Compositionally graded SnO₂/TiO₂ bi-layered compounds with dramatically enhanced charge transport efficiency for self-driven water purification applications

To maximize the advantages of thin-film-based TiO₂ photoelectrodes for transparent self-driven photoelectrochemical (PEC) reactions, we artificially designed a compositionally graded bi-layer compounds consisting of SnO₂ and TiO₂. This structure exhibited a vigorous photocatalytic activity, sufficient photovoltage, and long-term stability. A compositionally graded SnO₂/TiO₂ interface (G-SnTiO) for improved charge transport efficiency and sufficient photovoltage was derived by a solution process using simultaneous sintering after sol-gel coating the SnO₂/TiO₂ layers; the structure was verified by various analysis methods, such as transmission electron microscopy, energy dispersive X-ray spectroscopy, and secondary ion mass spectrometry. The high performance from the G-SnTiO structure was attributed to an effective charge separation from the formation of a heterostructure interface with reduced defects, resulting in a sufficient photovoltage for self-driving. To construct self-driven and sustainable overall cells without an external potential and considerable reduction in transparency, two-electrode PEC cells with a G-SnTiO photoanode and Cu₂O photocathode were fabricated with a regular hexahedron shape for a color degradation test of methylene-blue-incorporated electrolytes, and exhibited enhanced purification speed and robust durability.