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

A facile post-hydrothermal combined with chelation-mediated in-situ growth method was developed to fabricate CoOOH-rGO/Fe 2 O 3 with spatially separated CoOOH and rGO. rGO and CoOOH exhibit important functions that modulate the transfers of the electrons and holes, as well as suppress the bulk and the surface recombination, thus significantly improve the photoelectrochemical water oxidation performance of Fe 2 O 3 . • A hybrid CoOOH-rGO/Fe 2 O 3 with spatially separated structure was facilely fabricated. • CoOOH-rGO/Fe 2 O 3 exhibited outstanding photoelectrochemical water oxidation performance. • rGO as conductive network facilitates the electron transfer from Fe 2 O 3 to the substrate. • CoOOH passivates the surface states of Fe 2 O 3 and improves the charge separation and the charge transfer. As a promising photoanode for photoelectrochemical (PEC) water oxidation, hematite (Fe 2 O 3 ) 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 Fe 2 O 3 (CoOOH-rGO/Fe 2 O 3 ) 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 Fe 2 O 3 and CoOOH nanosheets distribute on the terminal of Fe 2 O 3 , forming a spatial separated nanostructure . The resultant CoOOH-rGO/Fe 2 O 3 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 Fe 2 O 3 . 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 Fe 2 O 3 to the substrate, while CoOOH evidently passivate the surface states of Fe 2 O 3 , 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.