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AFC (Alkaline Fuel Cell):

An alkaline fuel cell is a low-temperature cell whose working temperature is between 60 and 90 degrees Celsius. The electrolyte is an alkaline lye, which is contaminated with even the smallest impurities; for this reason the cell has to be operated with extremely pure fuel gases such as hydrogen and oxygen, for example. The AFC is primarily used in space travel and military technology (submarines). Although technically advanced, the high demands placed on gas purity mean that it is scarcely suited to everyday applications.

Anode:

Positively charged pole in an electrical system which attracts electrons from the surrounding material.

Autothermal reformer:

Has developed from a combination of steam reforming and partial oxidation. The reformer is used for the production and treatment of hydrogen. The required heat is generated by the reformer itself, it is "autarkic" therefore, and for this reason we use the technical expression "autothermal". In this respect methanol as well as any other hydrocarbon or hydrocarbon mixture (natural gas, petrol, diesel etc.) may be used. This takes place through precise dosage of the air and steam inflow. The two methods are combined with one another such that the advantage of oxidation (provision of heat energy) complements the advantage of steam reforming (higher hydrogen yield) to the best-possible extent and optimization of the efficiency may be attained. Disadvantage: The subsequent cleaning is very costly.

Biochemical production of hydrogen:

Another form of zero-emission hydrogen production has been implemented using green algae. As this process has only recently been discovered, considerable research work is required to attain higher yields of hydrogen. The principle is based on the enzyme "hydrogenase". With the aid of this enzyme the algae split water into hydrogen and oxygen. For energy production they use natural photosynthesis under the effect of sunlight. A research group in Bonn, Germany, has been investigating this phenomenon for a long time and is in a position to treble the hydrogen yield through genetic manipulation of the algae.

Biomass:

Biomass describes organic substances found on the earth in living, dead or decomposed organisms and their excrement. The biochemically stored solar energy in biomass may also be used as a sustainable energy carrier for the production of electrical energy or as a fuel (renewable energy carrier). The use of biomass for the generation of heat, electrical energy or as a fuel allows for a balanced CO2 audit, as only the amount of CO2 is emitted which was previously bound in a biochemical form.

Bivalent hydrogen motor:

In this conventional motor hydrogen as well as petrol may be used as a fuel (Clean Energy Fleet of the BMW Group).

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Catalytic steam cracking:

Process for the production of hydrogen. Methane (CH4) is mixed with steam on a nickel catalyst at a temperature of around 1,200 degrees Celsius. In addition to hydrogen, carbon monoxide (CO) is also produced. The resulting gas mixture is described as synthesis gas.

Cathode:

Negatively charged pole in an electrical system which gives off electrons to particles from the surrounding material.

Carbon monoxide:

Toxic flammable gas (CO) created during the fission of hydrocarbons (e.g. methane).

Cavendish:

The chemist Henry Cavendish (1731-1820) discovered oxygen as an element in 1766.

Clean Energy Partnership (CEP):

Consortium of the companies Aral, BMW Group, Berliner Verkehrsbetriebe (BVG), DaimlerChrysler, Ford, GM/Opel, Hydro/GHW, Linde, TOTAL, Vattenfall Europe, and Volkswagen which, with the support of the German government, has been endeavouring to furnish proof of the suitability of hydrogen in mobile applications since November 2004 in Berlin within the framework of a hydrogen demonstration project.

CO2 sequestration:

cf. Sequestration

Compressed gas cylinders:

Compressed gas cylinders are primarily deployed with mobile applications; they are made of steel or carbon fibre-reinforced composite material and may be filled to a pressure of as much as 350 bar. Compressed gas cylinders have a much greater weight than the hydrogen stored therein, however. Other possibilities for storage: Gasometers, pressurized cylinders, metal hydride storage systems and nanotubes.

