Hydrogen—The New Energy Vector for the Transition of Industries "Hard to Abate"

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20 June 2025

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20 October 2025

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Topic Information

Dear Colleagues,

The industrial sector accounts for the largest share of global energy consumption. Given a continuously increasing demand for industrial products, the key for industrial decarbonization is decoupling its production from the produced CO₂ emissions. The replacement of traditional energy production based on carbon sources with renewables is insufficient for the inversion of global warming. A major transformation and redesign of the global energy system is required towards decarbonisation and to achieve the Paris Agreement targets. This Grand transition is a complex and pressing issue, where global joint efforts and system solutions are essential; with hydrogen being one of them.

The present Topic aims to describe hydrogen properties as crucial energy vectors of the future. Present hydrogen production routes and methods of utilization will be underlined. Hydrogen will become a crucial energy vector and the other leg of the energy transition alongside renewable electricity by replacing coal, oil, gas, and conventional hydrogen across different segments of the economy. As an energy carrier, hydrogen’s versatility will be underlined as a key actor in decarbonization. Its energy storage capability during renewable production peaks is a crucial factor of its potential introduction in many civil and industrial sectors. Obviously, this depends on its “color”, which influences the new acceptability because of the major or minor weight of traditional carbon sources. As a matter of fact, the largest amount of attention will be devoted at the so called “green hydrogen” production route, which is based on renewables or on carbon-free power sources. Among the main civil and industrial applications, the role of hydrogen for the “hard to abate” industry decarbonization will be largely emphasized.

Hydrogen storage in innovative materials will be reviewed as a great solution for large scale production. In the present issue, the production routes based on hydrocarbons or clean sources will be also reviewed and compared. The properties of hydrogen as an energy carrier that is useful for the efficient reduction of iron ores will be described in the present issue. The basic mechanisms related to the direct reduction of iron ores through hydrogen will be detailed and analyzed. The kinetic analysis of hydrogen metallurgy in a wide range of conditions will be reviewed. Thermodynamic analysis in various gas mixture conditions employed during iron ore reduction will be detailed. A large amount of attention will be devoted to the energy efficiency of the reduction processes as a function of the different reducing gases that are employed. All of the previous factors will be described from the macro to the atomic scale.

The hydrogen production from non-renewable sources continues to grow all around the world because of the continuous need for such energetic vectors in modern industry. The decomposition of basic hydrocarbons for t hydrogen synthesis will be described in the present issue. First of all, the coal gasification procedure and reactors will be reviewed. Steam reforming and syngas production will be described in depth. The process performance will be analyzed and compared to those belonging to traditional conventional routes.

The decarbonization of human activities requires that hydrogen be produced through sustainable routes. One of the most promising ways to achieve this is through the electrolysis of water with the energy sources provided by renewables. The main available technologies that are available for hydrogen production through electrolysis will be reviewed in the present issue. The fundamentals of water electrolysis will be described. The problematics related to the desalinization and purification of sea water for its employment in water electrolyzers will be described. The fundamental aspects related to the choice of high-temperature or low-temperature technologies will be analyzed. The key aspects of the integration of water electrolysis with renewable sources will be discussed.

Hydrogen production and storage are the main issues related to its large-scale utilization. The large-scale implementation of water electrolysis for the production of green H₂ has mainly been hampered by cost issues. In the present issue, the main costs issues that are related to the hydrogen economy transition will be analyzed. The fundamental aspects of hydrogen production costs by each route will be highlighted. The forecasts related to new energy solutions for hydrogen production will be analyzed. The economic issues related to hydrogen production to direct reduction reactors will be underlined.

Prof. Dr. Pasquale Cavaliere
Prof. Dr. Geoffrey Brooks
Topic Editors

Keywords

Participating Journals

Journal Name	Impact Factor	CiteScore	Launched Year	First Decision (median)	APC
Energies energies	3.0	6.2	2008	17.5 Days	CHF 2600	Submit
Materials materials	3.1	5.8	2008	15.5 Days	CHF 2600	Submit
Catalysts catalysts	3.8	6.8	2011	12.9 Days	CHF 2200	Submit
Metals metals	2.6	4.9	2011	16.5 Days	CHF 2600	Submit
Hydrogen hydrogen	-	3.6	2020	15.4 Days	CHF 1000	Submit

