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Hydrogen may also be extracted from water via biological production in an algae bioreactor, or using electricity (by electrolysis) or heat (by thermolysis); these methods are presently not cost effective for bulk generation in comparison to chemical paths derived from hydrocarbons.
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Hydrogen can be generated from natural gas with approximately 80% efficiency, or other hydrocarbons to a varying degree of efficiency. The hydrocarbon conversion method releases greenhouse gases. Since the production is concentrated in one facility, it is possible to separate the gases and dispose of them properly, for example by injecting them in an oil or gas reservoir (see carbon capture), although this is not currently done in most cases. A carbon dioxide injection project has been started by Norwegian company StatoilHydro in the North Sea, at the Sleipner field.

Steam reforming

Commercial bulk hydrogen is usually produced by the steam reforming of natural gas. At high temperatures (700–1100 °C), steam (H2O) reacts with methane (CH4) to yield syngas.

CH4 + H2O → CO + 3 H2 - 191.7 kJ/mol

The heat required to drive the process is generally supplied by burning some portion of the methane. . . .

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The mechanism begins with hydrogen atoms diffusing through the metal. When these hydrogen atoms re-combine in minuscule voids of the metal matrix to hydrogen molecules, they create pressure from inside the cavity they are in. This pressure can increase to levels where the metal has reduced ductility and tensile strength, up to where it can crack open, in which case it would be called Hydrogen Induced Cracking (HIC). High-strength and low-alloy steels, aluminium, and titanium alloys are most susceptible.
Hydrogen embrittlement can happen during various manufacturing operations or operational use, anywhere where the metal comes in contact with atomic or molecular hydrogen. Processes which can lead to this include cathodic protection, phosphating, pickling, and electroplating. A special case is arc welding, in which the hydrogen is released from moisture (for example in the coating of the welding electrodes; to minimize this, special low-hydrogen electrodes are used for welding high-strength steels). Other mechanisms of introduction of hydrogen into metal are galvanic corrosion, chemical reactions of metal with acids, or with other chemicals (notably hydrogen sulfide in sulphide stress cracking, or SSC, a process of importance for the oil and gas industries).

Energy density is the amount of energy stored in a given system or region of space per unit volume, or per unit mass, depending on the context. In some cases it is obvious from context which quantity is most useful: for example, in rocketry, energy per unit mass is the most important parameter, but when studying pressurized gas or magnetohydrodynamics the energy per unit volume is more appropriate. In a few applications (comparing, for example, the effectiveness of hydrogen fuel to gasoline) both figures are appropriate and should be called out explicitly. (Hydrogen has a higher energy density per unit mass than does gasoline, but a much lower energy density per unit volume in most applications.)

The wide flammability range, 4% to 74% in air, and the small amount of energy required for ignition necessitate special handling to prevent the inadvertent mixing of hydrogen with air. . . .

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To function, the membrane must conduct hydrogen ions (protons) but not electrons as this would in effect "short circuit" the fuel cell. The membrane must also not allow either gas to pass to the other side of the cell, a problem known as gas crossover. Finally, the membrane must be resistant to the reducing environment at the cathode as well as the harsh oxidative environment at the anode.


Unfortunately, while the splitting of the hydrogen molecule is relatively easy by using a platinum catalyst, splitting the stronger oxygen molecule is more difficult, and this causes significant electric losses. An appropriate catalyst material for this process has not been discovered, and platinum is the best option. Another significant source of losses is the resistance of the membrane to proton flow, which is minimized by making it as thin as possible, on the order of 50 μm.