Cryogenic containers:

Cryogenic containers have a double-walled construction: As with a thermos flask there is a vacuum of around three centimetres in thickness between the inner and outer tank. The radiation loss is further reduced by thin layers of aluminium foil. These three centimetres of insulation have the same thermal conductivity resistance as a nine-metre thick layer of polystyrene. Cryogenic containers are used, for example, with LH2 tanks. A 140 litre tank weighs around 100 kilograms, of which some ten kilograms are accounted for by the stored hydrogen.

Cryogenic substances:

Greek krýos: cold, frost. Substances which do not become liquid until very low temperatures, such as helium, oxygen, nitrogen, natural gas and air. With respect to technical gases this is a reference to the supercooled range in which gases become liquid and may be stored with a higher density. With natural gas liquefaction (boiling point) begins at minus 161.5 degrees Celsius (111.5 K) and with hydrogen at minus 253 degrees Celsius (20 K). So that the change of state is maintained, special container insulation is required cryogenic containers.

Cryogenic variant:

Describes the process of accommodating a large amount of liquid hydrogen in a car tank in a special heat-insulated tank. Advantage: The necessary pressure is lower than with compressed gas and the storage tanks that have to be transported are lighter.

CUTE and HyFLEET:CUTE Project:

The CUTE (Clean Urban Transport for Europe) Project – which comprises 31 partners from the worlds of politics, business and science – was initiated in November 2001. CUTE is being co-funded by the European Union and is currently the mostly widely acknowledged field test for the use of fuel cell buses and their hydrogen supply. 27 buses have been deployed in the nine participating cities: Amsterdam, Barcelona, Hamburg, London, Luxembourg, Madrid, Porto, Stockholm and Stuttgart. There are a further six buses in the allied projects ECTOS (Reykjavik/Iceland, also funded by the EU) and STEP (Perth/Australia). The project has a wide remit: Thus, in addition to testing of the various possibilities for hydrogen production and supply, the performance, reliability and economic efficiency of the buses in comparison with vehicles powered by conventional fuels are also being examined. The project was continued under the name HyFLEET:CUTE as of 2006 and was characterized by testing of the HyFLEET buses from MAN, which have a hydrogen combustion engine. An initial small series of these was delivered to Berliner Verkehrsbetriebe (BVG). 

Density:

Density is expressed using the Greek letter rho and is one of the physical properties of a material; it is defined as the mass of a body (m) per unit of volume (V). The density of liquids depends to a great extent on the temperature; with gases the specific pressure is also relevant.

DMFC (Direct Methanol Fuel Cell):

The direct methanol fuel cell is still in its development phase. It is a further development of the PEMFC. In contrast to the latter no hydrogen is required, but rather the necessary protons are formed on the anode directly from a methanol-hydrogen mixture. These travel through the membrane as in the PEMFC and react on the cathode with the oxygen to form water. The DMFC works at a temperature of ca. 80 to 130 degrees Celsius. Diverse application possibilities have been forecast for this cell type in the mobile and portable sectors (e.g. notebooks, camcorders, mobile phones).

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Efficiency:

The general ratio of output to input; with a machine, for example, the ratio of the power output to power input. Efficiency is expressed using the Greek letter eta and has a value of between 0 and < 1 or, expressed as a percentage, between 0 and < 100 per cent. If waste heat released during a thermal conversion process is used again, for example to preheat air or oil or as district heating, the efficiency of the plant is increased as part of the heat lost in the process may nevertheless be utilized. The efficiency of a fuel cell drive unit now reaches values of as much as 50 per cent, hydrogen combustion engines a figure of around 35 per cent. By comparison: The maximum efficiencies of diesel engines in the commercial vehicle sector are ca. 44 per cent and between 20 and 24 per cent with passenger vehicle engines.

