Low-Cost Nanomaterials for Photoelectrochemical Water Splitting - Low-cost Nanomaterials: Toward Greener and More Efficient Energy Applications - page 265

Fig. 2 Band edge positions of several semiconductors in contact with aqueous electrolyte at
pH 1 with energy scale versus vacuum level and the normal hydrogen electrode (NHE).
Reproduced with permission from [ 23 ]
WO 3 ($40-60/Kg), and Fe 2 O 3 (less than $1/Kg) have been extensively studied
[ 23 , 96 ]. In this chapter, we will focus on the synthesis with low-cost techniques and
discuss their application in PEC water splitting.
2 Low-Cost Synthetic Methods
During the last two decades, a number of methods have been demonstrated for the
synthesis of metal oxide nanomaterials. Among these methods, hydrothermal and
solvothermal synthesis, sol-gel, electrochemical deposition, and anodization
method show great promise as low-cost and scalable approaches to prepare
nanomaterials for photoelectrodes, as these methods require simple equipment and
mild synthetic conditions. In this section, we are going to give a brief overview of
these low-cost synthetic methods.
2.1 Hydrothermal and Solvothermal Method
Hydrothermal synthesis is one of the most extensively used approaches to prepare
metal oxide nanomaterials such as TiO 2 [ 97 , 101 ], WO 3 [ 33 , 85 , 99 ], ZnO [ 24 ,
102 , 111 ] and Fe 2 O 3 [ 47 , 48 ]. Hydrothermal synthesis is typically performed in a