Hydrogen Accumulation Research Articles

Catalytic Hydrogen Storage Systems Based on Hydrogenation-Dehydrogenation Reactions

Hydrogen accumulation, storage and production systems are the important direction in the development of fundamental and applied aspects of alternative energy. Liquid organic hydrogen carriers (LOHC), polycyclic forms of the corresponding aromatic compounds, are an efficient way of hydrogen storage and release with a hydrogen content of up to 7.3 mas.%. This article compares LOHC as potential substrates for hydrogen storage and hydrogen evolution based on catalytic hydrogenation-dehydrogenation reactions, including cyclohexane, methylcyclohexane, decalin, perhydroterphenyl, bicyclohexyl, perhydrodibenzyltoluene and perhydroethylcarbazole. For each of the perhydrogenated substrates, data on the activity and selectivity of Pt-containing dehydrogenation catalysts are presented.

Seawater Splitting for Hydrogen Generation Using Zirconium and Its Niobium Alloy under Gamma Radiation.

Hydrogen production is produced for future green energy. The radiation–chemical yield for seawater without a catalyst, with Zr, and with Zr1%Nb (Zr = 99% Nb = 1%) were (G(H2) = 0.81, 307.1, and 437.4 molecules/100 eV, respectively. The radiation–thermal water decomposition increased in γ-radiation of the Zr1%Nb + SW system with increasing temperature. At T = 1273 K, it prevails over radiation processes. During the radiation and heat radiation heterogeneous procedures in the Zr1% Nb + SW system, the production of surface energetic sites and secondary electrons accelerated the accumulation of molecular hydrogen and Zr1%Nb oxidation. Thermal radiation and thermal processes caused the metal phase to collect thermal surface energetic sites for water breakdown and Zr 1%Nb oxidation starting at T = 573 K.

Atomically Thin Holey Two-Dimensional Ru2P Nanosheets for Enhanced Hydrogen Evolution Electrocatalysis

The defect engineering of low-dimensional nanostructured materials has led to increased scientific efforts owing to their high efficiency concerning high-performance electrocatalysts that play a crucial role in renewable energy technologies. Herein, we report an efficient methodology for fabricating atomically thin, holey metal-phosphide nanosheets with excellent electrocatalyst functionality. Two-dimensional, subnanometer-thick, holey Ru2P nanosheets containing crystal defects were synthesized via the phosphidation of monolayer RuO2 nanosheets. Holey Ru2P nanosheets exhibited superior electrocatalytic activity for the hydrogen evolution reaction (HER) compared to that exhibited by nonholey Ru2P nanoparticles. Further, holey Ru2P nanosheets exhibited overpotentials of 17 and 26 mV in acidic and alkaline electrolytes, respectively. Thus, they are among the best-performing Ru-P-based HER catalysts reported to date. In situ spectroscopic investigations indicated that the holey nanosheet morphology enhanced the accumulation of surface hydrogen through the adsorption of protons and/or water, resulting in an increased contribution of the Volmer-Tafel mechanism toward the exceptional HER activity of these ultrathin electrocatalysts.

A review of effective strides in amelioration of the biocompatibility of PEO coatings on Mg alloys

Recently, developing bioactive and biocompatible materials based on Mg and Mg-alloys for implant applications has drawn attention among researchers owing to their suitable body degradability. Implementing Mg and its alloys reduces the risk of long-term incompatibility with tissues because of their close mechanical properties and no need for re-operation to remove the implant. Nevertheless, the degradation rate of the implant needs to be controlled because production of hydrogen gas and accumulation of its bubbles increases local pH around the implants. To confine the integrity of implants and the body, the corrosion concern in the body fluid requires to be addressed. Surface modification as one of the effective strategies can improve corrosion resistance. Besides, it creates a suitable surface for bone grafting and cell growth. The development of proper surface-coated implants needs appropriate techniques and approaches. Plasma electrolytic oxidation (PEO) coating can provide long-term protection by providing a ceramic layer and improving the implant's biocompatibility. Herein, a general review of in-vivo and in-vitro evaluation of PEO coatings on Mg and Mg-alloys has been carried out. Recent advances in surface modification on Mg and Mg-alloys have been discussed, however, the need for reliable laboratory models to predict in-vivo degradation is still valid.

