Enhanced Photoelectrochemical Water Oxidation Performance in Bilayer TiO2 /α-Fe2 O3 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-Fe2 O3 nanorod (NR) arrays photoanode was prepared with deposited Cu-doped NiOx (Cu : NiOx ) 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 : NiOx HTL was introduced to form a build-in p-n electric field between Cu : NiOx 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 : NiOx /Co-Pi photoanode displayed an excellent photocurrent density of 2.43 mA cm-2 at 1.23 V versus the reversible hydrogen electrode (VRHE ), 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.