Gas Hydrates as High-Efficiency Storage System: Perspectives and Potentialities

Abstract

The growing economic efforts and investment for the production of green hydrogen make the definition of new competitive and environmentally friendly storage methods. This article deals with the proposal of gas hydrate production with binary or ternary H₂-based gaseous mixtures for hydrogen storage. In the text, the physical and chemical elements necessary to confirm the technical feasibility of the process are given. The proposed solution is also compared with the traditional ones in terms of energy costs, energy density, environmental sustainability, safety, ease of transport, future perspectives, and innovation level.

1. Introduction

Gas hydrates are ice-like solid crystalline compounds, where water molecules hydrogen bonding with the surroundings one and form the solid structures, while the gaseous molecules fit the cavities present within the solid lattice. Gaseous molecules are commonly referred as “hosts” and promote the formation of these solid structures, which thanks to their presence, are feasible even at thermodynamic conditions unsuitable for the formation of ice. Conversely, the molecules of water are named “hosts” [1]. The interaction between hosts and guest is exclusively physical; thus, the recovery of gas exclusively needs of the dissociation of water cages [2].

Since their discovery in 1810, the interest in gas hydrates gradually increased and reached its climax in the last decades [1]. The research on gas hydrates went through three different historical periods. The first began in 1810, when these compounds were studied mainly as a scientific curiosity. Then, in 1934, the capability of gas hydrates to interrupt the flow of gas in pipelines was ascertained, and the natural gas industries started investing in the research. In this period, particular attention was paid to defining inexpensive solutions to avoid their formation. The last period began in the mid-1960s and still continues. The scientific community finally understood the enormous potentialities hidden beyond gas hydrates: among them, the production of energy [3,4] and the storage of gases [5,6]. In the past decades, several natural reservoirs have been discovered worldwide [7]. These reservoirs exist mainly in deep oceans and continental margins (approximately 97%) and in permafrost regions (the remaining 3%). The most relevant offshore deposits were discovered in the Gulf of Mexico, South China Sea, Indian Ocean, Japan Sea, and Bearing Strait, while the most abundant reservoirs in permafrost regions are sited in Alaska, Siberia, and Qinghai-Tibet Plateau [8]. It was estimated the quantity of methane in the hydrates reservoir was between 10¹⁵ and 10¹⁷ m³ [1]. Moreover, the hydrate framework may reach very meaningful energy densities: one cubic meter of hydrate can contain from 164 to 180 m³ of methane (at standard conditions) and only 0.8 m³ of water [9].

The estimated quantities of methane contained into hydrates, allow to consider them as the most abundant energy source known by man. Based on these estimations, the energy producible with gas hydrates is at least twice the one that can still be produced with all the conventional energy sources currently available [10].

The storage of gas can be pursued for two main scopes: the capture and final/permanent disposal of greenhouse gases, such as carbon dioxide and flue-gas mixtures, or the storage of energy gases, such as methane and hydrogen, for the optimization of costs and/or the easy of transportation [11,12]. Similarly, the high energy density makes these compounds particularly suitable for gas storage. However, the quantity of gas per unit of volume that can be stored via gas hydrates is extremely variable: the type of crystalline structure plays a key role in this sense; moreover, the size of guest molecules, the presence of one or more different guest species, the diffusion of gas within the hydrate lattice, the specific growth of crystals, and so on, strongly intervene on the stored quantity of gas [13,14,15].

This article deals with the possibility of carrying out high-efficiency hydrogen storage via clathrate hydrate formation. Hydrogen hydrate does not exist in nature and, in the past decades, the research on this field was mainly focused on natural gas hydrates, with the aim of obtaining a new alternative energy source, and carbon dioxide hydrate, to improve the recovery of methane and to permanently store carbon dioxide. As a consequence of it, the literature is poor of information about hydrogen capture into hydrates and more efforts are required. Here, this promising option for hydrogen storage was proposed and supported by collecting and organizing the current knowledge about gas hydrates, in order to prove the technical feasibility of the process and its potential competitivity with the currently widespread storage techniques.

