Lattice distortion induced internal electric field in TiO2 photoelectrode for efficient charge separation and transfer

Providing sufficient driving force for charge separation and transfer (CST) is a critical issue in photoelectrochemical (PEC) energy conversion. Normally, the driving force is derived mainly from band bending at the photoelectrode/electrolyte interface but negligible in the bulk. To boost the bulky driving force, we report a rational strategy to create effective electric field via controllable lattice distortion in the bulk of a semiconductor film. This concept is verified by the lithiation of a classic TiO2 (Li-TiO2) photoelectrode, which leads to significant distortion of the TiO6 unit cells in the bulk with well-aligned dipole moment. A remarkable internal built-in electric field of 2.1x10(2)Vm(-1) throughout the Li-TiO2 film is created to provide strong driving force for bulky CST. The photoelectrode demonstrates an over 750% improvement of photocurrent density and 100mV negative shift of onset potential upon the lithiation compared to that of pristine TiO2 film. The driving force for charge transfer in photoelectrochemical systems is typically derived from band bending at a surface-electrolyte interface. In this work, battery-type lithiation of TiO2 generates a built-in electric field in the bulk material, giving a 750% enhancement in photocurrent density.