Hydrogen as a future energy source provides certain advantages: It is the most frequent occurring element in nature – most fixed stars consist largely of hydrogen – and is thus theoretically available without limitations.
At room temperature hydrogen is a colourless and inodorous gas, which is 14.4 times lighter than air. It is the element with the lowest density, hence it diffuses easily through porous partitions, but also through metals like platinum. Hydrogen as 1st element has the deepest melting and boiling temperature after helium and it usually appears in a two atom molecule form (H2). There are three natural isotopes: A normal hydrogen atom (isotope protium) consists of one proton and one electron. In contrast, heavy hydrogen (isotope deuterium) has an additional neutron and super heavy hydrogen (isotope tritium) has two additional neutrons. The occurence of deuterium in natural hydrogen lies at about 0.015 %. While pure hydrogen is not toxic for the human organism, heavy and super heavy hydrogen are considered as highly toxic.
Hydrogen atoms appear in bounded form within several compounds, for example in water or in organic compounds like hydrocarbons (methane, ethane, benzene), alcohols (methanol, ethanol), aldehydes, acids, fats, carbohydrates and proteins. Hydrogen atoms are frequently represented in human bodies and are involved in many important metabolic processes like the digestion.
Hydrogen molecules appear in two different chemical conditions, called ortho- and para-hydrogen. They vary in the orientation of their atomic spins. The spin indicates the angular momentum of the elementary particles of an atom. Ortho-hydrogen shows a parallel spin, while para-hydrogen has an anti-parallel spin. Para-hydrogen has a lower specific heat capacity than ortho-hydrogen. At ambient temperature ortho-hydrogen appears three times as often as para-hydrogen. A mixture of 25 % para- and 75 % ortho-hydrogen is called normal hydrogen (nH2). Below -200 °C there exists almost exclusively para-hydrogen. The mixture of para- and ortho-hydrogen are in a thermodynamical equilibrium. The conversion from one condition to the other is a slow process, which may last - without a catalytic converter - several days. It is possible to convert ortho- into para-hydrogen within several hours with the magnet caloric method, until a para-hydrogen concentration over 95% is reached.
In air hydrogen burns with a light blue flame into water:
2 H2 + O2 =>2 H2O H = 572 kJ/mol
Mixtures with oxygen or with chloric gas explode by ignition impetuously and are called oxyhydrogen gas mixtures. At the laboratory, the detection of hydrogen is carried out with the oxyhydrogen test. This test is also used to examine whether a gas contains a oxyhydrogen mixture or not. If a whistling bang resounds, it is oxyhydrogen. If a harmless and dull noise is produced, there is only pure hydrogen in the test tube. In combination with alkali metals or alkaline earth metals hydrogen builds hydrides due to exothermic reactions.
For the production of hydrogen several different strategies are used frequently. As hydrogen exists in the nature only in bounded form, its extraction calls for primary energy. Worldwide about 500 billion standard cubic meters of hydrogen are converted per year. Thereof 40% accrue in the chemical industry as by-product, for example during the production of chlorine using the chlorine - alkali electrolysis or the crude oil refinery process. About 20% of the hydrogen is used for the production of energy.
By far the largest part of the produced hydrogen is derived from fossil energy sources, from the catalytic steam fission of methane (natural gas reformation), the partial oxidation of heavy oil (diesel) or the gasification of coal. During these production processes based on carbonaceous elements, CO2 is produced. The production of hydrogen with electrolysis of water, which was made electrically conductible with caustic soda solution or oil of vitriol, allows a regenerative emission free energy chain by the use of wind-, water-, or sun energy. In the same way hydrogen can be produced with a series of chemical reactions with water, emission free but with more expensive chemical processes, for example from the reaction of alkali metals and water. More hydrogen production processes are still in the research and development stage, like the autothermic reformation, the Kværner-method and the gasification of biomass or organic waste. At the same time, methods for hydrogen production through biological processes are also investigated.
