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Raw materials are crucial to the economy. They form a strong industrial base in which a wide range of goods and applications of daily life as well as modern technologies are produced. Reliable...

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  • Dec 21, 2020







Hydrogen is the most common substance in the universe and the richest energy source for stars. Hydrogen (H) is the first element in the periodic table of modern chemistry and is also the smallest, lightest atom. Pure hydrogen occurs on Earth only in molecular form (H2). Hydrogen on Earth is usually found in compounds, most notably as water molecules (H2O). Hydrogen has long been regarded as an energy carrier of the future.

It is also discussed as the foundation of a sustainable hydrogen economy. Owing to its physical properties, hydrogen is an almost permanent gas. Hydrogen gas only liquefies at very low temperatures (below –253°C). As hydrogen has a very low density, it is usually stored under pressure. Liquefaction increases its density by a factor of 800. The characteristic property of hydrogen is its excellent flammability. Due to its chemical properties, hydrogen has to be handled with care.





The name “hydro-gène” (“water producer”) was first coined in 1787 by the French chemist Antoine Laurent de Lavoisier, from the Greek words “hydor” (water) and “genes” (producing). It had earlier been called “inflammable air” by the English chemist and physicist Henry Cavendish because of its high flammability. The German name “Wasserstoff” (“water substance”) likewise refers to its water producing properties.



Hydrogen (chemical symbol H for the Latin name hydrogenium) is the first element in the periodic table and also the simplest. Ordinary hydrogen consists of a positively charged nucleus (proton) and a negatively charged electron. Hydrogen has the lowest atomic weight of any element, at 1.008 grams per mol (g/mol); atomic hydrogen is 12 times lighter than carbon (C), 14 times lighter than nitrogen (N) and 16 times lighter than oxygen (O).



In addition to ordinary or light hydrogen 1 H (protium), there are also two other hydrogen atoms (isotopes): heavy hydrogen (2 H) or deuterium (D) and super-heavy hydrogen (3 H) or tritium (T), with additional neutrons. As the neutron in the hydrogen nucleus is roughly the same weight as the proton, deuterium is approximately twice as heavy and tritium approximately three times as heavy as protium. Almost all hydrogen (99.985%) is ordinary hydrogen, only 0.015% occurs as heavy hydrogen. The proportion of superheavy hydrogen is vanishingly small.



Under standard conditions, i.e. ambient temperature and atmospheric pressure of 1.013 bar, atomic hydrogen (H) does not occur. Instead, hydrogen exists in dimerised form, where two hydrogen atoms firmly combine to form a hydrogen molecule (H2). The molecular weight of a hydrogen molecule is then 2.016 g/mol. The H-H molecule has a relatively high bond energy of 436 kJ/ mol, which means that the H2 molecule is stable and chemically inert at room temperature. Only above temperatures of around 6000 degrees Celsius do hydrogen molecules break down almost completely into hydrogen atoms.



Depending on whether the protons of an H-H compound rotate in parallel or in opposite directions about their own axis (nuclear spin), the two modifications are known respectively as orthohydrogen and para-hydrogen. Ortho-hydrogen (o-H2) has a higher energy content than para-hydrogen (p-H2). In addition, their technical and physical properties differ slightly. Under prevailing thermodynamic conditions ortho- and para-hydrogen form an equilibrium mixture.



Under standard conditions hydrogen exists as a 75:25 mixture of o- and p-hydrogen, while cryogenic hydrogen consists almost entirely of p-H2. The conversion of o- to p-hydrogen is an exothermic chemical reaction in which energy is released. Therefore, even if cryogenic liquid hydrogen is completely isolated, evaporation occurs unless all o-H2 is converted into p-H2 (Hollemann/Wiberg 2007). In the rest of this study the term “hydrogen” will mostly be used as a synonym for the H2 molecule.