Electrolysis:

Method for the production of hydrogen: Using an electrical current water is split into its elements hydrogen und oxygen. In practice, to this end a direct current voltage is applied to the two electrodes in an electrolytic cell, to the positive and negative poles therefore, under water; in this respect the water is made electrically conductive using a sodium hydroxide solution or sulphuric acid. The hydrogen is released on the negative pole (cathode), oxygen on the positive pole (anode). Electrolysers are currently undergoing further development so as to make them suitable for use on an industrial scale.

Electro motor:

An electrical machine which generally converts electrical energy into mechanical energy with the aid of magnetic fields. In electro motors the power which is exerted by a magnetic field on the conductor of a coil is converted into motion. Thus the electro motor is the counterpart to the generator. Electro motors usually create rotary motion, yet can also create translatory motion (linear drive). The advantage is that they can run both forwards (motor operation) and backwards (generator mode). In generator mode the vehicle can brake and at the same time the battery may be recharged (recuperation brake). Thus the brake energy is not lost; we also speak of brake energy recuperation. The stored energy may be used to start the motor or with hybrid vehicles for acceleration. In conjunction with the fuel cell the electro motor functions as a drive unit.

Electrons:

Electrons (symbol e-) are tiny, negatively-charged elementary particles. They form the electron sheath of atoms (and ions). Their free movement in metals is the reason for the electrical conductivity of metal conductors. Their antiparticles are the positrons (symbol e+), which have all the same characteristics with the exception of their electric charge. Experimental proof of the existence of electrons was first provided in 1897 by the Englishman Joseph John Thomson. An electron is a "micro-object", i.e. just like light it has a wave and a particle character. Electrons may be dissolved in polar solvents such as water or alcohols in solution (solvatised electron). Hydrogen has only one proton and one electron and is thus the lightest of the chemical elements.

Energy carrier:

Substances which serve to convert or produce energy or which are energy themselves are described as energy carriers. We differentiate between primary energy and secondary energy. Hydrogen is a so-called energy carrier, i.e. it serves as a transport and storage medium. With the aid of corresponding end devices the consumer uses it for conversion into the required form of energy: into heat or electricity. Moreover it is a suitable fuel in combustion engines and as a drive unit in the transport sector.

Energy content:

Expressed as a ratio of mass, hydrogen has ca. three times more energy content than conventional fuels (ca. 33 kilowatt hours per kilogram). Liquid hydrogen has a greater energy content per volume than compressed gaseous hydrogen. The high energy content of hydrogen is an important prerequisite for its use as an energy store, for instance as a fuel for cars; in contrast to batteries it can guarantee that it is possible to attain a satisfactory range for the vehicle with the transportable mass.

Filler nozzles for LH2:

Modern coupling units have a sluice: This is first rinsed and cleaned with helium, only then are the valves opened. In the meantime the mechanical connection has been tested such that it may be created at ambient temperature without the coupling units having to be cooled or pre-heated in a time-consuming process.

Filling station robot:

The refuelling process with LH2 was performed by a robot at the hydrogen filling station at Munich Airport: With the aid of a laser and a camera system with special image recognition software the robot identified the exact position of the vehicle, monitored whether there was sufficient cooling of the fuel system, established a gastight connection between the vehicle and the refuelling station, tested this connection with the aid of cold helium gas, started the refuelling procedure by opening the refuelling valve, closed the pump system so that it was airtight, refuelled the vehicle, and ended the procedure as soon as the tank was full (max. 95 per cent of the maximum volume). 

Flame properties of hydrogen:

As hydrogen flames radiate in the infrared range they are scarcely visible to the naked eye. Due to its low substance density the gas rises very quickly. The combustion speed is relatively high, with the effect that the flames quickly spread but that the fire is soon over. The heat radiation is low because there are no smouldering hydrocarbon particles which can radiate heat. As long as no other substances are burnt at the same time, no smoke or fumes are produced.

Fleet operation:

Without a hydrogen filling station network the only possibility for hydrogen-powered vehicles is fleet operation, whereby the vehicles are deployed around a central filling station location. This solution is suited to urban or regional service providers, for example, such as public transportation, refuse disposal, as well as logistics and customer service vehicles.

