Chapter 7: Hierarchical Nanoheterostructures for Water Splitting

The Sun is considered to be a major promising source of energy for modern society because it is free in nature and available throughout the year. Therefore, solar energy conversion into chemical energy (hydrogen gas) draws great attention from the scientific community. Additionally, hydrogen fuel has a high specific energy density; thus it can be directly used to produce electricity via fuel cells and generators. The only by-product of these generators is clean water. Thus, photocatalytic water splitting has become a very important topic in research worldwide. In photocatalytic water splitting, metal oxides are extensively studied because they offer many advantages, including chemical stability, tuneable band gap structures, and are abundant on the Earth. This chapter discusses the fundamentals of the water-splitting processes, including the thermodynamic and kinetic limitations of water splitting. It also includes photo-active nanomaterials, new fabrication methods, and the standard measurements for the comparison of solar energy conversion efficiencies, as well as some recent techniques applied to the mechanistic studies of photoelectrochemical cells.