Due to the low density of hydrogen, the storage with sufficient energy density displays technical and economic challenges. Usual methods are the storage of compressed gaseous hydrogen, cryogenic liquid hydrogen and hydrogen storage in chemical or physical connections.
Gaseous hydrogen is compressed from 200 bar to 900 bar high and as CGH2 (compressed gaseous hydrogen) stored in pressure vessels. There are 4 types of pressure vessels, starting from simple steel bottles to full composite cylinders (CFRP).
In order to achieve higher energy densities, hydrogen is liquefied and cryogenically stored as LH2 (hydrogen liquid). Since the condensation of hydrogen at ambient pressure only occurs at -252.85 ° C, the effort for liquefaction is high and needs to be energetically optimized.
Unfortunately, a rumour has established in the past that hydrogen is not storable permanently. This applies only to the storage as cryogenic liquid hydrogen, because the LH2 vaporizes and needs to be blown off (Boil off). For decades, hydrogen has been stored in bundles (rack consisting of 12 gas bottles) and then stored permanently. Furthermore, hydrogen can be injected into the natural gas pipeline (taking into account the legally prescribed maximum percentage), like in the project W2H, to use the natural gas grid as storage system.
The contemporary energy supply is mainly based on the use of limited available resources of fossil fuels, which consist of a series of short- and long–chain hydrocarbon compounds. The energy generation via the combustion of carbonaceous fossil substances in air, which has accompanied the technical development of mankind since the activation of fire, causes - conditional on the procedure - the generation of the greenhouse gas carbon dioxide and several other harmful substances like hydrocarbons, nitrogen oxides and soot.
Inside internal combustion engines it is possible to burn hydrogen mostly ecologically compatible: no carbon monoxide, carbon dioxide or hydrocarbons are produced and the emission of nitrogen oxides can be kept low. If hydrogen is used in a fuel cell, it delivers in a “cold combustion” electrical energy without producing any harmful substances or noise. In order to make hydrogen industrially useable as an energy source for power generation in fuel cells, for power engines in fuel cells or in internal combustion engines, a series of economic and technical questions still needs to be solved first.
Literature & Links
Eichlseder, H., Klell, M.: Wasserstoff in der Fahrzeugtechnik. Erzeugung, Speicherung, Anwendung. 3. Auflage, Verlag Teubner+Vieweg, Wiesbaden, ISBN 9783834817549, 2012
Klell, M.: Storage of Hydrogen in Pure Form. In: Hirscher, M. (Hrsg.): Handbook of Hydrogen Storage. Wiley-VCH Verlag, Weinheim, ISBN 9783527322732, 2010
Pischinger, R., Klell, M., Sams, Th.: Thermodynamik der Verbrennungskraftmaschine. 3. Auflage, 1. Band der Reihe Der Fahrzeugantrieb. Hrsg. Helmut List, Springer- Verlag Wien New York, ISBN 9783211992760, 2009
Klell, M.: Höhere Thermodynamik. Vorlesungsskript der Technischen Universität Graz, 2016
Klell, M.: Wasserstoff in der Energie- und Verkehrstechnik. Vorlesungsskript der Technischen Universität Graz, 2015
Sartory, M.; Justl, M.; Salman, P. et al., Modular Concept of a Cost-Effective and Efficient On-Site Hydrogen Production Solution. SAE Technical Paper 2017-01-1287, 2017, doi:10.4271/2017-01-1287.
Brandstätter, S.; Striednig, M.; Aldrian, D. et al., Highly Integrated Fuel Cell Analysis Infrastructure for Advanced Research Topics. SAE Technical Paper 2017-01-1180, 2017, doi:10.4271/2017-01-1180.
Salman, P.; Wallnöfer-Ogris, E.; Sartory, M. et al., Hydrogen-Powered Fuel Cell Extender Vehicle - Long Driving Range with Zero-Emissions. SAE Technical Paper 2017-01-1185, 2017, doi:10.4271/2017-01-1185.