Fossil energy sources:

All primary energy sources which are derived from organic substances in the ground (crude oil, natural gas, diverse hydrocarbons, coal, etc.) are described as fossil or finite fuel sources. At present hydrogen is primarily produced from fossil sources, above all from natural gas. An emission-free hydrogen cycle, however, can only exist if hydrogen is produced from renewable energy sources and no CO2 is released. The production of hydrogen with the aid of renewable energy sources such as solar power, biomass, wind and hydropower is nowadays still much more expensive than with fossil energy carriers. However, if one takes into account the so-called external costs - for example the costs for the repair of environmental damage also caused by the combustion of coal, oil and gas - the cost comparison shifts in favour of renewable energies.

Fuel cell: 

Fuel cells convert hydrogen and oxygen into water, at the same time generating power and heat. The English researcher Sir William R. Grove, who designed the first functioning prototypes, laid the foundation for fuel cell technology in 1839. Fuel cells can either be powered with pure hydrogen or with a number of hydrogen compounds - for instance with natural gas, biogas, methanol or petrol. These substances first have to be chemically treated in an upstream reformer. This creates chemical compounds which contain hydrocarbons, and consequently combustion to carbon dioxide contributes to the greenhouse effect. The fuel cell is therefore only truly environmentally-friendly if it is powered with pure hydrogen.

Fuel cell bus:

Through the use of hydrogen in buses it is possible to reduce harmful emissions in inner cities and urban areas. The hydrogen is stored in a gaseous state at 350 bar in containers on the roof; an amount of 39 kilograms – corresponding to a range of 300 kilometres – meets the daily requirements of a bus. Buses with a fuel cell engine are very quiet and just as comfortable as conventional models. As scheduled passenger service buses such as the MAN fuel cell bus based on the Lion’s City model, which was tested in scheduled services at Munich Airport in 2005/2006, regularly return to their depot, one central filling station is sufficient. The additional weight of the fuel cells and of the storage unit offers enhanced benefits in terms of the ratio of transported passengers to weight than is the case with passenger vehicles. The particular feature of the MAN hybrid fuel cell bus is the combination of a passenger vehicle fuel cell unit with an electrical power of 68 kilowatts with a high-capacity energy storage unit. This combination allows for the storage of brake energy.

Fuel cell forklift truck:

Forklift trucks and similar logistics vehicles rank among the most common vehicle types at airports; it would be impossible to imagine modern industry without such vehicles. It has to be possible to deploy these indoors and outdoors. Forklift trucks are usually powered by either an internal combustion engine - this means harmful exhaust fumes and noise pollution, which are not acceptable in freight halls for example - or they draw their energy from a battery. The latter, however, has to be recharged for a period of ca. eight hours, something which involves considerable restrictions and additional time costs in operational flows. Power from a fuel cell, such as that which has been realized by Proton Motor in cooperation with Linde Gas and STILL for H2argemuc, is ideal in contrast: It does not emit any harmful emissions, at the end of the shift the forklift truck may be refuelled in eight minutes and is ready for operation again almost immediately. Thanks to the hybrid concept with an electrical energy storage unit, the brake energy may be utilized and the already excellent efficiency level of the fuel cell improved even further.

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GH2:

Under normal conditions hydrogen is gaseous. The refuelling of hydrogen vehicles with gaseous hydrogen has been conducted for decades without any problems.

H₂argemuc:

The hydrogen demonstration project was founded in 1997 by 13 partners with the support of the Bavarian state government, and opened the world’s first public hydrogen filling station in 1999. Upon attaining the objectives laid down in the initial portfolio this internationally acknowledged hydrogen project was concluded on 31.12.2006 after the fourth project phase. 

