Hydrogen: Fundamentals, Properties, and Future Propulsion

The Chemical Fundamentals of Hydrogen

Hydrogen (H2) has atomic number 1 in the periodic table and consists of one proton and one electron per atom. This simple structure makes it the lightest of all chemical elements. In nature, hydrogen occurs almost exclusively in molecular form, meaning as the diatomic molecule H2, in which two hydrogen atoms share an electron bond.
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The chemical name "Hydrogenium" derives from the Greek words "hydro" (water) and "genium" (producing), meaning "water producer." This name is no coincidence, because when hydrogen burns with oxygen, only water vapor is produced according to the reaction equation: 2H2 + O2 → 2H2O.
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As a nonmetal in the first main group, hydrogen exhibits unique chemical properties. It can act both as an electron donor and as an electron acceptor, allowing it to participate in versatile reactions with other elements. This flexibility makes hydrogen a valuable energy carrier and reaction partner in industrial processes.

What Does Hydrogen Look Like?

Hydrogen is completely invisible to the human eye. As a colorless gas, it has no optical properties that would distinguish it from clean air. This invisibility is one of the particular challenges in handling hydrogen, since leaks or accumulations cannot be detected visually.
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In its gaseous state at room temperature, hydrogen shows no characteristic features. It is odorless, tasteless, and leaves no visible traces. Only specialized detectors, or combustion where an almost invisible bluish flame appears, can confirm the presence of hydrogen.
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At extremely low temperatures of minus 253°C, liquid hydrogen is also colorless but has a slightly higher density. In this state it resembles distilled water, but it has completely different physical properties. Solid hydrogen, which forms only at minus 259°C, develops crystalline structures while remaining transparent and colorless.

What Is Hydrogen Made Of?

Hydrogen consists solely of protons and electrons in the simplest possible configuration. Each hydrogen atom contains exactly one proton in the nucleus and one electron in the electron shell. This minimalist structure gives hydrogen its characteristic lightness and reactivity.
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The hydrogen atom has three natural isotopes that differ in the number of neutrons in the nucleus. Protium, the most common type, contains only one proton and no neutrons. Deuterium has one additional neutron and occurs in small amounts. Tritium, with two neutrons, is radioactive and extremely rare.
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In molecular form H2, two hydrogen atoms are connected by a covalent bond. This bond is formed by sharing the two electrons between the atomic nuclei and provides stability to the hydrogen molecule. The bond energy is about 436 kJ/mol, which makes separating the atoms energy-intensive.
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The low mass of hydrogen results directly from this simple structure. With a molar mass of only 2 g/mol, hydrogen is about 14 times lighter than air, which leads to its characteristic buoyancy. This property was already used in early balloons and airships before the fire risk led to safer alternatives.

How Is Hydrogen Produced?

Hydrogen does not occur on Earth in pure form and must be obtained from compounds using various processes. The most important natural source is water (H2O), which is universally available and serves as a feedstock for hydrogen production.
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Electrolysis is the most environmentally friendly method for producing hydrogen. In this process, electric current is passed through water, splitting it into hydrogen and oxygen. If the electricity used comes from renewable energy sources, so-called green hydrogen is produced without CO2 emissions.
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Industrially, hydrogen is often produced through steam reforming of natural gas or other fossil fuels. In this process, methane (CH4) reacts with steam at high temperature to form hydrogen and carbon dioxide. Although it is cheaper than electrolysis, it produces CO2 emissions, which is why this gray hydrogen is considered a transitional technology.
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Other methods include the partial oxidation of hydrocarbons, the gasification of biomass, or thermochemical water splitting. Each method has specific advantages and disadvantages regarding efficiency, cost, and environmental impact, so the choice of production method depends on the application.

Physical Properties of Hydrogen

Hydrogen is characterized by exceptional physical properties that shape its use as an energy carrier. With a density of only 0.089 kg/m³ under standard conditions, it is the lightest of all gases. This low density leads to strong buoyancy in the atmosphere and requires special storage and handling methods.
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The diffusion rate of hydrogen far exceeds that of all other gases. Its molecules move about four times faster than those of oxygen, which leads to rapid dispersion in the surroundings. This property can improve safety because hydrogen dilutes quickly after leaks, but it can also contribute to unwanted material embrittlement.
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Hydrogen has the highest energy density per unit mass of all chemical fuels. With 120 MJ/kg, it delivers about three times as much energy per kilogram as gasoline or diesel. This exceptional gravimetric energy density makes hydrogen particularly attractive for transport applications where weight plays a critical role.
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The critical temperature of hydrogen is minus 240°C, and above this temperature it cannot be liquefied. Its boiling point is minus 253°C at atmospheric pressure. These extreme temperatures require complex cryogenic technology for storing liquid hydrogen, but they also provide a very high volumetric energy density.

Hydrogen in Nature and the Universe

Hydrogen is by far the most abundant element in the universe and accounts for about 75 percent of normal matter. In stars like our sun, hydrogen serves as the primary fuel for nuclear fusion, which produces helium and releases enormous amounts of energy that make life on Earth possible.
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On Earth, however, hydrogen is mainly present in bound form. The largest hydrogen reserve is found in the world’s oceans as part of water molecules. Organic compounds such as natural gas, crude oil, and biomass also contain significant amounts of chemically bound hydrogen.
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Free hydrogen occurs in Earth’s atmosphere only in trace amounts because its low mass causes it to continuously escape into space. The concentration is only about 0.00005 percent of the atmosphere. Nevertheless, these small amounts play an important role in atmospheric processes and the global cycle.
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Geological processes can generate hydrogen through reactions between water and iron-rich minerals. These natural hydrogen sources are gaining increasing scientific interest as potentially sustainable energy resources. Some studies are already exploring the economic use of such geological hydrogen deposits.