Key role of plastic strain gradient in hydrogen transport in polycrystalline materials

Hydrogen transport by moving dislocations is one of the key mechanisms for hydrogen embrittlement, which is considered responsible for local hydrogen accumulation at preferential crack initiation sites. Although numerous experiments corroborate this mechanism, there are few theoretical models for it available. In the present work, a novel hydrogen transport model is developed within the coupled framework of crystal plasticity and hydrogen balance. The hydrogen transport flux in the present model is divided into two parts: the first-order hydrogen transport flux driven by plastic strain and the second-order hydrogen transport flux driven by plastic strain gradient. With the calibrated parameters by fitting experimental results, the first-order hydrogen transport flux is negligible even for nickel with a low hydrogen diffusivity. In polycrystals, due to the intrinsic plastic heterogeneity induced by grain orientation mismatch, the second-order hydrogen transport flux results in significant dynamic hydrogen segregation at grain boundaries during deformation, which is expected to drive the hydrogen-induced intergranular cracking as observed in experiments. This dynamic segregation behavior is related to the evolution rate of geometrically necessary dislocations, depending on the grain boundary characters. The roles of grain refinement in hydrogen transport are clarified with the present model. This study shows the vital role of plastic strain gradient induced by grain boundary constraint in hydrogen transport, which is essential in understanding hydrogen migration and accumulation in deformed polycrystalline metals.

Study of Radiation Damage Processes Caused by Hydrogen Embrittlement in Lithium Ceramics under High-Temperature Irradiation

The aim of this work is to study the hydrogenation processes in lithium-containing ceramics under high-temperature irradiation. Irradiation was carried out with protons with an energy of 1 MeV and fluences of 1015–1017 ion/cm2 at irradiation temperatures of 300–1000 K. The choice of irradiation conditions is due to the possibility of simulation of the radiation damage accumulation processes in the near-surface layer of Li2TiO3 ceramics, as well as establishing the dependences of changes in structural parameters during temperature heating of samples during irradiation. It has been established that at irradiation fluences of 1015–1016 ion/cm2, the formation of dislocation defects is observed, the density of which has a pronounced dependence on the irradiation temperature. At irradiation fluence above 5 × 1016 ion/cm2, an increase in the crystal structure deformation is observed, due to swelling processes as a result of implanted hydrogen accumulation in the near-surface layer structure. At the same time, an increase in the irradiation temperature leads to a decrease in the swelling value, which is due to the accelerated migration of implanted hydrogen in the near-surface layer and its release through the existing pores. Results of mechanical tests showed that the swelling of the crystal structure and its deformation leads to embrittlement and a partial decrease in the strength of the near-surface layer. The obtained research results will further allow us to evaluate the resistance of lithium ceramics to the processes of hydrogenation and destruction as a result of the formation of gas-filled cavities in the structure of the near-surface layer.

Identification and classification of the flow pattern of hydrogen-air-steam mixture gas under steam condensation