2. Hydrates as an Opportunity for Gas Storage

As explained in the introduction, the capability of hydrates to host high quantities of gas in small volumes makes them a promising solution for the storage of energy gases and for the final disposal of greenhouse gases. This promising property urged numerous researchers to focus their attention on the production of gas hydrates for the storage of both waste and energy gases [16]. With the increasing consumption of methane, together with the expected massive diffusion of hydrogen consumption, the storage, and transportation of energy gases are gaining growing attention from researchers and industrialists [17]. For instance, methane can be liquefied at −83 °C and at least 5 MPa [18,19]. The production of methane hydrates would be feasible at milder thermodynamic conditions, with consequent lower costs, and would obtain comparable results in terms of quantities stored. In particular, it could be possible to achieve temperatures above the freezing point of water (2–3 °C) and at pressures lower than 6 MPa [20,21]. Specifically for methane, one cubic meter of hydrates can contain up to 172 m³ of methane [17].

The storage in solid form also allows to easily reach the standards in terms of safety, because pressure losses are avoided and, in case of accident, the release of gas would be drastically lower and more manageable. All these reasons drove the research and attracted investments [22,23].

About the possibility of storing greenhouse gases, it should be noted that, in addition to the identification of new and potentially carbon-neutral energy sources, the capture and storage of carbon dioxide (CCS) is currently the most effective strategy to preserve the economic development without neglecting the environmental issue [24,25]. Since 1997, the disposal of CO₂ in deep ocean sediments has started being considered one of the most effective solutions for CCS [26]. In some suitable sites, the thermodynamic conditions would ensure the permanence of CO₂ in the liquid state, and the related density would prevent any leak of it from sediments [27].

In addition to the presence of suitable thermodynamic conditions, at these low temperatures the solubility of carbon dioxide is relatively high [28] and the formation of hydrates occurs quickly and massively. At the local conditions, CO₂ hydrates have high thermodynamic stability and guarantee the safe and permanent disposal of carbon dioxide in solid form [29,30]. Different options are possible: gas hydrates could be directly produced with a flow of pure carbon dioxide [31] or CO₂-based gaseous mixtures, i.e., flue-gas, could be used.

Most researchers are currently focused on the formation and decomposition processes of CO₂ hydrates in porous media, with particular attention to the formation rate and the CO₂ storage efficiency under different operative conditions. In natural deposits, the kinetic of the process is strongly dependent on the physical and chemical properties of sediments. In addition, the temperature-dependent heat diffusion rate is a key factor for the storage of carbon dioxide, being one of the most relevant parameters for the formation and growth of hydrates. It was found that when the injection volume ratio of liquid CO₂ to water is 1:1, the maximum liquid CO₂ storage efficiency is reached [32]. The local pressure is a further key parameter for the kinetic of the process; higher pressures mean faster and more massive capture and, on the other side, higher costs. In this sense, an optimum must be fixed. In addition, the local temperature must be carefully taken into account. Higher temperatures obviously mean higher pressures; however, the phase boundary equilibrium for carbon dioxide hydrates changes very quickly for temperatures above 283 K (see Figure 1), thus making the overall storage conditions extremely disadvantaging.

Moreover, CO₂ could be also injected in natural gas hydrate reservoirs, for two different scopes: its storage together with the recovery of methane, or its storage with the contemporary prevention of accidental dissociation of methane hydrates. The “CO₂-CH₄ replacement process” was proposed for the first time in 1980 as a way to increase the methane recovery rate [33]. The feasibility of the exchange between these two species directly within the hydrate lattice is due to the greater capability of CO₂ to form hydrates at the same local conditions. Both these species form the same typology of hydrate, but the enthalpy of formation is lower for carbon dioxide: −57.98 kJ/mol against −54.49 kJ/mol [8]. The different conditions define a narrow thermodynamic region where methane is released, while carbon dioxide is captured [34]. Figure 1 shows the phase boundary equilibrium conditions for methane and carbon dioxide hydrates and denotes the thermodynamic area suitable for the replacement process.

Because the exchange ratio is theoretically equal to one, this solution would lead to a potential carbon-neutral energy source [36]. In addition, this solution allows to preserve the integrity of the hydrate lattice during the recovery of methane, thus reducing the risk of soil deformations and so on [37].

During replacement, one of the most limiting problems consists of the low permeability of the deposit, which often avoids the penetration of carbon dioxide within the deep layers and confines the exchange to the most superficial regions of the reservoir [38]. In previous studies, it was proved that this phenomenon could also assume advantageous implications [39]. The reason why the production of energy from natural hydrate reservoirs is still confined to a few semi-experimental plants is mainly related to the efficiency of the recovery process: the energy required is elevated enough to make the whole process not attractive for the natural gas industries. This condition does not change significantly if the extraction is carried out with replacement strategies.

