An Approach to Enhance PEC Water Splitting Performance through Al:Ti Codoping in Hematite (α-Fe2O3) Photoanode: The Effect of Al3+as a Codopant

Abstract

We achieved improved photoelectrochemical (PEC) efficiency by inducing strain through substitutional Al³⁺ doping in hematite, followed by codoping with Ti⁴⁺. The substitution of Al³⁺ for Fe³⁺ induces local strain within the lattice, reducing interionic distances and thereby enhancing the charge carrier transport properties. However, theoretical findings revealed initially unfavorable formation energy when Al³⁺ is doped into hematite, leading to significant lattice distortion due to size mismatch and thus limiting PEC activity. Co-doping Al³⁺ with Ti⁴⁺ in Fe₂O₃ restored the lattice symmetry by alleviating strain, resulting in a favorable formation energy. Additionally, Ti⁴⁺ contributes excess electrons, further increasing the electrical conductivity. By leveraging formation energy control through Ti doping, our optimized Al:Ti–Fe₂O₃ with a cocatalyst exhibited a photocurrent density of 4.00 mA cm^–2 at 1.23 V_RHE, representing a 6.5-fold improvement over Fe₂O₃ alone. Our study proposes an approach for utilizing Al³⁺ as a codopant in Fe₂O₃, which can potentially be extended to other codoped systems.