Surviving High-Temperature Calcination: ZrO₂ -Induced Hematite Nanotubes for Photoelectrochemical Water Oxidation

Nanotubular Fe₂ O₃ is a promising photoanode material, and producing morphologies that withstand high-temperature calcination (HTC) is urgently needed to enhance the photoelectrochemical (PEC) performance. This work describes the design and fabrication of Fe₂ O₃ nanotube arrays that survive HTC for the first time. By introducing a ZrO₂ shell on hydrothermal FeOOH nanorods by atomic layer deposition, subsequent high-temperature solid-state reaction converts FeOOH-ZrO₂ nanorods to ZrO₂ -induced Fe₂ O₃ nanotubes (Zr-Fe₂ O₃ NTs). The structural evolution of the hematite nanotubes is systematically explored. As a result of the nanostructuring and shortened charge collection distance, the nanotube photoanode shows a greatly improved PEC water oxidation activity, exhibiting a photocurrent density of 1.5 mA cm^-2 at 1.23 V (vs. reversible hydrogen electrode, RHE), which is the highest among hematite nanotube photoanodes without co-catalysts. Furthermore, a Co-Pi decorated Zr-Fe₂ O₃ NT photoanode reveals an enhanced onset potential of 0.65 V (vs. RHE) and a photocurrent of 1.87 mA cm^-2 (at 1.23 V vs. RHE).