High-temperature fuel cells:

Produce - in contrast to other fuel cell types - electricity and heat not only from hydrogen or methanol, but also from fuels which are more cost-favourable and more easily available: e.g. natural gas, petrol, diesel and biogas. These fuels are converted by an upstream reformer into hydrogen and carbon monoxide. The high-temperature fuel cell - also known as SOFC (solid oxide fuel cell) - is particularly suited to permanent operations - the electricity supply for buildings and motor vehicles therefore. Very often the process heat may also be used - in an optimum case with the newest generation of SOFCs (for example from Fraunhofer Institute for Ceramic Technologies) efficiency factors of over 90 per cent may be attained.

High-pressure cylinders:

Cylinders for the storage of highly compressed, gaseous hydrogen. They are filled at pressures of between 200 and 350 bar (700 bar is under development). This is much higher than with liquid gas tanks (12 bar). So that the forces are evenly distributed and stress is avoided these cylinders are cylindrical or spherical in shape.

Hindenburg incident:

36 people died in a spectacular accident involving the Hindenburg zeppelin with 200,000 cubic metres of hydrogen on board in Lakehurst / New Jersey (USA) on 6 May 1937. This incident has contributed to hydrogen still being deemed dangerous by many people even today. In the meantime studies have revealed that the accident was caused by an electrostatic charge: The highly flammable paint on the airship's shell caught fire and then ignited the hydrogen. The fire only lasted 32 seconds, there was no explosion. Later airships were nevertheless filled with the non-combustible inert gas helium.

Hydrogen:

At the beginning of the sixteenth century Paracelsus produced a combustible gas - in all probability hydrogen - by dissolving iron with acids; Robert Boyle also reported this phenomenon in the seventeenth century. Hydrogen was verified as an element in 1766 by Henry Cavendish. Shortly afterwards the chemist Antoine Laurent Lavoisier succeeded in demonstrating the composition of water. In 1787 the Frenchman dubbed hydrogen hydrogène (hydor = water, Greek; genes = creating). Hydrogen generally occurs as a molecule, as two hydrogen atoms usually combine to form hydrogen. In nature the H2 molecule is seldom found alone: As a rule it quickly finds an oxygen atom (O) and reacts to form water (H2O).

Hydrogen combustion engine:

In addition to fuel cell technology there is a second drive unit alternative. The hydrogen combustion engine functions in a similar manner to a four-stroke cycle engine, however the explosion in the cylinders is not brought about by a petrol-oxygen mixture, but by a hydrogen-oxygen mixture. The ratio of the gas volumes is typically two parts of hydrogen to one part of oxygen (oxyhydrogen gas). The end product of this combustion is pure water (H2O).

Hydrogen costs:

Fixing a price for hydrogen is difficult - the costs are too heavily dependent on the type and scope of production. Reliable statements will only be possible once series maturity has been attained. Four litres of LH2 and 3.5 cubic metres of CGH2 contain as much energy as about one litre of petrol. Under an EU directive (Section 15 sub-section 1 i Directive 2003/96/EC) hydrogen used as a fuel is subject to taxation. The possibility for tax relief is only available if hydrogen is used in "pilot projects for the technological development of environmentally-friendly products or with fuels from renewable raw materials". Tax concessions, similar to those currently seen with natural gas, may serve to aid the market launch of hydrogen.

Hydrogen economy:

The hydrogen economy could in the long term replace our current energy supply, which primarily comprises fossil fuels. Hydrogen is available in virtually unlimited amounts and thus, in principle, suited to meeting the world's constantly rising energy needs. As a rule we differentiate between three stages on the way to a hydrogen economy: Initially there is a clear reduction in energy consumption through cut-back measures. This phase is followed by a major expansion in the use of renewable energies. Only in the final phase (from around 2030 onwards) can hydrogen be produced in quantities relevant to our energy needs. Natural gas is regarded as a bridge energy on the way to a hydrogen economy because it is suited as a hydrogen source for the transition period.

