Section 3 Water Splitting

**174**

*Water Chemistry*

**References**

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[1] Satpati AK, Ravindran PV.

[2] Behpour M, Ghoreishi SM, Salavati-Niasari M, Ebrahimi B. Evaluating two new synthesized S-N Schiff bases on the corrosion of copper in 15% hydrochloric acid. Materials Chemistry and Physics.

[3] Bentiss F, Bouanis A, Mernari B, Traisnel M, Vezin H, Lagrenee M. Understanding the adsorption of 4H-1,2,4-triazole derivatives on mild steel surface in molar hydrochloric acid. Applied Surface Science.

[4] Tetsuo H. Kurita Handbook of Water Treatment. Second English ed. Japan: Kurita Water Industries Ltd; 1999

[5] Growcock FB, Lopp VR. The inhibition of steel corrosion in hydrochloric-acid with 3-phenyl-2-propyn-1-ol. Corrosion Science.

Electrochemical study of the inhibition of corrosion of stainless steel by 1,2,3-benzotriazole in acidic media. Materials Chemistry and Physics.

Chapter 10

Abstract

back-oxidation

1. Introduction

ΔH<sup>0</sup>

177

Water Splitting

Bahar Ipek and Deniz Uner

On the Limits of Photocatalytic

The major drawbacks on the limited H2 and O2 evolution activities of one-step photocatalytic water splitting systems are given here with the emphasis on charge recombination, back-oxidation reactions, and mass transfer limitations. Suppression of these unwanted phenomena is shown to be possible with the usage of small crystal-sized photocatalysts with low defect concentrations, presence of phase junctions, selection of co-catalyst that would be active for H2 evolution but inactive

for O2 reduction, coating of the co-catalyst or the whole photocatalyst with selectively permeable nanolayers, and usage of photocatalytic systems with high solid–liquid and liquid–gas surface areas. The mass transfer limitations are shown to be important especially in the liquid–gas interfaces for agitated and suspended systems with estimated H2 transfer rates in the range of 200–8000 μmol/h.

Keywords: hydrogen production, photocatalyst, water splitting, mass transfer,

Hydrogen gas is one of the best alternatives to fossil fuels since it has a high gravimetric energy density (142 MJ/kg) and it produces zero carbon upon combustion. Hydrogen is also used as a major reactant in environmentally important reactions such as carbon dioxide hydrogenation to methanol [1] or ammonia production (Haber-Bosch reaction) [2]. For hydrogen to be used as a clean energy source, its production via renewable ways is of great importance. It is conventionally produced

rxn = 206 kJ/mol, 700–1100°C [3]) and coal gasification, which results in significant amounts of carbon dioxide production. The renewable ways for carbon-free production include biological sources (microalgae and cyanobacteria) and electrolysis of water using wind energy and photovoltaic cells as electricity generation sources. In addition to the mentioned renewable ways, photocatalytic water splitting/oxidation is a promising alternative, in which solar energy is used as the driving force to split water molecules to hydrogen and oxygen on the surface of a catalyst. This renewable production method of hydrogen is advantageous over other

via steam reforming of methane and fossil fuels (energy intensive,

renewable methods due to the free source of energy and lower cost of the photocatalysts when compared to that of photovoltaic cells or wind turbines. Solar-driven catalytic (photocatalytic) reactions are considered to be of fundamental importance to the catalysis community since the solar energy is inexhaustible; i.e., the solar energy absorbed by the lands and oceans on an hourly basis (432 EJ/h
