogen in metal hydrides and liquid organic hydrides.

H₂ storage in pressure vessels involves two stages, such as hydrogen compression and hydrogen storage in the cylinder. At the first stage, it is necessary to reduce compression costs. At the second stage, storage pressure should be raised to increase the weight of stored H₂, while at the same time, it is necessary to reduce the weight of the cylinder’s shell; therefore, there is a need to use composite materials, which causes an increase in the price of the cylinder.

The main advantages of storing compressed hydrogen in cylinders:

• the technology is well developed and available (no more difficult than storing natural gas);
• ease of operation of the consumer and the absence of energy costs for the issuance of gas;
• the cost is relatively low.
• the disadvantages of gas balloon storage of compressed hydrogen are:
• low volume content (about 7.7 kg/m³ at a pressure of 10 MPa);
• the stored energy density at high pressures (up to 70 MPa) is comparable to liquid hydrogen, but the storage technology at such high pressures has not been fully developed;
• hydrogen compression to high pressures is in itself a complex engineering problem associated with possible gas leaks through seals, as well as with hydrogen corrosion of loaded structural materials;
• hydrogen compression is characterized by rather high energy consumption (10–15% of the calorific value of hydrogen);
• safety concerns (explosive gas under high pressure).

Storage of hydrogen in a liquefied form makes it possible to achieve a greater density than in the case of compressed storage. In a liquefied form, H₂ is stored at atmospheric pressure and, therefore, it is possible to have a greater unit volume than in the case of compressed hydrogen. A similar storage method is already used at spaceports and is well-practiced.

The main advantages of liquid hydrogen:

• high bulk density and high content of stored hydrogen (71 kg/m³);
• technologies for hydrogen liquefaction and its storage in a liquid state are well developed.

Significant disadvantages of liquid hydrogen are:

• high energy costs for liquefaction;
• significant losses due to evaporation;
• high costs for thermal insulation;
• the storage method is too expensive and competitive only in special cases.

An alternative way to store hydrogen is its chemical bonding or transformation into another substance. So, recently, methods of transporting and storing hydrogen in the form of a liquid organic hydride, or in the form of ammonia, have been developed [60,61]. The storage of these media is devoid of the disadvantages of storing hydrogen in compressed and liquefied form; however, the main disadvantage of this storage method is the need to convert hydrogen, which significantly increases costs. Thus, storage in the form of ammonia requires the construction of terminals for the production of ammonia, including an air separation plant.

Table 4. Scenario data on the cost of raw materials for hydrogen production.

Parameter	Case A (2030 Year)	Case B (2040 Year)	Case C (2050 Year)
Emissions CO2, USD/t	50	90	110
Electricity cost, USD/MWh	28	35	40
Water cost, USD/m3	4.1	4.5	4.6
Gas cost, USD/m3	0.57	0.96	1.23

Table 4. Scenario data on the cost of raw materials for hydrogen production.

Parameter	Case A (2030 Year)	Case B (2040 Year)	Case C (2050 Year)
Emissions CO2, USD/t	50	90	110
Electricity cost, USD/MWh	28	35	40
Water cost, USD/m3	4.1	4.5	4.6
Gas cost, USD/m3	0.57	0.96	1.23

An alternative and promising way of storing hydrogen is its pumping into natural underground cavities (e.g., salt caverns). This technology is widely used to store natural gas and is characterized by minimal investment, though geographical limitations minimize the usability of this storage method.

4. Hydrogen Transportation Methods

The main challenge to the widespread use of hydrogen transportation methods is a significant difference in hydrogen properties when compared with hydrocarbons (primarily boiling point and molecular weight).

Pipelines are one of the promising ways to transport hydrogen to consumers; however, the use of conventional gas pipelines intended for natural gas is not advisable because of the below reasons:

• high potential for embrittlement of hydrogen pipeline steel and welded joints;
• leaks of transported hydrogen through pipeline walls because of diffusion;
• high hydrogen compression costs.

Potential solutions include using fiber reinforced polymer (FRP) pipelines for hydrogen distribution [69].

The use of existing gas pipelines for pumping hydrogen is possible, but only in the case where hydrogen is mixed with natural gas (not more than 20%). This will enable the use of environmentally friendly fuel to reduce natural gas consumption, without the need to create new infrastructure. The restriction regarding fuel fractions is caused by the need to change the design of equipment used by main gas consumers (primarily gas turbine power units) due to the growing combustion temperature and burning velocity [70].

The United States has an extensive network of more than 1600 miles of dedicated hydrogen pipeline [71]. Hydrogen produced through clean pathways can be injected into natural gas pipelines, and the resulting blends can be used to generate heat and power with lower emissions than using natural gas alone.

