Co-dependency of TiO2 underlayer and ZrO2 top layer in sandwiched microwave-assisted Zr-Fe2O3 photoanodes for photoelectrochemical water splitting

Abstract

A variety of electron/hole recombination pathways limit the photoelectrochemical capabilities of hematite (Fe₂O₃) photoanodes. To address the recombination issue in hematite photoanodes, a microwave-assisted deposition technique with a systematic surface and underlayer modification is presented. The TiO₂ under-layered microwave-assisted Zr-Fe₂O₃ is quenched at high temperatures, and ex situ ZrO₂ formation, as well as in situ Zr doping into the hematite lattice, significantly reduced bulk and surface recombinations. High-resolution scanning electron microscopy (HRSEM) analysis reveals the influence of the TiO₂ underlayer on microwave-assisted Zr-Fe₂O₃ photoanodes. After high-temperature quenching of microwave-assisted Zr-Fe₂O₃, TEM, and XPS studies confirmed the coexistence of Zr, Ti co-doping, and ZrO₂ surface decorations. Significantly, the combination of a TiO₂ underlayer, microwave-assisted Fe₂O₃ formation, and in situ and ex situ ZrO₂ deposition effectively achieved a photocurrent density of 1.49 mA cm⁻² at 1.23 V_RHE applied potential in a TiO₂/α-Fe₂O₃/ZrO₂ (TZF2ZQ) photoanode. Furthermore, electrochemical analyses confirm that Zr doping, ZrO₂ surface passivation, and the TiO₂ underlayer reduce the bulk and surface resistances (R₁ and R₂) in the TZF2ZQ photoanode. The PEC water splitting experiments reveal 144 and 71 μmol of H₂ and O₂ evolution over the optimum TZF2ZQ photoanode within 5 hours. The consecutive role of the ZrO₂ top layer and TiO₂ underlayer in sandwiched Zr-Fe₂O₃ photoanodes is well clarified with the proposed charge transfer mechanism.