Hydrogen is the first and most important element in the universe. Its estimated mass fraction is in the order of 75%. In the early universe, some 13.8 billion years ago, hydrogen nuclei were formed by fusion at extremely high temperatures (nucleosynthesis). In the hot interior of stars, the subsequent stellar fusion of hydrogen to helium, also known as “hydrogen burning”, is the most important and richest source of energy in their life cycle. The age of a star can be determined from the distribution of the elements and the stellar mass.





Space is filled with highly diluted hydrogen and also contains gigantic gas clouds consisting of hydrogen. The sun, which is around 4.6 billion years old, is a so-called main sequence star, which releases its radiant energy from hydrogen burning. Hydrogen is also the most frequently occurring chemical element on the giant gas planets (Jupiter, Saturn) of our solar system.



Unlike in outer space, the proportion of hydrogen in the elements on Earth is much smaller. The part of the Earth that is accessible to humans makes up less than 1% of the Earth’s mass. In the region of the Earth’s crust, oceans and atmosphere, the mass fraction of hydrogen is just 0.9% (Mortimer/Müller 2010). The proportion of hydrogen in the Earth’s atmosphere is only 0.5 parts per million (ppm).



Furthermore, hydrogen on Earth exists only rarely in its pure form; in most cases it is found in chemically bonded form. The largest proportion of hydrogen on Earth occurs as a compound with oxygen, in the form of water or water vapour. Corresponding to the relative atomic masses of hydrogen and oxygen, water (H2O) consists of approximately 11.2 percent by weight hydrogen; in other words, the mass ratio of hydrogen to oxygen is around 1:8.



Moreover, hydrogen occurs in almost all organic compounds. It is not only living creatures that are composed of organic compounds. Fossil energy sources also consist primarily of carbon-hydrogen compounds. For example, the hydrocarbon methane, the main constituent of natural gas, is made up of one carbon atom and four hydrogen atoms (CH4). By contrast, in higher alkanes such as petrol and diesel fuel the carbon-hydrogen ratio is around 1:2, and in coal it is only around 1:1.



The higher the hydrogen content of a hydrocarbon, the lower the carbon dioxide content and hence the lower the greenhouse gas emissions on combustion (oxidation).



VISIONS OF A HYDROGEN ECONOMY - Water will be the coal of the future


Almost since its discovery, hydrogen has played an important part in contemporary visions of the future, especially in relation to the energy industry and locomotion.




As early as 1874, the French science fiction writer Jules Verne (1828 – 1905) in his novel “L’Île mystérieuse” (The Mysterious Island) saw hydrogen and oxygen as the energy sources of the future. In his vision, hydrogen would be obtained by the breaking down of water (via electrolysis). Water, resp. hydrogen, would replace coal, which at the time was the dominant energy source in the energy supply industry.



In the 1960s, the successful use of hydrogen as a rocket propellant and of fuel cells to operate auxiliary power units in space – especially in the context of the US Saturn/Apollo space travel programme – provided further impetus to the fantasies surrounding hydrogen. Also in the 1960s, first passenger cars were fitted with fuel cells as basic prototypes resp. technology demonstrators.



During the 1970s, under the impression of dwindling and ever more expensive fossil fuels, the concept of a (solar) hydrogen economy was developed, with H2 as the central energy carrier. Since the 1990s, hydrogen and fuel cells have made huge technical progress in the mobility sector. After the turn of the century, not least against the background of renewed global raw material shortages and increasingly urgent questions of sustainability, the prospects for a hydrogen economy were considered once again.


more recently

More recently, the focus has increasingly been on hydrogen’s role in a national and global energy transition. Within this context, the value added of hydrogen (from renewable energies via electrolysis) in an increasingly electrified energy world has also been subject to discussion. Nevertheless, an important role is envisaged for hydrogen – especially as a clean, storable and transportable energy store – in an electricity-based energy future.