With the research and the evolution of technologies, this problem will be surely overcome; however, the morphology and location of some reservoirs will make their exploitation unfeasible anyway. Because these reservoirs always form and growth at conditions close to those of equilibrium, even a little increase in temperature could cause the partial dissociation of them, with the consequent release of methane in the atmosphere. At the local conditions, carbon dioxide will immediately form hydrates, having higher stability than those containing methane. It was definitively proved that, the production of a shell of CO₂ hydrates around the exposed regions of the CH₄ hydrates reservoir, will prevent the dissociation of these latter structures, even if the local temperature increases about 2 °C (at the same pressure) [39]. Because the extraction of methane is not required, the process would be drastically easier and less expensive; moreover, two different targets would be pursued together: the capture and storage of carbon dioxide and the prevention of methane release into the atmosphere. This represents a promising application of hydrates as vector for gas storage, because it allows to obtain an extremely high CO₂ capture efficiency, mostly if considering that the global warming potential of methane is 25 times higher than the one of carbon dioxide [40,41].

3. Reasons beyond the Variation of Gas Hydrate Storage Capacity

As previously asserted, the configuration of water molecules produces a permanent electric dipole, and the following attraction between positive and negative poles generates the water hydrogen bonds [1]. Differently, the interaction between hosts and guests is exclusively physical. In fact, the only chemical interactions consist of van der Walls forces; while the energy required to break a hydrogen bond is equal to 5 kcal/mol, the one required for van der Waals bonds is equal to 0.3 kcal/mol [1]. Hydrate structures are based on five different polyhedral cavities, referred to as “$n_i^{mi}$”, where “ni” in the number of edges in the specific face and “mi” is the number of faces having “ni” edges. The hydrate structures consist of the aggregation of these different cavities. Laboratory studies proved the possible existence of seven different hydrate structures; however, only three of them were found in nature: the cubic Structure I (sI) [42], the cubic Structure II (sII) [43] and the hexagonal Structure H (sH) [44]. The different typologies of cages that form the as soon mentioned structures, are summarized in Figure 2.

The first structure has two small pentagonal dodecahedrons (5¹²) and six tetrakaidecahedrons (14-hedra, 5¹²6²), and its cavities can contain molecules having a diameter between 4.2 and 6 Å. Both methane and carbon dioxide naturally form this kind of structure, even if with different filling coefficients. The molecule of methane has a smaller size than the one of carbon dioxide and is capable of fitting both the types of cavities present in sI. Conversely, the molecule of carbon dioxide prefers the largest 5¹²6² cages and rarely enters the 5¹² cages [45]. Properly, for this reason, the CO₂/CH₄ exchange efficiency during replacement is far from 100% and is estimated to range between 64% and 75% [46,47]. It means that, depending on the size and morphology of the guest, the storage capacity of the hydrate lattice may vary significantly. Moreover, the smaller size of the guest does not directly mean a higher storage capability because the key factor in this sense is the filling ratio, which consists of the ratio between the molecular diameter and the cavity diameter. For the small pentagonal dodecahedron, this parameter is equal to 0.855 for methane and 1.00 for carbon dioxide [1]. Above the unity, the occupation of the cavity is not possible for the guest molecule; thus, it can be concluded that carbon dioxide can fit the small 5¹² cage, but the process is significantly more difficult than for methane. More in general, a high filling factor is preferable until it does not create geometrical interferences between the host and the guest molecules. Conversely, the filling ratio for 5¹²6² cages is equal to 0.744 for methane and 0.834 for carbon dioxide, proving that the capture of CO₂ molecules is more probable in these cavities. In conclusion, in the case of the sI structure, the storage efficiency of pure methane and of pure carbon dioxide will be lower than what could be obtained with a CO₂/CH₄ binary mixture. This concept could be further explained in terms of cage occupancy. This parameter represents the ratio between the occupancy of the specific guest molecule of the large cage (5¹²6²) and the occupancy of the small cage (5¹²). This value was experimentally proved to be equal to 1.26 for methane and 3.12 for carbon dioxide. Moreover, the same cavities, but in different hydrate structures, could lead to different results, in terms of gas capture, among each other. For instance, in sII, the filling factor for 5¹² cavities is equal to 0.837 for methane and 1.02 for carbon dioxide. In this different framework, this small cavity cannot host carbon dioxide anyway.

