Enhancement of Cocatalyst‐Coated ZnFe 2 O 4 Photoanode Grown in Situ on a Metallic Iron Substrate

MFe2O4 (M=Zn, Cu, Mg, Ca) spinel ferrites, with electronic band gaps between 1.4 and 2.1 eV and containing only earth-abundant elements, are promising visible-light-harvesting materials for photoelectrochemical (PEC) water splitting. In situ growth of semiconducting thin films directly on a metallic substrate usually produced highly mechanical stable photoelectrodes and lower interfacial transfer resistance. Here, we advanced the in-situ-grown ZnFe2O4 thin-film photoanode on a Fe substrate with an optically transparent FeNiOx electrocatalyst, giving a photocurrent of approximately 46 mu A cm(-2) at 1.23 V vs. RHE, which was 3.5 times larger as compared to pristine Fe/ZnFe2O4. Multiple electrochemical techniques were employed to elucidate the augmented effects of surface modification. Our results suggest that FeNiOx can accelerate the surface charge separation efficiency, thus improving the PEC performance. Additionally, low bulk charge separation efficiency was proposed to be the main hindrance for the ZnFe2O4 photoanode on a metallic Fe substrate.