Hydrogen in outer space:

Hydrogen is the most common chemical element in outer space. Hydrogen makes up 75 per cent of the total mass in the universe and 90 per cent of all atoms. The sun, as well as the large planets in our solar system, Jupiter and Saturn, is a gas planet, and like the majority of fixed stars and galaxies primarily consists of hydrogen; helium is produced from this hydrogen in the core of the fixed stars.

Hydrogen properties:

Hydrogen is extremely light and has a low density. It is non-toxic, does not cause any irritation, is environmentally neutral, odourless, taste-neutral, invisible, and highly volatile, does not explode when released, and is neither radioactive nor carcinogenic.

Hydrogen transport:

Hydrogen may be stored and transported as a compressed gas or as a supercooled liquid. Gaseous hydrogen may be transported in pipelines. For mobile storage systems - transport in boats, tankers and trains therefore, and as a fuel for aeroplanes and cars - liquid hydrogen is advantageous as it has greater energy content per volume than compressed gaseous hydrogen. Thus a 40-ton truck can only transport 530 kilograms of hydrogen in compressed gas cylinders due to the high "packaging weight", whereas a super-insulated tanker of the same weight with liquid hydrogen can transport 3,300 kilograms of hydrogen.

Hydrogen weight:

With a specific weight of 0.00008987 grams per cubic centimetre, hydrogen is the lightest element in the world. Hydrogen is 14 times lighter than air. It is at the beginning of the periodic table and has the atomic weight 1, i.e. a hydrogen atom merely comprises one proton and one electron.

HyFLEET:CUTE Project:

CUTE and HyFLEET:CUTE Project

Ignition energy:

The minimum amount of energy required to ignite a hydrogen-oxygen mixture; for hydrogen it is 0.017 millijoule and is thus relatively low (about one ten times less than that of other fuels). This figure alone, however, does not indicate how dangerous the fuel is as all fuel-air mixtures are very easily flammable.

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LH2:

Abbreviation for the English description for liquid hydrogen.

Liquid hydrogen:

At standard atmospheric pressure hydrogen liquefies at 20.3 Kelvin (only helium boils at a lower temperature) and has a triple point of 13 Kelvin. Liquid hydrogen is very cold, with a temperature of minus 253 degrees Celsius. However, it requires only a portion of the volume which it occupies in a gaseous, highly compressed state, thus allowing for the storage and transport of large amounts in a highly economical manner.

MCFC (Molten Carbonate Fuel Cell):

A high-temperature fuel cell with a working temperature of between 620 and 660 degree Celsius. The waste heat has a high temperature and may be used for steam production. Thanks to the high operating temperatures the MCFC is insensitive to carbon monoxide (CO), and the reforming of natural gas to hydrogen and carbon dioxide can take place internally. An external reformer is not required. The high temperatures and the aggressive liquid salts of the electrolytes place considerable demands on the material. For this reason researchers are focusing on the development of durable materials and resistant cathodes. Due to the production of steam, MCFC is suited to industrial combined heat and power generation and stationary energy generation with a medium and high power output.

Membrane:

A thin film which separates liquids and gases.

Metal hydrides:

Metals which can store hydrogen. Different metals have varying abilities to absorb hydrogen, with the effect that the absorption capacity per cubic centimetre of metal fluctuates between 20 and 600 cubic centimetres of gaseous hydrogen. Metal hydrides are similar to solutions of hydrogen in metal or alloys. Technically metal hydrides are mainly used to build metal hydride storage systems for hydrogen.

Metal hydride storage system:

Compact storage system for pure hydrogen, which is stored in the interstices of a mesh-like metal alloy. The storage takes place at slight overpressure (up to 30 bar) and usually works in a temperature range of 20 to 80 degrees Celsius. Metal hydride storage systems are suited, for example, to notebooks and other portable fuel cell applications. In addition to the small size, the high energy density is also advantageous. The devices function for longer with such a storage system than with conventional rechargeable batteries. Other possibilities for storage: Gasometers, pressurized cylinders, compressed gas cylinders and nanotubes.