Turning back to the different typologies of structure, the cubic sII is composed of 16 small pentagonal cavities (5¹²) and height tetrakaidecahedrons (16-hedra, 5¹²6⁴). It has a lower capture capability for the molecules commonly enclathrated in sI, while it can effectively host molecules having lower diameters, such as hydrogen, and slightly higher diameters (6–7 Å), such as propane. Properly due to the possibility for some guest molecules to be enclathrated in different structures, the transition between sI and sII is possible and is mainly a function of pressure. Finally, the hexagonal Structure H has three pentagonal dodecahedrons, one 16-hedra, and two irregular dodecahedrons (4³5⁶6³). The presence of this latter typology of the cage allows hosting gas molecules having larger diameters (up to 9 Å), such as pentane. The size of the guest is the most effective parameter during the formation of hydrates; however, also the shape of guests plays a role, which becomes crucial during the production of sH hydrates.

As previously explained, the storage of gas in the form of hydrates could be theoretically made with pure water, and the number of guests and host are encouraging: up to 180 m³ for gas and just 0.8 m³ for water. Nevertheless, the mechanical properties of gas hydrates are close to those of ice, except for the mechanical strength, which was found to be up to 20 times higher than that of Ih ice [48]. These two latter properties make the hydrate lattice extremely attractive for gas storage and, in particular, for hydrogen storage:

(i)

Water is an inexpensive material;

(ii)

The thermodynamic conditions required for the process are lower than those required for the traditional methods;

(iii)

The quantity of water per unit of volume is low, with obvious advantages in terms of weight;

(iv)

The solid storage makes transportation easier and less expensive;

(v)

The high mechanical strength ensures a high level of safety;

(vi)

In case of accidents, the release of gas would be extremely low, with consequent lower risks for operators and greater availability of time for solving the problem while containing the loss of gas.

However, the artificial production of hydrates for gas storage is a still far process from the technical maturity and cannot be considered yet as an available option [49]. The stochastic nature of the process is the first variable beyond this last consideration. The formation of hydrates is stochastic: equal tests, carried out with the same experimental conditions and with the same setup, often lead to (usually slightly) different results [50]. The problem is mainly related to the initial nucleation of hydrates, or the formation of the first clusters within the bulk phase. Here numerous elements could alter the process, both thermodynamically and kinetically. Among them, the presence of suitable sites for nucleation, the mixing level between water and guest molecules, the presence of impurities and their chemical composition, the electronegativity of the liquid phase (presence/absence, concentration, and typology of ions dissolved in water), and so on [51].

These conditions could be crucial for establishing the technical competitivity of the process, thus its feasibility. In order to provide a concrete criterion to quantify the stochasticity of the system and its potential effect on the storage process, the hydration number can be introduced. It indicates the molecules of water present in the hydrate lattice for each molecule of gas. For instance, in sI, the ideal hydration number is equal to 5.75 for molecules capable of occupying both types of cavities, while it is equal to 7.67 for those capable of fitting the 5¹²6² cages exclusively. It means that, in this type of structure, the storage of carbon dioxide would be less effective than that of methane, while the situation would be reversed in sII.

In particular, this latter structure is particularly suitable for the capture and storage of hydrocarbons: if all cavities are filled, each volume of sII hydrate could contain up to 182 volumes of gas as standard pressure and temperature, meaning that the gas density reached into the lattice would be equivalent to a highly compressed gas and only slightly lower if compared with the liquid storage of hydrocarbons [1]. Unfortunately, proper due to the stochastic nature of the process, it is impossible to fill all the cavities and the hydration number is consequently higher. This variation is absolutely not negligible: as a function of the cage occupancy, the hydration number might range from 5.75 to 19. While the first value corresponds to a highly effective gas storage, the second would determine the unfeasibility of the process.

