Facile Fabrication of a Highly Crystalline and Well-Interconnected Hematite Nanoparticle Photoanode for Efficient Visible-Light-Driven Water Oxidation.

Facile and scalable fabrication of α-FeO photoanodes using a precursor solution containing Fe ions and 1-ethylimidazole (EIm) in methanol was demonstrated to afford a rigidly adhered α-FeO film with a controllable thickness on a fluorine-doped tin oxide (FTO) substrate. EIm ligation to Fe ions in the precursor solution brought about high crystallinity of three-dimensionally well-interconnected nanoparticles of α-FeO upon sintering. This is responsible for the 13.6 times higher photocurrent density (at 1.23 V vs reference hydrogen electrode (RHE)) for photoelectrochemical (PEC) water oxidation on the α-FeO (w-α-FeO) photoanode prepared with EIm compared with that (w/o-α-FeO) prepared without EIm. The w-α-FeO photoanode provided the highest charge separation efficiency (η) value of 27% among the state-of-the-art pristine α-FeO photoanodes, providing incident photon-to-current conversion efficiency (IPCE) of 13% at 420 nm and 1.23 V vs RHE. The superior η for the w-α-FeO photoanode is attributed to the decreased recombination of the photogenerated charge carriers at the grain boundary between nanoparticles, in addition to the higher number of the catalytically active sites and the efficient bulk charge transport in the film, compared with w/o-α-FeO.