**4.2 H2S splitting**

Irritating smell of H2S gas is the reason for less research and development in this area as compared to water splitting. Earlier, Claus process is used for H2S splitting which is mainly focused on sulfur and not on hydrogen. Photocatalytic H2S splitting

**Figure 4.** *Photocatalytic H2S splitting reaction setup.*

*Hydrogen as a Clean Energy Source DOI: http://dx.doi.org/10.5772/intechopen.101536*

experiments for the generation of H2 can be performed under light source or in sunlight depending upon the band gap of semiconductor photocatalyst [21, 22]. For light source (under lamp) an assembly is kept in a fuming hood to avoid bad smell and a schematic representation of a setup is shown in **Figure 4**. This setup can be divided in A to I parts as shown below.

For avoiding over heating of the photoreactor (D) throughout the photoreaction water circulation is added, Photoreactors are of various capacity (100 to 1000 mL) can be used, the quantity of photocatalyst (0.05 to 1 gram) was decided in every photoreaction. A source of light (F) of intensity 450–600 W can be used as discussed in above water splitting set up. Hydrogen sulfide generated in (A-B) and collected extra amount in (C) is bubbled through the solution in the photoreactor under continuous stirring (E). Bubble rate differs as the capacity of photoreactor changes. The excess H2S was trapped in NaOH solution (G-H). The amount of evolved H2 was measured using graduated gas burette (I).

Large scale production of hydrogen using toxic H2S is also possible like water splitting as discussed above in water splitting setup section.

## **5. Large scale hydrogen production and usage**

Large scale production of hydrogen energy from water splitting is also possible by using this reaction setup. Appropriate photocatalyst with suitable band gap and light frequency source can leads to enhance hydrogen production. Quantity of photocatalyst and capacity of photoreactor promises the large-scale production of hydrogen energy. It can be achieved with proper engineering inside the lab as well as on roof of the lab under natural sunlight. Large scale production of hydrogen using toxic H2S is also possible like water splitting as discussed above. Hydrogen is a clean energy which have applications in soil refining, methanol generation, steel production and ammonia production. Nowadays, it is also used for all type of transportation (alternative for Compressed Natural Gas, CNG), power generation, homes and fuel in jets and ships. Recently, the worlds first hydrogen-powered train rolled in Germany. After this many countries tested hydrogen fuel-cell passenger trains. Also, a UK-based car manufacturer company produced a two-seater hydrogen vehicle. The US, Europe and China are the top consumers of hydrogen mainly in refineries sector. Alas, all these emerging hydrogen applications are not economical than the other energy resources as hydrogen costs around USD 12–16/Kg.

#### **6. Transportation and storage of hydrogen gas**

Nowadays, the production of H2 gas is not a new to a scientific community but the ways of transportation and storage of it is under continuous research. Transportation is mainly taking place either by road or by water routs in a cryogenic or compressed cylinders. As hydrogen is having low density the transportation is difficult and expensive so, for transporting H2 from industry to working sites is achieved using pipelines [23]. In many cases gas is compressed and then filled in appropriate cylinders as per the quantity and requirement. Laboratories and research centers require hydrogen in small quantities and transportation of such cylinders can be takes place using small trolleys. On the other hand, the amount of hydrogen required for industrial purpose is in large quantities which are once received by transported kept in a gas bank.

Storage of hydrogen gas as a future fuel is important because one cannot produce it efficiently and in large amount at the domestic or small industry level. For storage purpose research centers, industries and automobiles have well engineered tanks. The concept of adsorption is utilized for storage of gas, here a porous material with large surface areas like activated carbon are needed. In absorption metals are combined with hydrogen atoms to form a metal hydride. Palladium, zirconium and other transition metals are also reported for the large amount of gas absorption [24, 25].

Recently, photocatalytic solar hydrogen production from water splitting on a 100 m2 scale panel, carbon films, closed systems, plates and sheets is demonstrated by K. Domen research group. A 100 m<sup>2</sup> array of panel reactors and other setup types effective for more than 90 days. Lately, chemical combination between hydrogen and boron or nitrogen is under investigation. During this combination hydrogen molecules are dissociated and forms hydrogen atoms which then goes in the empty spaces between the metals lattice structure [26].
