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

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.