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

Highly ordered iron titanate (Fe 2 TiO 5 ) nanotube array photoanode is synthesized on F:SnO 2 glass with ultrathin anodized aluminum oxide as a hard template. Highly crystalline, yet the nanotube array morphology‐preserved Fe 2 TiO 5 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 TiO 2 underlayer, hydrogen treatment, and FeNiO x 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 V RHE under 1 sun (100 mW cm −2 ) irradiation, which corresponds to 2.6 times that of the previous best Fe 2 TiO 5 photoanode. In addition, the photocurrent onset potential shifts cathodically by ≈280 mV relative to the pristine nanotube array electrode.