Under normal or standard conditions, hydrogen is a colourless and odourless gas. Hydrogen is non-toxic and is not causing environmental damage – in that respect it is environmentally neutral.


physical & chemical

In terms of the properties of substances, a distinction is made between physical and chemical properties. Physical properties are determined by measurement and experimentation, while chemical properties are observed by means of chemical reactions. One of the most important chemical properties of energy sources is the behaviour of the substance when it is burned (redox behaviour), either in a hot conversion process or by cold electrochemical combustion. Physical and chemical properties of substances influence both the use and usefulness of a substance and the way in which it is handled; that applies in particular also to the safe handling and storage of energy sources such as hydrogen.






Hydrogen – by which both here and below we mean dihydrogen or equilibrium hydrogen mixtures (H2) – exists in gaseous form under normal conditions. For a long time hydrogen was believed to be a permanent gas, which cannot be converted into either of the other two states of aggregation, i.e. liquid or solid.


boiling point

In fact its boiling point is very low, at –252.76°C; this is close to the absolute zero temperature of –273.15°C and corresponds to 20.3 Kelvin (K) on the absolute temperature scale. Below this temperature hydrogen is liquid under normal pressure of 1.013 bar, above this point it is gaseous.



The state of aggregation is dependent not only on temperature, however, but also on pressure. Gases can thus also be liquefied by raising the pressure. However, there is a critical temperature above which a gas can no longer be liquefied, no matter how high the pressure. In the case of hydrogen the critical temperature is –239.96°C (33.19 K). If hydrogen is to be liquefied, its temperature must be below this point.


high pressure

Similarly, once it reaches a sufficiently high pressure, a gas can no longer be liquefied, even by lowering the temperature further. This pressure is known as the critical pressure, and for hydrogen it is 13.1 bar.








The critical temperature and critical pressure characterise the critical point of a substance. For hydrogen the critical point is approximately –240°C or 33.15K and 13 bar. At the critical point of a substance the liquid and gas phase merge. At the same time, the critical point marks the upper end of the vapour-pressure curve in the pressure-temperature phase diagram. The critical density at the critical point is 31 grams per litre (g/l).



The melting point, at which H2 changes from the liquid to the solid state of aggregation, is –259.19°C or 13.9K under normal pressure and is thus slightly lower again than the boiling point. This means that only the noble gas helium has lower boiling and melting points than hydrogen.



The triple or three phase point of a substance is the point in the phase diagram at which all three states of aggregation are in thermodynamic equilibrium; for hydrogen this point is at –259.19°C and 0.077 bar. The triple point is also the lowest point of the vapour-pressure curve. The vapour-pressure curve indicates pressure-temperature combinations at which the gas and liquid phases of hydrogen are in equilibrium. To the left of the vapour-pressure curve hydrogen is liquid, to the right it is gaseous.



To the right of and above the critical point, hydrogen becomes a supercritical fluid, which is neither gaseous nor liquid. Compared with that of methane, the vapour-pressure curve of hydrogen is very steep and short – over a small temperature and pressure range. As a consequence, liquefaction takes place primarily by cooling and less so by compression. By contrast, the compressed storage of hydrogen (at 350 or 700 bar) always takes place as a supercritical fluid.


temperature & pressure

In connection with temperature and pressure changes, a special feature of hydrogen that has to be taken into consideration is its negative Joule-Thomson coefficient: when air expands under normal conditions, it cools down – an effect which is used in the liquefaction of gases, specifically in the Hampson-Linde cycle for the cryocooling of gases. Hydrogen behaves quite differently: it heats up when its flow is throttled. Only below its inversion temperature of 202K (approx. –71°C) does hydrogen demonstrate a “normal” Joule-Thomson effect. By contrast, for the main constituents of air, nitrogen and oxygen, the inversion temperature is 621K and 764K respectively.



