A novel ternary nanostructured carbonaceous-metal-semiconductor eRGO/NiO/alpha-Fe2O3 heterojunction photoanode with enhanced charge transfer properties for photoelectrochemical water splitting

摘要

A novel ternary hematite (alpha-Fe2O3)-based nanostructured photoanode with excellent photoelectrochemical (PEC) performance consisting of 2D-electrochemical reduced graphene oxide (eRGO) and nickel oxide (NiO) was successfully developed through electrodeposition synthesis method. Surface morphology studies showed that the flexible eRGO sheets provided intimate and coherent interfaces between alpha-Fe2O3, NiO, and eRGO that enhanced charge transfer properties and thus, lowering the recombination rate of photogenerated electron-hole pairs. The incorporation of eRGO and NiO has also endowed alpha-Fe2O3 nanostructured photoanode with a wider spectral absorption range, where the light absorption intensities in the visible light and near infrared regions were improved. Electrochemical impedance spectroscopy analysis further confirmed that the ternary eRGO/NiO/alpha-Fe2O3 nanostructured photoanode possessed the lowest charge transfer resistance among all as-synthesized photoanodes. This indicates that the combinatorial effects of eRGO and NiO could improve the electron mobility and prolong the recombination process of photogenerated charge carriers that result in enhanced PEC performance. In this instance, the eRGO sheets act as surface passivation layer and electron transporting bridge that increase the electrons transfer at the semiconductor/liquid junction. Whilst NiO serves as hole scavenger that also effectively hinders the recombination of photogenerated electron-hole pairs, and provides electron donor centres that accelerate the interfacial charge transfer. Finally, the hydrogen evolution rate from the ternary eRGO/NiO/alpha-Fe2O3 nanostructured photoanode was measured to be 92 mu mol h(-1) cm(-2), which was about 3-fold higher than bare ct-Fe2O3 nanostructured photoanode. It is expected that the fundamental understanding gained through this study is helpful for the rational design and construction of highly efficient ternary nanostructured heterojunction photoanodes for application in PEC water splitting.