ZnFe 2 O 4 Dendrite/SnO 2 Helix 3D Hetero‐Structure Photoanodes for Enhanced Photoelectrochemical Water Splitting: Triple Functions of SnO 2 Nanohelix

An array of SnO 2 nanohelix structures is employed to fabricate a SnO 2 helix@ZnFe 2 O 4 dendrite core‐shell 3D heterostructure photoanode for photoelectrochemical (PEC) water splitting. The SnO 2 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 ZnFe 2 O 4 . Finally, it becomes a template for the formation of ZnFe 2 O 4 dendrite nanostructure shell. The ZnFe 2 O 4 dendrite/SnO 2 helix photoanode exhibits a remarkable increase in incident photon‐to‐electron conversion efficiency compared to unmodified ZnFe 2 O 4 with no ETL and modified one with "flat" SnO 2 ETL. The surface of the ZnFe 2 O 4 /SnO 2 helix photoanode is further modified with TiO 2 passivation layer and NiFeO x oxygen evolution co‐catalyst to achieve one of the best PEC performances among reported ZnFe 2 O 4 ‐based photoanodes.