**1. Introduction**

The fast and uncontrolled growing population is a result of urbanization and industrialization. States economic growth is dependent on the number of working industries in it. Also, to fulfill the demands of growing population textile, food, petrochemical, plastic, leather, and metal factories are emerging day by day [1–3]. Each of these industries helps to the mankind for their betterment and responsible for creating several pollutants, destroying agricultural lands and natural habitats. On the other hand, all these industries are working on non-renewable energy sources like wood, coal, natural gas, and petroleum products [4, 5]. Non-renewable energy sources are of one-time use, once used one cannot utilize them again. Two main problems are associated with non-renewable energy sources firstly when they burnt the produces harmful pollutants which is not acceptable [6, 7]. From past couple of decades scientific community, is engaged to solve the pollutants removal/degradation problems which are not economical. When fossil fuel gets extensively used, they produce global warming. Global warming is mainly caused by carbon dioxide emission. Carbon dioxide is when produce it remains in the atmosphere and absorbs the harmful infrared radiations which are reflected from earth surface. Secondly,

after consumption these energy sources are going to be extinct as their availability is limited [8]. Geographically, non-renewable energy stock is located only to certain territories hence, it might be the reason for clashes between energy enriched and energy deficient countries which may leads to the world war again. Because of all these problems like pollution, environmental and health hazards the use of nonrenewable energy sources for long period are not viable [9, 10].

Use of renewable energy sources like solar energy, hydro energy, wind energy, geothermal energy and nuclear energy are the only alternatives for all above said problems. Major advantages of renewable energy sources are that they when used does not create any type of pollution as well as one can use them in cyclic manner. Only one thing that we must keep in mind that these can not be used directly as an energy, but one must convert in the form of energy [11]. Also, sometimes for the energy conversion process complex, huge and expensive machinery may require. The ultimate solution for all above discussed problems is the use of hydrogen energy. The sustainable and better future is the motivation for the production and use of hydrogen energy.

Hydrogen gas is also known as a green fuel, as it when used does not produced any harmful and toxic pollutants. Hydrogen is a very first element from the periodic table with symbol H and atomic number 1. It is present in a S block, first A (IA) group with electronic configuration 1S1 . Because of only one electron present in its outermost shell, it can form only a single sigma bond with many other atoms. It is a nontoxic, colorless, odorless, and combustible element. Hydrogen is a nonmetal, present in a gaseous form under normal conditions. Hydrogen is at the top list in terms of abundance in the universe. Many studies shows that hydrogen is not only present on the planet earth but also it is present on and other planets too. Stars are producing helium from hydrogen under high temperature and pressure at their core. Being a smallest and lightest element hydrogen atom consist of one proton and one electron without any neutron.

Hydrogen has three isotopes adds proton (H), deuterium (D) and tritium (T) along with these chemists succeeded in the synthesis of 4H and 7H in a laboratory, which are not occurring naturally. Arrhenius theory of acids and bases is very useful in chemical science is depends on the hydrogen. Most of the chemical compounds which are synthesized in lab or naturally occurring are bonded to hydrogen because of its high reactivity. Water is a most important source for living organisms which is also known as a universal solvent is composed of two hydrogens and one oxygen. In the present chapter, different sources of hydrogen as an energy with photocatalytic hydrogen production methods mechanism from water and toxic hydrogen sulfide is depicted along with respective photocatalytic reaction setup for the generation of hydrogen. Both water and H2S splitting set ups are being reported in our latest work with the help of organic and inorganic semiconductor and composite photocatalyst materials.

### **2. Hydrogen production methods**

After realizing the importance of hydrogen in clean energy and future fuel till date, many methods are well known for the generation of hydrogen.

Hydrogen can be produced mainly from biological, electrolytic, photocatalytic, steam reforming and thermochemical methods as shown in **Figure 1**. Microorganisms (algae and bacteria) can also be responsible for the generation of hydrogen using biological processes. Water can be spilt by using both electrolytic and sunlight (photo) into hydrogen and oxygen. Also, hydrogen sulfide can used as *Hydrogen as a Clean Energy Source DOI: http://dx.doi.org/10.5772/intechopen.101536*

**Figure 1.** *Hydrogen production methods.*

a rich source for hydrogen, which photocatalytically splits into hydrogen as a clean energy and sulfur for agriculture [12].
