ABSTRACT
This chapter provides a comprehensive overview on the fundamental aspect of photoelectrochemical (PEC) water splitting to generate hydrogen. To accomplish semiconductor-assisted PEC water splitting, semiconductor must have desirable flat band positions to perform the reduction and oxidation reactions. More broadly, PEC cell is defined as an electrochemical cell that can convert light energy into a more useful energy product through light-induced electrochemical processes. In PEC cells, water splits into hydrogen and oxygen with the aid of photocatalyst, which absorbs the photon energy and converts it to electrochemical energy. The process of splitting water with the aid of electrical energy is called electrolysis of water and if it is aided by photon energy of sunlight it is called photocatalysis of water splitting. There are three steps involved in PEC water splitting reaction: absorption of photons followed by generation of charge carriers, charge carriers separation, and migration toward surface reaction sites to perform water redox reaction.
