Electrodeposited Aluminum-Doped α-Fe₂O₃ Photoelectrodes: Experiment and Theory

Substitutional doping can improve the electronic properties of α-Fe 2 O 3 for the solar photoelectrochemical (PEC) applications. Generally speaking, nonisovalent substitutional doping helps to enhance the electronic conductivity of α-Fe 2 O 3 . However, we found that the introduction of strain in the lattice, which is achieved by isovalent substitutional doping of an Al, can also improve the electronic properties. α-Fe 2 O 3 films with the Al dopant atomic concentration varying from 0 to 10% were prepared by electrodeposition, and their performance for photoelectrochemical hydrogen production was characterized. Results indicate that the incident photon conversion efficiency (IPCE) for ∼0.45 at-% Al substitution increases by 2- to 3-fold over undoped samples. Density-functional theory (DFT) was utilized to interpret the experimental findings. It was shown that although no substantial change to the electronic structure, a contraction of the crystal lattice due to the isovalent replacement of Fe 3+ by an Al 3+ benefits the small polaron migration, resulting in an improvement in conductivity compared to the undoped samples.