4. Hydrogen as “Future Fuel”

Nowadays, hydrogen is referred to as the “future fuel” and the most effective alternative to fossil fuels [52]. It has high energy content per unit mass, 142 MJ/kg, low mass density and is environmentally friendly because its combustion produces water exclusively [53,54]. In addition, hydrogen could be easily introduced to the existing natural gas infrastructure of buildings, thus having the possibility to cover in this way approximately the 10% of the global building heating demand [55]. According to the European Green Deal, in the next years, the production of green hydrogen will gradually increase; this is considered the key factor to achieving carbon neutrality in Europe by 2050. The European Strategy on Hydrogen is part of the European Green Deal and aims to increase the current production of green hydrogen via electrolysis, with the exclusive utilization of electrical energy produced with renewable energy sources (RES). In particular, the fixed target consists of achieving the technology for the production of one million tons/year of hydrogen by 2024 and ten million by 2030. More in general, hydrogen is thought to cover 18% of the total energy demand by 2050 and to provide up to 30 million new jobs [56,57,58]. The large-scale production of hydrogen would significantly contribute to solving the most limiting problem of RES or their non-programmability. However, the development of industries and facilities capable of producing these quantities must be accompanied by likewise efficient storage systems. Therefore, the H₂ production supply chain needs a well-dimensioned storage system. The whole chain has to be environmentally sustainable (in order to reach carbon neutrality), economically attractive, and totally safe for operators and users. As a consequence of it, the scientific community is expected to focus its attention on both improving the efficiency of hydrogen production and defining new promising solutions for its storage. In this sense, hydrogen hydrates are probably the most intriguing material paradigms for H₂ storage because of their attractive properties, such as the low energy consumption required for the charge and discharge processes, the cost-effectiveness, the level of safety, and the environmental sustainability of these systems [55].

5. Gas Hydrate as a Promising Solution for Hydrogen Storage

The most widespread strategies for hydrogen storage are high-pressure gas vessels [59], the use of porous materials [60], metal hydrides [61,62,63], and cryo-compressed storage [64]. These techniques offer different storage capacities, which are often depending on the physics of the storage mechanism. Together with the storage capacity, also the storage efficiency, which is directly related to the net energy stored, plays a key role.

Probably the main issue to solve for hydrogen storage is its particularly low density (equal to 0.089 kg/m³), which requires the use of large volumes or, as an alternative, extremely high pressures and/or low temperatures [65]. Conversely, it shows the best properties in terms of energy content by weight. The problem of volumes can be solved by using high-pressure vessels. However, extremely high pressures are required (the typical range is from 35 to 70 MPa). As a consequence of it, the vessel must be thought to tolerate these conditions, with further costs to consider [66,67]. The storage of hydrogen with metal hydrides probably offers the best performance in terms of compactness. Two different groups of materials are used for the scope: binary hydrides (MHx) and intermetallic hydrides (AmHxBn) [68]. The major limitation consists of the too-high alloy costs [69]. With the cryogenic strategy, hydrogen is liquefied in order to obtain high energy densities (per unit of volume) at low pressures. The major challenge is the need for extremely low temperatures (usually 20 K), which absorb approximately 35% of the energy content [70].

Within this scenario, the storage of hydrogen via the production of clathrate hydrate could lead to advantageous results. Since their discovery, gas hydrates have been frequently thought of as an alternative strategy for gas separation, gas capture for definitive disposal, and gas storage for further uses [71]. Since the 1990s, also the option of storing hydrogen in hydrates was proposed and experimentally tested [72]; however, the thermodynamic conditions required for the enclathration of pure hydrogen were found to be far from being competitive. At ambient conditions, approximately 200 MPa is required to form H₂ hydrates [73]. Fortunately, the addition of chemical promoters can drastically mitigate these conditions [74]. In 2008, Hashimoto and colleagues proved that, in the presence of THF and TBAB, hydrogen can form hydrates at 286 K and only 6 MPa [75]. The addition of chemical additives makes energy costs sustainable and competitive; on the other side, these additives are often expensive and harmful to the environment [76].

Hence the proposal of storing hydrogen into clathrate hydrates by first mixing it with complementary gases capable of reducing the pressure required for its enclathration [77,78]. In this direction, two promising and attractive possibilities consist of the mixing of hydrogen with carbon dioxide or with a mixture of small-chain hydrocarbons, such as ethane, propane, and butane (see Figure 3).

To reach a configuration of stability, it is important that the guest molecule has a diameter only slightly lower than the size of the hosting cavity; this explains why very high pressures are required for hydrogen capture. All the structures previously explained contain small and large cages. The molecule of hydrogen is capable of fitting both of them; moreover, considering its size of it, each cage can be fitted with more than one molecule [79].

A greater cage occupancy means higher stability for the hydrate structure; above all, the occupancy of large cages is required. While the occupancy of small cages can also be far from 100% [80], a configuration of suitable stability always needs large cage occupations close to the unit [81]. The previously mentioned gases could easily occupy the large cavities, thus facilitating the capture of H₂ molecules in the small cages, even at thermodynamic conditions widely milder than those required for pure hydrogen.

