**6. Water splitting by TiO2 thin films**

The first investigation of water splitting in 1972 by Fujishima and Honda, has attracted a large attention of researchers to developed photoelectrochemical water splitting (PEC) system for the generation of clean and renewable energy from solar light and water.

The hydrogen is produced from water using sunlight and semiconductors materials, which use light energy to directly dissociate water molecules into hydrogen and oxygen. Over the past few years, there is great interest on the evolution of hydrogen by PEC water splitting using various semiconducting oxides such as TiO2, which is considered as suitable photoanode for water splitting. In the PEC water splitting systems (**Figure 18**), the incident photons, with the energy level of the corresponding material band gap, induce the generation of electrons and holes in the conduction band (CB) and valence band (VB), respectively. In a photoanode, holes are driven to photoelectrode's surface to perform the oxygen evolution, meanwhile electrons are collected by the back contact and close the circuit performing the proton reduction reaction in the counter electrode.

The water splitting reaction can be expressed as below:

$$2\text{H}\_2\text{O} \rightarrow 2\text{H}\_2\text{(g)} + \text{O}\_2\text{(g)}\tag{5}$$

A. Sreedhar et al. [24] have demonstrated that the TiO2 films grown at a higher ion-beam-energy equal to 110 eV have a photocurrent density of 1.2210−5 A/cm2 under UV light and the TiO2 films decorated by AgNPs under visible illumination

**Figure 18.** *Schematic of TiO2 water split mechanism.*

*Titanium Dioxide Thin Films for Environmental Applications DOI: http://dx.doi.org/10.5772/intechopen.99726*

have superior photocurrents equal to 6.5310−5 A/cm2 , which are a promising photoanodes.

In another work of A. Sreedhar et al. [25] have illustrated that the ZnO/TiO2 films fabricated at 120 nm yielded with a dominant photocurrent density 4.710−6 A/cm2 is higher ten times than that of ZnO/TiO2–60 nm films (4.4910−7 A/cm2 ) and proposed that the film thickness parameter could be a promising pathway to promote the visible-light-driven PEC water splitting activity. C. W. Kim et al. [26] have reported that the TiO2 photoanode fabricated through hydrothermal method produce 18% of incident photon-to-current conversion efficiency at 0.65 V Ag/AgCl potential under AM 1.5 G illumination and the hydrogen production reached to 0.07 mmol cm−2 for 12 hrs. The TiO2 films with modified morphology synthesis by M. Ibadurrohman et al. [27] have photoconversion efficiency of 1.15% at −0.50 V vs. HgO/Hg, which is an exceptional PEC response and can be considered as promising photoanode.

## **7. Conclusion**

Titanium dioxide TiO2 is considered as a promising semiconductor for water treatment and H2 production due to their physical, structural and optical properties under UV and sun light. In this chapter, the structure, the morphology and the synthetic methods of TiO2 thin films were summarized. The recent researches have confirmed the effect of morphologies of the elaborate nanostructured TiO2 thin films on proprieties. The photo activity of TiO2 thin films has been evaluated for the removal of dyes, pharmaceuticals, PCCPs, pesticides, and industrial additives. TiO2 thin films have the possibility to produce hydrogen from solar energy and water with significant efficiencies. TiO2 thin films show a good performance to degrade pollutants and can be considered as a promising photoanode for water splitting.

### **Acknowledgements**

This project is carried out under the MOBIDOC scheme, through the PromESsE project managed by the ANPR and the PRF program EnviNanoMat. Grant ref.: PRF2019-D4P2 funded by The Ministry of Higher Education and Scientific Research.