Under the severe accident of the nuclear reactor, the strong coupling phenomenon exists between the transport and condensation of the steam-air-hydrogen multi-component gas in the containment atmosphere. Under this coupling effect, the flow patterns of mixture gas induced by condensation are critical to hydrogen accumulation risk assessment. The general flow characteristics of typical flow patterns were qualitatively predicted and confirmed in our previous work. However, the transient mass transfer process of multicomponent gases is complex, and flow pattern transitions are difficult to be captured. To further clarify these contents, experiments and corresponding numerical simulations are combined in the present work. The formation mechanism of the typical flow patterns is further revealed. The flow pattern transition boundaries of the mixture are quantified based on more data in confirmatory experiments. Experiments are performed under wider wall sub-cooling (ΔT = 60–110 °C) and wider range of steam concentration (Xsteam) from 16% to 90%, the volume concentration of helium in non-condensable gases (XHe/XNon) ranges from 10% to 70%. Results show that the homogeneous downward flow is generally formed when XHe/XNon < 40%. Under medium helium concentration (XHe/XNon: 42%–55%), when Xsteam > 30%, the flow pattern of the mixture gas is the separation flow. Under high helium concentration (XHe/XNon > 55%), the flow pattern of the mixture gas is the homogeneous upward flow when Xsteam > 20%. Furthermore, the empirical component correlations to classify the three flow patterns are proposed for the first time. Correlations and numerical simulation have good consistency in the prediction of flow patterns under most component conditions.

Friedel Oscillations Induce Hydrogen Accumulation near theΣ3 (111) Twin Boundaries in γ‐Fe

There is experimental evidence that Σ3(111) twin boundaries (TBs) in austenitic steels are susceptible to H embrittlement. However, first‐principles calculations have demonstrated that these TBs are not trapping sites for H. Density functional theory calculations of the interlayer distances and the solution energy of H in each interlayer space near the Σ3(111) TB in γ‐iron are performed. It is revealed that they both show oscillating behavior as a result of Friedel oscillations. Although the interlayer space at the TB is smaller and the solution energy is higher than that in the bulk, the second interlayer space near the TB is noticeably larger than the bulk value and hence a lower energy state for H. Friedel oscillations induced by TBs thus provide a thermodynamic driving force for H accumulation. Such enrichment is about 30% at strain‐free case and reaches 70% at a 3% tensile strain. It can be partly responsible for the H embrittlement taking place near the TBs.

Polystyrene microplastics and nanoplastics distinctively affect anaerobic sludge treatment for hydrogen and methane production

Microplastics and nanoplastics generally accumulated in waste activated sludge (WAS) after biological wastewater treatment. Currently, researches mainly focused on how plastics affected a particular sludge treatment method, without the comparison of different sludge systems. Herein, distinct responses of hydrogen-producing and methane-producing sludge systems were comprehensively evaluated with polystyrene microplastics (PS-MPs) and nanoplastics (PS-NPs) existence. Experimental results showed that PS particles would stimulate inhibition on anaerobic gas production except that PS-MPs were conducive to hydrogen accumulation, which was caused by the enhanced solubilization. Mechanistic investigation demonstrated that severe inhibition of PS-NPs to hydrogen production was derived from the excessively inhibitory hydrolysis despite of improving solubilization. Varying degrees of inhibition to acidification and methanation collectively contributed to reduced methane accumulation with exposure to PS-MPs and PS-NPs. Excessive oxidative stress would be generated in the presence of PS-MPs or PS-NPs, deteriorating microbial activities and richness of species responsible for hydrogen or methane production.

Influence of Plastic Deformation on the Hydrogen Embrittlement Susceptibility of Dual Phase Steels

The susceptibility of advanced high-strength steels (AHSS) to hydrogen embrittlement (HE) limits the broad utilization of these materials for body-in-white (BIW) components. The considerable decrease of both ductility and toughness due to local hydrogen accumulation inside of formed components may cause unpredictable time-delayed failure. In particular deep-drawn and punched AHSS components are prone to hydrogen absorption. This work investigates the influence of plastic deformation on hydrogen absorption of dual phase (DP) steels. For that purpose, tensile samples were machined out of three commercial 1.2 mm-thick DP sheets with ultimate tensile strengths of 626 MPa, 826 MPa and 1096 MPa. Samples were uniaxially pre-strained to 2 %, 5 %, 10 %, 15 % and 20 %. After pre-straining the samples were electrochemically charged with hydrogen, and the actual hydrogen contents were determined using a thermal desorption analyser (TDA). Before and after charging, the hardness of the samples was measured and the uniaxial quasi-static tensile properties were determined. In order to quantify the influence of plastic deformation on HE, slow strain rate tests (SSRT) were performed. The results of the tests were correlated with the fraction of martensite determined for each of the three steels.

