FeOOH Modified H-TiO2Nanorods Array (NRA) for Stable and Improved Low-Bias Photoelectrochemical Water Splitting

Iron oxyhydroxide (FeOOH) was implemented as a low-cost, stable, and earth-abundant catalyst on hydrogenated titania nanorods array (H-TiO2/FeOOH), for photoelectrochemical water splitting applications. The hydrogenation treatment enhanced the maximum photocurrent density delivered by the titania-based photoanode (from 0.65 mA cm-2 to 1 mA cm-2 at +1.23 V vs RHE) while the exploitation of FeOOH resulted in a significant improvement in the photoelectrochemical activity at low bias. The optimized photoelectrode showed ∼0.6 mA cm-2 at +0.4 V vs RHE, with a saturation current density of 1.05 mA cm-2. Insights on the role of FeOOH were revealed by electrochemical impedance and photoluminescence measurements, suggesting a reduction of the charge transfer resistance at the electrolyte interface and a lower frequency of recombination events. The H-TiO2/FeOOH photoelectrode showed a maximum applied bias photon-to-current efficiency (ABPE) of 0.68% with a 0.3 V bias, while for the bare TiO2 nanorods array the maximum value of 0.4% was found at a bias of 0.4 V. A stable photocurrent was measured in 1 M NaOH solution through a 5 h test at 1.23 V vs RHE, under illumination (1 sun), suggesting the compatibility of FeOOH in highly alkaline solutions.