Methane:

Hydrocarbon and the main constituent part of natural gas; hydrogen production on an industrial scale is also possible using the catalytic steam fission of methane (natural gas).

Methanol:

Certain fuel cell types can also process methanol, yet to do so require an upstream reformer. Methanol could be sold using a similar filling station network to that currently used for petrol. This liquid, which is harmful to humans, may be produced from natural gas as well as on a renewable basis from biomass. Disadvantages: Carbon monoxide (CO) is produced in the fuel cell; this contaminates the polymer membrane (PEM). Moreover, the membrane has to be kept moist and hydrocarbon deposits have to be avoided. While these problems may be overcome with additional catalytic converters, these increase the production and operating costs.

Nanotubes:

Research is being conducted on storing hydrogen in carbon nanotubes (CNT). These are microscopically-small tube-like structures (molecular nanotubes) made of carbon. Just like those of fullerenes or the layers of graphite their walls only comprise carbon, whereby the carbon atoms have a honeycomb structure with hexagons and three points of contact in each case. The diameter of the tubes is usually in the range of 1-50 nanometres (nm), yet tubes with a diameter of only 0.4 nm are also produced. Lengths of several millimetres for individual tubes and as much as 20 centimetres for tube bundles have already been attained. We differentiate between single-wall and multi-wall tubes, between closed and open tubes (with a lid which has a section from a fullerene structure), and between empty and filled tubes (for example with silver, liquid lead, or inert gases). In comparison with metals, carbon systems have a low density, are non-toxic and available in large amounts at relatively favourable prices. However graphite can only absorb very little water at room temperature. Scientists at TU Dresden and the National Research Council of Canada recently demonstrated in computer simulations that by including suitable "space molecules" in the graphite structure, molecular hydrogen can be stored at room temperature in amounts which surpass the storage capacity required by the US Department of Energy for practical deployment as a hydrogen storage system. Whether this is a breakthrough for hydrogen storage remains to be seen. Other possibilities for storage: Gasometers, pressurized cylinders, compressed gas cylinders and metal hydride storage systems.

Natural gas:

Natural gas has a major advantage compared to conventional fuels: When combusted it is particularly low in emissions. Furthermore, it is very similar to hydrogen gas in its vehicle-relevant properties. As this gas is very common for mobile and stationary applications such as heating for houses and the operation of power stations, the transition to a hydrogen world may be accelerated by adding hydrogen to the gas; adding up to ten per cent hydrogen is possible without any technical conversions (liquid natural gas). 2,500 busses and engines from MAN already operate with natural gas and serve as the technical basis for hydrogen internal combustion engines.

Nitrogen oxide:

Nitrogen oxide is a generic expression for the gaseous oxides of nitrogen.

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Oxyhydrogen reaction:

As the stoichiometric gas mixture of hydrogen and oxygen (2 H2 + O2) reacts with an explosion upon ignition, it is also known as detonating gas. In chemistry the so-called detonating gas probe is used to demonstrate the presence of hydrogen.

PEM fuel cell (PEMFC):

Abbreviation for Polymer Electrolyte Membrane. It separates the oxygen from the hydrogen, and is made of a polymer (a plastic therefore). On the anode electrically neutral hydrogen molecules are oxidised to hydrogen ions, whereby they lose their electron. The positively charged ions travel through the membrane to the negatively charged cathode. With the movement of the protons through the membrane a voltage is created between the electrodes. Electricity flows if a consumer load is connected.

Power density:

The expression power density is used with fuel cell systems in a different context. With a PEM system the power density is commonly stated as watts per square centimetre of membrane surface area. The numerical value thus represents the efficiency of the load transport.
Power density is also often stated as watts per volume unit. A high power density means lots of power in a small space, something which is particularly important for portable, mobile applications. With fuel cell vehicles the power density is often also stated as electrical power per kilogram weight of the drive system.