Microstructure and sulfide stress corrosion cracking of the Inconel 625/X80 weld overlay fabricated by cold metal transfer process

The use of cold metal transfer process (CMT) is an excellent alternative to depositing nickel-based alloys on oil and gas pipelines due to the relatively small dilution. However, sulfide stress corrosion cracking (SSCC) of dissimilar weld joints has proven to be an issue. Therefore, this study investigates the microstructure and SSCC behavior of an Inconel 625/X80 weld overlay fabricated CMT process focusing on the tempering effect. Four-point bending tests show a high SSCC susceptibility of the non-overlap zone due to the formation of coarse structure in the heat affected zone and narrow martensite layer along the fusion boundary. However, microstructural characterization indicates a tempering effect in the overlap zone, producing homogenized microstructure and less residual strain in the heat affected zone. Therefore, the SSCC resistance is greatly improved, especially for the fusion boundary, because reversed austenite in the martensite layer could decrease the accumulation of hydrogen at lath boundaries.

(Digital Presentation) Formation Mechanism and Defects of Electrodeposited Ca-P Coating on Biodegradable Mg-Zn-Ca Alloy

Biodegradable implants are a new concept to substitute current nondegradable medical materials. The biodegradable implant can decompose in the patients’ body when the treatment is finished and be discharged through metabolism. Mg alloys, with their biocompatibility and high reactivity, meet the requirements of a biodegradable material. Also, Mg has a similar density to the human bones and the lowest elastic modulus among the structural metallic biomaterials, which can mitigate the stress shielding effect. For Mg-Zn-Ca alloys, besides the merits of Mg, Zn is related to bone metabolism and osteopathic phosphate activity, while Ca is the main element of bones that is essential for the synthesis of bone compounds. However, the degradation rate of Mg alloy implants needs to be controlled, or the implant may corrode too fast, causing local hydrogen accumulation and alkalization that hurts the patients. One of the effective ways to improve the alloy corrosion resistance is by coating. Ca-P coatings, such as brushite (dicalcium phosphate dihydrate, DCPD) and hydroxyapatite (HA), can mitigate the degradation rate of Mg alloys and show good biocompatibility and osseointegration. Electrodeposition is a simple way to synthesize coatings on metallic materials with an easy experimental set-up, and the process parameters are highly controllable.Even though there are plenty of reports about the fabrication of Ca-P coatings on Mg alloys through electrodeposition, few of them focus on the film formation mechanism. Issues related to coating defect formation and inhomogeneity are rarely discussed. Therefore, this report focuses on the film formation mechanism and the relationship to the defects of the electrodeposited DCPD coating on a Mg-2.5wt%Zn-1wt%Ca alloy. By altering the deposition potential, the reduction reactions that proceed on the substrate are different. The involvement of H2O reduction affects the formation of DCPD and changes the microstructure of the coating. Combining electrochemical tests and microstructure analysis, the corrosion properties of the coatings are measured, and the results are linked to the difference in film microstructure and defects. With SEM/FIB cross-sectional observations, the formation mechanism of the coatings and the relationship to the process condition will be discussed. The degradation rate of Mg alloys can be tuned by understanding the DCPD film formation mechanism and the cause of the defects.

