FeS as hole transport pathway regulating charge transfer for efficient photoelectrochemical water splitting of hematite photoanodes

An efficient charge transport layer that enhances charge separation is crucial for achieving high solar-to- hydrogen (STH) conversion efficiencies in photoelectrochemical (PEC) water splitting. This study investigates the potential of FeS as a hole-transporting layer (HTL) in hematite (Fe2O3) photoanodes to enhance PEC water splitting performance. The integration of p-type FeS onto the Fe2O3 surface formed a p-n heterojunction, providing an additional driving force for the transfer of photogenerated holes from Ti-Fe2O3 to the oxygen- evolution co-catalyst (OEC) FeOOH, while also inhibiting the diffusion of photogenerated electrons. Additionally, the formation of S-Fe-O bonds at the Ti-Fe2O3/FeS interface significantly reduced interfacial defects, thereby improving charge separation. As a result, the optimal photoanode reached a high photocurrent density of 4.24 mA/cm2 at 1.23 V vs. RHE. Furthermore, a tandem device combining Ti-Fe2O3/FeS/FeOOH photoanodes with a Si solar cell demonstrated unbiased solar water splitting under parallel illumination mode, achieving an STH conversion efficiency of 4.7 %. This study underscores the effectiveness of FeS as a medium for hole extraction and transport medium in photoanodes, addressing the inherent recombination challenges of hematite and enabling efficient and stable water splitting.