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Published Papers (9 papers)

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All Energies Materials Catalysts Metals Hydrogen

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20 pages, 2728 KiB  

Open AccessReview

Contribution of Copper Slag to Water Treatment and Hydrogen Production by Photocatalytic Mechanisms in Aqueous Solutions: A Mini Review

by Susana I. Leiva-Guajardo, Norman Toro, Edward Fuentealba, Mauricio J. Morel, Álvaro Soliz, Carlos Portillo and Felipe M. Galleguillos Madrid

Materials 2024, 17(22), 5434; https://doi.org/10.3390/ma17225434 - 7 Nov 2024

Viewed by 849

Abstract

Hydrogen has emerged as a promising energy carrier, offering a viable solution to meet our current global energy demands. Solar energy is recognised as a primary source of renewable power, capable of producing hydrogen using solar cells. The pursuit of efficient, durable, and [...] Read more.

Hydrogen has emerged as a promising energy carrier, offering a viable solution to meet our current global energy demands. Solar energy is recognised as a primary source of renewable power, capable of producing hydrogen using solar cells. The pursuit of efficient, durable, and cost-effective photocatalysts is essential for the advancement of solar-driven hydrogen generation. Copper slag, a by-product of copper smelting and refining processes, primarily consists of metal oxides such as hematite, silica, and alumina. This composition makes it an attractive secondary resource for use as a photocatalyst, thereby diverting copper slag from landfills and generating 0.113 μmol/g h of hydrogen, as noted by Montoya. This review aims to thoroughly examine copper slag as a photocatalytic material, exploring its chemical, physical, photocatalytic, and electrochemical properties. Additionally, it evaluates its suitability for water treatment and its potential as an emerging material for large-scale solar hydrogen production. Full article

(This article belongs to the Topic Hydrogen—The New Energy Vector for the Transition of Industries "Hard to Abate")

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21 pages, 2373 KiB  

Open AccessArticle

Industrial Decarbonization through Blended Combustion of Natural Gas and Hydrogen

by Alessandro Franco and Michele Rocca

Hydrogen 2024, 5(3), 519-539; https://doi.org/10.3390/hydrogen5030029 - 26 Aug 2024

Viewed by 2498

Abstract

The transition to cleaner energy sources, particularly in hard-to-abate industrial sectors, often requires the gradual integration of new technologies. Hydrogen, crucial for decarbonization, is explored as a fuel in blended combustions. Blending or replacing fuels impacts combustion stability and heat transfer rates due [...] Read more.

The transition to cleaner energy sources, particularly in hard-to-abate industrial sectors, often requires the gradual integration of new technologies. Hydrogen, crucial for decarbonization, is explored as a fuel in blended combustions. Blending or replacing fuels impacts combustion stability and heat transfer rates due to differing densities. An extensive literature review examines blended combustion, focusing on hydrogen/methane mixtures. While industrial burners claim to accommodate up to 20% hydrogen, theoretical support is lacking. A novel thermodynamic analysis methodology is introduced, evaluating methane/hydrogen combustion using the Wobbe index. The findings highlight practical limitations beyond 25% hydrogen volume, necessitating a shift to “totally hydrogen” combustion. Blended combustion can be proposed as a medium-term strategy, acknowledging hydrogen’s limited penetration. Higher percentages require burner and infrastructure redesign. Full article

(This article belongs to the Topic Hydrogen—The New Energy Vector for the Transition of Industries "Hard to Abate")

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16 pages, 9331 KiB  

Open AccessArticle

In-Situ Hydrogen Charging Effect on the Fracture Behaviour of 42CrMo4 Steel Submitted to Various Quenched and Tempering Heat Treatments

by Atif Imdad and Francisco Javier Belzunce Varela

Hydrogen 2023, 4(4), 1035-1050; https://doi.org/10.3390/hydrogen4040060 - 11 Dec 2023

Viewed by 1267

Abstract

Research into safer, durable steels to be used in hydrogen-rich environments has been gaining importance in recent years. In this work, 42CrMo4 steel was subjected to quenched and tempered heat treatments using different temperature and time durations, in order to obtain different tempered [...] Read more.

