Enhanced Photoelectrochemical Water Oxidation Performance in Bilayer TiO<sub>2</sub>/α‐Fe<sub>2</sub>O<sub>3</sub> Nanorod Arrays Photoanode with Cu : NiO<sub><i>x</i></sub> as Hole Transport Layer and Co−Pi as Cocatalyst
Hongxing Li, Meisong Yin, Xianglin Li, Rong Mo
Abstract
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 TiO 2 /α‐Fe 2 O 3 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 TiO 2 /α‐Fe 2 O 3 composite obtained by a secondary hydrothermal process exhibited an inapparent bilayer structure by embedding the underlayer TiO 2 NR arrays at the bottom part of the post‐grown α‐Fe 2 O 3 NR arrays. The underlayer TiO 2 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‐Fe 2 O 3 NRs, which improved the hole extraction from α‐Fe 2 O 3 to Co−Pi OER catalyst. As expected, the as‐engineered TiO 2 /α‐Fe 2 O 3 /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‐Fe 2 O 3 (0.60 mA cm −2 ) and TiO 2 /α‐Fe 2 O 3 , 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.