Intrinsic and extrinsic doping to construct hematite nanorod p-n homojunctions for highly efficient PEC water splitting

Hematite (α-Fe2O3) as a promising photoanode material for photoelectrochemical (PEC) water splitting has some intrinsic shortcomings, such as low carrier concentration, fast electron-hole pair recombination, and thus poor PEC performance in practice. Herein, we fabricated p-n homojunctions on the α-Fe2O3 by introducing both intrinsic (oxygen vacancies, Vo) and extrinsic (Cu2+) dopants into the hematite lattice through a two-step hydrothermal process followed by an annealing treatment. Such α-Fe2O3 composite film photoanodes were characterized by surface analysis and photoelectrochemical test, and exhibited great PEC photolytic water properties. The Ultraviolet–visible (UV–vis) absorption results showed that the light absorption of the α-Fe2O3 with p-n homojunctions was greatly enhanced in the visible region. The introduction of intrinsic (Vo) and extrinsic (Cu2+) dopants into the α-Fe2O3 lattice enhanced the concentration of carriers by nearly two orders of magnitude, and the formation of the p-n homojunctions also effectively improved the separation efficiency of electron-hole pairs. The water oxidation photocurrent density of the α-Fe2O3 with the p-n homojunctions was measured to be 2.49 mA cm−2 at 1.23 V (vs. RHE), nearly two orders of magnitude higher than that of the pristine α-Fe2O3, and the reaction onset potential negatively shifted by more than 700 mV. Amazingly, the high potential photocurrent density at 1.6 V (vs. RHE) reached 4.79 mA cm−2, which is a high value very competitive among all the reported hematite photoanodes under the same conditions. Moreover, the high photocurrent density could retain 87% even after 3 h, indicating that the α-Fe2O3 p-n homojunction photoanode has also stable photo-electrochemical performance.