Interfacial engineering of hematite photoanodes toward high water splitting performance
Kelly T.C. Thomaz, Karen C. Bedin, Ingrid Rodríguez‐Gutiérrez, Nathália Carolina Verissimo, Jefferson Bettini, Flávio L. Souza
Abstract
Efficient and scalable photoelectrochemical water splitting electrode designs are a challenge. This study focuses on hafnium-modified hematite (X%Hf-HEM) photoanodes , prepared via spin-coating polymeric precursor solutions with varying Hf 4+ /Fe 3+ (mol) ratios (1.0%, 3.0%, 4.0%, and 5.0%) onto fluorine-doped tin oxide substrates. Structural, morphological, and compositional analyses confirm pure hematite phases in all X%Hf-HEM samples. Increasing Hf 4+ content correlated with reduced grain size , thickness, and surface roughness due to Hf 4+ segregation at grain boundaries during thermal treatment. Hafnium segregation at hematite grain boundaries and hematite|fluorine-doped tin oxide interfaces is confirmed using scanning transmission electron microscopy coupled with energy dispersive spectroscopy . Notably, the 4%Hf-HEM photoanode exhibits exceptional efficiency enhancement, outperforming HEM efficiency by 4.5 times. Gas chromatography results highlight O 2 and H 2 evolution rates of 14.49 ± 0.09 μmol/cm 2 /h and 8.1 ± 0.5 μmol/cm 2 /h, respectively, for 4%Hf-HEM, with a H 2 /O 2 ratio close to 2:1. The charge dynamics investigated from intensity-modulated photocurrent spectroscopy evidence the main Hf 4+ effect of improving charge separation, achieving greater efficiency for 4%Hf-HEM. Shifts in valence band maximum from ultraviolet photoelectron spectroscopy measurements indicate surface state presence, supported by η transfer trends calculated from intensity-modulated photocurrent spectroscopy. This research presents a scalable, cost-effective approach to multiinterface photoanode development, holding promise for innovative photoelectrochemical water splitting technologies.