Europe is taking the lead globally with pipelines planned on and offshore. The recently announced H₂Med Barcelona–Marseille subsea hydrogen pipeline is budgeted to cost around USD 2.1 billion for a stretch of 450 km, and it was recently announced that it will be extended to Germany too [72].

Another way to transport compressed hydrogen is ground and sea transport. To date, it involves using vehicles with a maximum capacity of up to 1 ton of hydrogen [73].

A low density of hydrogen is the cause of high costs of compressed hydrogen transportation. This problem can be solved by hydrogen transportation in a liquefied form. Due to the higher density of liquified hydrogen, it becomes possible to transport more fuel. An obvious disadvantage of this method is the need to provide low temperatures during transportation, which requires significant energy costs.

Transportation of liquid hydrogen is carried out by tank trucks with a capacity of 25 m³ and 45 m³. Hydrogen liquefaction is a highly energy-consuming process and, therefore, it is expensive, but transportation costs for liquid hydrogen are minimal and are roughly the same as the cost of delivery through pipelines.

A distinctive feature is that hydrogen is liquefied at a temperature of −253 °C, and special cryogenic tanks are necessary for its storage to minimize hydrogen losses. To this end, there are studies of materials, and aluminum tanks and containers of synthetic materials can be used as advanced technology.

In 2021, Kawasaki Heavy Industries obtained approval in principle from Nippon Kaiji Kyokai for a large, 160,000 m³ liquefied hydrogen carrier [74]. The carrier is designed to transport cryogenic liquefied hydrogen, cooled down to a temperature of –253 °C and reduced to one eight-hundredth its initial volume, by sea in large amounts on each voyage, helping to reduce hydrogen supply costs.

Railway transport for transportation of liquid hydrogen has rather a restricted application because of the limited railway network. In cryogenic railway tanks, hydrogen loss is about the same as in the case of tank trucks. With single chilldowns in tank trucks, up to 15% of hydrogen is lost, while losses associated with bad thermal insulation are 0.5% per day of the transported hydrogen amount.

There are also options to transport hydrogen using carriers, which can be hydrogen chemical compounds, such as ammonia or hydrocarbons. They go into chemical reactions to produce hydrogen. For example, an alternative option for transporting hydrogen is its conversion to ammonia or another form, such as a liquid organic hydrogen carrier (LOHC), to transport hydrogen in usual ways without significant costs to maintain the physical form and with minimal leaks. At a normal temperature, ammonia is liquefied at a pressure of 1.0 MPa, and it can be transported by pipes and stored in a liquid form (ammonia’s liquefaction temperature is −33 °C). Hydrogen is produced from ammonia through catalytic decomposition, with 5.65 kg of ammonia needed to produce 1 kg of hydrogen. However, a key drawback of this transportation method is the need to create ammonia/liquid organic hydrogen carrier plants with further decomposition at consumers.

The choice of a hydrogen delivery option is primarily based on transportation costs. They depend on many factors from the amount of transported fuel to the distance between the manufacturer and the consumer. They affect both the capital cost of means of transportation (i.e., pipelines or ground transport) and operating costs (i.e., electricity costs for pumping hydrogen or truck fuel). Figure 3 presents tips on how to choose the most cost-efficient methods of hydrogen transportation over small and long distances, depending on the transported amount.

5. Supply Chain Management and Optimization

A wide variety of hydrogen production, transportation, and storage methods dictates the need to create approaches to selecting the most cost-efficient way of hydrogen fuel supply to the buyer.

5.1. Supply Chain Optimization Algorithm

This study sets out a systematic algorithm for calculating the final cost price of a hydrogen supply chain, including production, transportation, and storage. It starts with entering data on hydrogen fuel production, transportation, and storage, including information about the availability of various facilities and geographical location of the consumer, to calculate cost prices of consumables, which will be also entered into the database. Once the initial data are entered, the next step is to choose a hydrogen production method.

The selection of a production method is followed by calculations of the hydrogen production cost price. If it is not minimal, then the algorithm returns to the selection stage. If it is optimal, then the algorithm proceeds to the next step to choose a transportation method. This is followed by calculations of transportation costs to be compared with the lowest hydrogen price. If it is not optimal, then the algorithm returns to transportation selection. If it is the lowest, then the algorithm proceeds to the next step to choose a storage method.

This is followed by calculations of hydrogen storage costs to be compared with the lowest price. If it is higher than the minimum, then the algorithm returns to storage selection. If it is optimal, then the algorithm continues to generate the most cost-efficient chain of production, transportation, and storage methods, which results in the lowest cost of hydrogen production.

