Enhanced Solar Water Splitting by Swift Charge Separation in Au/FeOOH Sandwiched Single-Crystalline Fe2O3 Nanoflake Photoelectrodes

Abstract

In this work, single crystalline α-Fe2O3 nanoflakes (NFs) are formed in a highly dense array by Au seeding of a Fe substrate by a thermal oxidation technique. The NFs are conformally decorated with a thin FeOOH cocatalyst layer. Photoelectrochemical (PEC) measurements show that this photoanode, incorporating α-Fe2O3/FeOOH NFs rooted on the Au/Fe structure, exhibits significantly enhanced PEC water oxidation performance compared to the plain α-Fe2O3 nanostructure on the Fe substrate. The α-Fe2O3/FeOOH NFs on Au/Fe photoanode yields a photocurrent density of 3.1 mA cm−2 at 1.5 VRHE, and a remarkably low onset potential of 0.5–0.6 VRHE in 1 m KOH under AM 1.5G (100 mW cm−2) simulated sunlight illumination. The enhancement in PEC performance can be attributed to a synergistic effect of the FeOOH top decoration and the Au underlayer, whereby FeOOH facilitates hole transfer at the interface of electrode/electrolyte and the Au layer provides a sink for the electron transport to the back contact. This results in a drastically improved charge-separation efficiency in the single crystalline α-Fe2O3 NF photoanode.