Construction of NiFeCoOOH/Fe ₂ O ₃ Heterojunction Photoanodes for Photoelectrochemical Water Oxidation

Abstract

Abstract Photoelectrochemical (PEC) water oxidation is pivotal for solar‐to‐chemical energy conversion, yet its efficiency remains constrained by sluggish charge transfer and high electron‐hole recombination rates in photoanodes. In this study, we reported the construction of NiFeCoOOH/Fe 2 O 3 heterojunction photoanodes via a simple drop‐coating method to boost PEC performance. The optimized NiFeCoOOH/Fe 2 O 3 ‐5 sample exhibits a photocurrent density of 0.637 mA/cm 2 at 1.23 V versus RHE, doubling that of pure Fe 2 O 3 . Structural and morphological characterizations including SEM, XPS, and XRD confirm the successful formation of the heterostructure, where NiFeCoOOH nanolayers are uniformly anchored onto Fe 2 O 3 nanorods. Electrochemical analyses (EIS, Mott–Schottky, and OCP) reveal that the heterojunction significantly promotes photogenerated charge separation and suppresses recombination, primarily attributed to the built‐in electric field at the interface. Reduced impedance and altered flat‐band potential verifying improved charge transfer kinetics and increased carrier concentration. This work demonstrates that integrating trimetallic NiFeCoOOH with Fe 2 O 3 via heterostructure engineering represents an effective strategy to enhance PEC water oxidation, providing a promising strategy for designing high‐performance iron‐based photoanodes in renewable energy applications.