The document summarizes different methods for photolysis of water, which is the process of splitting water into hydrogen and oxygen using light. It describes (1) electrolysis, thermal decomposition, photobiological, and photoelectrochemical water splitting. Photoelectrochemical water splitting involves using semiconductors to obtain electrical energy for splitting water. It can use photovoltaic cells, semiconductor-liquid junctions, or a combination. The document also discusses the role of band gaps in metal oxides used as photocatalysts and explains photobiological water splitting using algae. It concludes that hydrogen is a promising fuel that can be obtained through photosplitting of water.

1. Photolysis of Water
Prepared By : Yaseen Aziz
Roll No : 23609
Dept. Of Chemistry, Kashmir University

2. Water splitting-a general introduction :
• Water splitting is the general term for a chemical reaction in which water is separated into
oxygen and hydrogen.
• This can be achieved through following ways:
a) Electrolysis
b) Thermal decomposition of water
c) Photobiological water splitting
d) Photoelectrochemical water splitting
e) Photocatalytic water splitting

3. • Need for photosplitting of water:
 Hydrogen economy
Hydrogen-a clean, pure fuel with very high calorific value (150 kJ/mol).
• “We are at the peak of the oil age but the beginning of the hydrogen age.
Anything else is an interim solution. The transition will be very messy, and will
take many technological paths .....but the future will be hydrogen fuel cells.”
- Herman Kuipers

4. Redox stability field of water:

6. Basic principle of overall water splitting on a Processes involved in photocatalytic overall
semiconductor particle. water splitting on a semiconductor particle.

7. Basic principle of photocatalytic reactions in the presence of sacrificial reagents.

8.  The band gap in Metal oxide plays a crucial role in using them as photocatalysts. This can be
illustrated by the following diagram:

9. • Photoelectrochemical splitting of water:
• Water is broken down into H2 and O2 by electrolysis, but the electrical energy is obtained
by a photoelectrochemical cell (PEC) process, based on semiconductors.
• This is also named as ‘artificial photosynthesis.’
• The photoelectrochemical (PEC) path to water splitting involves separating the oxidation
and reduction processes into half-cell reactions.
• Three methods are possible:
 PV approach i.e. using photovoltaic cells
 SCLJ approach i.e. semiconductor-liquid junctions
 Combination of the two (PV/SCLJ approach)

10. Schematic representation of a PV approach

11. Schematic representation of a SCLJ approach

12. Schematic representation of a PV/SCLJ approach

13. Photobiological water splitting:
• Produces H2 called as biological hydrogen, in algae bioreactors.
• Discovered in 1990’s
• When algae are deprived of sulphur they produce H2 instead of O2 i.e. normal
photosynthesis is inhibited.
• Efficiency is 7-10 %, producing 10-12 ml H2 per culture litre per hour.

15. Conclusion:
• Hydrogen as fuel is a promising substitute to the non-renewable sources of energy.
• It is clean, pure and eco-friendly fuel.
• It can be obtained in large amounts provided a viable procedure of water splitting is
made available and the problem of H2 storage is overcomed.
• Photosplitting of water is a pure, clean, less energy consuming and easily available
source of H2 production.
• The research field is wide open and challenging.

16. THANKS A LOT
for
Listening Patiently!