Research into safer, durable steels to be used in hydrogen-rich environments has been gaining importance in recent years. In this work, 42CrMo4 steel was subjected to quenched and tempered heat treatments using different temperature and time durations, in order to obtain different tempered martensite microstructures. Tensile tests on smooth and notched specimens were then performed in the air as well as with in situ electrochemical hydrogen charging using two different hydrogenated conditions. The harmful effects of hydrogen are more evident in tensile tests performed on notched specimens. The harder (stronger) the steel, the more hydrogen embrittlement occurs. As the steel’s internal local hydrogen concentration rises, its strength must be gradually reduced in order to choose the best steel. The observed embrittlement differences are explained by modifications in the operative failure micromechanisms. These change from ductile (microvoid coalescence) in the absence of hydrogen, or under low hydrogen levels in the case of the softest steels, to brittle (cleavage or even intergranular fracture) under the most severe conditions. Full article

(This article belongs to the Topic Hydrogen—The New Energy Vector for the Transition of Industries "Hard to Abate")

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11 pages, 4131 KiB  

Open AccessArticle

Comparison of Microstructures of Magnetite Reduced by H₂ and CO under Microwave Field

by Meijie Zhou, Liqun Ai, Lukuo Hong, Caijiao Sun, Yipang Yuan and Shuai Tong

Metals 2023, 13(8), 1367; https://doi.org/10.3390/met13081367 - 29 Jul 2023

Cited by 1 | Viewed by 1211

Abstract

The reduction of magnetite in H₂ and CO atmospheres was compared using a microwave-heating technique. The reduction of magnetite in a mixed H₂ + CO atmosphere was compared with respect to the effects of a microwave field and a conventional field. [...] Read more.

The reduction of magnetite in H₂ and CO atmospheres was compared using a microwave-heating technique. The reduction of magnetite in a mixed H₂ + CO atmosphere was compared with respect to the effects of a microwave field and a conventional field. Microstructural changes were observed using an electron microscope. The results show that the metallization rate and reduction degree of the H₂-reduced magnetite are much higher than those of the magnetite reduced by CO at 900–1100 ℃. The Fe phase generated by H₂ reduction forms a cavity structure, and the Fe phase generated by CO reduction forms a dense block. Under conventional heating conditions, the higher the H₂ content in a pure CO atmosphere, the better the reduction effect. Under the effect of a microwave field, the atmosphere with the highest reduction rate was 50% H₂ + 50% CO. Compared with conventional heating, the bubble holes formed by reduced iron in microwave field are larger under the same conditions. Full article

(This article belongs to the Topic Hydrogen—The New Energy Vector for the Transition of Industries "Hard to Abate")

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20 pages, 2643 KiB  

Open AccessArticle

NO_x Emission Limits in a Fuel-Flexible and Defossilized Industry—Quo Vadis?

by Nico Schmitz, Lukas Sankowski, Elsa Busson, Thomas Echterhof and Herbert Pfeifer

Energies 2023, 16(15), 5663; https://doi.org/10.3390/en16155663 - 27 Jul 2023

Cited by 2 | Viewed by 2338

Abstract

The reduction of $\mathrm{C}{\mathrm{O}}_2$ emissions in hard-to-abate industries is described in several proposals on the European and National levels. In order to meet the defined goals, the utilization of sustainable, non-fossil fuels for process heat generation in industrial furnaces needs to [...] Read more.

The reduction of $\mathrm{C}{\mathrm{O}}_2$ emissions in hard-to-abate industries is described in several proposals on the European and National levels. In order to meet the defined goals, the utilization of sustainable, non-fossil fuels for process heat generation in industrial furnaces needs to be intensified. The focus mainly lies on hydrogen (${\mathrm{H}}_2$) and its derivates. Furthermore, biofuels, e.g., dimethyl ether (DME), are considered. Besides possible changes in the process itself when substituting natural gas (NG) with alternative fuels, the emission of nitrogen oxides ($\mathrm{N}{\mathrm{O}}_{\mathrm{x}}$) is a major topic of interest. In current European standards and regulations, the $\mathrm{N}{\mathrm{O}}_{\mathrm{x}}$ emissions are specified in mg per m³ of dry off-gas and refer to a reference oxygen concentration. Within this study, this limit specification is investigated for its suitability for the use of various fuel-oxidizer combinations in industrial combustion applications. Natural gas is used as a reference, while hydrogen and DME are considered sustainable alternatives. Air and pure oxygen (${\mathrm{O}}_2$) are considered oxidizers. It is shown that the current specification, which is built on the use of fossil fuels, leads to non-comparable values for alternative fuels. Therefore, alternative $\mathrm{N}{\mathrm{O}}_{\mathrm{x}}$ limit definitions are discussed in detail. The most suitable alternative was found to be mg per kWh. This limit specification is finally being investigated for its compliance with current regulations on various aspects of Continuous Emission Monitoring Systems. Full article

