High-performance n-Si/α-Fe2O3 core/shell nanowire array photoanode towards photoelectrochemical water splitting

Abstract

Many narrow band-gap semiconductors cannot fulfil the energetic requirements for water splitting, thus the assistance of large external voltages to complete the water decomposition reaction is required. Through thermal decomposition of Fe(NO₃)₃ on n-Si nanowires prepared by the chemical etching method, we fabricated a high-performance n-Si/α-Fe₂O₃ core/shell nanowire array photoanode that exhibited a low photocurrent onset potential of 0.5 V vs. RHE and a high photocurrent of 5.28 mA cm⁻² at 1.23 V vs. RHE, under simulated AM 1.5G irradiation. The photocurrent onset potential represents one of the lowest in n-Si or α-Fe₂O₃ based photoanodes, and the photocurrent is much larger than most of those observed on α-Fe₂O₃. The impact of the thickness of the α-Fe₂O₃ shell on the photoelectrochemical performance of the present photoanode was investigated in detail. It was found that both the photocurrent and the onset potential depend strongly on the α-Fe₂O₃ shell thickness. Mott–Schottky measurements and energy band calculation reveal that the energy band edge positions of the n-Si are closely related to the thickness of the α-Fe₂O₃. The α-Fe₂O₃ shell with an optimized thickness is favorable for locating the energy bands of the n-Si at relatively high levels and maximizing the charge collection in α-Fe₂O₃, and thus achieving the low photocurrent onset potential and high photocurrent.