Hydrogen Diffusion on, into and in Magnesium Probed by DFT: A Review

Hydrogen is an energy carrier that can be a sustainable solution for alternative energy with zero greenhouse gas emissions. Hydrogen storage is a key point for hydrogen energy. Metals provide an access for safe, controlled and reversible hydrogen storage and release. Magnesium, due to its outstanding hydrogen storage capacity, high natural abundance, low cost and non-toxicity is one of the most attractive materials for hydrogen storage. The economic efficiency of Mg as a hydrogen accumulator is limited by its sluggish hydrogen sorption kinetics and high stability of its hydride MgH2. Many attempts have been made to overcome these shortcomings. On a microscopic level, hydrogen absorption by metal is a complex multistep process that is impossible to survey experimentally. Theoretical studies help to elucidate this process and focus experimental efforts on the design of new effective Mg-based materials for hydrogen storage. This review reports on the results obtained within a density functional theory approach to studying hydrogen interactions with magnesium surfaces, diffusion on Mg surfaces, into and in bulk Mg, as well as hydrogen induced phase transformations in MgHx and hydrogen desorption from MgH2 surfaces.

Modeling and research of power supply systems with renewable energy sources and hydrogen fuel cells

Currently, the creation of environmentally friendly energy systems, including only renewable energy sources, is an urgent task. In this paper, such an autonomous power supply system (microgrid) for isolated consumers is investigated. It includes photovoltaic converters, wind turbines, an electrolyzer, fuel cells, electrical energy and hydrogen storage. For its study, an original optimization mathematical model was used. The optimal structure of the system and its operation modes are determined according to the criterion of minimum total discounted costs, taking into account energy balances and a number of additional conditions and constrains. It is shown that the use of energy sources of various types and energy storage devices makes it possible to smooth out the uneven generation of solar and wind power plants. It has been established that it is expedient to use electric batteries for short-term, and hydrogen accumulators – for long-term energy storage.

Silanized Graphene Oxide-Supported Pd Nanoparticles and Silicone Rubber for Enhanced Hydrogen Elimination.

Hydrogen is a dangerous gas because it reacts very easily with oxygen to explode, and the accumulation of hydrogen in confined spaces is a safety hazard. Composites consisting of polymers and catalysts are a common getter, where the commonly used catalyst is usually commercial Pd/C. However, it often shows poor compatibility with polymers, making it difficult to form a homogeneous and stable composite. In this work, palladium chloride (PdCl2) was converted to palladium (Pd) nanoparticles by reduction reaction and supported on graphene oxide (GO) modified by silanization. Spherical Pd nanoparticles with a size of 2–36 nm were uniformly distributed over the Silanized graphene oxide (SGO) matrix. When mixed with Pd/SGO, polymethylvinylsiloxane can be cured to silicone rubber (SR) by B2O3. Afterwards, the vinyl in the polymer can interact with hydrogen under the catalysis of Pd through the addition reaction, thus achieving the purpose of hydrogen elimination. The polymer elastomers with excellent self-healing properties and improved hydrogen elimination performance were prepared and were superior to the commercial Pd/C. In addition, excellent environmental adaptability was also demonstrated. The new getter SR-Pd/SGO provides a new avenue for developing polymer getters with superior properties.

Peracetic acid promotes biohydrogen production from anaerobic dark fermentation of waste activated sludge

Peracetic acid (PAA), a widely used organic peroxide with strong disinfection and oxidizing effect, has recently attracted research interest in waste activated sludge (WAS) treatment to achieve sludge reduction and resource utilization. However, its impact on hydrogen accumulation from WAS dark fermentation has not been documented. This study therefore is intended to fill in this knowledge gap and clarify the underlying mechanism of PAA-promoted hydrogen generation. Batch experiments revealed that when raised PAA dosage from 0 to 8 mg/g TSS (total suspended solids), cumulative hydrogen production within 168 h fermentation increased from 1.3 to 14.2 mL/g VSS (volatile suspended solids), however, further increase PAA dosage to 10 mg/g TSS resulted in a slight decrease in hydrogen yield. Mechanism studies revealed that PAA was beneficial to sludge disintegration (10 mg/g TSS PAA increased SCOD (soluble chemical oxygen demand) by 254 %). Although PAA inhibited the activity of all microorganism involved in dark fermentation, the inhibitory effect on hydrogen consumers were much more serious than that on hydrogen producers (−45.8 % versus −5.1 % and − 7.3 %). The fermentation was found to shift from propionate type to acetate and butyrate type, favoring hydrogen production. Moreover, the methane production process was effectively inhibited by PAA, which meant less hydrogen consumption. Microbial community analysis results unveiled that PAA increased the abundances of hydrolytic bacteria (e.g., norank_f__Saprospiraceae) and hydrogen producers (e.g., Clostridium_sensu_stricto_10). These findings obtained in this work provide new insights into oxidants-involved sludge treatment process and might have important implication for WAS treatment and bioenergy production in the future.

