Enhanced Photoelectrochemical Water Oxidation Performance in Bilayer TiO /α-Fe O Nanorod Arrays Photoanode with Cu : NiO as Hole Transport Layer and Co-Pi as Cocatalyst.

Efficient charge transfer and excellent surface water oxidation kinetics are key factors in determining the photoelectrochemical (PEC) water splitting performance in photoelectrodes. Herein, a bilayer TiO /α-Fe O nanorod (NR) arrays photoanode was prepared with deposited Cu-doped NiO (Cu : NiO ) hole transport layer (HTL) and Co-Pi oxygen evolution reaction (OER) cocatalyst for PEC water oxidation. The hierarchical TiO /α-Fe O composite obtained by a secondary hydrothermal process exhibited an inapparent bilayer structure by embedding the underlayer TiO NR arrays at the bottom part of the post-grown α-Fe O NR arrays. The underlayer TiO NRs acted as an effective shuttling pathway for transferring photoelectrons generated in the upper hematite light absorber layer. A p-type inter-Cu : NiO HTL was introduced to form a build-in p-n electric field between Cu : NiO and α-Fe O NRs, which improved the hole extraction from α-Fe O to Co-Pi OER catalyst. As expected, the as-engineered TiO /α-Fe O /Cu : NiO /Co-Pi photoanode displayed an excellent photocurrent density of 2.43 mA cm at 1.23 V versus the reversible hydrogen electrode (V ), up to 4.05 and 2.23 times greater than those of the bare α-Fe O (0.60 mA cm ) and TiO /α-Fe O , respectively. The results demonstrate that the bottom-up engineering of electron-hole transport channels and cocatalyst modification is an attractive maneuver to enhance the PEC water oxidation activity in hematite and other photoanodes.