Protected Hematite Nanorod Arrays with Molecular Complex Co-Catalyst for Efficient and Stable Photoelectrochemical Water Oxidation

Herein, a hybrid structure of hematite (α-Fe₂O₃) nanorod arrays is designed, with surface catalyzed by Co molecular complex (Co(dca)₂, dca: dicyanamide) and then protected by TiO₂ thin overlayer, for efficient and stable photoelectrochemical (PEC) water oxidation. The obtained α-Fe₂O₃/Co(dca)₂/TiO₂ hybrid nanorod arrays show much improved and stabilized PEC performance as compared to the pristine, and even the Co(dca)₂ or TiO₂ modified α-Fe₂O₃, with a photocurrent density of 0.35 mA cm^–2 obtained at 1.23 V vs. reversible hydrogen electrode (RHE), and an incident photon-to-current conversion efficiency (IPCE) reaching 16 % at 400 nm at 1.6 V vs. RHE. It has been demonstrated that the adsorbed Co(dca)₂ molecular complex could effectively promote the interface charge transfer process and accelerate the water oxidation reaction kinetics, meanwhile the atomic layer deposited TiO₂ overlayer could passivate the surface defects of α-Fe₂O₃ and suppress the surface charge carrier recombination. Moreover, the TiO₂ overlayer could effectively protect Co(dca)₂ from detaching from the α-Fe₂O₃ surface and thus stabilize the PEC activity for water oxidation reaction. The present study provides some available thoughts and methods for rational design of highly efficient photoelectrodes for water splitting from the perspective of the surface and interface engineered charge carrier transfer and water oxidation processes.