Computational and Experimental Realization of Metal-Ion-Doped Orthorhombic Sn ₃ O ₄ for Visible-Light-Active Photocatalysis

The orthorhombic tri-tin tetraoxide (Sn₃O₄) is a newly discovered polymorph and has attracted great attention due to its visible-light absorption capability. To improve performance and broaden the material space based on orthorhombic Sn₃O₄, impurity doping represents a promising approach. In this study, we predict stable cation-doped orthorhombic Sn₃O₄ crystals using machine learning interatomic potential (MLIP) calculations. Several candidate cations such as boron (B), aluminum (Al), strontium (Sr), and yttrium (Y) have been predicted as stable dopants in orthorhombic Sn₃O₄ with low Gibbs energies of formation. Based on this prediction, we synthesized cation-doped Sn₃O₄ powder samples using a hydrothermal method. We confirmed that the cations predicted to be stable by the MLIP could be synthesized into the orthorhombic powder phase. Among the samples, the Al-doped Sn₃O₄ powder exhibited superior photocatalytic hydrogen production activity under visible light. Furthermore, we fabricated thin films of Al-doped Sn₃O₄ and optimized the doping amount of Al to achieve high photocatalytic activity. The 5% Al-doped Sn₃O₄ exhibited the highest activity owing to its high crystallinity and optimal morphology for better separation of photogenerated carriers. The Al-doped orthorhombic Sn₃O₄ is promising for application as a visible light-active photocatalyst.