In connection with temperature and pressure changes, a special feature of hydrogen that has to be taken into consideration is its negative Joule-Thomson coefficient: when air expands under normal conditions, it cools down – an effect which is used in the liquefaction of gases, specifically in the Hampson-Linde cycle for the cryocooling of gases. Hydrogen behaves quite differently: it heats up when its flow is throttled. Only below its inversion temperature of 202K (approx. –71°C) does hydrogen demonstrate a “normal” Joule-Thomson effect. By contrast, for the main constituents of air, nitrogen and oxygen, the inversion temperature is 621K and 764K respectively.



Density is a physical quantity that is defined by the ratio of mass per volume. Gases have a very low density in comparison to liquid and solid substances. At a temperature of 0°C or 273.15K, the density of hydrogen in its gaseous state is 0.089 grams per litre (g/l). Since air is around 14 times heavier than gaseous hydrogen, with a density of 1.29g/l, hydrogen has a high buoyancy in the atmosphere. Hydrogen volatilises quickly in the open air.



Liquefaction plays an important part in the storage and transport of hydrogen as an energy source. In the liquid state at the boiling point, at –253°C (20.3K) and 1.013 bar, hydrogen has a density of 70.79 g/l. At the melting point, at –259.2°C (13.9K) and 1.013 bar, its density is 76.3 g/l.



Liquefaction increases the density of hydrogen by a factor of around 800, and the storage volume falls correspondingly. For the purposes of comparison, when Liquefied Petroleum Gas (LPG) is liquefied, the density or volume factor, depending on the proportion of butane/propane, is around 250; when methane is liquefied to form Liquefied Natural Gas (LNG), the factor is around 600.



Another relevant feature of hydrogen is its extremely high diffusibility. As the lightest gas, hydrogen can diffuse into another medium, passing through porous material or even metals (Hollemann/Wiberg 2007). This can also cause materials to become brittle. In storage, the high diffusivity requires the use of special materials for the storage containers – for example austenitic steels or coatings with diffusion barrier layers. Otherwise, diffusion losses of the stored hydrogen can occur.




The most characteristic chemical property of hydrogen is its flammability. When hydrogen is burned in ambient air, the flame is scarcely visible in daylight, since the flame is characterised by low heat radiation and a high ultraviolet component. In comparison with other fuels, it is striking that hydrogen is combustible in a very broad concentration spectrum. The ignition range of hydrogen, marked by its lower and upper explosive limit, is correspondingly large: the lower limit is at a concentration of 4 vol%, the upper limit at 77 vol%. The liquid and gaseous fuels that are currently in use have much lower ignition ranges. Only ethanol, which is contained in petrol for example, has a higher upper explosive limit, at 27 vol.%.






Its combustion properties make hydrogen an interesting combustion fuel: If hydrogen were to be used in internal combustion engines, the broad ignition limits would allow for extremely lean air/hydrogen gas mixtures. While petrol engines run at a stoichiometric combustion air ratio (λ =1) and modern diesel engines typically operate at λ =2, lambda values of up to 10 would be possible with hydrogen-operated combustion engines. Lean combustion is more efficient than stoichiometric combustion.



The autoignition temperature of pure hydrogen is 585°C, which is higher than that of conventional fuels. However, the minimum ignition energy of 0.02 MJ is much lower than that of other fuels. Hydrogen is therefore classified as an extremely flammable gas. However, a simple electrostatic discharge (with an energy of around 10 MJ) would also be sufficient to ignite almost any other fuel. The maximum flame velocity of hydrogen is 346cm/s, which is around eight times higher than that of methane (43cm/s).



Regarding the thermal behaviour of hydrogen, it has been found that because of the strong bond between the hydrogen atoms of the hydrogen molecule, considerable amounts of energy – in other words high temperatures – are needed to form new molecular bonds. Hydrogen exists almost entirely in atomic form only above a temperature of 6,000 K. In addition to high temperatures, catalysts are also often used for chemical reactions involving hydrogen.