Salman, P.; Sartory, M.; Klell, M.: wind2hydrogen – Umwandlung von erneuerbarem Strom in Wasserstoff zur Speicherung und zum Transport im Erdgasnetz. – in: 14.Symposium Energieinnovation, Graz, 2016
Striednig, M.; Brandstätter, S.; Sartory, M.; Klell, M.: Thermodynamic real gas analysis of a tank filling process. – In: International Journal of Hydrogen Energy, Vol. 39 Issue 16, 2014, pp 8495-8509
Klell, M.; Eichlseder, H.; Sartory, M.;: Mixtures of hydrogen and methane in the internal combustion engine – Synergies, potential and regulations. – in: International Journal of Hydrogen Energy, Vol. 37 Issue 15, 2012, pp 11531 – 11540
Eichlseder, H.; Klell, M.; Schaffer, K., M.; Leitner, D.; Sartory, M.;: CO2-frei Mobilität mit einem multivalenten Fahrzeug für variablen Erdgas/Wasserstoff-Mischbetrieb. – in: 11.Symposium Energieinnovation, Graz, 2010
Klell, M.; Beermann, M.; Jungmeier, G.; Böhme, W.: Electrolytic cogeneration of renewable hydrogen, oxygen and heat: operational, economic and environmental aspects of a large scale integration. – In: 18th World Hydrogen Energy Conference, Essen, 2010, pp 111-122
Eichlseder, H.; Klell, M.; Schaffer, K.M.; Leitner, D.; Sartory, M.: Potenzial eines Fahrzeugs für variablen Erdgas/Wasserstoff-Mischbetrieb. – in: ATZ/MTZ-Konferenz Energie „CO2 – Die Herausforderung für unsere Zukunft“., München, 2010
Klell, M.; Eichlseder, H.; Sartory, M.: Variable Mixtures of Hydrogen and Methane in the Internal Combustion Engine of a Prototype Vehicle - Regulations, Safety and Potential. – In: International Journal of Vehicle Design, Vol. 54 Issue 2, 2010, pp 137-155
Klell, M.; Sartory, M.: Standards und Sicherheitskonzepte für Fahrzeuge mit Gasbetrieb. – in: 4.Tagung Gasfahrzeuge., Stuttgart, 2009
Eichlseder, H.; Klell, M.; Schaffer, K.; Leitner, D.; Sartory, M.: Potential of Synergies in a Vehicle for Variable Mixtures of CNG and Hydrogen. In: SAE Paper No. 2009-01-1420, 2009, pp 1-9
Klell, M.; Eichlseder, H.; Schaffer, K.; Leitner, D.; Sartory, M.: Potential of Synergies in a Vehicle for Variable Mixtures of CNG and Hydrogen. In: SAE technical papers SP-2251, 2009, pp 19-28
Schaffer, K.M.; Eichlseder, H.; Leitner, D.; Klell, M.; Sartory, M.: Synergiepotenzial eines Fahrzeugs mit variablem Erdgas/Wasserstoff-Mischbetrieb. – in: Gasfahrzeuge – Die Schlüsseltechnologie auf dem Weg zum emissionsfreien Antrieb?., Berlin, 2008
Riedler, J.; Klell, M.; Flamant, G.: High Efficiency Solar Reactor for Hydrogen Production Using Iron Oxide. – In: 9th Symposium Gleisdorf Solar, Gleisdorf, 2008
Klell, M.: Hydrogen, Natural Gas and H2NG mixtures in the ICE. – In: International Conference on Transport Fuels: Crucial factor and driver towards sustainable mobility. Federal Ministry for Transport, Innovation and Technology, Vienna, 2008
Klell, M.: Hydrogen as Future Energy Source. – In: Welding in the World Vol.52, 2008, pp 415 - 421
Klell, M.: Hydrogen in Austria – Activities and Perspectives. – In: International German Hydrogen Energy Congress, 2006, in press