Unravelling the role of the combined effect of metallic charge transfer channel and SiO_x overlayer in the Zr/Si-Fe₂O₃:Au:SiO_x nanorod arrays to boost photoelectrochemical water splitting

Hematite (α-Fe₂O₃) based photoanodes have been extensively studied due to various intriguing features that make them viable candidates for a photoelectrochemical (PEC) water splitting photoanode. Herein, we propose a Zr-doped Fe₂O₃ photoanode decorated with facilely spin-coated Au nanoparticles (NPs) and microwave-assisted attached Si co-doping in conjunction with a SiO_x overlayer that displayed a remarkable photocurrent density of 2.01 mA/cm² at 1.23 V vs. RHE. The kinetic dynamics at the photoelectrode/electrolyte interface was examined by employing systematic electrochemical investigations. The Au NPs played a dual role in increasing PEC water splitting. First, the Schottky interface that was formed between Au NPs and Zr-Fe₂O₃ electrode ensured the prevention of electron flow from the photoanode to the metal, increasing the number of available charges as well as suppressing surface charge recombination. Second, Au extracted photoholes from the bulk of the Zr-Fe₂O₃ and transported them to the outer SiO_x overlayer, while the SiO_x overlayer efficiently collected the photoholes and promoted the hole injection into the electrolyte. Further, Si co-doping enhanced bulk conductivity by reducing bulk charge transfer resistance and improving charge carrier density. This study outlines a technique to design a metallic charge transfer path with an overlayer for solar energy conversion.