Pressurized cylinders:

Hydrogen in its gaseous state is stored in pressurized cylinders of ca. 30
to 700 bar at ambient temperature. Other possibilities for storage: Gasometers, compressed gas cylinders, metal hydride storage systems and nanotubes.

Reformer in vehicles:

The reformer belongs to the peripheral equipment of fuel cells, which are not supplied with pure hydrogen. It forms the core of the fuel gas treatment. Here the fuel gas (e.g. natural gas) is converted into process gas rich in hydrogen using catalytic and thermal methods.

Renewable (regenerative) energy sources:

Among the renewable energy sources are not just solar energy but also biomass as well as water (hydro) and wind energy - energy sources which in contrast to finite, fossil energy sources are available in practically unlimited amounts and whose combustion produces scarcely any environmentally-damaging emissions.

Safety aspects with the use of liquid hydrogen in the transport sector:

In the test program run by TÜV SÜD in cooperation with the BMW Group and Linde Gas various scenarios were reconstructed so as to observe the performance of liquid hydrogen tanks in hazardous situations: Thus, for instance, filled tanks with blocked safety valves were destroyed under high pressure. The additional safety valves in the inner tank ensured in such an extreme case that the stored hydrogen is released without any major endangerment. The tanks displayed similar conduct upon deformation or serious damage using massive objects. In not one single case did a tank explode, as special pressure-relief joints prevented the tank from exploding.

Secondary energy carrier:

Electrical, thermal or mechanical energy which is acquired through technical conversion from primary energy sources. Examples are electricity and hydrogen. Energy is lost during the conversion process.

Sequestration:

In addition to renewable energies, energy savings and more efficient power stations, the sequestration of carbon dioxide, the capture and storage of this climate-damaging gas therefore, is increasingly gaining in significance as a measure to combat the threat of climate change. Climate-damaging gases which are produced during the combustion and extraction of fossil fuels are stored underground in geological formations.

SOFC:

SOFC stands for Solid Oxide Fuel Cell - a high-temperature fuel cell.

Stack:

Stack of fuel or electrolytic cells which are interconnected in series or in parallel.

Steam reformer:

This form of hydrogen production has already been extensively tested and is mature; there are already large-scale plants with a capacity of 100,000 cubic metres per hour. The steam reformer is also utilized for hydrogen production within the framework of the H2argemuc project. Hydrocarbons, which are very common in nature (natural gas, methanol, biogas), are separated from the hydrogen in two processes. In the first stage the hydrocarbon reacts with water in the reformer at a temperature of 800 to 900 degrees Celsius and a pressure of around 25 bar. Nickel catalysts help to initiate the reaction. The resulting carbon monoxide (CO) is then separated and in a second stage, known as the shift reaction, is mixed with steam, again producing more hydrogen. The gas is then cleaned using pressure swing adsorption (PSA). The residues are 60 per cent combustible and are returned to the reformer for combustion. In this manner hydrogen may be produced very efficiently.

Storage:

Fundamentally hydrogen may be stored in a liquid and a gaseous form. Possibilities for storage: Gasometers, pressurized cylinders, compressed gas cylinders, metal hydride storage systems and nanotubes.

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VES /Verkehrswirtschaftliche Energiestrategie:

The project idea of the Clean Energy Partnership (CEP) goes back to resolutions adopted by the Verkehrswirtschaftliche Energiestrategie (VES). This initiative of companies from the automobile and energy industries, which is supported by the German government, has set itself the goal of agreeing upon a renewable producible fuel which offers considerable potential for a reduction in CO2 in the entire energy chain and which may be used with a diversity of vehicle drive units. In June 2001 VES agreed that hydrogen is the fuel with the greatest long-term potential for the future; the CEP filling station in Berlin was then designed and implemented as a practical test. In March 2006 the second filling station was opened in Berlin.

Water:

H2O. Water is a very stable compound; in order to break this down - for instance when producing hydrogen - energy is required.