(This article belongs to the Topic Hydrogen—The New Energy Vector for the Transition of Industries "Hard to Abate")

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20 pages, 22980 KiB  

Open AccessArticle

Kinetics Study on the Hydrogen Reduction of Bauxite Residue-Calcite Sintered Pellets at Elevated Temperature

by Manish Kumar Kar, Casper van der Eijk and Jafar Safarian

Metals 2023, 13(4), 644; https://doi.org/10.3390/met13040644 - 23 Mar 2023

Cited by 3 | Viewed by 1786

Abstract

In this study, the isothermal reduction of bauxite residue-calcite sintered pellets by hydrogen at elevated temperatures and different gas flow rates was investigated. A thermogravimetric technique was applied to study the kinetics of the direct reduction by H₂ at 500–1000 °C. It [...] Read more.

In this study, the isothermal reduction of bauxite residue-calcite sintered pellets by hydrogen at elevated temperatures and different gas flow rates was investigated. A thermogravimetric technique was applied to study the kinetics of the direct reduction by H₂ at 500–1000 °C. It was observed that iron in sintered oxide pellets mainly exists in the form of brownmillerite, srebrodolskite and fayalite. The reduction of brownmillerite, the dominant Fe-containing phase, with hydrogen produces mayenite, calcite and metallic iron. X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray fluorescence (XRF), BET surface area, pycnometer and mercury intrusion porosimeter analyses were adopted on reduced pellets to interpret the experimental results. The order of the reduction process changes from first-order reaction kinetics to second-order with an increasing reduction temperature. The change in reaction order may be due to sintering at higher reduction temperatures and corresponding physical and microstructural changes in pellets. The activation energy of reduction was calculated as 55.1–96.6 kJ/mol based on the experimental conditions and using different kinetic model equations. From the experimental observations, it was found that 1000 °C with 60 min is the most suitable condition for bauxite residue-CaO sintered pellets’ reduction with hydrogen. Full article

(This article belongs to the Topic Hydrogen—The New Energy Vector for the Transition of Industries "Hard to Abate")

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18 pages, 6405 KiB  

Open AccessArticle

Characterization, Calcination and Pre-Reduction of Polymetallic Manganese Nodules by Hydrogen and Methane

by Ole Kristian Brustad, Jonas Låstad, Arman Hoseinpur and Jafar Safarian

Metals 2022, 12(12), 2013; https://doi.org/10.3390/met12122013 - 24 Nov 2022

Cited by 2 | Viewed by 1677

Abstract

A polymetallic manganese nodule was characterized and further calcined and pre-reduced by H₂, CH₄, and H₂-CH₄ mixtures at elevated temperatures. It was found that the main Mn and Fe elements coexisted in the ore in different [...] Read more.

A polymetallic manganese nodule was characterized and further calcined and pre-reduced by H₂, CH₄, and H₂-CH₄ mixtures at elevated temperatures. It was found that the main Mn and Fe elements coexisted in the ore in different minerals, and the Mn/Fe ratio varies in the ore. Moreover, Cu, Ni and Co are distributed with Mn and Fe, and no known minerals of these elements were identified. The calcination of the ore was carried out through calcination in air in a muffle furnace, and under Ar in a thermogravimetry (TG) furnace. It was found that manganese and iron oxides are evolved from a variety of oxide and hydroxides in the ore during calcination. The pre-reduction of the calcined ore particles by H₂ gas in the TG furnace indicated fast reduction by hydrogen. The pre-reduction of the calcined ore by H₂, CH₄, and H₂-CH₄ mixtures in a stationary bed reactor and further characterization of the products indicated the same products. It was found that the pre-reduction by all the applied gases at elevated temperatures yield a pre-reduced ore that contains metallic Fe, Cu, Ni, and Co, while MnO co-exist as the dominant phase. Full article

