Nanoporous hematite structures to overcome short diffusion lengths in water splitting

Abstract

In this report, we show that by creating a nanoporous haematite (alpha-Fe2O3) structure using boric acid (H3BO3) treatment, the chronic issue of the short diffusion length of carriers in alpha-Fe2O3 for photo-electrochemical (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 alpha-Fe2O3 nanorods, composed of similar to 15 nm alpha-Fe2O3 domains. The nanoporous alpha-Fe2O3 suppresses recombination by providing the facile extraction of holes from the surface of favorably sized alpha-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 electro-chemical 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.