Alkali Treatment for Enhanced Photoelectrochemical\nWater Oxidation on Hematite Photoanode

Abstract

As one of the most\npopular photoanode materials for photoelectrochemical\n(PEC) water splitting, hematite (α-Fe₂O₃) suffers from low conductivity, severe electron–hole recombination,\nand sluggish water oxidation kinetics unfortunately. Herein, we report\nan alkali-treatment method to effectively accelerate the water oxidation\nkinetics of α-Fe₂O₃ and titanium doped\nα-Fe₂O₃ (Ti:α-Fe₂O₃) nanorod array photoanodes. The purpose of Ti-doping is to\nincrease the conductivity of α-Fe₂O₃.\nThe photocurrent densities increased 3- and 2-times for α-Fe₂O₃ and Ti:α-Fe₂O₃ photoanodes\nafter KOH treatment, respectively. Transmission electron microscopy\n(TEM) and X-ray photoelectron spectroscopy (XPS) analyses demonstrated\nthat a conformal thin layer grafted with hydroxyl (−OH) groups\nwas formed on the hematite surface. Linear sweep voltammetry (LSV)\ncurves under light irradiation and in the dark indicated that the\nthin OH-grafted overlayer behaved like an electrocatalyst to accelerate\nthe water oxidation kinetics on hematite photoanodes. Moreover, XPS\nvalence band (XPS-VB) spectra, Mott–Schottky analysis, and\nelectrochemical impedance spectroscopy (EIS) revealed that a type\nII heterojunction was <i>in situ</i> formed by the OH-grafted\noverlayer on the hematite nanorod surface, which substantially enhanced\nthe surface charge separation efficiency. The improved PEC performance\ncould be attributed to the accelerated water oxidation kinetics and\nenhanced surface charge transfer.