Electrochemically grown Fe2O3/Fe3O4 heterostructure nanotubes with In2O3 induced tandem internal electric fields for enhanced photoelectrochemical water oxidation

Nanostructured hematite (alpha-Fe2O3) shows promise as a semiconductor for photoelectrochemical (PEC) water oxidation. However, it suffers from inadequate charge separation, limited hole-collection efficiency and sluggish kinetics. Herein, a nanotubular Fe2O3/Fe3O4 p-n heterojunction is prepared via electrochemical anodization to in situ construct an internal electric field (IEF) that facilitates charge separation from photoactive hematite. Additionally, In2O3 clusters are introduced to form a second IEF with dual-phase iron oxides, exploiting their Fermi level difference. The unique configuration of the dual IEFs in a novel tandem way synergistically promotes charge carrier separation/migration, enhancing PEC performance. Specifically, the 1(st) IEF between Fe2O3 and Fe3O4 accelerates electron migration from Fe3O4 to Fe2O3 (with holes transporting in the opposite direction), while the 2(nd) IEF at the In2O3 and Fe2O3/Fe3O4 interface drives holes towards the In2O3 surface, enhancing the hole-collection efficiency. The composite photoanode achieves a state-of-the-art current density of 11.5 mA cm(-2) at 1.55 V-RHE and a superior applied bias photon-to-current efficiency of 0.44% at 0.95 V. DFT calculations reveal that In2O3 induces an electron-deficient surface, creating favorable adsorption sites for oppositely charged key intermediates (*OOH). This work presents a novel approach for modulating reaction kinetics via the construction of tandem IEFs and holds great significance for the rational design of efficient PEC catalysts.