Hydrogen is the most abundant chemical element in the universe, found in the Sun, other stars and the gas planets in our solar system. It occurs naturally on Earth, but not in large enough quantities to be produced cost-competitively. It therefore needs to be separated from other elements.
On Earth, hydrogenThe simplest and lightest atom, the most abundant element in the universe. is generally found in compounds with other elements. The most common are carbon, with which it forms methane (CH4)The main component of natural gas deposits and oil deposit gas caps. Methane is produced naturally by landfills..., and oxygen, with which it forms water (H2O). How is pure hydrogen made? To obtain pure hydrogen for industrial applications, it must be separated from the chemical elements to which it is bound.
Hydrogen can be produced by electrolysis using renewably-sourced electricity
Hydrogen Production Process Technologies
Today, 95% of hydrogen is produced either from wood or from fossil fuels, such as natural gas and oil. Three types of production process are currently in use:
- The most common hydrogen production process is natural gas reforming — sometimes called steam methane reforming because it uses high-temperature steam. When exposed to steam and heatIn the field of statistical thermodynamics today, heat refers to the transfer of the thermal agitation of the particles making up matter..., the carbon (C) atoms of methane (CH4) separate. After two successive reactions, they reform separately to produce hydrogen (H2) and carbon dioxide (CO2Along with water vapor, carbon dioxide is the primary greenhouse gas (GHG) in the Earth's atmosphere...). This operation therefore requires natural gas.
- Another process is charcoalCharcoal is carbon produced by the pyrolysis of wood in the absence of oxygen... gasification1. Charcoal consists mainly of carbon and water. Burned in a reactor at a very high temperature of between 1,200 and 1,500 °C, the charcoal releases gas that separates and reforms to produce hydrogen (H2) and carbon monoxideCarbon monoxide is a carbon oxide with a chemical formula of CO. It is produced by the partial oxidation of carbon-containing compounds... (CO).
- Hydrogen can also be produced using electricityForm of energy resulting from the movement of charged particles (electrons) through a conductor..., through electrolysis of water. An electric current is used to split water (H2O) into oxygen (O2) and hydrogen (H2). This method is not as cost-effective as using fossil fuels. Hydrogen produced by steam methane reforming costs around €1.5 per kilogram at the plant gate (excluding distribution costs), triple the cost of natural gas. Hydrogen produced using electrolysis is currently around four times more expensive, even before the cost of the electricity required is factored in.
Only 1% of the hydrogen produced in France is obtained using electrolysis technology. But as new uses for hydrogen energy emerge, requiring purer hydrogen, the horizons for this technology are broadening. R&D work aims to lower production costs, especially by using high-temperature (or steam) electrolysis at 700 to 800 °C.
Producing “Clean” Hydrogen
To ensure that this new energy carrierA synonym of secondary energy (see definition). is “green” — meaning that it emits little greenhouse gasGas with physical properties that cause the Earth's atmosphere to warm up. There are a number of naturally occurring greenhouse gases... — hydrogen production has to be as clean as possible.
Reforming produces few greenhouse gases when combined with carbon capture and storage processes; however, these significantly increase costs.
Today, 95% of hydrogen is produced from fossil fuels
Gasification is another option, because it covers the entire solid biomassIn the energy sector, biomass is defined as all organic matter of plant or animal origin... pathway: many types of organic matter can be burned to produce biogasA product of the methanation (anaerobic digestion) of organic waste.... Although wood (in the form of charcoal) is the main feedstock used, plant waste such as straw is also suitable. Because biomass sources can be replanted, the carbon footprintThe carbon footprint (also known as greenhouse gas inventory) of a good or service measures the impact human activities have on the environment ... is low.
Electrolysis also produces clean hydrogen when “green” electricity is used. But to overcome the issue of cost-competitiveness, large amounts of inexpensive electricity are needed year-round. Prototypes are under study, especially in Germany, to use intermittent production spikes from wind and solar energy. But for now, the cost of electrolysis is still prohibitive.
Other hydrogen production processes are also being examined2
- Some modified microorganisms can produce hydrogen when exposed to sunlight, a process known as biological hydrogen production by photosynthetic microorganisms.
- In photoelectrolysis, a photoelectrochemical cell submerged in water uses sunlight to separate the water into hydrogen and oxygen bubbles.
- In the thermochemical cycle, water is heated to 800 to 1,000 °C, with the moleculeA group of two or more atoms, from the simplest of combinations to macromolecules that can contain several thousand atoms... splitting to release hydrogen. The main drawback of this method is that it requires nuclear powerIn physics, power is the amount of energy supplied by a system per unit time. In simpler terms, power can be viewed as energy output... to heat the water: the cost is high and production depends on uraniumGray, very dense radioactive metal that is relatively abundant in the Earth's crust and oceans in the form of UO2... stocks.