Preferential Locations of Hydrogen Accumulation and Damage in 1.2 GPa and 1.8 GPa Grade Hot-Stamped Steels: A Comparative Study

In this work, hydrogen segregation and damage sites in 1.2 GPa and 1.8 GPa grade hot-stamped steels were comparatively investigated by hydrogen permeation experiments and the hydrogen microprint technique (HMT). Compared with 1.2 GPa steel, 1.8 GPa steel exhibited a lower hydrogen diffusion coefficient (Deff) and a higher number of hydrogen trapping sites (Nt) due to its finer microstructure and richer nano-sized precipitates. The results of HMT showed that the grain boundaries in both steels played a role in initial hydrogen segregation, and then the martensitic laths became the locations of hydrogen accumulation. For 1.2 GPa and 1.8 GPa steels, however, hydrogen accumulation appeared preferentially on martensitic laths and grain boundaries, respectively, resulting in various damage behaviors. The introduced nano-sized carbides as “good hydrogen traps” played an important role in hydrogen diffusion, accumulation, and damage, which greatly alleviated hydrogen-induced cracking for the 1.8 GPa steel. Moreover, electron backscatter diffraction (EBSD) analysis further revealed that the damage behavior was also controlled by the low-angle grain boundary, stress distribution, and recrystallization fraction of the samples.

Effect of Residual Stress on Hydrogen Diffusion in Thick Butt-Welded High-Strength Steel Plates

Thick high-strength steel plates are increasingly being used for ship structures. Moreover, hydrogen enters the process of manufacturing and service, and large residual tensile stress occurs near the weld. Such stress can facilitate the diffusion and accumulation of hydrogen in the material, leading to hydrogen embrittlement fracture of the shell. Therefore, residual-stress-induced diffusion and accumulation of hydrogen in the stress concentration region of thick butt-welded high-strength steel plate structures need to be studied. In this study, manual metal arc welding was realized by numerical simulation of residual stress in a thick butt-welded high-strength steel plate model using the thermoelastic–plastic theory and a double ellipsoidal heat source model. To analyze residual stress, a set of numerical simulation methods was obtained through comparative analysis of the test results of relevant literature. Residual and hydrostatic stress distributions were determined based on these methods. Then, hydrogen diffusion parameters in each region of the model were obtained through experimental tests. Finally, the results of the residual stress field were used as the predefined field of hydrogen diffusion to conduct a numerical simulation analysis. The distribution of hydrogen diffusion under the influence of residual stress was obtained based on the theory of stress-induced hydrogen diffusion. The weak area of the welding joint was found to be near the weld toe, which exhibited high hydrostatic stress and hydrogen concentration. Further, the maximum hydrogen concentration value of the vertical weld path was approximately 6.1 ppm, and the maximum value of the path parallel to the weld centerline and 31 mm away from the weld centerline was approximately 6.22 ppm. Finally, the hydrostatic tensile stress in the vertical weld path was maximized (~345 MPa), degrading the material properties and causing hydrogen-related cracking. Hence, a reliable method for the analysis of hydrogen diffusion according to residual stress in thick high-strength steel plates was obtained. This work could provide a research basis for controlling and eliminating the adverse effects of hydrogen on the mechanical properties of ship structures and ensuring the safe service of marine equipment.

