Role of lithium doping on α-Fe2O3 photoanode for enhanced photoelectrochemical water oxidation

High-valent or equivalent foreign element doping could improve the charge separation of the hematite (α-Fe2O3) for enhancing the photoelectrochemical (PEC) water oxidation. However, the induced extra surface states would anodically shift the onset potential. This work reported a two-step hydrothermal method to prepare the low-valent Li doped α-Fe2O3 that alleviated the charge recombination and partially removed the surface states. Thus, the photocurrent density of optimized Li-doped α-Fe2O3 was 0.75 mA/cm2 (1.23 VRHE), up to 3.6 times higher than that of pristine α-Fe2O3 (0.21 mA/cm2). Meanwhile, the onset potential also shifted negatively to 0.68 VRHE by 100 mV. The Density Functional Theory (DFT) revealed the Li atoms occupied the interstitial sites of the oxygen octahedron, and the introduced half-filled states in the bandgap can expand the light absorbance and improve the charge transport. The synergetic effects of enhanced charge separation efficiency and removal of surface states contributed to efficient PEC water oxidation. The low valent ions Li+ are used as the dopant, the performance and the corresponding mechanism are revealed and clarified. The photocurrent density increases from 0.21 mA/cm2 for α-Fe2O3 to 0.75 mA/cm2 (1.23 VRHE) after Li doping. The photocurrent density increase can be attributed to the introduced half-filled states in the bandgap that expand the light absorbance and the improved charge separation efficiency, which are validated by both the experimental and theoretical results. [Display omitted] •N-type Li doped α-Fe2O3 is successfully prepared by hydrothermal method.•The doping of Li decreases the oxygen vacancies in the α-Fe2O3 surface.•The surface states are partially removed in the Li doped α-Fe2O3.•Increased charge separation efficiency is achieved upon Li doping.