**Abstract**

The quest of conquering balanced environment for the ultimate search of "Who am I" furnished to pollution and energy crises. As the viable world development is dependent on effective utilization of available renewable energy resources. Hydrogen fuel as an energy source is the future for many upcoming generations as it never produces pollutants. 6, 13 Pentacenequinone (PENQ ) is recently developed and reported organic photocatalyst for the generation of hydrogen from water as well as hydrogen sulfide. PENQ can be synthesized and characterized using different methods and techniques/approaches that are listed in this chapter. Green Solid state synthesis method of PENQ is the most promising one as it gives high yield at room temperature and without solvents. Structural characterization of this novel organic catalyst were done using powdered XRD. Cyclic voltammetry is used for the calculating the difference between valance and conduction band levels in the organic PENQ catalyst. After complete structural and morphological characterization, organic PENQ was explored for the hydrogen production from hydrogen sulfide. This photocatalytic nature was also being confirmed using its composites/ coupled systems (PENQ: TiO2 and PENQ: MoS2) using hydrogen sulfide and water.

**Keywords:** hydrogen, organic, photocatalysis, semiconductor

## **1. Introduction**

Considering the utmost importance of Hydrogen (H2) gas for energy fuel source, scientists has made efforts to find novel ways to get inexpensive H2 production. Hydrogen generation is the one area of researchers are digging but the storage is the main issue [1]. In this context Titanium dioxide is the very first photocatalyst reported for the production of hydrogen by Gratzel et al. For the improvement in the rate of produced hydrogen there are so many effective improvements are reported like co-catalysts, composites, coupling of two catalyst systems. Metals sulfides and oxides with this type of modifications are also reported [2, 3]. In the category of metal sulfides some binary and ternary sulfides showed excellent result with photocatalytic

hydrogen generation. Moreover, graphene based semiconductor photocatalyst materials are also proved best for both generation and storage. As compared to the bulk nanomaterial semiconductor materials are having more surface area, good optical absorption, tunable electronic properties, and lesser charge recombination rate [4–7].

On the other hand, the search of an organic semiconductors for the hydrogen generation is still in progress. Organic five ring system Pentacene (PEN) is well studied semiconductor material in electronic applications. PEN and its derivatives are well utilized in mainly flexible and advanced electronic devices. Recently, it is also showed some very important uses in battery based devices as well as in catalysis [8]. On the other side, PEN and its derivatives are not much stable in air as well as in presence of light [9]. So, unwanted efforts were needed to save it from both light and air. Normally, PEN when come in contact with atmospheric air get oxidize to produce PENQ. This oxidized form of PEN is lately reported as a very important organic semiconductor photocatalyst. As like PEN this oxidized form is also has five aromatic rings with Quinone functional group in the center ring. Interestingly, this PENQ is again reported mostly as a starting compound to get substituted PENQ with fascinating properties [10].

Because of two extra oxygen atoms it gets stabilized and found very effective stability in both air and light. Overall molecular mass, melting point and resistivity towards the acids and other solvents increases. PENQ is with light yellow color and having absorption band edge well in visible region makes it a promising candidate for the photocatalysis applications. Keeping in mind this PENQ was reported for hydrogen generation from hydrogen sulfide gas as well as for the MB dye degradation. After this individual report, it is also found more effective when coupled with inorganic semiconductor materials like TiO2 and ZnO [10–14]. When it combined with other semiconducting materials it produces more hydrogen than the individual one. Yuan et al. very recently proved the effectiveness of this system for the generation of hydrogen from water. These all the modifications on PENQ catalyst is discussed in the present chapter.

By considering the utmost importance of hydrogen energy many attempts were done to produce it using different approaches. Hydrogen energy can be generating from biological, electrolytical, photocatalytical, steam reforming. Out of these photocatalytic method is the simplest and useful to get hydrogen from water and H2S gas [15–17]. In photocatalysis, photocatalyst is the main hero which alter the rate of hydrogen generation. Plenty of inorganic and organic materials were reported for the production of hydrogen using photocatalysis method.

Also, after the individual organic or inorganic catalysts reports their combinations (composites/hybrid materials) were also reported with enhanced hydrogen production rates. Herein, PENQ and composites synthesis, characterization and photocatalytic activity towards hydrogen production using both water and H2S were discussed. Enhancement in catalytic activity with the addition of inorganic materials and their effects were also discussed. During the photocatalysis reactions the main role of organic photocatalyst material is to provide necessary charges to complete the reduction reactions. Herein, this main process light is used to stimulate an organic semiconductor material termed as a catalyst which improves the rate of the process [18–20]. Generally, electrons and hole are produced when light absorbed by the semiconductor material.

The photocatalysis mechanism for the organic and inorganic material is the same [21, 22]. In short light is responsible for the traveling electrons from VB to CB [19, 23–26]. Main advantage of organic semiconductors over inorganic semiconductor is that they have high molar absorption coefficient [20, 27].

*Organic Semiconductor for Hydrogen Production DOI: http://dx.doi.org/10.5772/intechopen.107008*
