A coral-like hematite photoanode on a macroporous SnO2: Sb substrate for enhanced photoelectrochemical water oxidation

Abstract

Oxygen evolution over semiconductor photoanodes plays a decisive role in water splitting via photoelectrochemical (PEC) process. While the hematite photoanode with a photocurrent threshold of 600 nm is promising for practical PEC water oxidation, it still suffers from the small minority carrier diffusion length, which makes it difficult to realize adequate light absorption and efficient charge separation concurrently. To address this issue, hematite nanorods were grown on macroporous SnO2:Sb substrates, forming a coral-like hematite (ATO-Fe2O3) photoanode. The ATO-Fe2O3 photoanode exhibited a 150 mV cathodic shift of onset relative to Fe2O3 nanorods directly on planar SnO2:F (FTO-Fe2O3). The photocurrent density reached 1.32 mA cm−2 at 1.23 V vs. RHE, approximately 8.8 times higher than FTO-Fe2O3, and it was further increased to 1.81 mA cm−2 after passivation with a thin TiO2 overlayer. The improved photocurrent was attributed to the increased light harvesting, reduced charge transfer resistance (Rct), and smaller contact area of oxygen bubble to hematite photoanode. Our research confirmed the effectiveness of macroporous ATO templated coral-like morphology on balancing the adequate light absorption and efficient charge separation issues of hematite photoanodes. This research may also be applicable to other semiconductor photoanodes for high-efficiency PEC water splitting.