In situ growth of α-Fe2O3@Co3O4 core–shell wormlike nanoarrays for a highly efficient photoelectrochemical water oxidation reaction

Abstract

Photoelectrochemical (PEC) water splitting represents a promising strategy to convert solar energy into chemical energy in the form of hydrogen, but its performance is severely limited by the sluggish water oxidation reaction. Herein, for the first time, we report the direct assembly of an ultrathin, uniform, and dense layer of Co₃O₄ on wormlike nanostructured hematite (WN-α-Fe₂O₃) to form a large-area and high-density WN-α-Fe₂O₃@Co₃O₄ core–shell nanoarray via in situ hydrothermal growth followed by calcination, in which the electrostatic force between WN-α-Fe₂O₃ and the reactants, pH- and temperature-controlled structures of WN-α-Fe₂O₃, and ultralow nucleation rate of Co₃O₄ precursors all play critical roles. The obtained heteronanostructure array shows a photocurrent density of 3.48 mA cm⁻², which is 4.05 times higher than that of pristine WN-α-Fe₂O₃ (0.86 mA cm⁻²), an onset potential of ∼0.62 V, 60 mV lower than that of α-Fe₂O₃ (∼0.68 V), and a photoconversion efficiency of 0.55%, 3.93 times higher than that of WN-α-Fe₂O₃ (0.14%). This is among the highest performances reported for Fe₂O₃-based photoanodes for water splitting. It is discovered that the Co₃O₄ shells can significantly enhance the charge separation, accelerate the charge transport and transfer, and reduce the charge transfer resistance from the photoelectrode to the electrolyte for a fast water oxidation reaction, thereby greatly promoting the PEC water oxidation performance of pristine WN-α-Fe₂O₃. This work not only creates a novel low-cost and Earth-abundant WN-α-Fe₂O₃@Co₃O₄ photoelectrode with superior PEC water oxidation performance and provides scientific insights into the enhancement mechanism, but also offers a general strategy for the in situ growth of water oxidation catalysts on various photoelectrodes with 3-D complex geometries for PEC water splitting.