The final step includes the most cost-efficient chain of production, transportation, and storage methods, which ensures the lowest hydrogen price for the consumer. The algorithm ends with an optimized process of effective and cost-efficient hydrogen fuel production, transportation, and storage. Figure 4 shows the block diagram of the optimization algorithm.

5.2. Supply Chain Optimization

This sensitivity analysis checks how the increase in prices for various components will affect the results of hydrogen supplies. Data on forecast changes are shown in Table 4. Scenarios of projected prices for various components and their changes were carried out until 2050.

Mathematical models of the problem of optimizing hydrogen supply chains are formulated in the form of linear programming with mixed integers. Forecasted estimates of the cost of all existing types of raw materials necessary for the production, transportation and storage of hydrogen, such as the cost of electricity, and CO₂ emissions were chosen as the scenarios under study.

The economic assessment is carried out using the leveled costs approach, in this case, for the supply of hydrogen. All costs incurred during the life cycle of the hydrogen supply are calculated on an annualized basis over the life of the components. If nothing else is specified, it is assumed that the total service life is 20 years. The main cost components are capital costs for the construction of production operating costs, including maintenance, expenses for consumables, mainly for fuel, and income from by-products, which are set depending on the annual amount of hydrogen supplied and reduced to the unit cost of production (H₂). The results of the simulation are shown in Figure 5.

For electrolysis, the most sensitive input parameter is the cost of electricity, and the final cost of hydrogen varies from 9.06 to 17.84 USD/kg H₂. For other analyzed technologies, such as SMR, the cost varies in the range from 7.9 to 8.85 USD/kg H₂, pyrolysis from 9.4 to 11.81 USD/kg H₂, and the cost of hydrogen gasification under given scenario conditions ranges from 10.58 to 12.56 USD/kg H₂. Such a high value of the cost is associated with taking into account penalties for CO₂ emissions. For SMR, the next most sensitive parameter is the cost of natural gas and emissions per quota, while electrolysis is more sensitive in terms of electricity costs. For biophotolysis and pyrolysis, an external power source and the variation in prices for these resources practically do not affect the result.

Thus, it is obvious that under the scenario of an increase in resource prices according to forecast estimates until 2050, there is no significant change in the priority of choosing hydrogen production technology.

Two technologies currently used for hydrogen production—methane steam reforming (SMR) and coal gasification—are characterized by low cost. At the same time, they have a strong impact on climate change. Given the fact that in the near future no new innovative technologies will be developed for the production of hydrogen by 2040, taking into account the increase in prices for the most required resources, it will be preferable to produce hydrogen using SMR.

The technology of water electrolysis for hydrogen production is competitive in the considered scenario conditions. With the introduction of fines for CO₂ emissions, it becomes possible to compare eco-friendly technologies for the production of green hydrogen with all other types and at the same time determine the cheapest source of hydrogen. However, such a technical and economic formulation of the problem deprives us of the opportunity to correctly assess the environmental effect. Proposals to eliminate this gap between environmental and economic results intended to further reduce energy costs and investment costs for electrolyzers.

6. Conclusions

Hydrogen energy is a rapidly developing sector with many government and commercial projects being implemented today. This is due to a trend for energy decarbonization to fight against global climate change. The latest achievements in the development and modernization of hydrogen production, storage, and transportation technologies contribute to the implementation of commercially rewarding hydrogen projects; however, the issue of choosing the most cost-efficient supply chains is still of current importance.

This paper explores the main existing and promising methods of hydrogen production, storage, and transportation and presents data on how different factors, from costs of electricity necessary for electrolyzers to costs of CO₂ quotas, affect the final hydrogen price.

The cost of hydrogen production is directly determined by the cost of electricity and the chosen production technology. A significant influence is exerted on electrolysis, in which the maximum consumption of electrical energy, with a price increase of 20 USD/MWh unit cost, increases by 2.2 USD/kg H₂. In turn, the influence on coal gasification and steam reforming of methane is less significant, but the cost of greenhouse gas emission quotas will be a more determining factor for these methods.

It also outlines an approach to determining the most cost-efficient hydrogen supply chain, considering both the main cost indicators for the production, storage, and transportation, and external factors, such as electricity prices, with recommendations on how to choose hydrogen production, storage, and transportation methods to build cost-efficient supply chains.

The use of methane steam conversion technology remains one of the cheapest for hydrogen production today. This is due to the availability of natural gas for reforming, as well as the relatively low prices of emission quotas in many countries. In the future, with the development and spread of renewable energy sources, the production of green hydrogen by electrolysis may become more in demand.

Thus, the development of hydrogen energy technologies, namely, methods of production, storage and transportation, as well as approaches to choosing the most optimal logistics chains can contribute to reducing the final cost for consumers and accelerate the process of decarbonization of the world’s economies.