Transient Analysis of Passive Autocatalytic Hydrogen Recombiners Using Computational Fluid Dynamics

Abstract Passive autocatalytic recombiners (PARs) are being used in most modern nuclear power plants (NPPs) for mitigating the hydrogen risk both in normal and accidental scenarios. Development of a systematic model of PARs based on computational fluid dynamics (CFD) is the subject of this paper. 2D simulations of AREVA (a nuclear technology company) recombiner have been performed to validate PARs data and then the developed methodology has been applied to a Chashma NPP-II (C-2) recombiners to assess their performance. Two cases have been discussed; one with constant velocity at inlet and other one is devoted to the startup response of the PAR. Within the recombiner, the hydrogen and oxygen recombine on catalytic plates surface by an exothermic reaction to produce steam. Reaction heat is dissipated among the plates, surroundings and air inside the PAR. Flow inside the PAR will continue downwards until the gas absorbs enough heat to become lighter in weight than the gas outside the PAR. In addition, hydrogen accumulation in containment dome of a C-2 has been modeled and the results have been compared with methods for estimation of leakages and consequences of releases (melcor) code results. Without PARs, hydrogen got buildup within the containment dome, but when PARs are activated, hydrogen concentration first started to rise until the recombination reaction activated at about ∼2% hydrogen concentration. The comparison shows that the results obtained by the model agree well with the melcor results.

Natural sources and conditions of geological hydrogen generation (in the context of hydrogen depositssearches)

World energy problems can largely be solved in the event of discovering huge amounts of gaseous hydrogen in a free state, which is considered as a promising alternative to the reserves of traditional fossil fuel in the earth’s crust. However, the hydrogen industry’s development is inhibited by many challenges, in particular, in geology. Today there is neither strategy for exploration activity nor resource evaluation due to the lack of relevant experience and practical recommendations aimed at geological hydrogen. The purpose of the work is to establish and analyze potential ways and geological conditions for the formation, migration, and accumulation of hydrogen of natural origin in the earth’s crust for the further justification of the concept of the search of free hydrogen accumulation. The author has considered all possible theoretical natural sources and ways of generating hydrogen naturally. Its origin is generally assumed to magmatic, thermogenic, endogenous, biogenic, as well as one that is caused by radiolysis, decomposition of organic matter, the interaction of water with reducing agents in the mantle. All known possible ways of the genesis of free hydrogen in natural conditions are analyzed. Geologically controlled sources of natural hydrogen can be grouped according to the main processes: aqueous processes of hydrolysis (several processes including the oxidation of iron minerals, radiolysis, cataclasis and metamorphism; decomposition of organic matter (including thermal maturing); decomposition of hydrogen-containing compounds (in particular, methane and/or ammonia at metamorphisms); deep degassing of Earth’s interior. Potential location areas of free hydrogen in a geological environment are analyzed. Natural conditions for high/increased hydrogen content have basins with the presence of hydrocarbons, recent deposits with prolific organic, coal beds, zones of tectonic faults, extrusive magmatic bodies, alkaline magmatic complexes, geothermal fields, crystalline basements, geologic formation of rocks enriched with potassium, salt-bearing sections and ultrabasic rocks. Due to the uncertainty concerning the ways and conditions for generating hydrogen in the earth’s crust, geological searches and possible further study of hydrogen accumulations require a mix of methods and approaches used for traditional searches of hydrocarbon deposits – conventional oil and gas fields (source rocks, basin, cap) given the features of free hydrogen, in particular, mobility and reactive capacity of its molecule. Regardless of the genesis of hydrogen, the main search criteria should be focused on the ways of its migration and the availability of a basin and a cap. This approach maximally combines hypotheses competing among themselves (from the viewpoint of the genesis of hydrogen). It is required the geological structure with the corresponding basin and fluid trap (cap), which, unlike the fluid traps in the usual sense, should be not only impermeable but also chemically neutral in relation to hydrogen.