ZnFe₂O₄ Dendrite/SnO₂ Helix 3D Hetero‐Structure Photoanodes for Enhanced Photoelectrochemical Water Splitting: Triple Functions of SnO₂ Nanohelix

Abstract An array of SnO₂ nanohelix structures is employed to fabricate a SnO₂ helix@ZnFe₂O₄ dendrite core‐shell 3D heterostructure photoanode for photoelectrochemical (PEC) water splitting. The SnO₂ helix provides triple critical functions to enhance the PEC performance of the photoanode. First, it scatters the incident light to achieve a higher light harvesting efficiency. Second, it provides a facile electron pathway as an electron transfer layer (ETL) while blocking hole transport to mitigate charge recombination in the bulk of ZnFe₂O₄. Finally, it becomes a template for the formation of ZnFe₂O₄ dendrite nanostructure shell. The ZnFe₂O₄ dendrite/SnO₂ helix photoanode exhibits a remarkable increase in incident photon‐to‐electron conversion efficiency compared to unmodified ZnFe₂O₄ with no ETL and modified one with "flat" SnO₂ ETL. The surface of the ZnFe₂O₄/SnO₂ helix photoanode is further modified with TiO₂ passivation layer and NiFeO_x oxygen evolution co‐catalyst to achieve one of the best PEC performances among reported ZnFe₂O₄‐based photoanodes.