Safety Aspects When Handling Hydrogen

Safe handling of hydrogen requires a solid understanding of its specific hazard characteristics. Hydrogen is highly flammable and forms explosive mixtures with oxygen at concentrations between 4 and 75 percent. This wide explosive range significantly exceeds that of conventional fuels and requires correspondingly careful handling.
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The ignition energy of hydrogen is exceptionally low at just 0.02 mJ, which is about one tenth of that of gasoline vapors. Even static electricity can be enough to ignite a hydrogen-air mixture. At the same time, hydrogen burns with an almost invisible flame, which makes firefighting more difficult.
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Modern safety technologies, however, have developed proven solutions to these challenges. Hydrogen detectors can identify even the smallest leaks before dangerous concentrations develop. Pressure relief valves and specialized ventilation systems ensure safe pressure reduction and dilution.
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Hydrogen’s low density also contributes to safety because released gas rises quickly and dilutes in the atmosphere. With proper installation and maintenance, hydrogen systems today achieve safety standards that match or exceed those of conventional fuels.

Hydrogen as the Energy Carrier of the Future

The unique properties of hydrogen position it as a central building block of the energy transition. As a versatile energy carrier, hydrogen can store electrical energy, transport it, and convert it back into usable form when needed. This flexibility makes it essential for integrating renewable energy.
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Hydrogen fuel cells convert chemical energy directly into electricity, without moving parts and with very high efficiency. The only byproduct is pure water vapor, which makes them a truly zero-emission energy source. Applications range from vehicles and household power to large industrial facilities.
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Hydrogen internal combustion engines (H2ICE) are another promising technology. These engines burn hydrogen directly in the cylinder and produce zero CO2 emissions. Companies develop highly efficient H2ICE systems that can retrofit existing internal combustion engines for sustainable hydrogen operation.
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Using hydrogen in hard-to-electrify sectors such as heavy-duty transport, shipping, and the steel industry offers unique decarbonization options. Longer ranges and short refueling times make hydrogen powertrains particularly attractive in applications where battery systems reach their limits.

Hydrogen Technologies in Practice

Modern hydrogen technologies are already widely used in practice and continue to evolve. In the automotive industry, manufacturers rely on both fuel cells and hydrogen internal combustion engines for different vehicle classes. Hydrogen-powered buses, trucks, and passenger cars demonstrate their everyday suitability on a daily basis.
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Industrial applications use hydrogen for high-temperature processes where electric alternatives would be uneconomical. Steel plants are increasingly replacing coking coal with hydrogen for iron reduction, which can transform the most CO2-intensive industrial process. Chemical production and refinery processes already use large quantities of hydrogen today.
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In the energy sector, hydrogen enables long-term storage of renewable electricity through power-to-gas processes. Surplus wind and solar energy produces hydrogen via electrolysis, which can be converted back into electricity when needed. This sector-coupling function makes hydrogen a key element for 100 percent renewable energy systems.
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Specialized engineering firms support companies in developing customized hydrogen solutions. From concept development through simulation to prototype validation, innovative H2ICE systems are created that successfully retrofit conventional engines for zero-emission hydrogen operation.

Conclusion: Hydrogen as a Catalyst for the Energy Transition

As the simplest yet most energy-rich element, hydrogen combines unique properties that make it an ideal energy carrier for a sustainable future. Its ability to be produced from water and to generate only water vapor during use makes it an excellent solution for zero-emission energy systems.
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The development of hydrogen technologies is advancing rapidly and is already enabling practical solutions in transport, industry, and energy supply. Specialized partners are driving this progress and help companies unlock the potential of hydrogen for their specific applications.
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Ready for the hydrogen future? Contact Felsaris for individual consulting on hydrogen propulsion solutions and H2ICE development for your company.

Frequently Asked Questions About Hydrogen

Is hydrogen more dangerous than other fuels?

Hydrogen has specific safety characteristics that differ from other fuels. While it is highly flammable and has a low ignition energy, its rapid rise and dilution in the atmosphere can improve safety. With modern safety technologies, hydrogen systems achieve very high safety standards.

How is green hydrogen produced?

Green hydrogen is produced by electrolysis of water using electricity from renewable energy sources such as wind, solar, or hydropower. Water (H2O) is split into hydrogen and oxygen without producing CO2 emissions. This makes green hydrogen the most sustainable form of hydrogen production.

Can existing internal combustion engines be converted to hydrogen?

Yes, existing internal combustion engines can be converted to hydrogen operation (H2ICE). However, this requires substantial modifications to the injection system, ignition, valves, and other components. Companies that specialize in these conversions can achieve full original performance with zero CO2 emissions.

How long can hydrogen be stored?

With proper storage, hydrogen can be stored virtually indefinitely because it is chemically stable. Storage duration mainly depends on the tightness of the storage system. High-pressure tanks and cryogenic storage enable long-term storage for months or years without significant losses.

What does hydrogen cost compared with fossil fuels?

Hydrogen costs vary widely depending on the production method and volume. Green hydrogen is currently still more expensive than fossil fuels, but costs are steadily decreasing due to economies of scale and technological progress. When total costs are considered, including CO2 pricing, hydrogen is becoming increasingly competitive.