Figure 4 resumes the phase equilibrium boundary conditions for hydrate made with exclusively those complementary gases.

At temperatures below 280 K, the compounds (especially the small-chain hydrocarbons) form hydrate at approximately room pressure. Their size is appropriate to fill, with a cage occupancy ratio close to one, the 14-hedra and 16-hedra cages, thus providing high stability to the whole hydrate lattice.

Considering the difference in size, all of these species can be easily separated from hydrogen after the storage period. The diagrams suggest preferring hydrocarbons; however, the use of carbon dioxide could have a higher significance from an environmental point of view. In addition, the industry is widely structured for CO₂/H₂ separation, being the water-gas shift one of the most applied solutions for the industrial production of hydrogen.

Similar studies have already been approached in the past decades: in 2013, Babu and colleagues tested the formation of clathrate hydrates with a ternary (H₂/CO₂/C₃H₈) gaseous mixture [87]. They were able to produce hydrate at pressures ranging from 2.51 to 7.9 MPa and at corresponding temperatures equal to 275.3–283.2 K. In this work, as in similar studies, the concentration of hydrogen within the hydrate lattice was the most limiting factor. In addition, recent studies confirm the advantages, in terms of reduced pressures required, associated with the enclathration of hydrogen mixed with natural gas mixtures [88,89,90].

The main challenge for the upcoming years will consist of increasing this parameter until making the process preferable to the traditional storage techniques. Considering the energy costs expected for this solution (based on the current literature), the costs related to the traditional ones, the quantity of energy stored per unit of volume and per unit of mass, and also taking into account key parameters such as safety for humans and for the environment, ease of transport and so on, Figure 5 shows the expected results for H₂ storage via clathrate hydrates, which can be pursued by improving the current investments on this field of research.

The expected results, shown in Figure 5, are based on the energy content of hydrogen and the expected storage capacity of hydrates. This latter parameter considered the average storage capability of hydrates (already discussed in Section 1), which can arrive up to 180 m³ of gas (at standard pressure and temperature conditions) per cubic meter of hydrates, the average cage occupancy of water cages into the hydrate lattice (more details about it are given in Section 3). Regarding the energy required to carry out the process, we consider the thermodynamic conditions indicated in Figure 4 and refer to previous studies of us where energy flows were calculated on the basis of experimental results.

Finally, in Figure 5, the term “Innovation level” considers, as the name suggests, the innovation of the proposal, its technological maturity (currently far from the traditional techniques), and possible improvements achievable with scientific research.

6. Conclusions

This brief discussion deals with the importance of storage strategies as a key factor in answering the non-programmability of RES. In particular, the growing attention to green hydrogen production will inevitably lead to scientific and economic efforts for the implementation of new alternative storage methods. In this context, the capture of hydrogen in clathrate hydrates would offer several advantages. If mixed with “help gases”, such as carbon dioxide and small-chain hydrocarbons, its capture is possible at relatively mild thermodynamic conditions. The storage is in solid form, which means higher safety for the operators, ease of transportation, and fewer requirements for the vessels than what is required for high-compressed and liquid hydrogen storage. The added gases could be easily separated from hydrogen because of the difference in size. Finally, the hydrate crystalline structure would exclusively consist of water molecules, without the need to use environmental-unfriendly and expensive additives. This lecture provides a description of the proposed storage technique and offers a comparison with the traditional solutions. Moreover, it provides some physical and chemical elements of H₂-based hydrates to confirm their technical feasibility. Based on the current literature and on previous experimental studies, the thermodynamic conditions to apply for the process were indicated. A brief comparison with those of conventional methods immediately proves that one of the most attractive elements of the present proposal is the possibility of working at relatively low pressures. Finally, the comparison with traditional strategies was also proposed in terms of energy stored (per unit of mass and per unit of volume), energy stored/energy spent ratio, and innovation level. The values shown in the text represent the expected results of this research and are referred to the related theory and the current experimental evidence. Based on this, the storage of hydrogen in the form of clathrate hydrates could represent an attractive and competitive option for the near future, and considering the growing investments and efforts in the production of green hydrogen, it is widely worthy of further investigations and experimental studies. Future works will be focused on experimental validation of the present proposal, with particular attention to the standards and requirements of the final consumers.