A hybrid CoOOH-rGO/Fe2O3 photoanode with spatial charge separation and charge transfer for efficient photoelectrochemical water oxidation

Abstract

As a promising photoanode for photoelectrochemical (PEC) water oxidation, hematite (Fe2O3) still suffers from poor charge mobility and serious charges recombination and sluggish surface oxygen evolution kinetics. Herein, a hybrid photoanode of cobalt (oxy)hydroxide coupled with reduced graphene oxide modified Fe2O3 (CoOOH-rGO/Fe2O3) is well crafted by a facile hydrothermal synthesis with a chelation-mediated in-situ growth method. Morphology characterizations indicate rGO forms the internal network among isolated Fe2O3 and CoOOH nanosheets distribute on the terminal of Fe2O3, forming a spatial separated nanostructure. The resultant CoOOH-rGO/Fe2O3 exhibits an obviously reduced onset potential of ca. 150 mV and a significantly enhanced photocurrent density of 2.56 mA cm−2 at 1.23 V, which is ca. 3.3 times higher than that of bare Fe2O3. Especially, the functions of rGO and CoOOH are studied by using electrochemical impedance spectroscopy, open circuit potentials and intensity modulated photocurrent spectroscopy. It is found rGO act as conductive network which facilitates the electron transfer from Fe2O3 to the substrate, while CoOOH evidently passivate the surface states of Fe2O3, improve charge separation and provide catalytic active sites for water oxidation. The spatial charge separation and charge transfer caused by CoOOH and rGO are responsible for the enhanced PEC performance of water oxidation. The rational design and the facile fabrication strategy exhibit great potential to be used for other PEC system with great efficiency.