Molecular hydrogen (H2) is relatively inert. Nevertheless, by punctual heating of a 2:1 hydrogen/oxygen mixture (oxyhydrogen gas) to approximately 600°C, a chain reaction can be started which leads to an explosive propagation of the temperature rise throughout the entire gas mixture. The water vapour formed by the high heat of reaction then achieves a much greater volume than the original hydrogen/oxygen mixture. The sudden propagation of the water vapour leads to a so-called oxyhydrogen or Knallgas reaction.



For that reason, to avoid an oxyhydrogen/ Knallgas reaction when working with hydrogen, an oxyhydrogen gas sample should always be taken or oxygen should only be added to the hydrogen at the moment of ignition. Likewise, in gas mixtures containing hydrogen and chlorine gas or fluorine, the reaction to hydrogen chloride or hydrogen fluoride can result in explosive exothermic reactions.



Its chemical properties make hydrogen an excellent combustion and automotive fuel. Nevertheless, handling hydrogen requires care, and in particular compliance with safety regulations.





Over the years Shell has produced a number of scenario studies on key energy issues. These have included studies on important energy consumption sectors such as passenger cars and commercial vehicles (lorries and buses) and the supply of energy and heat to private households, as well as studies on the state of and prospects for individual energy sources and fuels, including biofuels, natural gas and liquefied petroleum gas. 

Shell has been involved in hydrogen production as well as in research, development and application for decades, with a dedicated business unit, Shell Hydrogen. Now, in cooperation with the Wuppertal Institute in Germany, Shell has conducted a study on hydrogen as a future energy source.

The study looks at the current state of hydrogen supply pathways and hydrogen application technologies and explores the potential and prospects for hydrogen as an energy source in the global energy system of tomorrow. The study focuses on the use of hydrogen in road transport and specifically in fuel cell electric vehicles (FCEVs), but it also examines non-automotive resp. stationary applications.








Economizing on iridium - iridium is an ideal catalyst for the electrolytic production of hydrogen from water




Economizing on iridium



Iridium is an ideal catalyst for the electrolytic production of hydrogen from water -- but it is extremely expensive. But now a new kind of electrode made of highly porous material does an excellent job with just a hint of iridium.



Today, the royal road to the effective electrolysis of water for the production of hydrogen gas in so called proton exchange membrane (PEM) electrolyzers is to reduce the amount of catalytically highly active but scare nobel metal iridium and at the same time maintain the hydrogen output.



In this type of electrolyzer cell the hydrogen ions migrate via a proton exchange membrane from the oxygen producing anode to the hydrogen producing cathode. The membrane-based technique offers many advantages. The catalyst coated membrane itself is very thin, which makes the electrolytic cell itself small and more versatile, and the absence of a liquid electrolyte means that the whole system requires virtually no maintenance.



Such cells also allow hydrogen production at elevated pressures facilitating and lowing the energy demand for further storage as compressed gas. Finally dynamic load operation is possible with the PEM-technology to react to fluctuations in available current within seconds which renders it suitable for the coupling to renewable energy sources.


iridium oxide

But the technology also has one major drawback. Formation of oxygen at the anode is dependent on the use of iridium oxide (IrO2) as a catalyst. IrO2 is a very stable and efficient promoter of this reaction. The problem is that iridium itself is rarer than gold or even platinum, and it is at least as expensive as the latter. Many attempts have been made to find an alternative, but nothing yet tested approaches the long-term stability and catalytic activity of iridium oxide.





Raw materials are crucial to the economy. They form a strong industrial base in which a wide range of goods and applications of daily life as well as modern technologies are produced. Reliable and unhindered access to certain raw materials froms worldwide a upcoming challenge to be solved. Analytical thinking, goal-oriented approaches and the fascination of "out of the box thinking" enables me to channel challenges in the daily business into opportunities and to create benefits where nobody expects them. I'm fascinated by the impossible and always motivated to initiate and realize them through innovative and creative approaches. 



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