Enhanced Photoelectrochemical Water Oxidation Performance in Bilayer TiO2/α‐Fe2O3 Nanorod Arrays Photoanode with Cu : NiOx as Hole Transport Layer and Co−Pi as Cocatalyst

Abstract

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‐Fe₂O₃ 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‐Fe₂O₃ 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‐Fe₂O₃ 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‐Fe₂O₃ NRs, which improved the hole extraction from α‐Fe₂O₃ to Co−Pi OER catalyst. As expected, the as‐engineered TiO₂/α‐Fe₂O₃/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‐Fe₂O₃ (0.60 mA cm⁻²) and TiO₂/α‐Fe₂O₃, 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.