Rational Band Structure Engineering of TiO$_{2}$ for Photoelectrochemical Water Splitting

The search for new semiconducting materials or the engineering of existing semiconductors for commercially viable photoelectrochemical (PEC) water splitting has been extremely challenging. Meeting that challenge requires the discovery of a semiconductor with several tightly coupled material property criteria such as appropriate band gap (1.6 -- 2.2 eV), efficient visible light absorption, high carrier mobility, and correct band edge positions that straddle the water redox potentials. However, previous searches/modifications of semiconducting materials for PEC water splitting application have often focused on a particular individual criterion such as band gap, neglecting the possible detrimental consequence to other important criteria. In this talk, general strategies for the rational design of semiconductors such as TiO$_{2}$ to simultaneously meet all of the requirements for a high efficiency solar-driven PEC water splitting device are discussed. Density-functional theory calculations reveal that with appropriate donor-acceptor co-incorporation, heavily doped anatase TiO$_{2}$ hold great potential to satisfy all of the criteria for a viable PEC device. Other approaches to modify the band structure of TiO$_{2}$, such as the application of strain, will also be discussed.