Quantum‐Dot‐Sensitized TiO2 Inverse Opals for Photoelectrochemical Hydrogen Generation

With the increasing concern over the global energy crisis and the greenhouse effect by carbon dioxide emissions, development of clean and sustainable energy solutions to the alternatives of traditional fossil fuels has attracted considerable interest in both the scientific and industrial community.[1,2] Photoelectrochemical (PEC) water splitting provides a promising approach to address the above issues simultaneously by capturing and storing solar energy in the chemical bond of H2. [3–6] Titanium dioxide (TiO2) has been one of the most attractive materials in this area due to its high photoactivity coupled with low cost and excellent chemical stability.[7] However, the only obstacle is its large bandgap (≈3.2 eV), which results in limited solar-light harvesting. In the past few decades, tremendous effort has been made to improve the water splitting efficiency. In general, two main approaches have been developed to enhance the visible-light absorption. One is narrowing of the bandgap of TiO2 by doping with either transition-metal ions[8] or nonmetal elements such as N[9] and C;[10] the other is to sensitize with narrow-bandgap semiconductor quantum dots (QDs) such as CdS,[11,12] CdSe,[13] CdTe,[14] and so on. Furthermore, a purpose-designed nanoarchitecture of the photoelectrode is equally essential to the performance, which leads to increased surface area, improved electron transportation, and reduced minority-carrier diffusion length and electron–hole recombination loss.[15,16] In particular, periodically