HfO₂ Functionalized Hematite Nanorods for Enhanced Photoelectrochemical Water Splitting

Hematite (α-Fe₂O₃) has been extensively suggested as a superior photoanode for the photoelectrochemical (PEC) water splitting, owing to its natural abundance, high chemical stability, and theoretical solar-to-hydrogen (STH) efficiency (16.8%). Nevertheless, the recalcitrant electron−hole recombination resulting in poor charge separation and injection efficiency limits its PEC performance. Herein, a simple hydrothermal/atomic layer deposition (ALD) process was used to fabricate two types of HfO₂ functionalized hematite (i.e., HfO₂ overlayer and nanoparticles modified α-Fe₂O₃, HfFe-L and HfFe-P for short) photoanodes. It was revealed that HfO₂ overlayer and nanoparticles could successfully passiviate the surface trap states of hematite, resulted in enhanced PEC performances for both HfFe-L and HfFe-P. More surprisingly, the photocurrent density of the HfFe-P reached as high as 1.21 mA cm-2 at 1.23 _vs. RHE, with ~4.8 and ~3.3 fold enhancement as compared to that of the bare hematite and even HfFe-L, respectively. Such great PEC performance enhancement in HfFe-P was revealed to be attributed to the multifunction of HfO₂ nanoparticles distributed on the surface of hematite nanorod arrays, which not only passivated surface defects to suppress the surface charge recombination by eliminating the surface trapping states, but can also facilitated the hole extraction from bulk of hematite to hematite/electrolyte interface.