Nanoporous hematite structures to overcome short diffusion lengths in water splitting

Abstract

In this report, we show that by creating a nanoporous haematite (α-Fe₂O₃) structure using boric acid (H₃BO₃) treatment, the chronic issue of the short diffusion length of carriers in α-Fe₂O₃ for photoelectrochemical (PEC) applications can be successfully addressed. The slow release of Fe³⁺ ions because of the presence of H₃BO₃ leads to the creation of smaller dimension FeOOH nanorods, creating nanoporous α-Fe₂O₃ nanorods, composed of ∼15 nm α-Fe₂O₃ domains. The nanoporous α-Fe₂O₃ suppresses recombination by providing the facile extraction of holes from the surface of favorably sized α-Fe₂O₃ domains. The optimized nanoporous sample showed a photocurrent density of 1.41 mA cm⁻² at a reversible hydrogen electrode of 1.23 V, which is 1.7 times higher than that of pristine hematite. The electrochemical impedance spectroscopy and incident photon-to-current efficiency data, and Mott–Schottky plots confirmed the superior performance of the nanoporous samples. Our impressive results may pave the way for designing devices for advanced energy conversion applications as well as fabricating a high efficiency hematite-based PEC system.