Engineering Highly Ordered Iron Titanate Nanotube Array Photoanodes for Enhanced Solar Water Splitting Activity

Abstract

Highly ordered iron titanate (Fe2TiO5) nanotube array photoanode is synthesized on F:SnO2 glass with ultrathin anodized aluminum oxide as a hard template. Highly crystalline, yet the nanotube array morphology‐preserved Fe2TiO5 is fabricated by hybrid microwave annealing (HMA). The effects of the synthesis parameters on photoelectrochemical (PEC) water splitting activity under simulated sunlight are systematically studied including HMA time, pore size, wall thickness, and length of the nanotubes to optimize the nanotube array photoanode. In addition, triple modification strategies of TiO2 underlayer, hydrogen treatment, and FeNiOx cocatalyst loading effectively improve the PEC activity further. The systematically engineered nanotube array photoanode achieves a photocurrent density of 0.93 mA cm−2 at 1.23 VRHE under 1 sun (100 mW cm−2) irradiation, which corresponds to 2.6 times that of the previous best Fe2TiO5 photoanode. In addition, the photocurrent onset potential shifts cathodically by ≈280 mV relative to the pristine nanotube array electrode.

Fluorine‐Doped Tin Oxide/Alumina as Long‐Term Robust Conducting Support for Earth‐Abundant Water Oxidation Electrocatalysts

“…Two solutions were prepared for the depositions. Solution A: 0.01 M K 3 [Fe(CN) 6 ], and solution B: 0.01 M Co(NO 3 ) 2 ·6H 2 O. Five deposition cycles were performed, where AAO/FTO and Glass/FTO samples were dipped, first, in solution A and, second, in solution B for 15 minutes in each case, followed by air drying overnight.…”

“…For instance, AAO is attractive as template or host material for the growth of ordered nanotube or nanowire arrays for electrochemical applications like energy storage and conversion . As a few examples, AAO templates have been used to fabricate a nanostructured CdS‐CdTe solar cell or a photoanode for water splitting based on Fe 2 TiO 5 nanotubes . In these cases the AAO support is removed after the deposition of the guest material leading to free‐standing nanoporous structures.…”

“…Our strategy in the present work consists of a controlled deposition of a conductive material over the AAO surface before the PB addition. SnO 2 is one of the most studied members in the family of transparent conductive oxides (TCO) and, particularly, F‐doped tin oxide (FTO) ,. Besides its transparency in the visible region of the electromagnetic spectrum and low electrical resistance, it can be easily deposited on different surfaces by spray pyrolysis .…”

“…[4] As a few examples, AAO templates have been used to fabricate a nanostructured CdS-CdTe solar cell [5] or a photoanode for water splitting based on Fe 2 TiO 5 nanotubes. [6] In these cases the AAO support is removed after the deposition of the guest material leading to free-standing nanoporous structures. The AAO removal is typically performed by immersing the composite material into a concentrated NaOH or H 3 PO 4 solution.…”

“…SnO 2 is one of the most studied members in the family of transparent conductive oxides (TCO) and, particularly, F-doped tin oxide (FTO). [6,[33][34][35][36] Besides its transparency in the visible region of the electromagnetic spectrum and low electrical resistance, it can be easily deposited on different surfaces by spray pyrolysis. [35][36] We propose for the first time in literature the use of FTO-covered AAO as water oxidation catalyst support.…”