Multifunctional Ultrathin Amorphous CoFe-Prussian Blue Analogue Catalysts for Efficiently Boosting the Oxygen Evolution Activity of Antimony-Doped TiO₂ Nanorods Photoanode

Developing efficient, durable, and inexpensive oxygen evolution catalysts (OECs) have no alternative to designing efficient photoanodes for water splitting. Here, we demonstrate a simple strategy of fabricating a CoFe Prussian blue analogue (CoFe-PBA) water oxidation catalyst-coupled antimony-doped TiO2 (Sb-TiO2) nanorod (NR) photoanode with enhanced photocurrent density (1.48 mA cm–2 at 1.23 V vs reversible hydrogen electrode (RHE)), high photoconversion efficiency (0.53% at 0.42 VRHE), and reduced onset potential (0.05 VRHE). Synergistic coupling between the CoFe-PBA and Sb-TiO2 NRs leads to numerous advantages, where the light-harvesting efficiency of the nano-heterostructure photoanode enhances >50% in the visible wavelength region. The CoFe-PBA catalyst also reduces the bulk carrier recombination in Sb-TiO2 NRs, serving as a surface passivation overlayer. The density functional theory (DFT) and valance band (VB) X-ray photoelectron spectroscopy (XPS) studies demonstrate the tuning of the electronic structure of the hybrid photoanode with a favorable band alignment enabling rapid photocarrier injection. Ultrathin CoFe-PBA catalysts also accelerate hole extraction from Sb-TiO2 NRs and readily transfer the holes toward the electrode/electrolyte interface, boosting the hole transfer efficiency (∼95% at 1.23 VRHE) and prolonging the hole lifetime for water oxidation. This work highlights the mechanism of the multifunctional activity of CoFe-PBA-coupled Sb-TiO2 NR photoanodes.