Gradient Si- and Ti-doped Fe₂O₃ hierarchical homojunction photoanode for efficient solar water splitting: Effect of facile microwave-assisted growth of Si-FeOOH on Ti-FeOOH nanocorals

The construction of a homojunction is an effective approach for addressing issues such as slow charge separation and charge-transfer kinetics in photoanodes. In the present work, we designed a gradient Si- and Ti-doped Fe₂O₃ homojunction photoanode to improve the photoelectrochemical (PEC) performance of a Ti-doped Fe₂O₃ photoanode. Ti-FeOOH nanocorals were synthesized using a hydrothermal process, and Si-FeOOH was grown on Ti-FeOOH nanocorals using a rapid and facile microwave-assisted (MW) technique. By varying the MW irradiation time, the thickness of the Si/Ti:Fe₂O₃ photoanode was adjusted and an optimized 3-Si/Ti:Fe₂O₃ photoelectrode was achieved with a significantly enhanced photocurrent density (1.37 mA cm⁻² at 1.23 V vs. RHE) and a cathodic shift of the onset potential (150 mV) compared with that of bare Ti-Fe₂O₃. This enhanced PEC performance can be ascribed to homojunction formation and Si gradient doping. The Si dopant increased the donor concentration and the formation of a homojunction improved the intrinsic built-in electric field, thereby promoting charge separation and charge transfer. Furthermore, the as-formed homojunction passivated the surface-trapping states, consequently improving the charge transfer efficiency (60% at 1.23 V_RHE) at the photoanode/electrolyte interface. These findings could pave the way for the microwave-assisted fabrication of diverse efficient homojunction photoanodes for PEC water splitting applications.