(This article belongs to the Topic Hydrogen—The New Energy Vector for the Transition of Industries "Hard to Abate")

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17 pages, 6885 KiB  

Open AccessArticle

Isothermal Hydrogen Reduction of a Lime-Added Bauxite Residue Agglomerate at Elevated Temperatures for Iron and Alumina Recovery

by Olivia Bogen Skibelid, Sander Ose Velle, Frida Vollan, Casper Van der Eijk, Arman Hoseinpur-Kermani and Jafar Safarian

Materials 2022, 15(17), 6012; https://doi.org/10.3390/ma15176012 - 31 Aug 2022

Cited by 11 | Viewed by 2123

Abstract

The hydrogen reduction of bauxite residue lime pellets at elevated temperatures was carried out to recover iron and alumina from the bauxite residue in a new process route. Prior to the H₂ reduction, oxide pellets were initially prepared via the mixing of [...] Read more.

The hydrogen reduction of bauxite residue lime pellets at elevated temperatures was carried out to recover iron and alumina from the bauxite residue in a new process route. Prior to the H₂ reduction, oxide pellets were initially prepared via the mixing of an industrial bauxite residue with fine calcite powder followed by calcination and high-temperature sintering. The chemical, compositional, and microstructural properties of both oxide and reduced pellets were studied by advanced characterization techniques. It was found that iron in the oxide pellets is mainly in the form of brownmillerite, and calcium–iron–titanate phases, while upon reduction they are converted to wüstite and shulamitite intermediate phases and further to metallic iron. Moreover, it was found that the reduction at lower temperature of 1000 °C is faster than that at higher temperatures of 1100 °C and 1200 °C. The slower rate and extent of reduction at the higher temperatures is attributed to the porosity loss and reduction mechanism change to a diffusion-controlled process step. In addition, it was found that Al-containing phases in the raw materials are converted mainly to gehlenite in sintered pellets and further to the leachable mayenite phase. The alkaline leaching of selected reduced pellets by a sodium carbonate solution yielded up to 87% Al recovery into the solution, while the metallic iron was not affected. Full article

(This article belongs to the Topic Hydrogen—The New Energy Vector for the Transition of Industries "Hard to Abate")

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18 pages, 10287 KiB  

Open AccessArticle

Metal Mesh and Narrow Band Gap Mn_0.5Cd_0.5S Photocatalyst Cooperation for Efficient Hydrogen Production

by Haifeng Zhu, Renjie Ding, Xinle Dou, Jiashun Zhou, Huihua Luo, Lijie Duan, Yaping Zhang and Lianqing Yu

Materials 2022, 15(17), 5861; https://doi.org/10.3390/ma15175861 - 25 Aug 2022

Cited by 7 | Viewed by 1863

Abstract

A novel co-catalyst system under visible-light irradiation was constructed using high-purity metal and alloy mesh and a Mn_0.5Cd_0.5S photocatalyst with a narrow band gap (1.91 eV) prepared by hydrothermal synthesis. The hydrogen production rate of Mn_0.5Cd_0.5 [...] Read more.

A novel co-catalyst system under visible-light irradiation was constructed using high-purity metal and alloy mesh and a Mn_0.5Cd_0.5S photocatalyst with a narrow band gap (1.91 eV) prepared by hydrothermal synthesis. The hydrogen production rate of Mn_0.5Cd_0.5S changed from 2.21 to 6.63 mmol·(g·h)⁻¹ with the amount of thioacetamide, which was used as the sulphur source. The introduction of Ag, Mo, Ni, Cu, and Cu–Ni alloy meshes efficiently improved the H₂ production rate of the co-catalyst system, especially for the Ni mesh. The improvement can reach an approximately six times greater production, with the highest H₂ production rate being 37.65 mmol·(g·h)⁻¹. The results showed that some bulk non-noble metal meshes can act as good or better than some noble metal nanoparticles deposited on the main photocatalyst for H₂ evolution due to the promotion of photoinduced electron transfer, increase in redox reaction sites, and prevention of the recombination of carriers. Full article

(This article belongs to the Topic Hydrogen—The New Energy Vector for the Transition of Industries "Hard to Abate")

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