Epitaxial, Energetic, and Morphological Synergy on Photocharge Collection of the Fe₂TiO₅/ZnO Nanodendrite Heterojunction Array Photoelectrode for Photoelectrochemical Water Oxidation

Conformal orthorhombic Fe₂TiO₅layers are epitaxially grown on them-planes of the ZnO nanodendrite (ND) scaffold with the lattice matching relations of (100)_Fe2TiO5∥(110)_ZnOand (010)_Fe2TiO5∥(001)_ZnOusing metal-organic decomposition. The photoelectrochemical water splitting performance of the epitaxial Fe₂TiO₅/ZnO ND heterojunction array photoanode with an ND length of 2 μm is substantially enhanced compared to the planar Fe₂TiO₅photoanode. The photocurrent density increases from 0.033 to 1.04 mA cm^-2at 1.23 V versus reversible hydrogen electrode (RHE) under AM 1.5G (100 mW cm^-2). It is mainly ascribed to the improved charge separation and injection efficiencies of the photoelectrode with a vertical ND structure in coalition with the epitaxial Fe₂TiO₅/ZnO heterojunction of type-II band alignment. At 1.23 V versus RHE, a Faradaic efficiency of ∼90% for solar water oxidation is acquired from the epitaxial Fe₂TiO₅/ZnO ND heterojunction array photoanode. By elongating the length of the ND heterojunction array from 2 to 3 μm, 1.5-fold enhancement in the photocurrent density is obtained because of the decoupled light harvesting and hole transport paths. With further deposition of the cocatalyst cobalt phosphate (Co-Pi), the Co-Pi/Fe₂TiO₅/ZnO ND heterojunction array photoelectrode exhibits a further elevated photocurrent density of 2.14 mA cm^-2at 1.23 V versus RHE.