Quasi-Topotactic Transformation of FeOOH Nanorods to Robust Fe₂O₃ Porous Nanopillars Triggered with a Facile Rapid Dehydration Strategy for Efficient Photoelectrochemical Water Splitting

A facile rapid dehydration (RD) strategy is explored for quasi-topotactic transformation of FeOOH nanorods to robust Fe₂O₃ porous nanopillars, avoiding collapse, shrink, and coalescence, and compared with a conventional treatment route. Additionally, the so-called RD process is capable of generating a beneficial porous structure for photoelectrochemical water oxidation. The obtained RD-Fe₂O₃ photoanode exhibits a photocurrent density as high as 2.0 mA cm^–2 at 1.23 V versus reversible hydrogen electrode (RHE) and a saturated photocurrent density of 3.5 mA cm^–2 at 1.71 V versus RHE without any cocatalysts, which is about 270% improved photocurrent density over Fe₂O₃ with the conventional temperature-rising route (0.75 mA cm^–2 at 1.23 V vs RHE and 1.48 mA cm^–2 at 1.71 V vs RHE, respectively). The enhanced photocurrent on RD-Fe₂O₃ is attributed to a synergistic effect of the following factors: (i) preservation of single crystalline nanopillars decreases the charge-carrier recombination; (ii) formation of long nanopillars enhances light harvesting; and (iii) the porous structure shortens the hole transport distance from the bulk material to the electrode–electrolyte interface