**2.1 Biological method**

Microorganisms such as algae and bacteria in absence of sunlight with organic matter can produce hydrogen using many biological reactions. In this method bacteria (microorganisms) break down the organic matter such as biomass, sugar, corn or waste and releases hydrogen gas. This method is also known as dark fermentation as no light is involved [13]. Biological method is under research and development stage as the efficiency of this process is not up to the mark.

#### **2.2 Thermochemical method**

Natural gas, coal, hydrocarbons and biomass is also rich with the hydrogen content. Thermal process like steam reforming is responsible for releasing hydrogen from these sources. Hydrogen when combines with carbon produces a hydrocarbon which are available naturally and are one of the main sources of hydrogen. Hydrocarbons like methane, ethane and propane (alkene and alkyne) are key compounds of hydrogen. More than 90% of hydrogen which we get nowadays is coming from hydrocarbons which has a fossil origin. These hydrocarbons are quite stable than the other sources of hydrogen and does not leave hydrogen easily unless catalysis process is used. Breaking of sigma bond present in carbon and hydrogen is most difficult but can be achieved by steam reforming in case of methane.

$$\text{CH}\_4 + \text{H}\_2\text{O} \rightarrow \text{CO} + \text{3H}\_2\tag{1}$$

Generally, in steam reforming process water (steam) and methane are mixed in presence of catalyst (noble metals) inside a tube in appropriate proportion. Main advantage of using this process to produce hydrogen is that many companies/industries are already with all the equipment's setups are present. Perfect engineering and research and development in hydrogen generation from hydrocarbons field will fulfill the need of many upcoming generations [14].
