Enhanced Photoelectrochemical Water Oxidation Performance in Bilayer TiO₂ /α-Fe₂ O₃ Nanorod Arrays Photoanode with...

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 TiO₂ /α-Fe₂ O₃ nanorod (NR) arrays photoanode was prepared with deposited Cu-doped NiO_x (Cu : NiO_x ) hole transport layer (HTL) and Co-Pi oxygen evolution reaction (OER) cocatalyst for PEC water oxidation. The hierarchical TiO₂ /α-Fe₂ O₃ composite obtained by a secondary hydrothermal process exhibited an inapparent bilayer structure by embedding the underlayer TiO₂ NR arrays at the bottom part of the post-grown α-Fe₂ O₃ NR arrays. The underlayer TiO₂ NRs acted as an effective shuttling pathway for transferring photoelectrons generated in the upper hematite light absorber layer. A p-type inter-Cu : NiO_x HTL was introduced to form a build-in p-n electric field between Cu : NiO_x and α-Fe₂ O₃ NRs, which improved the hole extraction from α-Fe₂ O₃ to Co-Pi OER catalyst. As expected, the as-engineered TiO₂ /α-Fe₂ O₃ /Cu : NiO_x /Co-Pi photoanode displayed an excellent photocurrent density of 2.43 mA cm^-2 at 1.23 V versus the reversible hydrogen electrode (V_RHE ), up to 4.05 and 2.23 times greater than those of the bare α-Fe₂ O₃ (0.60 mA cm^-2 ) and TiO₂ /α-Fe₂ O₃ , 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.