H2 production

Hydrogen might be the most abundant element on earth but it can be found rarely in its pure form.

Practically, this fact means that in order to produce hydrogen, it needs to be extracted from its compound.
Of course, this extraction process needs energy but hydrogen can be produced or extracted using virtually any primary source of energy, be it fossil or renewable. Characteristically, hydrogen can be produced using diverse resources including fossil fuels, such as natural gas and coal, biomass, non-food crops, nuclear energy and renewable energy sources, such as wind, solar, geothermal, and hydroelectric power to split water. This diversity of potential supply sources is THE most important reason why hydrogen is such a promising energy carrier. 

Although most of the world’s hydrogen production today is being produced through a more CO2 intensive process called Steam Methane Reforming (SMR), hydrogen can also be produced through a process that makes use of renewable electricity, leading to the production of “green” or CO2 neutral hydrogen. 
The current (new methods are being researched every day) most notable production pathways are the following:

Electrolysis and high temperature Electrolysis

Method: Electrolysis
In short: 
Process where water (H2O) is split into hydrogen (H2 ) and oxygen (O2) gas with energy input and heat in the case of high temperature Electrolysis.
In Practice: 
An electric current splits water into its constituent parts. If renewable energy is used, the gas has a zero-carbon footprint, and is known as green hydrogen.

Steam Methane Reforming

Method: Reforming – most notably Reforming of natural gas but also biogas  
In short:
 The primary ways in which natural gas, mostly methane, is converted to hydrogen involve reaction with either steam (steam reforming or steam methane reforming SMR when methane is used), oxygen (partial oxidation), or both in sequence (autothermal reforming)
In practice: 
Steam reforming: Pure water vapour is used as the oxidant. The reaction requires the introduction of heat (“endothermic”).

  • Partial oxidation: Oxygen or air is used in this method. The process releases heat (“exothermic”).
  • Autothermal reforming: This process is a combination of steam reforming and partial oxidation and operates with a mixture of air and water vapour. The ratio of the two oxidants is adjusted so that no heat needs to be introduced or discharged (“isothermal”).

Hydrogen as a by-product or Industrial Residual Hydrogen

Method: Hydrogen from other industrial processes that create hydrogen as a by-product
In Short: Electrochemical processes, such as the industrial production of caustic soda and chlorine produce hydrogen as a waste product.
In Practice: 
Producing chlorine and caustic soda comes down to passing an electric current through brine (a solution of salt – sodium chloride – in water). The brine dissociates and recombines through exchange of electrons (delivered by the current) into gaseous chlorine, dissolved caustic soda1 and hydrogen. By the nature of the chemical reaction, chlorine, caustic soda and hydrogen are always manufactured in a fixed ratio: 1.1 tons of caustic and 0.03 tons of hydrogen per tons of chlorine.